sammicurr86

450hp/500tq vs 500hp/615tq BBO. What would be the mpg difference? Assuming the engines were built in becoming everyday drivers in mind.

Anybody with similar specs feel free to chime in.

Fun71

At that power level why worry about MPG?

steverw

You know having cars like these, MPG cannot be a worry, cause its not going to be good. My 65 Vette does not get good milage, but better since i changed from 3.73 gear to a 3.08. Im sure my Olds wont get great milage, but i do have an overdrive for it. I just say if milage is a worry then have another car to drive that gets good milage and dont drive the Olds everyday.

oldcutlass

It really depends on the method that the increase in HP was attained. The engine is an air pump if the same amount of air is moving in and out then no difference in MPG.

70cutty

Depends on how heavy your right foot is. My engine is in that category, I believe I get between 8-12 MPG rough estimate, I haven't really calculated and depending on the driving.

sammicurr86

Figured. Anyone come close to getting it around the mid-teens? Is it even possible?

jensenracing77

To many variables. You could get over 20 if you wanted to gear it correct with over drive. Put it in a small car.... defeats the reason for high HP though....

VinMichael

I'm going to try for it. I'm doing a 10.3:1 455 with multiport EFI. Should be somewhere in the power range you noted. Car will have a lockup 2004R and 3.73 gears.

Durf

Have to agree with Fun71 at that HP level mpg is second to the smile factor LOL. But my 73 Hurst is in the middle of your HP range. Turbo 400,3.73 rear,@3900 LB. If the wife is with me @ 10.5 mpg. If I am alone I can burn some fuel fast. I asked santa aka (THE WIFE) for a 950 holly for Xmas so next year 10.5 mpg will be a pipedream. Hope that helps.

VC455

The mileage depends on the compression ratio and cam specs. Generally, a cam with higher horsepower potential will have greater overlap. In terms of this discussion, it means that as you go higher in HP, the exhaust valve will open earlier, wasting the remaining pressure = lower mpg.

My wagon with the factory 365 hp engine, T-400, and 2.56 gears got around 15 mpg at steady 60 mph on the highway.

Overdrive and a lockup converter will do wonders for mileage.

If using a carb, send it--with your car specs--to a good rebuilder such as The Carb Shop. Even at 500 hp, your mileage can be in the mid-teens if you choose an overall drive ratio about 2.00:1.

rjohnson442

I found a formula once that said 1hp will burn 1 gallon per an hour at WOT. Now I kinda find that hard to believe but that would be a 50 Gallon difference over an hour @ WOT.
Anyone have a boat and we can test this theory

jeure

I have a 455 putting out 500hp and a little over 600tq that was built by Mark Remmel. It has efi, 700r4 with lockup converter. Rear end is 3.73 At 60 mph, I am turning 2000 rpm. I still drive it too hard, but get between 8-10 mpg. Not good, but I did not set it up to sip gas. Those 2 black marks are just too much fun and nailing it at 60 is a thrill.

olds 307 and 403

I am getting 21 mpg imperial with an Olds 260, TH350 and 2.78 gears. I plan adding a 2004R to try and hit 30 mpg cruising this summer, right around 1500 rpm at 60 mph! Then I plan on upgrading the cam in the 350 along with Holley Sniper injection and adding 3.90 posi gears in the back. Probably put it back to 20 mpg and more like 350 HP. A big block due to cubes and friction from the big bearings just don't pull great mileage, even near stock. Maybe a heavy duty 5 or 6 SPD manual with OD might help a bit even over an OD auto, less power loss and more efficient.

bccan

434 SBO (465/530, low 12) will average appx 15mpg in a mix of town, secondary highway & speed limit interstate driving. That breaks down roughly to 12+ around town & nearly 20mpg on interstate but I usually drive too fast to actually get that, I tend more towards 75-80 (2600 @ 80) on interstate.

Good mileage can be attributed to well tuned Qjet combined w/ OD trans which puts rpm @ 2300 rpm rolling 70mph. Around town it is pretty much idle & tip in throttle, rarely spins more than 2000rpm as it hits OD between 30-35 @ such light throttle. Abundant torque makes it always effortless.

coppercutlass

355 sbo , runs mid 12's , 3.90's driven on the highway alot . Im lucky to see 10 mpg. I beat the crap out of it like a rented mule.