General Category > Quadrajet Carb Talk and Tips
adapter plate
Cliff Ruggles:
"I have 1/2 inch clearance now with 14x3 GM drop base air cleaner. Adapter plates are generally 3/4 inch thick so I would have to use a shorter air filter ( not the best scenario)."
Drop base air cleaners are power robbers right to start with, I've dyno and drag tested several varieties and they all lost power. I see folks install "high rise" intakes, custom spacers and other "high performance" parts all the time, then cripple any potential improvements restricting air flow to the engine with shorter air filters and lid too close to the carb.
Related but when I was racing the Ventura a lot I went to an RPM intake over the factory unit. It required a shorter Shaker assembly and I had to use a 1" shorter air filter moving the lid closer to the carb. That deal absolutely KILLED the engine at the track. It even induced a stumble/hesitation/bog anytime I went quickly to full throttle that would not tune-out.
So I removed the air filter and made a custom one for the opening in the Shaker, problem solved.
A few years later I decided to remove the RPM intake and go back to the stock intake, stock air filter, lid and Shaker parts. I was street driving the car more and racing it less. I also put the choke flap back in the carb and electric choke on the side of it.
Just for fun I took the car to the track after the changes and guess what? It ran quicker in 60' and short times with the stock parts! The engine didn't "feel" as strong on the street as the big RPM intake really shines in the upper mid-range and top end, but even with a stronger top end charge the loss in short times had the stock intake a winner over the high rise aftermarket unit.......
old cars:
tayto .. I am near London in Ontario,Canada. today 87 octane is 78 cents
I don't think I have ever seen a GM air cleaner that wasn't a drop base. Some more or less.
The one I am using is from a replica 1969 396 375hp bbc. It is identical to the one on my brother in laws 1969 Chevelle Copo 427 / 425 hp which he has owned since 1969.
I doubt it was a power killer.
Intake: Once you reach around 500 hp on a BBC single plane intakes come into play quite well and low speed torque suffers very little especially if we consider I am using a 780 holley instead of 850 or larger (even though my build could use more cfm). The smaller venturi ( 1.4 inch) of the 780 holley keeps booster signal up. 850 holley has a venturi 1.5 inches. Add to that the small port heads I used which keeps velocity high. Result: Torque makers.
Cliff Ruggles:
Have you actually tested anything being talked about here? If so I'd LOVE to see the dyno sheets, or time slips......
old cars:
That's a very good point Cliff. I do not have acesss to a dyno and I am not a racer. I put a lot of faith in David Vizards testing.
Would like to say that I have read a lot of your Quadrajet tuning tips and have your book . I am honestly amazed to the depth of your knowledge on quadrajet carbs. I enjoy reading your responses to people having tuning problems. I have a soft spot for quadrajets but I know my knowledge of them would never come close to yours.
We are all grateful you share your knowledge. Thank you Cliff
Cliff Ruggles:
I wasn't asking to be critical but some of the responses sounded familiar to me.
I test EVERYTHING so don't just assume that what I read or am told is actually gospel no matter what the source.
Here are a few of the things I have tested back to back on the dyno.
Every intake that will bolt to my engine.
Every possible type of 1" spacer.
Three different cams, flat hydraulic, flat solid, and hydraulic roller, back to back but it took 3 days.
Every possible type of modern carb against my Q-jet, including an 850 Demon, HP 950 Holley, 4781-2 Holley, Thermoquad, Edelbrock 750 cfm AFB clone, and their Thunder Series AVS clone.
MSD with a 6AL box against a factory HEI.
Here are a few of the things I've tested at the track, on a car that doesn't spin and runs right on the dial in:
Every intake that will fit under my hood, Performer, Performer RPM, factory cast iron, factory aluminum, Street Dominator, Torker, Torker II, P4B, the P4B-QJ, and the Tomohawk. I also added spacers to them.
All sorts of air cleaners, none at all, and the K & N XTreme lid.
Every carb mentioned above and on several private track rentals I've carried as many as 7 different carbs with us and ran them all day long on two different vehicles.
Every type of 1" spacer, fully open, fully divided, four hole, and semi-open.
Moved the same cam with a 9 keyway timing set four times and ran it after each movement, 107ICL, 109ICL, 111ICL and 113ICL (you will LOVE those results). I also street tested the different cam positions to evaluate off idle power/smoothness and how responsive the engine was in the normal driving range.
On the street and at the track I've tested 4 different types of DOT tires.
I've also tested a LOT of torque converters, 13", 12", 11", 10", and 9.5", street and at the track.
You made mention earlier of "high stall converters" to go with larger cams. That comment told me that you really need to do some testing in that area. If you find a good converter guy you absolutely and for sure can "have your cake and eat it to". My car uses a custom built 10" converter that so close to a stock full size converter you'd never know it's in there. The trans engages firmly with some RPM drop. Against the brakes it overcomes the tires at 1800rpm's. Moves out with normal throttle right off idle, and very well coupled in the "normal" driving range. You'd be hard pressed to see much past 2200rpm's heavy throttle in high gear climbing a steep grade at 30-40mph.
Take the car to the track, heat up the tires, and WHAM.....it leaves at 3500rpm's and runs 1.59-1.61 60' times and even better goes thru the traps with less than 100rpm's slippage!
https://www.youtube.com/watch?v=6zVdoLR-VzM
Continued......
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