I have a 1965 olds 442 that i am going to put t56 6 speed manual in.I have two choices of 6 speed trans a wide ratio that will put me at 1231rpm at 60mph.The close ratio puts me at 1551rpm.I am worried the wide ratio at 1231 will be lugging the engine and hurt mpg and has a 2.97 which i think is to low a gear. I am building a 455 13-1 comp. for e85 that will have 400-450hp.This car is being built for cruising on the weekends and going to car shows.Any imput would be appreciated.

 

Here's a thought, just don't put it in high gear until your going fast enough so it doesn't lug it.
And 13.0:1 on E85 is doable but remember the winter formula won't be as potent so you'll need to tune accordingly.

 

I have been researching vehichles with 6 speed trans.A 2001 corvette 6 speed turned 1368rpm at 60mph it had 350hp 350lbft of torque at 5600 rpm.A lot of people on the corvette forum say they get the best mpg in 6th at 60mph.I have never had a 455 and i would like to get everybodys opinion based on their experience so i can get this set up right.I think a 455 would be better running low rpm than 350 in a corvette. cutlassefi i will have to talk to you about what you think i should run for a cam

 

All I know is having a 5 speed increased my gas mileage substantially. The answer to your question as to best mph for best mpg would be the speed 0. Make car noises in your driveway. You know, like you did as a kid! Think of the savings!

 

Lug? You think that you're going to lug that torque monster down? Not unless you are under about 600 RPM.

Go for the wide ratio if you are shooting for your best cruising MPG. Just keep in mind with E85 you will use quite a bit more fuel than regular gasoline.

 

I've rethought my answer. If it's only going to be for cruising and car shows why are you concerned about mileage, especially as mentioned, taking into consideration you'll use about 30% more fuel with E85?
And on second thought, if you're going to have iron heads unless you're going EFI I'd cap your compression at 12.0:1, max.

Jmo.

 

I've found downhill, tail wind, engine shut off, and being towed - usually does above 10mpg. Sorry. I currently get about 7 - 8 mpg. Engine i'm having built - have no clue what the mpg is going to be.

 

13:1 and only 400-450 hp tells me your cam is relatively small. I'm guessing your dynamic compression will be through the roof.
You might want to rethink that cam for that compression ratio.

 

I am not sure I get this, you are worried about 200rpm difference??? Also if you are worried about MPG you choose the wrong hobby and a wrong engine for your car.

My BBO usually runs at 3000 rpm on the freeway and on a good day, with strong tailwind I get about 8-10 MPG, but I wouldn't change a thing.

 

-dw- over on ROP has a 455 in his G-Body that gets like 21-24mpg on the highway.......can't remember now, somewhere in that range. Anyways, the car goes 12.00s down the 1/4 mile with J heads, with overdrive he goes everywhere at a nice cruising rpm.

His car runs on pump gas, though.......not e85.

 

Personally, I do not believe anybody that says his 455 get 20+ MPG.

 

I am with those who are telling you that it does not matter. If it does you are in the wrong hobby. I drive my 67 convertible through about 8 tanks a season and maybe two more the rest of the year as the weather allows. Who give a rip what mileage it gets. I don't use E85 ever. We have non-ethanol fuel available at a few stations around here. I make a point of getting it. It costs a little more but the car runs so much better and I don't have the issues related to E85 then.

Well worth the couple of bucks a tank in my opinion.

 

But lowering the cruising RPM by 200 will save a person 45 cents a tank.

I think any Olds owner that's concerned with MPG should sell their car and buy a Prius.
Sorry JMO.

 

You don't have to believe it. But you should take his test. Go for a ride with him on a full tank of gas. He will give you a 40oz. of soda to start the trip. You can't go pee until he stops at the next station for gas.

And why is everyone busting the OPs chops here. God forbid someone wants to try to design a driveline to achieve better gas mileage.

 

i have a t56 with a .5 overdrive, about 2000 rpm at 80mph. 66 cutlass with a 350 and i might be getting 15-17 mpg range. if you get your engine on a dyno just gear your car so at cruise speed you are at your peak torque, supposedly you get the the best mpg there because thats where the engine is the most efficient

 

I got 19 mpg with my 70 Toronado. Didn't happen all the time but it is doable under the right conditions. I wouldn't expect that kind of mileage or anything close to it though on any built 455. Even a mild build.

 

As said E-85 makes it totally backwards for mpg, expect single digits. Now with aluminum heads, small roller cam and mid 9 to 1 compression and a carb tune spot on, prefer a Qjet or 750 Street Demon for mpg, high teens should be possible and close to 400 HP. More importantly massive torque 500+, a lot just off idle, either trans should work but 1500 rpm is plenty low for good mpg. I agree reasonable mileage shouldn't be thrown out the window. My 403 never ran great track times but was fun and got 20+ imperial when it had OD and 2.56 gears on the highway. My 350 might get close to that and run faster but my town mpg is definitely worse with a properly tuned carb, any motor with a larger can will be harder on fuel idiling around especially.