Thread: V8 What size? Best mileage?

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Okay, recently my father and I purchased a 1955 Pontiac Chieftan. Its a great looking car. This is our first classic car but its never to early to start right? Course the floor boards need replacing and there are some dents but all and all its nice. The engine runs but we definately want to replace it. Problem is we know next to nothing about engines. We want to put a v-8 in it to keep with the spirit of 55 being the first year that GM put v-8s in, but we don't know what size or how to get better mileage. This is primarily my fathers car. He will use it on a day to day basis basically, so he would want the car to have good mileage. He's not that into performance so what would be the best way to go? What size and what trans should we get? Also, what are different strategies to getting better gas mileage with a V-8, what parts? We would be looking at getting a crate motor rather then rebuilding another engine. Also if you recommend a specific engine and know a website that sells them let me know the site and the price.

Thanks in advance.

I have a 1956 pontiac(canadian model) I've had it for about 2 years. when i fisrt got it it needed some work and i threw a 305 chev in it just to get it around. it was a used engine outta an old 79 presianne it ran very well and was good on gas i used a 350 turbo trans.for milage and low cost a decent 305 works good.. i changed to a 350 to have a little more fun but i paid for it in milage...

We would be more interested in replacing the engine with a brand new one rather then rebuilding the original engine.


Jayman...305 huh? I was thinking about that as well. Do you have any idea what kind of mileage it got with that set up?

Yeah I guess your right but what is the average? For instance with new cars when they list the mileage a car gets on the pamplet. Thats what I want, whats the average mileage for a 305 for city and highway.

Alright I understand, but is that the package you would also suggest? A 305 with a 350 turbo trans?

a mild 350 with a 5 speed

Its an automatic to begin with I don't think I would want to change it to manual. Its up to my dad really but that doesn't seem like something he would want to do.

then have an overdrive

We would keep the engine just incase we wished to sell it but it doesnt look like we are gonna sell it anytime soon. Maybe we'll just end up putting a 350/350 in who knows. My father is going to talk with our mechanic tomorrow.

If you've got $1700 to burn and want to keep the car original, you could bolt up an overdrive unit in place of the original tailhousing.

Originally posted by 55Chieftan
We want to put a v-8 in it to keep with the spirit of 55 being the first year that GM put v-8s in

GM used V-8s in a number of cars before 1955, so I'm not sure what you mean by keeping the spirit of 55.

If I remember correctly the 55 Pontiac motor is the same family as the 389 and 455. I'd consider replacing your current motor with one of the newer motors from that group.

Just my two cents...

With the 305 I got about 27 Mpg that was when it was stock....a fresh 350 moves the car very well.. that style of pontiac wasnt exactly light..(as i found out at the strip 14.87 with the 350... lol). currently i'm running a 350 4 bolt main outta 77 vette. it didnt have a whole lot of miles on it i gave it a quick freshen up and it works very well... a simple change of intake,carb and headers made it work very well and i plan on installing a cam and vortec heads next to give it a boost.....i'm currently getting 22MPG

22mpg now thats pretty god. Yeah the Pontiac is pretty heavy I heard its around 3,800 if I remember correctly. 14.87 with a 350? God lol. Well hopefully I can talk him into a 350 and then doing some accessories like what you have planned for. Do you think a brand new 350 crate motor would get the same mileage as the one out of the vette?

GO with a 350 engine with about 300 horsepower and a 700R4 automatic tranny which has an overdrive and a lock-up converter. You could get 25 plus mpg.

Now, if you take 'er to Canada, you will get 20% more mpg. That means you could get 30 up here.

How will he get 20% more in canada? colder air? ya lost me on that one.