Thread: Trying for better milage

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Originally Posted by Langan

Come on someone has had to have tried this..........Jim

You will probably be OK with the 500,back in the Jimmy Carter "gas crisis" days Holley came out with the 450 CFM Economaster.This was a spreadbore replacement for the Quadrajet,the key is to run either carb with an intake with smaller runners for more velocity like the Edelbrock SP2P or the Streetmaster or Offenhauser Dual-Port,with the right matching Cam 22-25 MPG was attainable.

I think it's gonna be tough to beat a Quadrajet for mileage. In my opinion, the tiny little primaries are the best it's gonna get and the huge secondaries will provide all the CFM you can handle with a street motor. Most 2-bbl throttle bores are larger than the primaries on mid-sized 4-bbl carbs. I've been gathering all the info I can find on Quadrajets and will share it with you.....

Click on the links posted in this thread for additional info....
http://www.montecarloss.com/communit...547#Post572547

http://www.florida4x4.com/tech/quadrajet/index.php

http://209.85.173.104/search?q=cache...lnk&cd=2&gl=us

http://www.highperformancepontiac.co...cuum_hose.html

http://www.geocities.com/gtopercy/Pi...rajetTech.html

http://www.buickpartsdirectory.com/carbs.htm

http://www.73-87.com/7387garage/drivetrain/myqjet.htm

http://www.highperformancepontiac.co...ing/index.html

http://www.mako.com.au/buick/html/qjet_tips.htm

If your carb is dialed in right, it doesn't make much difference what the CFM rating is. That's at wide open, and you aren't cruising at WOT. For the around-town stop and go driving you do, a smaller carb might be more driveable just because you won't have to deliberately "feather"the throttle at every start to avoid dumping a bucketfull of expensive fun juice down the tubes. For highway use in the real world, I get much better economy with a well set up AFB than even a two barrel, Ford, Chev, Dodge, all have AFB's, all work better than the stock ones did.
i have a 318 pickup with an ancient SP-2P intake, and it does make a noticeable difference to mileage by keeping the velocity up, but the power just isn't there.

I recently removed the 2bbl from my son's car and replaced it with a rebuilt edelbrock 1406. (Chevy 350/350) I also tuned and tweaked my timing. The MPG improved dramatically. I can get 21+ mpg on the highway now in a big heavy mid '70's Monte Carlo. With your tranny, gears, and tall tires, you will probably be able to get considerably better than that. I am inclined to believe that my timing adjustments did more for my gas mileage than the carb swap. Dig around on this forum for the "HEI Recurve" post. Some here said B.S. to my results, but that happens from time to time.

BTW: I totally agree with Tech on the Quadrajet, I used the edelbrock because the intake I had was a square bore. A QJ would have been my first choice.