Inliners International Forums General Discussion Engines 270 GMC

I just bought a 270 gmc to replace my 248 in my 54 gmc 3/4 ton. The engine is in a 58 Gmc med duty truck. I have to pull it out yet but is the factory head on this 270 the same as my 248 as patricks suggests? Am I now on the look out for a 270H head?

Check the casting numbers on the head, or measure the size of the intake and exhaust ports. That will tell the tale.

God's Peace to you.

d
Inliner #1450

This might help:

I don't know what the intent of your use is but I have helped a few guys build 270's which were very good performers and did not use any big port head. If you really want a big port go with the 302 "D" shaped chamber. A flat top piston and .100" off the bottom of the head will give you more compression than doing the same to a "H" head.

It's been my experience to use a small port head(last small chamber) with a big port manifold and taper the head out to the manifold size; starting abour 1/2" back in the port..This give you a venturi affect and the velocity of the fuel going in loads the cylinder for excellant torque. That's what you are really looking for. You can put in larger valves if you wish but for me on the street to 4000 rpm small makes torque. I have never had any problem with ever taking .125" off the bottom of a head but I would not reccommend over .100" on a street engine..Good Luck..#35

A buddy who ports and polishes heads for a living made an interesting comment to me about domed or shaped piston tops; he said that they tend to interfere with combustion when compared to flat top pistons. Whether or not this is correct I don't know, but it sounds logical.

he said that when the spark first ignites in the chamber, that energy has to flow up and over a dome top before it ignites the other side completely and then it focuses the energy to drive the piston down.

He prefers flat top pistons for his work for this reason and feels they are a better performer.

Not looking to start a debate here as I'm not qualified to say yea or nay, but I thought this was an interesting take and it was "shareworthy" if you will.

The plan is to use it in a GMC my grandfather and I restored when I was in high school. It now has a 248 but I would like it to have some more power and add some vintage or vintage appearing speed parts. Kinda like if you were a farm boy in the 50s early 60s and your old man gave you his old truck. It is a 3/4 but the front axle has been changed to 1/2 ton and the rear to a car axle with 3.55 posi. I would like more power just for the fact of when it gets done I would like to take it on the power tour or whatever and all hot rods need more power. It will be lowered and get chrome reverses keep the 4 speed and the floor starter and maybe add hidden a/c. We have used it on our farm since 1964. Be cool to use it to pull some other vintage car to the races or a show. My buddy is building a hot buick 8.