Cliff's Quadrajet Parts and Rebuild Kits
General Category => Quadrajet Carb Talk and Tips => Topic started by: Miles on September 28, 2017, 08:19:50 AM
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Good morning,
on a dyno, is a vacuum of 1.4" an indication that the carb is too small or is that a normal reading.
Thank you
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Yes, specially if it's near max rpm. Should be 0.5" or less, ideally. Actually it means your engine is too big or you're making too much hp =D
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Don't be too quick to blame the carburetor, could be other things including the intake port capacity, intake manifold, etc.
What are the engine specs and dyno numbers?
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463 cid, 10.49 static compression ratio, 230/236 at 0.50, 112 LSA, gross lift .575/.585, 108 ICL, full roller, CNC ported fast burn aluminium heads 204 cc ports flow 305/220 at .55 lift. EPS 800 95/110 jets 65/47 rods and 750 HP 73/73 jets, HEI 16 initial 29 total no vacuum can, port matched high rise dual plane no heat
490HP at 5200 and 552 lbft at 4200 0.6" vacuum at 3000 rpm 1.35" vacuum at 5200 rpm with the EPS 800, 500 HP at 5300 rpm and 561 lbft at 4000 rpm no vacuum numbers with the Holley 750.
I'm just wondering what the ball park vacuum number at WOT max rpm is for a street engine. I've heard anything over 1.5 is a restriction in a street set up and racers like 0.5-0.75". Don't know it that is true or BS.
Thank you.
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Most of the ones we've done have been around .4 to .9" at WOT.
I don't pay a lot of attention to such things to be real honest. In a street driven vehicle the engine will spend very little time right up at the shift point anyhow.
Far more important is average power and power in the loaded rpm range where the dyno can measure it. The broader and flatter the power curve (torque) is the better.
Great torque numbers, HP seem a bit "light" for the CID and head flow and it's quitting pretty early in the rpm range, probably needs a bit more cam, or just could be the dyno as they vary some place to place.
I'd also add that making peak torque at 4200rpms should put peak HP up near 5600-5800rpm's based on the builds we've done here with similar CID, head flow, cam specs, etc.
I would run vacuum advance if this is street driven, about 10-14 degrees would be enough. There I no reason not to use it, and you simply loose power and efficiency in the "normal" driving range running w/o it......Cliff
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I'm getting intermittent detonation, worse with the vacuum advance and part throttle pulls. Has 210 psi cranking pressure I may install a larger cam to reduce the pressure and up the high rpm power. Always used vacuum but can't here.
BSFC is .397-.465, air fuel was 10.5 to 11.5 we leaned it to 11.5 to 12.5 Idles and cruises at 13.5-14.5
Thanks for your response.
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It's not really my style to be critical of what others are doing but I don't like the cam choice for that build. It's 463cid and 10.5 to 1 compression, and no mention of the actual seat timing or duration at .002 or .006" tappet lift, but that cam isn't nearly enough to see full potential from the engine. With that much head flow and the good cylinder filling abilities of a roller profile no doubt cranking compression with be high and it will not want a lot of timing and prone to detonation on pump gas.
I've ran into this many times over the years helping folks out with this sort of thing. Big engines with relatively high compression ratios and excellent flowing heads need a lot of cam to make them happy.
When you don't give an engine enough cam it responds by acting like it's a lot higher static compression ratio than it really is. If your dynamic compression is too high, it's not going to like a lot of timing from the vacuum advance at light load either.
I had a 455 Pontiac in here a few years back with an XR276HR cam from Comp, 224/230 on a 110LSA. The engine was only 9.5 to 1 compression but acted more like 11.5 to 1. It POUNDED like sledgehammers at heavy and full throttle and wouldn't take any vacuum advance at all w/o light throttle pinging. It was also WAY down on power from what it should have been. I returned it to the owner not being able to fix it because he didn't want to change the cam.
Jump ahead till last year, a customer built a 455 Pontiac engine with that same XR276HR cam, it was only 9.3 to 1 compression and topped with ported 250cfm heads. It didn't make nearly the power they were expecting and pinged on the dyno hard enough to knock the rod bearings out of it.
The owner/builder called me, of course blaming the Q-jet for all the issues. Even the dyno operator said the Quadrajunk was at fault. I advised that they change the camshaft and provided specs for different one.
The XR276HR cam only made 428hp at 4800rpms and peak tq.
The cam I spec'd out was 289/308 seat timing, 236/245 @ .050" on a 114LSA. I used .380" lobes for a lot more lift as well. They installed the cam and no other changes.
The custom cam made 514hp @ 5800rpms and torque jumped up to 569ft lbs peak and a BUTTLOAD more average power.
Even better the new cam idled better and managed pump gas w/o any issues anyplace.......Cliff
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PS: I'd add here that those Edelbrock carburetors are pure JUNK! I've exploited them over the years, dyno, street and at the track and consider them hopeless. They show up all over the place simply because they are cheap, and do OK at powering an engine well enough to move a vehicle back and forth to car cruises and shows.
The weighted secondary air door is HOPELESS, and the factory ditched that design WAY back in the 1968 when they couldn't get the thru emission testing put in place at that time......FWIW.....
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Thank you for your reply.
Timing at 0.006 is 286/289.
Don't be shy about giving me advice, that's why I logged on to this forum.
I've given up on the EPS carb and trying to make up my mind what size replacement to use, thus the question about vacuum drop at WOT.
I also agree about the camshaft. When I built this thing I was more concerned about torque than HP, wanted to be able to go over the Rockies without changing down to fourth gear. Must have had in my mind a Chieftain or a Tropedo, not a Firebird. I only need fourth and fifth to move this thing around. I'm also not worried about actual HP numbers, nice to say one has 540 HP but how often would I drive it at 6500 rpm? I have a street car not a race car. I used the dyno more for break in and tuning than getting a number.
Didn't really want to admit the poor choice of camshaft but realized this summer I'd have to change for a larger one. The intake valve closes at 43* abdc at 50 which is giving me a rather high effective compression ratio. I calculated the cranking cylinder pressure to be around 190 but it's 210 and I've tested the gauge against two vacuum gauges on a vacuum pump. I've had the distributor in and out a couple of dozen times welding and grinding the plate trying to get the timing where it would give me the most power and not knock. Got most HP and torque on the dyno at 29 degrees.
What intake was on that 455 which switched to the 236/245 cam? Was it a roller or flat? Those specs are close to Dave's O.F. but a LSA of 112 instead of 114.
Would you be willing to suggest a camshaft for mine if I gave you all the parameters of the car and usage?
Once again,
Thank you.
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For sure some changes are in order as 210 cranking pressure is pretty high and tells you that it's closing the intake valve very early and dynamic compression will also be very high and at low rpm's.
The detonation thing happens much easier below and at peak VE because the events are happening much slower and in any N/A engine cylinder filling is more effective at low rpm's. Roller camshafts also contribute more to that deal as they will by design improve cylinder filling at relatively low engine speeds. Hence why the XR276HR cam is a HORRIBLE choice for a 455 Pontiac engine build with much past about 8.5 to 1 compression in it, and even then it's not enough cam to effectively use good flowing heads or make acceptable upper mid-range and top end power.
Nearly everyone in this hobby looks at everything "static", especially cam specs. One has to realize that as the rpms increase the time in milliseconds the valves are open decreases. So what we need to do is to concentrate our efforts to keep cylinder pressure low enough thru peak torque so we can manage pump gas with a "normal" tune.
This is best done with camshafts that have a lot of off seat timing, wide LSA and later intake closing. What this does to the power curve is to make it broad, flat and smooth. Camshafts with short seat timing events, tight LSA and earlier closing intake do just the opposite, they narrow up the power curve, higher peak torque and it will occur earlier in the rpm range. As you are finding out you also get the same result with a smaller cam even if it's out on a 112LSA. So two things work against us here as far as building a moderate compression ratio engine for pump gas, cam too small, and/or LSA too tight.
To date I've never used Dave's "Stump Puller" camshaft simply because most of the 455 engine builds we do here are at least 10.5 to 1 compression and the larger Old Faithful cam suits them much better.
There are other players in the "recipe" to effectively manage pump fuel than just the camshaft, but it is a "key" ingredient and when it's too small the engine really never has a fighting chance to make optimum power or effectively manage pump gas so we're shot down twice before we even get started.
I've also found that quench distance is a BIG deal here as well, as is LSA. For the big Pontiac engines we've found two things to be true in recent years. The wider we go with LSA the more power we are rewarded with, and the tighter the quench the less timing is needed to make best power and they manage pump fuel better. For this reason our street engine builds these days use higher compression, lots of off seat timing, wide LSA and quench is NEVER over .039" for any reason.....Cliff
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I bought that SP in 2011, took me a year or so to get the thing in the car, but I've been wanting to change it out for a larger cam ever since. Was going to run the OF or something close, but change to a solid roller as my comp hydraulic rollers just wont hold oil. I'm on my second set of the 857-16s and they are just no good.
I was going to put solid Crowers on the hydraulic roller SP but that is not big enough, so while I'm changing the camshaft anyway I suppose a solid roller grind makes more sense as it [I think] has softer lead ramps?
Yes Quench is an important factor, I have mine zero decked with flat tops, just the thickness of the MLS gasket for quench distance.
What was the ICL of the 236-245 that went into the 455?
I've been putting off changing the carb and the camshaft for a couple of years but as I found some metal specs in the oil filter yesterday, I'll have to pull the 428 out and tear it down, both to find the cause and clean the entire engine. That did not make my day!
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We've seen troubles with the retrofit HR lifters as well.
My own engine uses the Old Faithful camshaft and Crower HIPPO solid roller lifters set at .005" lash. It has been flawless since 2009 aside from the PRW roller rocker arms that failed and put a ton of metal into my assembly.
I swapped them out for Crower Enduro roller rockers but a bit too late and need to take the engine down and re-ring it.
The PRW roller rockers wear out between the pins and rollers, and we have since removed every set we used or sold and replaced them.
The OF clone we used in the build mentioned above had the ICL at 110.....Cliff
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Thanks Cliff,
Lifters and now the rockers? Crap, I also have PRW rockers. Do you know the part number of the ones that failed or is all PRW rockers that are failing?
Al
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Mine are stainless PQ. I see Dave no longer lists them on his site. Maybe for that reason.
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Mine were the stainless steel full rollers. They look like very good parts and we've had no issues with the needle bearing part of them.
Every single set otherwise developed a LOT of play at the pins/roller tips.
All of those engines also showed a LOT of very fine metal on the magnetic drain plugs (Morroso pans) that we were unable to discover a source for initially. At each oil change the drain plug would have a teaspoon or so or metal "toothpaste" on it, coming directly from the rollers and pins of the PRW rocker arms.
I sent my set back to them for analysis and they admitted that the pins had a poor finish on them back in 2009 when purchased, but they had since corrected that issue. Even after they told us that we've seen quite a few others have the same issues and some of those rockers were very recent production.....FWIW......Cliff
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Cliff,
Thanks for the info. I bought mine in October 2011, sounds like the same ones you had. I'll be pulling my engine and tearing it down when I get a chance. Just hope the metal didn't wipe the crank or cylinder walls. At the least I'll need bearings, cam, lifters, rockers and push rods.
Did you get the aluminium or the steel enduros?
Al
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Steel Enduro's.
The only other full roller rocker arms we've used here w/o issues have been Harland Sharp or Crane Gold Race......
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Cliff,
Are you using the OF shaft with the solids as that was the camshaft you already had in it when you had lifter troubles? If you were to start from scratch would you use the old faithful or a sollid roller camshaft?
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Not having lifter troubles, they are rock solid now since 2009. The problem was with the PRW stainless steel full roller rockers.
Every set we put in service now has failed on the roller tip end developing WAY too much clearance between the pins and rollers and putting a LOT of ground up metal into the assemblies......Cliff
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I understand about the rockers and metal in the oil as that is what I now have, but I'm wondering if you chose the hydraulic cam and solid lifters as you already had the camshaft installed? Would you use a solid camshaft if you were starting over or is there an advantage using the OF camshaft with the solid roller lifters over a solid grind?
Al
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The "hybrid" set-up works well on that cam because it is an older design. Tight lashing the HIPPO solid roller lifters simply takes the hydraulic action out of the equation, pretty much like have a true anti pump-up hydraulic lifter in there. It's a great set-up and trouble free now for many years, and the quietest valve train I've ever had on one of these engines.
I'd go this route again w/o hesitation. It's a little bit of a PITA to lash the valves on my car as the wiper motor is in the way of removing the drivers side valve cover and getting in there to set the valves, but worth the extra effort.....IMHO......Cliff
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Well I got mine apart and the metal came from a broken Comp Cams hydraulic roller lifter. The cup piece broke into five chunks and some chips, some of it going into the oil. I have marks on the crank, cylinders and pistons.
The PRW stainless roller rockers looked OK but I can feel the bearings grind if I hold the main shaft and spin the rocker around it.
Sigh!
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Correction, I noticed the #2 exhaust rocker had made contact with the poly lock. I took two of them apart, both had considerable wear of the trunnion under the bearings even had bearing shaped imprints on the shaft. Rocker is stainless but the shaft is made of soft steel. No wonder yours filled your engine with metal. If they didn't want to use stainless for the trunnion they should have used a stainless inner race.
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PRW kept the set I sent back and did admit problems with early units prior to 2010 or so. Even so we are still seeing problems with more recent units, if you do some Internet searching you'll see that quite a few folks are finding out about the pin to roller and bearing issues, etc.......Cliff
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Hey Cliff, how long have you had the enduro rockers in the engine, running time? Are the trunnions [pivot shafts] stainless as well or just the rocker body?
Have you ever taken one out and tested the feel of the bearings by spinning the rocker arm around the pivot? Just wondering about the quality of the steel used for the trunnion, obviously the ones on mine were not high. I don't want to go through this again.
Thanks for all the info you've posted.
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Mine were purchased and installed around 2009, then removed about 2 years ago and sent back to PRW.
Nothing wrong with them anyplace aside from the rollers and pins running thru them. Some of them had as much as .015" clearance, and ALL of them were worn some in that area.
Made sense to me and was the source of the fine ground up material I was getting on the oil pans magnetic drain plug.......Cliff
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Cliff,
You said you set your lash a five thou. on your engine with the OF camshaft, Crower solid HIPPO lifters and the Crower SS full roller rockers. Is that your lash setting hot?
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I set them at .005" dead cold. They open up to about .008"/010", intake/exhaust respectively when fully warmed up......
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Cliff,
I finally have the engine put together and spent the last two weeks building a test stand to run it on. I went with the Crower solid rollers and the Crower stainless roller rockers. Set them 5 thou cold and they were about 7-9 hot.
When checking hot, using stepped feelers, I noticed I could get a 7 thou in and push it right over the step onto the 9 thou, but when I put a 8-10 feeler there it wouldn't fit. I think the roller may be rolling right over the step and lifting the valve to get the 9 in. Think I'm nuts or is that possible. Is it better to set these from the side so the roller can't roll onto the feeler?
Do you have iron heads on your engine, just wondering if my aluminium heads would change hot to colt a great amount from iron?
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I have aluminum heads on my engine.....Cliff
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Have about four hours on the new build. I can hear the solid lifters but a lot quieter than it ran with the crappy Comp hydraulic rollers.
I think I can feel a little less torque with this camshaft but that could be my imagination as I expect it to have a bit less than the SP. So far happy with it.
Ran out of money buying all the parts and getting the crank ground so I couldn't afford to dyno it before I put it in the car. Wont know how it compares to the SP with the hydraulic lifters. The Torque Masters car club from Sidney on Vancouver Island are having a dyno day in Victoria. I'm going over there on Saturday, will do a couple pulls on the chassis dyno, Wont be a direct comparison but I'll know what it's doing at the wheels.
Cliff you mentioned you removed or replaced every set of PRW rockers you've installed or sold and also mentioned 455 builds. You must be doing more than Quadrajets, do you also have an engine building shop?
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Yes, but we quit doing engines (that require shipping) a couple of years ago. We still do a few here and there, mostly for our own vehicles.
There just isn't any money to be made in that sort of work, they take up WAY too much room and WAY too long to get them finished, plus it's never easy, always lots of problems/obstacles to overcome along the way.
We also do transmissions, but not that many these days, and once in a while set up a diff, but for the most part carburetors and distributors are the main stay here......Cliff