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Old 05-20-2010, 04:08 PM
350pano 350pano is offline
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chevy milage best option, transmission, heads or rear end

Hi everyone,

Just a quick couple of questions relating to milage on a chevy.

Car is 68-69 327 chev, 3608 pound car, 350 turbo trans, very mild cam, Barry Grant Demon Jnr Carb 625, Edlebrook Performer RPM manifold, crappy 882 heads (75cc? low compression?) running either 95 or 98 octane, HEI, recently reconditioned, running full manifold vacume advance.

I have been trying to tune it myself for the last few months, and recently took it to a dyno to see if I was in the ballpark. They were happy with the carb tuning, and couldn't improve the timing curve, so I though I did ok. The motor has loads of torque at low revs, about 850nm, but it drops off rapidly so its only about 170 rwhp.

The end result is that there is no further room for improving the MPG. At present it is achieving 14 MPG, and it doesnt seem to matter too much whether it is highway or city, always returns about the same MPG.

So, seeing as I can't get any more improvements thru tuning, I am wondering what the best option would be to try to get a few more MPG, would love to get to 18 or 20.

Three options I can think of, wondering which would have the biggest effect on milage.

1. REplacing the th350 trans with a 700r4 (very costly but option 1 still.)
2. Changing rear end. At present has a 3.08, I believe there is a 2.78:1 ratio, I am guessing but woud this drop the revs about 300 rpm? Would the torque at low revs motor still be able to get this thing moving ok?
3. 3rd option, would fitting smaller chamber more modern heads help the MPG by increasing compression ratio etc?
4. Just thought of this, would changing the cam to one that produces torque at a higher rev range have any positive effect on the milage? On the assumption that higher horsepower engine requires less effort to get the car moving or keep it going?

So thats all I can think of. I drive like a nana, not after power or speed, more just a car I can afford to drive!

I would be very grateful for any ideas or options you can think of to try to get another 2-4 (or better) MPG, and any comments or suggestions on the 4 options above would be much apreciated.

Cheers guys

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