Gas mileage #'s

I had a L88 engine short block with the cast iron head versions of the aluminum heads. The compression ratio was originally 12.5:1. I had the piston domes machined down to arrive at a 11.5:1 compression ratio. The car had a 3.08:1 rear end differential. The engine was in a 1969 Coupe and I had Hooker header sidepipe exhausts; i.e. open exhausts. With a full tank, 20 gallons, I could drive to Las Vegas (300 miles) with about 1/4 tank of fuel remaining. My engine guy estimated that by lowering my compression ratio one point , I lost 50 hp. So 550 hp - 50 hp, meant that the car was getting approx 20 mph/gallon with a 500 hp engine. Of course, with a 3.08 rear end at 70 mph, my engine was turning very low rpm and correspondingly producingly very low hp at that rpm rating.
 
Bee Jay said:
I've got 3.55 gears and a 700r4 trans. I run a Summit 1105 cam, 224/234 duration at .050, AFR 195 heads, and Holley Throttle Body Injection. I drive 200 miles and I fill up with 20 gallons. I have a heavy foot, but 10mpg gets old when it's $5 a gallon. I hope to improve my gas mileage significantly by switching to a milder LT4 Hot Cam hydrualic roller,218.228 duration at .050. Rollers are supposed to have less friction, right? Less friction, less duration, better gas mileage right? My 1500HD Crew Cap with a 6.0 liter LS engine gets 14mph on the road. I should get at least that with my 3200 lb Corvette, right? Maybe I shouldn't give a damn like kwplot.
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11.04mpg on my last tank. Damn.
Bee Jay
 
I just returned from a 9,200 mile 37 day cross country cruise in my 67 Coupe. Average mileage was 17.6 MPG (high of 19.8 & low of 15.5 depending on terrain). My engine is a zz454 440 HP big block with a Tremec TKO-600 (.64 OD) and 3.70 rear end. 75 MPH is 2,200 RPM. With the old M21 my mileage was around 12.
Roy :D
 

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Last time I took mine out for a long cruise, I went 170 miles on 10 gallons of gas. Not bad for an original drivetrain. '75 L48 (165hp) 4speed with, I believe, 3.54 rear.
 
67-427ci said:
I just returned from a 9,200 mile 37 day cross country cruise in my 67 Coupe. Average mileage was 17.6 MPG (high of 19.8 & low of 15.5 depending on terrain). My engine is a zz454 440 HP big block with a Tremec TKO-600 (.64 OD) and 3.70 rear end. 75 MPH is 2,200 RPM. With the old M21 my mileage was around 12.
Roy :D
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:shocking:

that's GREAT MPG there, hope your trip was as fine...looks like FUN...

:1st: start a thread with some pix....:beer:
 
Bee Jay said:
Bee Jay said:
I've got 3.55 gears and a 700r4 trans. I run a Summit 1105 cam, 224/234 duration at .050, AFR 195 heads, and Holley Throttle Body Injection. I drive 200 miles and I fill up with 20 gallons. I have a heavy foot, but 10mpg gets old when it's $5 a gallon. I hope to improve my gas mileage significantly by switching to a milder LT4 Hot Cam hydrualic roller,218.228 duration at .050. Rollers are supposed to have less friction, right? Less friction, less duration, better gas mileage right?

11.04mpg on my last tank. Damn.
Bee Jay
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To get the best MPG is not just lowering the rpm. You get the best MPG where the motor is operating efficiently. Crane cams used to print the operating range on cams. If it said 2800 - 3400 rpm that is where you are going to get the best MPG.

So BJ my 700R4 equipped Vette worked best with a 4.11 rear end to get the rpm for efficiency up for my typical freeway speed. Actually 3.90 would have been the choice.

Your TQ converter could be robbing you of a couple of MPG. Are you running in lockup OD?.

Even my present motor gets over a 14 average just screwing off in town the whole 25 gallons. My last tank was 386 miles and 23.6 gallons
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i don't even know LOL my combo is not setup for MPG it is sep up for fun.... 3000stall and a healthy big block the only thing i got going is the 3.25 gears.....

but as gkull said it is not about rpm it is about the whole combo the cam gearing and load people with big cams and low rpm will not be a good thing... the motor is just not efficient there......
 
well with my mildly built 355 i get about 12 in the city (washington dc area)....now if you can get me out on an interstate with the 700r4 od and the 3.08 i get 23-26 at 65-70
 
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