[JimiHendrix]

Hello, I am getting very worried about the way gas prices are going. I just wanted to do something to my Chevelle that would not only increase performance, but also give my gas mileage a shot in the arm! I have noticed a trend in two different methods of acheiving these goals: Overdrive and Fuel Injection. I have been batting around the idea of going with a Tremec 5 speed, but have also been considering Fuel Injection for better throttle response and smoother cruising speeds.

Which do you guys think would be better in getting more mileage and performance. I spend about half my driving on the highway, and the rest stop and go through town. The chevelle is my daily driver, so that's why I am soo conserned. Thanks for the help guys!!!

 

[Redrum]

The overdrive tranny is by far the best way to improve performance and gas mileage. Absolutely positively the best all around improvement on a performance car. I went from under 15 MPG on the road to over 20 MPG in my corvette and I am not exagerating any........ nada....... none. The move from a 400 to a 700R4 was the best money ever spent.

Yes, the tranny only decreased the RPM's by 30% and the mileage went up more than that. It is because the engine is now running in a more fuel efficent range and not using so much HP just to spin at 3000+ RPM's. I can actually lock the tranny up at 1200 RPM and cruise at 35 MPH basically at idle!

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Redrum (or Mike)
68 Corvette - 383 CI 427 HP
69 SS Chevelle being updated to Pro-Touring
97 Z-28

 

[rpol7966]

I have a story that will help you decide in favor of the overdrive tansmission.
A friend has a '93 454SS pickup which came with a 4l80E overdrive transmission hooked to a 4.10 geared rearend. We talked about improving mileage so he decided to switch rearends to a 3.08. He wanted to establish a basis for comparison so he topped off his tank and drove the truck in stock form (4.10 gears)70 miles round trip at 65 MPH. He then topped off the tank and figured his mileage. In stock form he got 13.5 MPG at 65 MPH.
He changed rearends to the 3.08 topped of his tank and repeated the 70 mile roundtrip at 65 MPH. Topped off the tank a figured the mileage. The truck got 19.6 MPG just by changing the rearend. An increase of 6.1 MPG!
Keep in mind that an engine is nothing more than an air pump. To reduce fuel use, you must reduce fuel intake.......the fewer revolutions of an engine, the less fuel introduced into the combustion chamber.
I have an '81 El Camino with a Vette TPI engine that will get 18-19 MPG with a Saginaw 4-speed. It has a 2.73 rear gear. I'm sure that it might get better mileage with a 5-speed OD.
I also think there is a point where high gears used with an overdrive transmission can give an adverse affect. Lugging an engine will hurt economy. So keep in mind that gearing must be balanced to give best ecomomy.
What are other's views?

 

[1966_L78]

The overdrive tranny should give the biggest gain in mileage for a car driven mainly where the overdrive will be used.

Not positive on the Tremic, but some overdrive trannys have lower ratios for 1st, 2nd and 3rd. Therefore at lower speeds, the engine would spin more, basically it would use more gas, although tailoring your shift points will overcome alot of that.

The fuel injection shouldn't really affect mileage too much compared to a properly tuned carb.

 

[ZZ69chevelle]

I say, do both. I'm pulling down 17 city 26 highway in my Z28 with the 4l60E and the LT1, and that's with 3:42's The tranny will improve mileage the most though.

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Steve Beuth

69 Malibu ZZ4-350
93 Camaro Z28
99 Silverado
Chevelle pics

 

[DaveB]

well, some people i hear of that put fi in their cars get over 25mpg.. i personally dont knowwhich i would chose really. they are both expensive as hell

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Dave
72 Chevelle 350
My car

 

[1Fast7D]

<BLOCKQUOTE>quote:</font><HR>Originally posted by DaveB:
well, some people i hear of that put fi in their cars get over 25mpg..

<HR></BLOCKQUOTE> Well I can't keep my foot out of it long enough to ever get decent mpg.



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Undee's70SS