Thread: Trying for better milage

Tweet

I drive my 34 as a daily driver. It is a stock 350 ( the one from 87 trucks that have no fuel pump boss ) lowest performer Chev makes,700R4,3-1 gears and 28" tall tires. Because it is light weight I get away with it.
My question is I have a 600cfm on it now leaned to the bone. If I run a 500 cfm does anyone think I will get better milage?
In LA you idle more than you drive and with the gears and trans motor never see any RPM.....Thanks Jim

A 600 is sized pretty close to ideal for a 350 CI engine. I don't know if less cfms would reduce gas consumption or not. Gastrick put trips on his Deuce recently and says the gas milage has improved over a single four barrel because of running on the smaller two barrel, so maybe.

You might have it put on a scope to see what your air/ mixture is and all that stuff. I had that done to a 351 Cleveland I had one time and it really told us a lot about what was going on in each cylinder.

Don

Thanks you hit the idea rite on. Back in the day 350's came with a 2 barrel, don't know the cfm. They were real peppy just no RPM's. I don't want to change manifold thats why I hopping a 500cfm will work...............Thanks Jim

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

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.

Unless you have a 500 CFM carb laying there ready to install it would take you about a zillion miles to recoup the cost of a new carb with the minimal mpg gain you would get.

As others have said, getting everything else in the engine tuned and tweaked for mileage and adjusting your driving habits would show you a better return on the money invested.

Your biggest return on the dollar would be to ride the bus to work.......

I just went from a 500 Carter to a Quadrajet on my Pontiac......much better mileage with the Quad...........But, then again, the 500 could have used a rebuild.

The carb is actually the last thing that causes low mileage, assuming it's set up right. Cam, C.R., gears, firm skinny tires, wheel alignment, brake drag adjusted out, all make more difference than you'll gain from a smaller or different make carb.

What about a tri power?