Quadrajet Dyno Results

by Dave Knutsen


I was fortunate enough to be able to spend a day tuning a 455 Buick on a dyno and learned some interesting things. I was under the assumption that the lower letter hanger and thinner rods would indeed build more power as I've always heard our Buicks like lots of carb and fuel. WRONG. The engine we dyno'd was a 500 horse mild street engine that runs on 91 pump gas. The best power was made with a P hanger and AY rods which is a .057" tip. The P hanger has a height dimension of .590". The B hanger has a height dimension of .525". We started with a H hanger and went richer (smaller letter) and then worked out way up in hangers till we found the best power. Same with the secondary rods. We tried CC (.0303" tip), BG (.0400" tip), AX (.0400" tip but different A & B steps), CE (.0413" tip), AU (.0530" tip, which is stock Stage 1), AY (.0570" tip, which turned out to be the best), BT (.0600" tip) and CL (.0670" tip). Now this engine had the factory cast iron exhaust manifolds that were ported by Greg Gessler. We thought that we'd pick up power especially on the top end with some headers, so we bolted on a set of Mickey Thompson equal length headers with the 1 7/8" primaries and 3 1/2" collectors. I think it picked up one horsepower and about 4 foot pounds of torque. We then bolted on a race prepped 750 Holley that was ported and flowed 940 cfm, no appreciable power gain. And its important to note that the 800 QJ that was built by a very respected Super Stock racer out of Calif. only picked up about 1 horsepower over a 750 QJ that we built ourselves. So don't buy into the hype of having to have an 800 QJ to build power, the stock 750 (1967 thru 1970) big block carb can and does build basically the same kind of power.


Quadrajet Tuning Dyno Sheet 1


Quadrajet Tuning Dyno Sheet 2


Quadrajet Tuning Dyno Sheet 3

Quadrajet Tuning Dyno Sheet 4


Quadrajet Tuning Dyno Sheet 5