Technical Silv-O-lite Racing Pistons ID (GMC 270?) # 5567

Anybody have a book to ID these pistons?

I know they are GMC... But what size engine?

I was told GMC 270, but they are 3.875” (which is fine) and sit 0.1875” lower in the bore than stock????

Measured another 248ci and the deck height is the same? Is there a lower deck height engine?


Sent from my iPhone using The H.A.M.B. mobile app

 

They look like 3 ring standard replacement slugs for the early domed engine.

 

Thanks for the reply, I looked closer in the speed manual. These are 270 pistons, just an odd size.

I’m going to have to take off 0.125” the deck and 0.090” off the head to get about 11:1 CR.

Here is pics from the manual.


Sent from my iPhone using The H.A.M.B. mobile app

 

''I was told GMC 270, but they are 3.875” (which is fine) and sit 0.1875” lower in the bore than stock????''
Sounds like your crank is a 228-248. 4 or 6 bolt flange ? Better to use a 270 shaft so the block needs just a cleanup on the surface. A 3 7/8'' bore with a 4'' shaft is 283 cubes ...

Any more than .060 off the head requires hogging out the holes on the tappet cover or making a new one from stainless or aluminum sheet stock ...

 

Inliner 2318, they are for the 270 H head or can be used in the small port 228-270 also, The early 270 has the open style chamber and the last 270 had a different chamber than the others. The 228-248 has a shorter stroke. I thought 3/16". I believe all deck heights are the same and the pistons made for the 228-248 had the pin in a different location. I believe all the rods were the same length also,7". The only block I have that is different is a 1940 270, the first year. It is currently bored to 3-31/32" to fit in an under 300" class of racing from the 40's. I understand it can go to 4" but I have never had it sonic tested. JD Inliner #35

 

I found it easier to add a turbocharger to increase combustion pressure. I don't like all that milling. I bored mine to 3 15/16 = 292 cid Pretty common.