[charles vance]

Which engine would get better fuel mileage, everthing(cam, intake, carb, weight of car, gear ratio... etc.) being equal.

[Junkyard Dog]

If everything else was equal, it would be the same.

[68lemans462]

Originally Posted by charles vance

Which engine would get better fuel mileage, everthing(cam, intake, carb, weight of car, gear ratio... etc.) being equal.

do you honestly think anybody here is gonna recommend a chubby motor? I doubt it.

[J.D.]

ill go out on a limb and say the pontiac would get better milage because it weighs less than a bbc engine.

[69birdboy]

From my experiences with stock v-8's, the differences in mileage are not noticeable. I can't tell the difference in mileage between a truck with a chevy 305, a big car with an olds 455, a trans am with a pontiac 400, a truck with a chevy 402, another big car with an olds 350, and a truck with a chevy 350. Every one of them gets 13.0 mpg, and is bone stock. The 455 is even a 2 barrel. Gear ratios range from 2.42 - 3.55, and all are automatic.


So, my guess is, the exact same mileage with either one.

[67 Lamnas]

If a person is putting together an engine that displaces around 7.5 liters, why is that person concerned with fuel mileage or economy?

[MrPushrod]

fuel mileage?
What's that?
My foot is too heavy.

[1971WARBIRD]

i go by,fun per gallon,not miles per gallon.i would almost think the pontiac.it has a longer stroke,right?wouldn't that mean more torque at a lower rpm,and torque is what moves us right?even then i'd bet it would only be a very small amount.

[Half-Inch Stud]

Everything else same (Temp, compression, ping-limited Advance, the lowest Octane gasoline that either engine could stand) then the PMD will provide better MPG on the MERIT of the smaller Bore with 0.21" more stroke. That ALLOWS more ping-free Advance on the proper head for more ping-free Torque.

454 with Delco surround sound crankin Gordon Lightfoot MIGHT WIN if the ping overcomes the driver.

[Skip Fix]

My wifes 454 73 truck WITH headers averaged 9mpg! Towing 7mpg and with that 20 gallon tank didn't get very far between fillups moving from Texas to San Jose and back! But I swear it was as fast as my TA with the stock 180 hp 400!

[Ron Genovese]

Hold on! You are going to install either a 455 pontiac or a 454 chevy & are concerned about gas mileage?

[455Grandville]

The difference between the two probably wouldnt be much; my stock 455 with 2.56s out back gets 14mpg highway if that helps any.

[uneasyrider]

No joke, with 2.73's mind you and keeping my foot out of it (and that's HARD to do) I can get 18mpg out of my TA on the highway. As far as that goes though I think if it were a BBC in the same "situation" it would too. If they are in good tune most V8's pulling the same weight with about the same gearing get about the same mileage as far as I've seen.

[charles vance]

My 455 is shot: Spunned bearings, I have a complete 454 bbc, I was trying to make a deal with the local machinist. He told me that he had a 455 crank and rods that I could possibly use(trade/money). He also told me that a 455 pontiac would indeed use more fuel than the BBC. Mybe he's trying to screw me over................SOME HOW!!!

Also; buying pontiac parts thur ebay and machine shops, HELL I never knew GM perduced so many GTO's.....SD's........HO's........and other RARE ASS PARTS!!!!!!!

It's like, every part that is for sell come off of a SD or something!!!!!!!!!

[PunchT37]

Originally Posted by Ron Genovese

Hold on! You are going to install either a 455 pontiac or a 454 chevy & are concerned about gas mileage?

I`m tellin ya. They`ll both drink gas. Watcha puttin it in?

[67 Lamnas]

[QUOTE=charles vance]My 455 is shot: Spunned bearings, I have a complete 454 bbc, I was trying to make a deal with the local machinist. He told me that he had a 455 crank and rods that I could possibly use(trade/money). He also told me that a 455 pontiac would indeed use more fuel than the BBC. Mybe he's trying to screw me over................SOME HOW!!!


The above is a great reason not to use this Chevy mentality machinist for the work on your Pontiac.

[TJH]

As has been said, if you're worried about gas mileage, you shouldn't be looking at EITHER engine.
The machinist is indeed full of ****. I'd take my 455 elsewhere to be rebuilt.
And if you're seriously thinking about putting a 454 Chevy into a Pontiac, grab that 455 crank, and smack yourself in the head with it, repeatedly, until you come to your senses.
Your car will thank you for it.

[67 Lamnas]

It's like my grandma asking "what's the rated horsepower and torque of my Buick Park Avenue?"

Who cares?

[b-man]

Originally Posted by charles vance

Which engine would get better fuel mileage, everthing(cam, intake, carb, weight of car, gear ratio... etc.) being equal.

The Pontiac 455.

I would say due to the efficient, somewhat small venturi-shaped intake port. Along with the longer stroke of the 455 (4.21" vs 4.00" for the 454) that lets you get up to your cruising speed with less throttle opening.

Big Pontiac V8s have been known to be more fuel-efficient than the Chevys.

Your machinist is FOS.

[Thumpin455_GTO]

Well having some of each, and having friends who run the 454s, I have yet to see a 454 with the same power level as my 455s get the same mileage. I have gotten well over 20mpg with an overdrive trans in a 70 GTO with a 455 and a Qjet. While the 454 in the 3/4 ton outside used 16 gallons traveling 35 miles. Sure its a truck, but highway mileage varied by that much?

Anyway.. in the spring a 454 is going in the 1/2 ton shortbox where there is a 400 Pontiac sitting, and then possibly an OD trans along with a new intake, headers, cam, lifters springs, and a Qjet built to Cliff specs to see if it can get over 10mpg. 15 would be acceptable, but I will squeeze it for all its capable of.

Pontiacs have high velocity ports, that means a good carb signal doesnt it? That also translates to better efficiency. Port design as well as chamber design have an effect on mileage..

I would go with the Pontiac, and put the 454 in a truck.. Oh wait.. I am!