302 GMC big six engine buildup for 33 Plymouth

I ran several GMC engines a while back. Like your thinking. I setteled on Arias pistons and likely they still have the print for 9.5 to 1 pistons I used. Nothing wrong with the other piston makers mentioned.

 

Have you checked the numbers on the block? That truck could have been built with a 302, but it looks like the engine has a 1 bbl carb on it. Didn't all 302's, (and big port 270's), have 2 bbls? Perhaps the intake was changed at one time?

 

LAROKE, That is a sweet clean set-up you have...what truck is that jimmy in?

It is very cool that a 16 year old young man is interested in a jimmy...there is hope yet for the young hot rodders coming up....If I hear one more rice grinder with a BUZZ muffler I am going too loose it!

 

Yes I believe the carb may have been changed, but as you can see it has the governor unique to the 302, and all numbers say likewise, let me make it clear that THE ENGINE IS UNMISTAKEABLY AND IRREVOKEABLY A 302 GMC

 

You picked a great motor.. Here is my Jimmy in a Belly Tanker...

 

Nice piece...how fast does your Hotrod go?

 

This is great! I am building a 302 at the moment as well for a vintage fuel compe***ion coupe and hopefully I can have it done by August. Richfox, do you remember the compression height of the piston you used? I know the stock compression height for a gmc 302 is 2.067 inches. If you kept the 7 inch rod length, did you mill the head or make up the compression ratio with the piston? Also who makes lifters for a GMC inline six? Any one out there offering roller lifters? I talked to Doug Robinson about his GMC and he had a custom roller set-up. This is what Hot Rodding is about. The old dogs showing the young pups new tricks. I am only 24 years old myself and building this coupe with my dad has been invaluable to me. Thanks for any and all help, and good luck with the build.

 

It has been some time since I ran a GMC. All the Arias pistons I bought had a small popup in the piston. At times I ran a long rod. I think + 1/2 but it may hav been 5/8. I also at times ran a Howard head with flat top pistons .300 down for a 13 to 1 CR and a Hourning head which was about 12.5 to 1 with the same pistons as the stock head9.5. I don't think it's hard to get new stock lifters. Don't know about rollers

 

Thanx, it's a '37 Chevy, Also built by Truckedup.

 

You have to mock up the block with the stock piston and measure the distance below TDC. Then with that info you can get pistons made.To get more than 8.5 compression even with a lot of head milling ,the piston will need a a dome.This is with the stock GMC 302 head having an combustion chamber volume of 118 cc's.If using an aftermarket head it's the same only different
Some guys will mill the **** out of the head,I don't know if that's the best idea...especially if having custom pistons made anyways.
Victor and Felpro head gaskets are around .058 compressed thickness.Be nice if the head gasket was around .040 for better quench,custom head gasket too maybe.
The stock lifters can be refaced if not too worn.Roller cam stuff is available,for a price.

 

Who should i have machine the head, and what should i have done to it? no milling for CR or anything, just flow

 

If ANYONE has a 33-34 mopar trunk lid or 1933 plymouth drivers side window trim i would be more than interested

 

Here's what I was told about the head of the 302. First it's best to get your compression from the pistons and just clean the head to seat right. Next when porting and polishing be very conservative because there is less material between the air and water than other heads. Also when porting don't touch the bottom of the runner. Air doesn't like to make 90 degree turns so just work the sides and top. California Bill's Chevrolet, GMC and Buick Speed Manual is a great source of information on GM's straight engines. But do keep in mind that it was written over 50 years ago and should be read with the understanding that there has been leaps and bounds in technology since then.

 

Is there anyone specialized or seasoned in the porting of this head?

 

302's were always 2bbl, not 1bbl. Take a look at the stamped pad next to the distributor. The displacement is usually stamped on that pad. Or get the casting number from the block and check it against the casting number list over at Inliners.org

Have you looked at what it costs to build a GMC engine?

 

Nice find and great engine. We raced a 12 port head version 302 inline in the Los Angeles area for years. First with a log manifold with five (5) two barrel carburetors and then we met Al Gonzales (ALGON) injectors and the whole machine changed and it really ran then. Your idea is a great one. Might I suggest you look at the website, www.inliners.org? Good bunch of folks and all enjoying some type of an inline engine. Lots of parts available through their Advertisers Index too. Congratulations and good luck. Those are another torque monster too!
Normbc9

 

just a note on the engine it has 160 + on all 6 cylinders so luckily the bottom end may not need to much to be a driver.

 

What are you doing with the Cab and front clip? I am looking for a 55-57
GMC cab and front clip for my project

 

Nice car. Nice engine. There shouldn't be anything wrong with putting them together.

The actual auto manufactures are not nearly as loyal as us hobbyists. They'll stick anything under the hood to make a buck. Truck manufacturers are even more prone to stick another brand under the hood to get the job done.

 

Funny you guys brought up this old thread, I wonder what happened to Surfin the original poster, I was hitting him up to see what he did with his extra parts a couple months ago and have not had a reply. Hopefully he sees this.

 

Nice reading this post. Funny how folks seem to think that horsepower seems to grow on trees for us to pluck. The advent of th SBC crate ads have dull a lot of senses. The 302 GMC engine in my avatar has more trick stuff than anyone will ever know. It could never ever drive on the street and is south, way south of 400 hp and its pushed a 32 Ford grille shell and open wheels to 170 mph. I'll be estatic if the 12 port I'm building for LSR will make that much and it will have 15-1 comp. If you want big numbers a power adder is the only option. Nitrous, a supercharger, or nitro. Then you better have some real good parts and some extras too. All in all fun to read even from 2012.

 

I would drive the **** out of the parts truck!

 

jimmy six's roadster....

 

My brother is the one with the couple, I will have to tell him to get back on. College has put the build on hold for the time being

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