i have a 70 455 (stock) would i gain any performance ,or horsepower by going from a 750 Qjet to an 800Qjet ?? i have several 800s that need to be rebuilt. just dont want to spend the time and money if it wont really make a differance thanks
Put a vacuum gauge on the engine, and tape it to the windshield. Drive the car at WOT, and look to see if there is a vacuum reading on the gauge. If so, the carburetor is a restriction. You might benefit from the bigger carburetor.
there are factors that can make a big carb run bad and a small carb run good. the best thing is to do is run a side by side comparison at a track. since you have both carbs let us know which runs best. good luck
I like the above comment. For a stock engine there might be some small margin of improvement by going from a 750 to an 800 q-jet if you're trying to eek out the last tenth of a second at the track, but there's a ton of optimization to be done regardless of which carb you try. With incorrect jetting/metering, you could hurt yourself just as likely as help. Devon
Need a little more information. Does the car have headers? Cam? If it isn't too far from stock, leave the jetting alone.
ok thanks, yes it is all stock with the exeption of a 2.5" flowmaster exhaust, that i just put on. i hated to take of the born with fatory exhaust, :ball: but for a brand new complete set of flowmasters exhaust for $110.00 i couldnt resist. couldnt really feel any seat of the pants improvement thoughou:
You would probably see it at the track, but might not feel it in the butt dyno. If you have the stock carburetor with stock jetting, I would leave it. If you had headers, you would need to jet up because it would be lean.
At the dragstrip there is very little measurable difference between a 750 cfm q-jet and 800 cfm unit if both are well prepared. The last time I did a back to back drag strip test the ET difference was less than .02 seconds and .30 mph, running mid-11's and making apprx 514hp. I've also dyno tested 750's and 800's back to back. The most recent was a 455 cid engine making 505hp. The smaller 750cfm carb gave up apprx 7 peak HP, but the numbers were dead even to apprx 4400rpm's. If you are running a stock or near stock engine, not really worth the effort to upgrade to a larger 800cfm unit if the 750 is in good shape. One other advantage provided by the larger 800's, is driving on the primary side only. Since it provides more total cfm capacity, high vehicle speeds can be obtained without opening up the secondaries. This is most advantageous in towing applicaitions, or when setting them up for boats, not really a big deal for musclecars driven on the street......Cliff
