The Stovebolt Site Forums The Shop Area Engine Shop 316 GMC/Pontiac

Anyone know what parts interchange and what parts don't between the the ealy 287,316,336,347,370,389 and the later 63 to 81 326,389,400,350,301,421,428,455????
Do all intakes interchange how about distributors and can the later heads be fitted with the water ports at the front like the ealy heads?????
Are the bell housings differant and is 63 when everything changed???

There is a bit more info on these old GMC/ Poncho V8s at www.oldgmctrucks.com. I'm not sure of the differences myself, and what will interchange. My 336 seems to be getting tired, and I was hoping to be able to swap out the crankshaft from a 389 to get more stroke. I'm not sure how practical that would be.

John

Pontiac V8's have the advantage of having as much displacement as a Chevy big block in a package almost as small as a Chevy small block. If you can locate a 455 Buick, Olds, or Pontiac, you get a LOT of torque on crap gas.

Grant, check out this site,
http://www.wallaceracing.com/interchange.htm

They have a lot information on the older Pontiac's plus the a lot of High performance stuff. Look around on the site, they have more then anyone, so you may have to do some digging there.

Down on the left on the home page are books for sale, my dads book is listed there, ( How to Build Max performance Pontiac V8's). Let me know if you can't find what you are looking for. Joe

Two books you NEED TO READ: the book by Jim Hand mentioned by Joe in the previous post, and another book by Pete McCarthy. I don't remember the exact title, but it has to do with Pontiac Performance 1955 - 1979. Jim's book is an excellent "how-to" and Pete's book has much specification data.

While there is a LOT of interchangability (it fits); one must be careful that the part that fits will actually work. As an example, Pontiac used head volume to control compression. It is quite possible to change heads and end up with totally unworkable compression ratios.

Jon.

Hey thank you guys for your help and prompt responses. Joe H thank you for the link to Wallace Racing, if I understand the chart looks like the early 55 to 64 are all different and specific to one or two years for most parts, i.e. bell housing looks to have changed 5 times up to the late BOP housing witch is not what I wanted to hear. I would like to know more about what the differences are, and maybe if minor machine work would allow more interchangeability.

Give Tom a call at the following site. He is long time Pontiac racer who deals with the older engines. He will tell you what you need to know.
http://www.wilhiteauto.net/about.htm

You can always put a later model bellhousing in if you are sticking with a manual transmission can't you? So we are not much help on the older engines or GMC's. Now if you want to build a later model engine, we can really help. Joe

Thanks Joe I really don't care about bell housing changes other than the bolt pattern at the rear or the motor and if a later motor will bolt to the trucks bell housing.
For the front of the motor can I make the early water pump with the external water ports in the heads work with a later 455 I would like to put a 455 in it and leave it looking 100% stock.

The 400 / 455's need the correct harmonic balancer installed, I don't think you will get the early front cover to work with the late balancer. You will need a 69' or new front cover and water pump for the big engines. You will also need a big radiator to cool the 455, it has less water capacity then the 389/400's so they tend to run a little hotter.

How about just painting up the new motor to look like the old one? Add vintage valve covers and air cleaner and moet people wouldn't know the difference.

One thing to think about, it cost just the same money to build a 455 as it does a 400, 389 will be more then both due to demand of parts, 421/428 cost even more money then the 389. You can now buy stroker cranks for the 400 block that will make 455 or bigger engines out of them. The 400 block had stronger webbing and more metal in the lower end. You can also get 505 inch Pontiac blocks that look stock. The stroker kits (crank, rods, pistons) are pretty cheap compared to finding 455 which are getting scarce. Joe

It looks as if there is an early and a late 389 I would really like to build more usable power and keep the reverse flow water pump as it is the only really distinctive difference. The later heads look to have the boss for the reverse flow fittings still on them they just don't tap the bolt holes and plug the water passage with a soft plug. It would be cool if I could use a later motor and bolt all the original accessories on it.
I still don’t know what I am going to do with this truck but if I keep it I want to work it but would like it to remain as close to original as possible

Oh BTW I still haven't found info on the different bell housing bolt patterns or if there are different ones. I may have to just pull this motor to find out for my self.

BOP's usually had a different bellhousing bolt pattern than Chevys. And this is because at one time they had their own engines...but not anymore.

WHAT YEAR OF GMC ARE YOU WORKING ON?? I MAY KNOW OF SOME HELP FOR YOU.

RICO

rico_bob this is a 56 1 1/2 ton, from what I can see though the 52 years of grease and dirt with it in the truck it looks like it may be a standard BOP bolt pattern but I can't tell for sure I do know that the early Buick nail heads up to 63 anyway had a different bolt pattern that was round and nothing like the later BOP pattern.

Hot Rod Dad I am familiar with the Chevy and BOP housings I am not sure if this old of a motor 56 316 V8 Pontiac used the BOP pattern.

Yeah, I'm just not sure either...

from what i have found 60' is the cutoff year for the early bolt pattern. wilcap makes a adaptor for 60'-64' to use b.o.p. pattern. the later blocks have different starter mounting.