Inliners International Forums General Discussion Engines NOS GMC Head

Fellas, I don't know squat about early GMC heads but I just came across what appears to be an early nos GMC head in the box that is advertised on ebay as an inline chevy head but is described in the body of the ad as a head for a 228, 248 270 GMC head. It is not a chevy head and to the extent I recognize anything, the combustion chamber is not a chevy chamber so it may very well be a nos GMC head. Just thought I would pass it along.

http://www.ebay.com/itm/Nos-chevy-head-i...9de&vxp=mtr

Looks like a 270 and 302 head to me. I don't know a ton about GMC heads either. lol

Could be a 2136477, listed in this article from Patrick's catalog.

Hello Charlie,

I have moderately hopped up GMC 302 in a 1940 Chevy which has been on the road and sometimes race over 22 years. It still runs great. The 302 head is different from the smaller engine heads. All 302 head intake port ring outer diameters are 1 3/4 inches. I think the 270 H heads are also 1 3/4. All the other smaller engines have smaller intake ports and smaller valves. Ported heads are usually enlarge to the 1 3/4 inch outer port ring diameter and larger Chevy V8 valves are installed. My head has been ported.

That is a small port head that requires a lump on top of the piston to make compression. Often referred to as a 477 head.

A good deal for someone with a stock motor with a cracked head, but not a great head for a performance build.

The other small port head is the newer 819 head which can be milled 0.020 - 0.030 and used with flat top pistons to get 9:1 compression and with oversize valves and a little porting makes a decent performance head for a solid reliable driver.

The only reason the big ports are needed is for a race motor. The small ports work fine on a street set up with either style chamber, with the right pistons. California Bill recommended them for the street.

How many different casting numbers were made for GMC 6s? I know that there were a couple of different port sizes with the 302 being the biggest. Jay 6155

There were 4 heads for the whole run. Check the link to Patrick' catalog in cletis's post above. The head on my 270 is the last one that Patrick likes the least but it is fine for a hot street build.

Thanks for the info. Just curious , none of the numbers listed in the tech tips match the numbers at patricks. I like learning about these and stovebolt engines. Jay6155

Did you click on the "check it out" by the GMC at the top of the Casting# page? Those are the GMC numbers.

Ok I just did. Now I get it. Thanks jay6155