Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: 73ss on May 15, 2021, 05:21:53 PM
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I need some help getting the idle dialed in.
Recipe: 17084228, single main air bleed.
Main air: .088
Upper idle air bleed: .070, Lower: .077
idle tube: .038, idle down: .058
Idle port: .090, Bypass: .125
75 jet, 50m rod, 1/4 float.
Engine: 489 BBC, Brodix race rite oval port heads. 10:1 squeeze. Domed pistons.
pistons 10 in the hole, block has been decked. .040 cometic head gaskets.
cam: Howards roller, intake: 232, ex: 246 @ .050. .601, .612 lift. 114 lobe sep, 110 intake center line.
Timing: 20 degrees lead, stable in and out of gear. 850 rpm.
I can only get 10in of vacuum with 20 degrees lead. Engine idles fairly well, doesn't stall. Slight hesitation right of of idle. If I disable the accelerator pump, The off idle hesitation is all but gone. I assume this is because too much transfer slot is exposed.
If I close off the choke at idle, I get 11 inch of vacuum and about 50rpm increase. This tells me I'm lean on idle. Mixture screws are unresponsive past 4.5 turns out. I did open the idle down from .054 to .058. It did make a difference but it acts like it wants more. I currently have 2/3 of transfer slot exposed. Boosters are not dripping at idle. Engine will stall with mixture screws seated. Plugs are white.
Carb feels good otherwise, No stumble going to WOT from stop, May need to tweak ATP or primary rod size yet.
Any suggestions on what to do next, Increase idle tube, idle down channel? Decrease lower idle air bleed?
Thanks for any suggestions or help.
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I have measured mid-70´s Chevy BB and 350 HD Truck Q-jets with up to .044" idle tubes from factory.
I would say your race-engine needs larger than .038" idle tubes.
Also, most if not all BB Chevy in the high performance era uses .138" idle air bypass.
And i would open the idle needle ports to .095".
HTH
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You would be better off reducing the LIAB than putting in larger idle tubes.
Before doing anything remove a small manifold vacuum hose and see if it wants or needs any additional idle bypass air?
A few days ago I set up one of those later truck carbs for a 690hp Big Block Chevy engine and used .038" idle tubes. I reduced the LIAB's to .063", .070" uppers, and .055" DCR's with .136" bypass air. It was well on the idle system and excellent response with the mixtures screws with only .089" holes under them.
The larger LIAB's vent enough to require much larger DCR's and idle tubes with heavy cammed engines. Even when you open them up to compensate the response at the mixture screws isn't nearly as good vs closing down the LIAB's.
I'd also add here that you aren't making nearly the vacuum I'd expect from that cam in a 489CID build at 10 to 1 compression with 20 degrees initial timing in it. Not quite sure what's up with that deal but it shouldn't need much past 10 or 12 degrees timing to make 12-14" vacuum at 750rpm's with that cam.
What are the actual seat timing numbers (advertised) duration and where are they rating it at, .006" etc?.........Cliff
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Advertised duration is : 284.6 in 298.6 ex. It's not listed as to what the rating is.
I am puzzled as well with the low vacuum and 20 degrees of lead. I did verify TDC and the timing pointer when the heads were off, spot on. I would like to think I got the quench good. The shop said pistons are 10 in the hole, I measured around .008, It was hard for me to get a precise measurement due to the domes and several thousands worth of piston rock at TDC. I went with the cometic gaskets , they have a smaller crevice volume than the fel-pro equivalents. I was expecting at least 12"s of vacuum with around 14~16 degrees of lead.
Pulling a small vacuum hose has no effect, I did block off one of the idle bypass slots in the air horn with a piece of tape. RPM's dropped but idle did smooth out somewhat, so I think I am close on that.
The throttle is open far enough that the ported vacuum advance port is just on the verge of working, But not far enough to cause nozzle drip.
I verified the ignition system is working correctly by swapping out the MSD setup with "old reliable", a known good working points distributor that I have for troubleshooting. No difference, Pops right off at the flick of the key.
The original '73 7043202 ? BB carb does in fact have the .138" bypass ports. Idle discharge ports measured out at .082.
Thank you for the replies!!!
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That is NOT a big cam in that build. I suspect late intake closing or the compression ratio is less than calculated, or a little of both. The 114LSA is the right way to go with the big CID engines, they thrive on it. I like the ICL around 109-110 as well. I typically use cams around 244/254 @ .050" in them if they are around 10 to 10.5 to 1 and pump gas street builds. They will act no bigger than using a 234/244 @ .050"ish cam in a 454-468 build.
My smaller 455 CID engine at 11.2 to 1 compression idles with 13.5" vacuum with only 10 degrees initial timing. My cam is close in duration at 289/308 @ .006", 236/245 @ .050", 112LSA with the ICL at 109.5 degrees.
I've built 496-505cid engines with bigger cams than you are using around 10 to 1 compression and they idled with at least 12" with only 10 degrees initial timing at 750-800rpm's and nothing really special required from the carb in terms of bypass air, idle tubes or DCR's......FWIW......Cliff
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Specs are @ .050 : Intake closes at 46.3 ABDC opens at 6.3 BTDC.
Exhaust closes at 5.3 ATDC opens at 61.3 BBDC.
Your thoughts? (Tried to post pic of card but I can't shrink them small enough to post)
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My 421 sbc idle about 12" cam is 227/239/107/103. 18 deg initial 10 vac.
Carb has LIAB .063 move the UIAB to the cover .043 tube is .031 I think DCR is .05 I think.
This is the best one I've done.
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My thoughts.
Anytime I've found myself having to run more than about 10-14 degrees initial timing to get good vacuum at idle the cam has been just a tad big for the CID and static compression ratio.
I ran into this about 15 years ago after assembling a 455 Pontiac engine. I did NOT choose any of the parts, just hired to assemble and dyno it.
It used the same cam I've put in other 455 builds and the same CNC ported aftermarket aluminum heads. The only difference was this engine had lower compression, around 9.8 to 1 instead of 10.5 or so.
One wouldn't think that would be a big deal but that engine didn't like 10-12 degrees timing at idle, and it needed more idle fuel and bypass air to be happy. I'd also add this it wasn't quite as "peppy" right off idle, at low RPM's, and it made less power on the dyno as well.
Not a deal breaker for sure, but the experience taught me that it would have been a little happier with about 5-8 degrees less duration, or a half point or more compression......
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I'm slowly making some progress. I shrunk the LIAB's down to .063 and it did not like it. Lost control of mixture screws and had a noticeably stinkier exhaust, lost a tad bit of vacuum. Opened them back up to .070, seems better. I'm able to get a decent idle, in and out of gear, 11~12"vacuum with 18 Degree initial and another 10 from the vacuum advance for a total of 28. vacuum wanders from 11~12".
We tried a friends QFT 750 holley. With that carb, I'm able to get a steady 12" vacuum without the added timing from the vacuum advance, for a total of 18. We cracked open the secondary adjustment screw to stay of the front transfer slots to get a nice idle. Exhaust had a better note to it as well. The QFT has the 4 corner idle and only needed 7/8 turn on each screw to be happy. Better throttle response when slowly cracking the throttle open also. I probably could have taken a few more degrees of timing out at idle and still had a good idle. Nice and steady on the vacuum gauge.
This tells me that the engine is capable of producing at least 12" without the need for added vacuum advance at idle that the Q-jet wants. Not sure what to try next. It didn't like the LIAB's taken down to .063. A little better with them opened up to .070. No difference when pulling off a small vacuum line. It picks up about 30 rpm and a tad more vacuum if I partially close of the choke.
Since it responded to opening up the idle down to .058 I'm thinking opening them up to .060. Take the idle tubes up to .039~.040?
Any thoughts or tips would be appreciated. Thanks
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The results make no sense to me.
IF you close down the LIAB this puts more fuel to the mixture screws.
IF you tip in the choke flap and get an improvement in vacuum richening it up, then it wants more idle fuel at the mixture screws.
In some cases when making the LIAB smaller I've also had to use smaller idle tubes and/or smaller DCR's at the same time to get control of things.
One thing for sure is that on engines with low vacuum at idle speed smaller LIAB's produce more sensitivity at the mixture screws and clean up the idle some.
I've also found that with some engines smaller IAB's just work better. This simply happens when the vacuum is low and signal to the idle system is a little "weak".
Holley carbs shine in that area because they were NOT produced to have to pass emissions so very generous in the idle and off idle system, always have been. This is good for idle with big cams but heavy fuel consumption is typically the result.
The Q-jet actually has an EXCELLENT idle system and the bypass air being a controlled vacuum leak is superior to drilling holes in plates or opening up the plates to add air. If we raise the throttle plates in a Q-jet to add idle air they very quickly pull from the boosters (nozzle drip) as the system is considerably more efficient than a Holley style carburetor.
In any case you are still baffling me with the engine wanting all that timing and "low" vacuum even when you throw timing and fuel at it. I've build hundreds of engines and the only time I've ran into that sort of thing was full-race stuff with super tight LSA camshafts, locked out timing, and "flooding" them with fuel to keep things happy. In a "race" engine nobody cares anyhow.......Cliff
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I started out with the above specs. .077 LIAB size. I closed up the LIAB's to .063. This resulted in a very rich idle and no control of the mixture screws, Very little difference with them fully seated. engine would not stall. By closing up the bleeds this provided more than enough fuel at the transfer slots to keep things running, correct? Engine would load up if I closed up the choke flap.
I then opened them back up to .070. This resulted in regaining control of the mixture screws. Engine will stall fully seated. If I close up the choke it will stabilize the idle somewhat and pick up about 30 rpm.
Any idle circuit mods also effect the amount of fuel at the transfer slots correct?
I think I need more bypass to get it off of the transfer slots and also slightly more idle fuel. I have quite a bit of transfer slot exposed, but not opened so far as to have any nozzle drip.
With the holley, I was able to ditch additional timing from the vacuum advance at an idle and have a nice steady 12" of vacuum. Tryin to get the Q-jet to do the same.
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You were on the right track with the smaller LIAB's, just too much transfer slot exposed and probably DCR's a little to generous.
That engine should EASILY be pulling 2-3" more vacuum than it is without a butt-ton of timing at idle, at least by looking at the specs you provided. I'd be real tempted to advance the cam 2 degrees, I'll bet that will make the process a lot easier.
In any and all cases we still have to give the engine what it wants to make it happy. Believe me I've tuned engines effectively that had 5-6" vacuum at idle and struggled below 1000rpm's! You will get there, it's just going to take exactly the right combination of timing, bypass air and idle fuel
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That engine should EASILY be pulling 2-3" more vacuum than it is without a butt-ton of timing at idle, at least by looking at the specs you provided. I'd be real tempted to advance the cam 2 degrees, I'll bet that will make the process a lot easier.
I did call Howard's last week for their feedback on this cam. Said it should be pulling 13", especially in a near 500 inch engine. Asked what my cranking compression was, 160 psi. (forgot to mention that in my original post). The tech said that's good but could be a tad higher. He asked if I degreed the cam. No. He suggested advancing it 2 degrees......
Also suggested getting some miles on it before getting to carried away.
I've got to give Howard's some credit. Answered the phone right away, didn't get put on hold, didn't treat me like a idiot, and didn't even bash on the Q-Jet like so many of them like to do. I went with Howard's because they had the largest selection of Gen 6 cams. All of comp's stuff for this generation was the extreme thump your mama stuff and we all know how that works out.
I do appreciate help on this. Thanks
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Last time I looked it was 2021, but I still hear folks "bash" Quadrajets and regurgitate old, inaccurate and outdated information about them.
I woln't touch one made in 1965-66, and try to avoid most of them made before 1969. By the time Rochester corrected the main issues with them it was too late and they had a BAD reputation for bogging and leaking bottom plugs. To this day folks still think all of them are leaking and dab a big glob of monkey chit over the plugs when the "rebuild" them.
The same idiots that tell you to throw it away will tell you to put a Holley Street Avenger on it in the same breath. What a complete and utter POS those are. I've had locals bring vehicles up here using them and despite my best efforts I can't get them to work for chit.
Judging by what I saw at the Car Show at First Friday in town couple of weeks ago Edelbrock Performer carbs are the "go-to" for most. There were at least 150 cars there and at least 80 percent of them had one of those AFB clones sitting on an adapter or aftermarket aluminum intake. Didn't really see too many Holley carbs, and not surprised and the newer varieties aren't all that great.
If I mess with a Holley carb it's going to be from the 70's or early 80's, downleg boosters and rear metering block. My favorite is the 4781-2 850 DP and early 750/780 cfm vacuum secondary models.
I avoid the Edelbrock AFB clones like the plague. It's cool to see what folks do to install them. Cut the factory fuel line with a hacksaw blade, run a long piece of rubber hose around to the left rear fuel supply and secure it with a couple of hose clamps. Talks about a fire waiting to happen....YIKES!.......
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Single plane or dual plane intake . Idle Rpm ? Vacuum readings in and out of gear.
Optimal idle advance is typically about 32 degrees. So you could have 12 initial and 20 vacuum advance.
You shouldn't need those huge idle tubes and down channel then.
I run a similar cam with 17080213 Quadrajet in my BBC that idles 900 rpm with 14" vacuum in neutral and 750 rpm 12" vacuum in gear. relatively smooth idle.
Next I converted it to DMAB. Idle fuel ratio 13:1 , cruise fuel ratio 15.5:1 with .031" idle tube and .046" down channel.
If you want throttle feel/response like that 750 holley you will need to work on the linkage of that quadrajet to get the secondary butterflies opening much quicker. Then you'll never look back.
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73SS have you checked your damper for TDC.
Nice carb old cars.
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"Next I converted it to DMAB."
Old Cars, could you describe this modification?
Pics?
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73SS have you checked your damper for TDC.
Nice carb old cars.
Yes, during the build with a dial indicator, spot on. I would like to think that nothing slipped on the damper, but anything is possible. The entire rotating assy came as a kit.
The car is starting to come around as I get some miles on it. Was able to close the throttle a tad and get it off the transfer slots some more. I'm going to leave the lower bleeds at .070 and try some .039 tubes this weekend. If it doesn't respond well to that I'll put the .038's back in.
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"Next I converted it to DMAB."
Old Cars, could you describe this modification?
Pics?
Don't know if he did his the same, but mine I blocked original bleed & added 2 about where they would be on an older DMAB carb. I also reduced the LIAB to .063 & moved the upper to the lid.
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It's all in the details.
Blurbs about making modifications without specifics don't provide the readers with anything they can work with.
So basically not helping the situation any if at all.
Generic answers don't help either. Like optimal advance at idle being 32 degrees. Where does that come from? Why is 32 degrees the magic number for these engines? Is that proven fact and well documented or did someone just happened to find an engine once that like that much timing at idle and ran poorly if you tried anything else?
I've tuned engines that HATED much more than 8-10 degrees at idle, and others that had to have 35 degrees to even have a snowballs chance in hell of idling under 1000rpms.
Once again, it's all in the details and generic or blanket statements don't really help much when it comes to these things.......FWIW.....
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Was simply referring to the setup I used. "77 cruiser " understood.
No need to revert to "bashing"
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Was simply referring to the setup I used. "77 cruiser " understood.
No need to revert to "bashing"
Are you saying you plugged the Truck style single main air bleeds (sizes?) and drilled holes in airhorn and float bowl to copy Passenger car style main air bleeds (sizes?)
Pictures?
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"Was simply referring to the setup I used. "77 cruiser " understood.
No need to revert to "bashing"
If you consider asking for "details" bashing then you are once again mistaken.
You came on a thread were someone is asking for help and made a few blurbs but not enough detail for them to have something to work with.
I know full well how a SMAB carb could be converted to the earlier design but it would NOT be a good course of action. The SMAB design is much more efficient and why the factory experimented with it in 1977-78 on the divorced choke truck units, then went to that set-up across the board in the early 1980's.
It simply works better and doesn't require nearly the metering area and metering area change from the upper section of the rods to the power tips.
Even so it really has NOTHING to do with the issues that are going on here. The problem is idle and for some reason this engine build isn't making nearly the vacuum that it should. I've built smaller engines with less compression and cam and they made more vacuum at idle with a LOT less initial timing that the big 489 is making here.
I'm suspecting a more fundamental issue like late intake closing, but that's just a guess on the information that I've seen to date......Cliff
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Are you saying you plugged the Truck style single main air bleeds (sizes?) and drilled holes in airhorn and float bowl to copy Passenger car style main air bleeds (sizes?)
Yes
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picture
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Thanks for the pics, as with anything else a picture is worth a 1000 words.
For the readers, using a tiny direct main bleed/blocking the indirect bleed and relocated the upper IAB's to the airhorn would pull a LOT of fuel from the idle and main system. Haven't tried that and woln't be in one of those but I be assured it will fatten it up everyplace and no doubt it would be fine with .031 idle tubes and .046" DCR's at 14" vacuum at idle speed, especially if you didn't open up the LIAB in the truck big block carb.
Those carbs were pretty "fat" without any modifications and why Edelbrock patterned their "850" cfm model 1910's after them. In stock form with a .038" idle tube and .055" DCR's the 1910's have enough idle fuel for a Pro-Stock dragster engine!.........Probably why a lot of customers call up here bitching about them being a little "fat" at idle on their "mild" street engine build......FWIW......Cliff
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If that thumb wasn't in the pic I'd swear that was my carb. ;)
If you have time & an extra core try one.
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PLENTY of spare cores, no time and no need to go that direction. My personal carb is custom tuned using one of the "recipes" in my book. Nothing will outrun it, and believe me the dyno shop I use has tried, and I've ran every size and type of carb out there against it at the track and it's always posted quickest ET and highest MPH.
For certain applications I will relocate the upper idle bleed to the airhorn and use a small size and block the ones in the main casting above the DCR's.
The factory actually did this on a few of the "high performance" units. Coincidentally was working on one of them today from a 1970 Ford 429 Cobra Jet engine. Talk about a "special" carb. It had tiny MAB's and about the smallest upper IAB's you will find on any Q-jet in the airhorn. They worked well for what they were designed for as the 429 CJ engines were heavy breathers and poor signal to the carb at idle, off idle and low RPM's..........
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other than getting away from large idle tubes and dcr's, what are the benefits of this modification?
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Basically blocking the indirect upper IAB in the main casting and moving it to the airhorn requires a much smaller size to be used.
Keep in mind that an upper bleed in one location or the other is required or the fuel bowl will syphon down after the engine is shut down.
When the throttle plates are closed and engine is idling there is high vacuum or strong "pull" at the mixture screw holes and any exposed transfer slot.
For most stock engines the signal is very strong and fuel pulled easily into the engine. The factory used a lower idle airbleed just above the throttle plates as a vent and to reduce the signal some, and other upper airbleed to reduce it even more and provide a vent to prevent syphoning.
The sizes of these holes vary considerably depending on carburetor part number and application. It is part of the total calibration since it not only provides idle fuel it also provides fuel thru transition to the main system as more transfer slot is exposed.
Once in a while I'll venture in that direction with a carb I'm building here. When I do it's typically when the engine "builder" has went with a pretty "hefty" can on a tight LSA and the compression ratio isn't going to be high enough to provide good signal at idle speed. Experience has taught me when to do this and we almost always increase base timing at the same time, so I may have the owner send the distributor here as well so I can shorted up the curve some.......Cliff
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I installed .039 idle tubes over the weekend. It made a small improvement. Now it responds to pulling off a small vacuum line to where it didn't before.
Question: Did all BB carbs have a .136 bypass or just the smogger units? My original '73 carb is at .136. Do any of you go this big on a BB carb? I'm currently at .125"
To re-cap, I started with 10" vacuum and am now up to 12, 850 rpm, But it still requires lots of timing lead. Its getting there in small steps. I'll have to put my carb tuning skills on hold (Or lack thereof) :D for a while until I get a fuel pressure issue solved. I'll start a new post for that rant.
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I have found most if not all 1970-74 Chevy 454 units uses .138" idle bypass air.
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While trying to get this thing dialed in, I have found that the #2 plug turns black. I had convinced myself that the intake was not sealed properly and causing all of my issues. I pulled it off and took it to the machine shop, They said it was slightly bowed and took a small amount off. While I had it apart, I took the springs off on #2 to check for sticky guides or valves not sealing. I do not have leak down test equipment but the cylinder had what sounded like minimal leakage while filled with compressed air. everything checked out great. I tested the plug wires and they all ohmed out within spec, I decided to replace them anyhow since they are about 7 yrs old. Put it all back together and the same thing. Does not idle well and #2 turns black. Temp readings with a laser temperature gun show that # 2 is running about 250 degrees, the remaining 7 are all high 300's low 400's. I have read on line where the experts say that this is a irrelevant test at idle. The rest of the plugs look ok, some darker than others but #2 is turning black. It doesn't look like oil, the black easily flakes of the plug to where oil will be sticky. The engine hasn't used any oil. Buy comparison, #1 plug is white, looks like it is running lean if anything. Compression test is +- 3 psi across the board. Plugs actually look good after a good 10~15 mile run, but then #2 gets black with idling and in town driving.
I don't claim to be an expert but I've been doing this 25yrs and am stumped. I've never had a motor that has needed this much timing or fuel at idle. Could my intake be junk and just not sealing ? I would think it would suck oil from the bottom side if that were the case. Why would #2 appear to be getting all the fuel? One side of the carb dumping more fuel than the other and it's all running to #2? I have no nozzle drip at all. Any ideas?
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Did you replace the spark plug or move the one on the troubled cylinder to a different location?
Where is you PCV hooked up?
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Replaced the plug, PVC is on right valve cover connected to the correct port on front of baseplate. Stock aluminum gen 6 valve covers.
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I was hoping it would be something that simple like the PCV plugged into one of the runners and not into the carb to be evenly distributed to all cylinders.
A few years ago my engine developed a slight miss at idle and low RPM's. Started idling rough as well. I isolated the troubled cylinder by removing one spark plug wire at a time from the HEI until I got little to no change. Coincidentally it was the #2 cylinder.
At that point I replaced the plug and wire, no improvement. Then I did a compression test and it was same as all the other cylinders.
Hum? So I removed the intake and replaced the intake gaskets and it corrected the issue. Good thing that I did because the gaskets were failing everyplace. They were the grey paper type gaskets. I replaced them with the Felpro blue variety with the metal reinforced centers and material bonded to both sides and haven't had any issues since......
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Thoughts on this? I don't like the way the plug is slightly recessed. I noticed this while assembling the motor and sent some pics to Brodix and they said it would be fine. This is the correct NGK plug that Brodix lists for this head. Could this have something to do with why this motor needs so much lead? I would think that the plug should be at least flush with the head opposite side of the valves.
I finally figured out how to re-size images!!! ;D
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There called extended tip spark plugs.
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pics
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There called extended tip spark plugs.
Thank you for the info. I did some research and decided upon an autolite 3924, extended tip. Installed a few and rotated motor over with no interference. Edelbrock & Trick flow both list the 3924 for their BB oval port heads. It didn't make any difference on the amount of timing lead that it needs, but I'll be curious to see if the #2 plug stays clean.
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Wanted to give an update. I my above post I described how the #2 plug was turning black and was stumped as to why. I decided to pull the engine back out because I was never satisfied with the way it idled and wanted to degree and or replace the cam. I did a leak down test and all cylinders are 10~13% on the gauge with the exception on #5, It has a 35% leak past the intake valve, you can hear and feel the air escaping from the intake. #7 is the next to fire followed by #2. Since the #5 is still on it's intake stroke while #7 begins to open I'm thinking that when #5 starts the compression stroke, #2 is starting its intake stroke and receiving what is getting pushed past the #5 valve. # 5 & 2 do both share the same side of the intake, dual plane. I think this is why #2 is rich and turns the plug black. #2 also runs about 100 degrees colder than the other cylinders using a infrared heat gun.
What do you all think about this? That's the only thing I can come up with as to why it turns black. I second guessed myself and thought maybe I installed a ring upside down on that cylinder but the leak down and compression results are good.
I was quite surprised to find a leaky valve, When I got the heads we tested all the valves with a home-made tool to seal the ports and pull a vacuum on each valve to check for leaks. More than half of the valves were leaking. These were new heads, I called Brodix and they said to send them in for repair but I decided to lap all of the valves myself. Afterwards all valves held 20"'s vacuum for 15 mins or more and I called it good.
I also bought the tools to degree the cam and after checking I found it is 2 degrees retarded. I have it installed straight up. I have the specs above, open to cam suggestions, I don't think I made a good choice on the cam.
I did take the car to the track, Ran consistent low 12.30's @ 110, 1.7 60'. OK but was expecting more for a near 500 inch motor. 4100# chevelle, Through a full exhaust, 3.73, 2500 convertor. Q-jet ran flawless.
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Advancing the cam 2 degrees isn't going to do much for it and may even slow it down a bit. The cam is pretty small right to start with for 489cid with 10 to 1 squeeze and the head flow available. That's about how much cam I'd use in a 454 build with less compression.
Below is a dyno chart from a 455 cid engine with less than 9 to 1 compression using Pontiac Super Duty round port heads and a 230/236/112lsa HR cam. Idled with 16" vacuum at 800rpm's and I knew right then we needed a little more cam in it.
Low 12's at 110mph is showing about 460-480hp being used just doing some rough "math" in my head using the vehicle weight. Certainly some room to grow there for sure......IMHO......Cliff
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You didn't answer what intake manifold you are using, at least not that I could find
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You didn't answer what intake manifold you are using, at least not that I could find
Edelbrock performer RPM Q-jet. part # 7164
I believe my original poor idle problem was due to #5 intake leaking and also a poor cam choice.
233.6in 246.6ex @ .050, 110C/L, 114 lobe sep.
Too much exhaust duration for the amount of intake duration? This cam would be better suited for a blown application. Lift, duration & center line were all spot on with the degree wheel, other than everything being 2 degrees late. Cranking compression isn't that great either at 155 psi.
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I'm not sure exactly what's going on but something isn't quite right with the build.
489cid, 10 to 1 compression, 230/246/114LSA cam and you are only seeing 155psi cranking pressure and it takes 20 degrees initial timing to produce 10" vacuum at idle speed. It should EASILY make 13-14" vacuum at 700-750rpms with only 10-12 degrees initial timing and cranking pressure is down at least 20psi......IMHO
Hopefully you'll get it figured out at some point......Cliff
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What is the compression height of the piston and what is the head gasket thickness?
Did you perform the compression test with the throttle all the way open and all the plugs removed?
Seems low.
Put a mighty vac on the brake booster and see if it holds. Trans vac line too.
How did the valve springs look on the #2 hole?
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What is the compression height of the piston and what is the head gasket thickness? Machinist said pistons are 10 in the hole. I measured around .008", Hard for me to get a good measurement due to dome and piston rock at TDC. Head gasket is cometic, .040 thick.
Did you perform the compression test with the throttle all the way open and all the plugs removed?
Seems low. Yes
Put a mighty vac on the brake booster and see if it holds. Trans vac line too. Brake booster good, OD trans no vac line.
How did the valve springs look on the #2 hole? Springs & valves are great, Not sticking, Valves seal excellent on that hole. Rocker geometry is good.
I think this cam has too much overlap, card says 63.6 * overlap for advertised and 11.6* overlap at .050 lift.
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What is the advertised duration and check point?
The cam in my 455 is 289/308 @ .006" tappet lift, 112LSA and ICL at 109.5 and it makes 13.5" vacuum at 750rpms with only 10 degrees timing in it. Cranking pressure is 198-200psi across the board..
230/246 @ .050" is not a big cam in that engine and with 114LSA it shouldn't have a lot of overlap.
Late intake closing lowers cranking compression and will make the engine somewhat "lazy". Even with that said that little cam in a near 500CID engine with 10 to 1 compression it should me idling with a LOT more vacuum and not having to run more than 10-12 degrees initial timing.
Something is fundamentally wrong someplace......IMHO......
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I agree with your comments, Thanks for the tips. Some of the poor vacuum should be due to the #5 intake not sealing well. I don't see anywhere on the card at what lift they take the advertised duration at.
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"Degrees of Duration" 284.6*/289.6*
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You will find measurements of the lobes, intake BHR233353 and exhaust BHR247360, here:
https://www.howardscams.com/sites/default/files/lobe%20list%20email%201-20-2014.pdf
HTH
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guess my post got cut short... both howards cams i've installed the advertised duration was at .006" HTH.
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Thanks for the replies, I think this cam would be better suited for a 454 with the stock heads. Any cam recomendations?
I took the head off with the leaky #5 valve and found that the valves have been floating, The intake valve kissed and took it out of round ever so slightly. Cant see it without a dial indicator. One of the spring shims got beat to hell as well. I installed the recommended howards springs that match this cam, Set them to the correct height, within a few thousands. I had 2 of the springs tested and they are about 20 ponds light on the seat pressure. I didn't realize I was getting into float, I've got a 6K rev limiter. It would start to break up just before 6K, I figured my rev limiter was off by a few hundred and it was valve float that was causing the breakup. Cam and springs are supposed to be good to 6400.
Looks like I'll be needing to replace all of the springs and a valve, Anybody have a trusted brand that they use?
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Common problem running into issues at high RPM's with HR lifter set-ups. Spring pressure may not be the answer and for sure that cam isn't making power past 6000rpm's in that application so really no need to rev it that high.
I've dyno'd plenty of big CID engines and a 230 @ .050" cam isn't making power in a 450-470cid engine must past 5500rpm's and some quit down around 5000-5200......
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I talked with a tech at Howards and apparently the cam that I have is more for blower & nitrous use for a 454 and not a stroker, which he said is contributing the low psi on a compression test. Also the springs they listed are the minimum requirement. Would be nice if that was made clear in their catalog.
Anyhow he recommended a 243/249 @ .050. 640/640 lift. 112 LSA 108 centerline.
Lunati also has a similar grind: 240/245 @ .050. 612/612 lift 112 LSA 110 centerline.
Thoughts on these please.
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David Vizard. These are tight LSA for BBC. Do not compare this to a Pontiac
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"I talked with a tech at Howards and apparently the cam that I have is more for blower & nitrous use for a 454 and not a stroker, which he said is contributing the low psi on a compression test."
That statement really doesn't make any sense to me. So the tiny cam on a wide LSA without much overlap makes "low" vacuum at idle speed on a stroked 489cid engine with 10 to 1 compression?
So tell me how going to a bigger cam on a tighter LSA is going to improve that deal?
I would suggest correcting your leaking valve issues and advancing the current cam to see if it helps some before jumping to a different cam and having to change valve springs, etc......
As far as the Vizard stuff goes I'm sure some folks do well with it. I've ventured down that path a few times and wasn't overly impressed aside for the "raspy" idle quality, stinky exhaust and nitrous-like power curve punching a butt-load of power into the mid-range. If those are your goals for the project then you may be happy with all that.
Related to the topic recently a customer called up here building a 454 Motorhome engine for his 1 ton dually and went that route. I asked him why he thought going to a really tight LSA cam with the ICL clear down around 100 degrees was going to be a home-run in that application. He very quickly snapped at me that Vizard does this all the time with excellent results plus he wanted TONS of low end torque and didn't care what the engine did at higher RPM's.
Not wanting to be critical of others I didn't comment and sold him the parts needed to get his carb up to par. He called back several times wanting tech help and was NOT happy at all with the 454 he built using one of those cams. He kept screaming "turd" thru the phone and I guess it was all the carburetors fault instead of the poor cam choice.....FWIW.
Anyhow, these engines are sensitive to intake closing point, and overlap. Doesn't matter if it's a Ford 460, Pontiac 455 or Chevy 454, they all respond in similar fashion and the camshaft is a BIG player in how well the engine works. It should be very carefully chosen based on CID, the static compression ratio, head flow and intended use of the vehicle.
I see the results of this sort of thing a LOT here. The first thing folks need to keep in mind is that an engine up around 500cid with pretty high compression is NOT going to be happy at all with a relatively "small" cam in it. Just in shear terms of cylinder filling abilities alone using a cam that's a very good choice for a smaller engine isn't going to be the ideal cam for your much larger engine, all else being equal.........Cliff
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David Vizard teamed up with Lunati Camshafts to have a series of cams ground to his specs . Lunati – Flat tappet hydraulic custom ground on Voodoo lobes
with lunati spring package and lifters
specs: 273 duration 107 LCA at 4 degrees advance
227@.050 - valve lift .552 inch with 1.72 rockers
This is the one I used which was ground on Voodoo lobes , which are famous for making power. This is an agressive lobe and the builder must keep this in mind. David Vizard dyno tests on a a 460 cu in BBC with prepped peanut port heads resulted with 450 ft lb torque at 2600 rpm and 550 ft lb at 3800 rpm, HP at 5600 rpm was 512.
Peanut port heads are truck heads with ports of only about 250cc. These were often thought of as throw aways until some builders dyno tested these heads in nearly stock form only to find out they delivered nearly 500 hp. David Vizard did a pocket port with a 2.190 intake valve. Thats all. Of course a good valve job.
On a 468 cu in BBC build with stock Edelbrock E-Street heads , Victor Jr intake, and 850 Holley peak torque was 588 ft lbs and peak HP was 581. Same cam. A Holley 950 HP further boosted torque to 598 ft lbs and 599 HP. And torque at 3000 rpm was 550 ft lbs. This was a 10:1 compression engine. With a port job to these heads and a flat mill to bring compression to 10.5, output climbed to 611 ft lbs and 626 hp. We have already reached a well built Stroker 496 cu in output with more camshaft.
I live in southern Ontario Canada where we have 2 drag strips close by.
I have a friend with 1969 El Camino custom built 496 BBC who occasionally runs at the drags. The engine with AFR heads was dynoed at 630 hp. This car runs 11.4 at the strip with a 3:73 rear gear ratio . I have helped him out numerous times. He does not drive the car far because the fuel mileage is poor to say the least. I have another friend with a 1972 GTO 480 something pontiac stroker he built himself. He runs 11.3 at the drags and uses the car as a daily driver. This car has a 3.08 rear axle and gets decent fuel mileage with good manners. Very impressive true street car.
There is a trend these days to build a true street car and good HP with very good fuel mileage. My car is a 1975 Monte Carlo 454 BBC with peanut port heads that I use for touring and practically a daily driver in the summer. This is a 3900 lb car with a 2.73:1 rear axle and 400 turbo trans. Performance is outstanding in the lower rpm range on up. I get 15 mpg on the highway without trying hard. No I don’t have any time slips. My brother in law has a 1969 Chevelle 427 cu in 425 hp and 4:11 rear axle. This is an original car that he has owned since 1969. I have driven this many times. Those cars did not start making horse power until the upper rpm range and he shifts it at 7000 rpm. Although this car may be the envy of many it does not have the low rpm street performance of my Monte Carlo or the previously mentioned GTO, even with a 4:11 rear axle.
I don’t really care what camshaft people choose (unless I am building the engine.)
David Vizard was once asked his opinion on something. His answer was . “ I don’t have an opinion I have a dyno.”
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I get involved with quite a few Pure Stock and FAST Class cars because they are required to use factory iron heads, stock intakes and Q-jet carburetors. I've helped out quite a few folks with big block Chevy engine set-ups for both classes.
You'd be amazed at the power we've made with those "door stop" flat iron intake manifolds teamed up with factory iron heads. One of the very first ones I got involved with was a 1970 Chevelle's 454 engine (stroked to 496). I helped with the cam choice and did the Q-jet and factory points distributor for it. He had the heads opened up for the larger 2.19/1.88 valves and some minor work in the bowls and short turns. Dyno day came and he was getting all sorts of "flack" from the dyno shop he carried it to for testing. They were FULL of under the breath rude comments telling him it wouldn't make chit for power and to get rid of the POS iron intake and Quadra-Junk carburetor sitting on it. Keep in mind that the engine was totally "stock" in appearance by Class rules. He told me that when they made the first pull on it that the dyno operator and his staff were dialing 911 and heading for the exit doors! After giving him all sorts of crap about the parts being used it cranked out close to 600hp and over 600ft lbs torque on the very first pull!
The cam I selected for it was a custom ground HR Comp cam with XFI lobes and wide LSA to keep vacuum high and idle relatively smooth to meet class rules. I don't remember the exact cam specs but it was in the 255-260 @ .050" range and around .650" lift at the valves.
I've never read one word of any posted literature or articles by Dave Vizard so can't comment on anything about any of that.
I will say that I've used PLENTY of tight LSA cams over the years with advanced ICL. No problem making power with them, but the nasty idle quality, stinky exhaust and "reversion" we saw at low RPM's keeps me from going that direction with street engine builds.
It's pretty rare if I'll use a cam with an LSA tighter than 112 degrees and ICL in the 108-110 range. I also use higher compression and really tight squish with my street and street/strip engines plus good flowing heads and superb exhaust systems.
Most "builders" use lower compression then try to bring back the lost power and efficiency by using smaller cams on tighter LSA's. To each his own with that deal and to date I've never seen a rule book about any of this stuff, so do what you like and what makes you happy........
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All beer is good beer some are just better than others.
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Same thing with camshafts, all are good just some better than others.
Attached is an overlapping dyno sheet showing what happened when a back to back cam swap was made with no other changes. Nothing fancy about the engine, just a basic Pontiac 400 with a stroker kit installed to get it to 463CID, 9.3 to 1 compression, and factory iron heads flowing 250cfm. So really no better if as good than a well prepared set of Chevy peanut ports.
The first cam is the "famous" XR276HR Comp Cams HR. They recommend that cam to nearly everyone that calls them for a HR cam choice. It was also Butler's (company that specializes in Pontiac engines) "go-to" cam until I sent them the dyno sheets.
Anyhow, the XR276HR cam is pretty aggressive with short seat timing events, tight LSA (110) and ICL advanced 4 degrees (106). It sports 276/284 @ .006" duration and 224/230 @ .050".
The problem and why it was replaced. It was too good at cylinder filling and causing pinging/detonation of pump fuel. Yes, what folks don't realize here is that you can put a small cam in a big engine and make too much cylinder pressure for pump gas even below the proverbial "brick wall" of 9.5 to 1 compression.
My suggestion was to put a bigger cam in the engine on a wider LSA so I recommended using older Magnum lobes with 289/308 duration @ .006" and 236/245 @ .050" and to move it out on a 114LSA and install it with the ICL at 110 degrees.
No other changes made. The results were no more pinging, smoother idle and a nice power increase over a broader RPM range........
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A few years ago my brother rebuilt the engine in his 1970 GTO 455 4spd , 355:1 rear axle . He has owned this car since new and it is still stock down to the carb and exhaust manifolds. He just street drives now and not that often. This is the camshaft he chose. He says he is very happy with it for what he does.
Part Number: 60918
Pontiac Hydraulic Flat Tappet Camshaft
Pontiac - 287, 301, 316, 341, 350, 370, 389, 400, 421 & 455
Performance level 3 - Torque Beast - Delivers impressive midrange and top end power. Healthy sound. Economical price.
INT/EXH - 288/298 Dur @ .050” Lift: 214°/224° RR: 1.5/1.5 Gross Lift: .444”/.467” LSA: 112° RPM: 1750 to 4500 Redline: 5000
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That cam isn't a Crower grind, it's actually an old "generic" cam that's been marketed and sold under at least a dozen labels over the years.
The companies selling them "juggle" the specs slightly to make it look like their own cam, but they simply buy them directly from CMC then re-box/sell.
It's actually an excellent camshaft for a Pontiac 400 engine build with moderate compression. A tad small for a 455 but still works pretty well there too. Marketed by Summit Racing as the 2801 and often called the 068 "high lift" cam in Pontiac circles. Pretty popular overall and has a lot of seat timing plus considerably more lift than the factory 068 and 744 Ram Air camshafts. The gentle ramps are easy on the valve train and wide LSA makes for smooth idle, strong low end/mid-range power and good street manners.
Here is a link to some Pontiac camshafts that were sold over the years. Drop down to 214/224 @ .050" offerings and you will see how many Companies market that grind and notice how the "advertised" specs are different since they are trying to make it look like something they grind "in house".........
http://www.pontiacpower.org/PontiacCams.htm