Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: olnick on February 12, 2018, 02:27:31 PM
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Hello all: I completed the second recipe on the carb.
Original: was a bear to get started cold, Ran okay after it was HOT. got 18-20 MPG idle needles did next to nothing ran with them 8 turns dr 10 turns psg side. secondaries were working!
with changes:
idle tube .036
idle down ch. .048
up air bleed .067
lower air bleed .070
idle by pass air .050X2=.100
Holes under idle mix screws .098
main air bleed .070
Needle seat .125
Main air bleed horn .070
MJ 71
rods 41K
hanger K
sec rods CH
spring 3/4 turn
pull off 2 sec.
sec flaps 1.308
APT .047 down 1 1/2 turns in from flush
starts right up from cold if not sitting more than 2 days! if more than two days need to crank to get fuel into bowl.
runs great from cold through HOT MPG 12-14 on a good day!!
By pass air was not correct: I was able to use a different PCV valve to fine tune the bypass air.
Idle needles: Will stall if both turned all the way in. After 1 1/2-2 turns out NO difference psg side 1 1/2 dr side 2 turns out. I can unscrew them all the way without taking them out it continues to run.
17-18 in vacuum.
I have a Rhodes cam and lifters installed
CAM HAS 211 DEGREES AT .O50
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Hello olnick and welcome to the forum. I don't claim to be an expert but if you don't mind, I have a few comments regarding your build. The carb you built is the kind that I prefer. I've built quite a few of them and in fact, I'm actually building one right now. Here are my comments/interrogations on your build.
The idle air bypass is already .070" on each side on this carb number, what was yours before and after, as I'm not sure I understand your .050 x 2.
Also, 1.5 to 2 turns out is next to nothing with those metric threads. I can see you increased the size of the idle tube but not the idle down channel restriction ?
CH rods is kind of lean on the secondary side.
I can see that you reduced the size of the main air bleeds, both upper and lower, as those are usually .120" on those carbs. Did you use the small brass inserts that Cliff sells ? They work great for that.
Did you try playing with your APT position ? Usually quite a few MPGs there if you're off.
what is the car/engine combo ?
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What are the engine specs?
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Thank you Frank400! I re read my notes:
The idle air for each side measure .o5o in. Dr side .050 + psg Side .050 =.10 total
The idle down ch went from .048 to .052 my error from notes
MJ 71 to 73 again my error my notes!
I do have a draw full of secondary needles. recommend??
Yes I did have the little brass caps, they work great to re-size the bypass holes!
I have NOT tried to adj the APT yet.
SBC 355cid. "heavy" cast heads 1.94 In. 1.50 Ex. 9.5:1 CR with flat top pistons. 12 deg initial adv. 36 deg total max adv mech. ported vacuum 10 deg max.
Rhodes cam and lifters installed 10W/30 full syn oil
THE CAM HAS 211 DEGREES AT .O50
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What are the casting numbers on the heads?
What are the rest of the cam specs, grind number, who made it?
Big difference in idle and off idle fuel requirements for a "211 @ .050" cam if on is ground on a 107LSA and another on a 114LSA.
Head castings numbers tell me chamber size and flow characteristics (power potential).......Cliff
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Thanks for all the support and input, It will be great to once and for all have it running right!!
The cam info kept getting deleted in all my prior posts??
Rhodes lifters and cam. This was a package deal Rhodes had once offered back in the mid 1980's.
Per: Rhodes spec: 211 deg at .050 lift with .435 valve lift. the cam has a 112 deg lobe spread with approx 298 deg advertised duration. the cam was ground with a 4 deg advance built in. It is a single pattern cam. The built in 4 deg advance might count for the higher than expected vacuum reading?
Tomorrow, I'll pull a valve cover and get the casting #
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Single pattern cams are fine for SBC builds especially if you are using good heads. The dual pattern stuff didn't get popular until the "smog" years when they started making heads with very restrictive exhaust ports, like the 882 and similar castings.
Chevy didn't figure out how important head flow was, and combustion chamber shapes until the late 1980's when they started making the Vortec heads. By the mid 1990's the heads deficiencies were corrected, and power and efficiency was back........Cliff
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Head casting # 333882 Date code? "1243" right under the head casting # located between 1st and 2nd cyl. No other cast #'s on the head. heavy casting shown as 1974 head??
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Unfortunately those are what we call the "worst of the worst" for smog heads. Those heads were the biggest reason that 350SBC's thru 1973 made the grade and 1974 and later 350's didn't.
The biggest reason is the super-restrictive exhaust port which does not have a "double pass" down both sides of the valve guide. The tiny opening left by all that additional material makes them flow very poorly.
I think the engineers did that to help provide some additional "natural EGR" for emissions, but that's just a guess. The first attempt to improve emissions came in 1970 when they took the EXCELLENT 041 and 186 castings and opened the chambers up to 76cc. The result was the 441 casting. Several similar versions of the 441 followed in 1971, 72 an 73, most were 336, 487 and finally 993's. The later 487's and all 993's had factory hardened exhaust seats. ALL of those castings had the big ports like the earlier 291, 461, 462, 186 and 041 heads. Although the chambers were bigger, opening them up unshrouded the valves a bit and the later heads are actually EXCELLENT from a performance standpoint, it's just more difficult to obtain optimum compression ratios with them.
I found out about those heads way back when I first got into this hobby and traded for a set ready to go for my 1970 GM truck. The original heads, casting #441's were slam worn out. That engine otherwise was a very strong runner, got excellent fuel economy, etc. All I did was bolt on the 882 heads and it absolutely KILLED that engine. It felt like it lost at least 100hp if not more!
Back then I had to fart in my pocket to have a cent, had just got married and starting a family, but took the 441 heads to a machine shop and paid the price. Put them back on the engine and power was restored and then some, with no other changes.
Looking back on it now it was a good lesson learned and I've never been one to put my hand on a hot burner more than once!
Sorry for the bearer of bad news, no intention to put a big black cloud over the project, but using those heads is costing a LOT of power and efficiency.........IMHO.......Cliff
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Well: I'll be looking for some heads! the 041 you mention do not have accessory holes! I need my A/C P/S and Alternator!! I have not seen any 441 heads listed anywhere either??
How are the 487 heads? would I just be better off going with a set of vortec?? and find an intake that will mount the Qjet?
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I've got a set of those 882's. They were removed from a 74 Z-28. They have 2.02 valves and screw in studs & guide plates. To the best of my knowledge this was the last year for 2.02's & the screw in studs.
I've had them for years and figure someone who is doing the "numbers matching" thing might want them for a '74 Z-28 or L-82 vette resto. I'll never use them. Someday I'll put them on flea-bay and see what happens.
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Hey Olnick,
the 041 heads DO have holes at the end. They are 69 heads with 64cc. I know as I have a set.
Frank.
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041 heads were used in 1969 and 1970 on the 300hp 350cid engines. They are very similar to the 186 castings used in the same time period. All of those castings will have machined ends and accessory bolt holes.
The 041's are "sleeper" heads and most have slightly larger combustion chambers even though they are advertised at 64cc. I've built a good many SBC's with them and the vast majority of the 041's we've used were closer to 66-68cc.
The earlier big valve/big port "double hump" heads will not have accessory bot holes.
Some time in the 1970 model year run they revised the 041 heads and opened up the chambers, these will be the 441 castings. They still retained the larger spark plugs that require a gasket and big intake/exhaust ports. 336 castings started showing up and are pretty much identical to the 441's.
The 487's were next and ran thru 1972 and very late versions will have factory hardened exhaust seats. In 1973 all of those heads were hardened seat and they changed the numbers to 993. The 993's had every so slightly smaller intake ports as well.
The 882's came in 1974, and are the worst heads ever to sit on a 350 engine. Power and efficiency went into the toilette and fuel economy on those engines was HORRIBLE. I think the factory was really trying to please the EPA at that point and those engines showed up with TONS of vacuum hoses and devices to clean up the exhaust emissions, with no attempt to make those engines efficient in terms of power production/fuel economy.
For quite a few years crappy heads continued to show up on SBC engines until they finally figured out that by increasing the compression ratios and going back to more efficient combustion chambers that these engines could make the grade in all areas.
There were still a few "turds" produced for castings well into the late 1980's early 1990's, among them are the "swirl" intake ports (early Vortec designs). Those heads are FANTASTIC for a truck engine build with all it's emphasis on low end power, but no so great for anything else.
Kind of interesting is that the later "Vortec" and other similar designs for the LT engines are EXCELLENT heads in every respect when it comes to compression, port flow and combustion efficiency.
The big problem I have with factory heads is that all of the "early" heads prior to the 993's that have good ports are soft seats, and most are pressed in studs. The 993's are hardened seat, but often cracked as the factory induction hardening process leaves them a bit too brittle in that area.
The later Vortec heads, although dirt cheap and readily available have MAJOR shortcomings including a "goofy" intake bolt pattern (requires purchasing an aftermarket intake for older engine builds), they are "paper" thin and crack easily, and pressed in stud w/o guide plates.
"continued"
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So what is one to do when building one of these engines and in need of better heads. I use and recommend upper the bar and buying World Products SR, Sportsman, Dart Iron Eagle, Trick Flow, or other similiar aftermarket heads. You will find the additional money spent over Vortec heads (for example) rewards the end user with a really nice set of heads having ALL of the needed features that the difficult to find factory heads should have had anyhow.
This will include multiple bolt patterns for valve covers, early intake bolt pattern, screw in studs, guide plates, EXCELLENT flow characteristics, high efficiency "modern" combustion chambers and hardened exhaust seats. They also come with one piece stainless steel valves and various spring options with excellent retainers. They also have combustion chamber sizes in many offerings so one can attain an "optimum" compression ratio based on the CID and piston being used.
The very WORST aftermarket heads are at least as good as or better than the best factory heads in terms of port size and flow.
My favorites are the SR Torquer and Sportsman heads, but I've assembled a good many SBC engines with similar offerings from other vendors and most have been very good to excellent. I've had to toss the springs a few times finding them too stiff for my liking, but overall most have been fine.
I still prefer to buy them bare and install my own components. Ups the cost slightly but for sure you know EXACTLY what is in them, and with a little research one can source out everything and not break the bank in the process. Also consider that with any mass produced part from any supplier, they may be areas that need attention. Starting with bare heads I can buy good valves for them and check the fit at the seats, then put good PC seals on them, custom springs for what I'm doing, good retainers/keeps, screw in studs, guide plates, etc.
Anyhow, that's the basic lesson on SBC cylinder heads even though I only scratched the surface on the topic.
I'd add here that I've built more than most who will read this, and dyno most of them, then follow up with drag strip numbers. If anyone needs any more details or advice, etc, feel free to PM me on the topic......Cliff
PS: due to time/space I left out quite a few factory casting numbers made that were good to excellent, and just focused on the ones that are the most common to find at slap meets and such.....
PSS: also consider that when it may appear that I'm "bashing" 882 (and similar castings) that those heads were placed on engines with pathetically "low" compression ratios, so they aren't going to do much anyhow, and tiny little cams with retarded lobe positions, tons of emission devices, CAT's, and carburetors that were set up too lean anyhow. Even with that said the only thing I use 882 castings for are door stops, as there are just so many better choices out there it makes no sense to start out with the worst of the worst for an SBC engine build....
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I found a set of "186" date code a.3.9 Would they be worth the effort? I do believe they have the bolt holes in the ends. excellent price as well! thought I would check prior to purchase.
they are 1.94/1.5 valves.
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186 castings from 1969-1970 are about at good as it gets for a factory iron head.
I don't buy them these days simply because by the time you completely rebuild them and convert to screw in studs, guide plates, hardened exhaust seats, etc, you can purchase a complete set of World Products SR heads (for example) for about the same money.
The 186 castings are pretty much duplicates of the older 291/461/462 castings that had the "double hump" on each end and no accessory bolt holes, but the 186's have the flat machined pads and the bolt holes.
I wouldn't stick my nose up at a set of them, they are actually pretty valuable to restorers, but take into consideration the cost involved with getting them rebuilt and up to par for this new fuel.
Also consider that the ports are apprx 165/65cc and the SR heads are 170cc, and they come with 2.02/1.60 valves, so have improved flow potential plus all the additional benefits mentioned. Going from memory they are available in several versions, 67cc combustion chambers, 76cc chambers and even a smaller offering for 305 Chevy engines.........Cliff
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With the 882 heads you probably don't have any where near 9.5-1 C/R unless the block has been decked or you have a .015 shim head gasket.
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Good point Jim.
Very few of these engines are anywhere near as high in compression as the owner/builder thinks they are.
Quench distance is a very important part of engine building, and folks don't put enough compression in these engines anyhow.
SBC engines absolutely LOVE very tight quench. I shoot for around .030-.035" for my engines. The tighter quench improves combustion efficiency, it will run cooler, take less timing/fuel to be happy, and less octane at any given compression ratio.
Higher compression also improves idle quality and low speed manners with any given cam choice.....Cliff
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Flat tops can be quite a bit in the hole depending on brand and deck height, ask me how I know.
I run 64cc Vortecs with flat tops. lucky to be around 8.7 or so doing the math.
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I have #3973487 heads on my 350. How are they at performance potential? I know the combustion chambers are large for the lower '71 compression ratios.
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487 castings are excellent. Pretty much identical to the 1970 441's but have the smaller tapered seat spark plugs. They have the larger combustion chambers, most will be 1.94/1.50" valves and pressed in studs. Very late production versions may have hardened exhaust seats but most will not.
To this day I'm not sure why many aftermarket pistons end up WAY down in the hole at TDC. I suspect that the folks making them as "replacement" pistons didn't want to raise the compression ratio with the larger overbore sizes.
I've seen this sort of thing with a LOT of TRW and Speed Pro forgings over the years, and I avoid them for that reason. Not uncommon at all to see them .030-.035" below the deck at TDC.
Almost all of the engines I build here get decked and squared, so we mock them up and measure how far the new pistons are below the deck, record the information, then take it apart and send it to the machine shop.
Pretty easy to establish tight quench using a Felpro blue head gasket that crushes to .039".
For SBC builds I've also left the pistons in the hole .015-.018" if the surfaces were in great shape, and use .020" steel shim gaskets same as the factory did for many years.
What most folks do here instead is they don't even check piston to deck clearance, and run out a buy a gasket set with thick "rebuilder" head gaskets in it. They think their new build is 9.5 to 1 compression (for example) and it will be at least half a point, if not quite a bit lower.
Building one of these engines with a lot of quench in it works against you in just about every area. They will run hotter, make a LOT less power, use more fuel, takes more timing to make them happy, and less vacuum produced at idle plus worse throttle response/street manners with any particular camshaft.
Establishing tight quench with your engine build is just one area that you can gain significant benefits. There are quite a few other places to improve engine power and efficiency, and when you put all of them together the differences between two engines using very close or the same parts can be amazing.......Cliff
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Thank you. I agree that quench is important but missed that boat with my 350. I bought this engine as a completed fresh rebuilt long block. Bone stock 350 with cast dished "rebuilder" pistons. Even though the deck had a clean-up cut the pistons still measured around .020 down in the hole. I had the heads off to measure deck height and have a look at things and should've used steel shim gaskets to bring up the CR some, but used the .039 Fel Pro units. I calculated 8.0 compression ratio. One advantage though is that it runs great without a hint of ping on 87 octane and 38 deg total timing plus 12 deg manifold vacuum advance. It runs surprisingly strong (a relative term) for what it is with stock .390 lift cam, stock iron intake and exhaust manifolds, tuned Q jet, and points type ignition with Pertronix I ignitor.
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Most of the engines I build here make best peak power with closer to 30 degrees total timing. This shows us how important tight quench is far as combustion efficiency is concerned........Cliff
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30 degree's is not what I was expecting for total timing. Alway's thought the SBC liked 34-36 or a little more. At what RPM is the timing all in?
Phil
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Tighter quench, more efficient combustion chambers, optimum compression ratios for the octane, and very well chosen camshaft will require LESS fuel and timing to make best power.
Couple of years ago I built a 455 for my Ventura. It was very tight quench, exactly zero deck, good flowing heads, well chosen cam, etc. It went on the dyno and cranked out 455.4hp and 540tq, and only required 30 degrees total timing to make those numbers. That engine was used as part of the High Performance Pontiac and Popular Hot Rodding articles for the KRE aluminum head testing.
A customer of ours set out to duplicate that engine, used the exact same heads, cam with the same .050" specs but "modern" lobe profiles, same stock iron intake, q-jet and HEI. He took that engine to the same dyno and made 390hp, 499tq.
Turns out that his attempts to "duplicate" our engine came up a bit short, simply because he failed to follow the "recipe" exactly and just figured a little extra quench and "modern" cam with less seat timing but more lift would get the job done.
I was lucky in this deal as very early on I used .020" steel shim head gaskets on all of my SBC engine builds simply because that's what was there when I took them apart. The "rebuilder" gaskets are much thicker, usually around .040-.060" and they lower the compression close to half a point and increase quench distance at the same time. Nearly every single SBC engine that gets "rebuilt" will have the pistons pretty far down in the holes at TDC and a thick head gasket on it. Folks come up considerable short on engine power all the time with that deal, even following engine builds they read about in magazines and on line, and never know why more times than not they don't make the grade.
I've also had some in here to tune that ran pretty hot and sensitive to low octane fuel when they shouldn't have, mostly because they simply had WAY too much quench in them.
Thinking back the worst one we worked with here was a Pontiac 400 with "builder" pistons that were nearly .040" below the deck at TDC and it had really thick Detroit head gaskets on it. Although the compression ratio was only about 9.3 to 1, it ran hot, overheated and POUNDED like sledgehammers with any attempts to put some timing in it to make acceptable power. This was quite a while ago and early in my learning curve so it took me a while to figure it out.
We ended up pulling that engine and replacing the pistons with a much better flat top design with 2 valve reliefs, zero decked it, .039" thick head gaskets, then a cam with 10 degrees more duration to compliment the new compression ratio just over 10 to 1. The result was an engine that idled better, didn't even think about running hot, overheating, pinging on pump gas, and it would literally tear your head slam off when you went to full throttle! It literally felt at least 100hp stronger than before, yet same CID and head flow.
No need to mention how thrilled the owner was with the end result, and we once again educated ourselves as to how important these things are when it comes to building engines.......Cliff