Piston identification.

[Bruce B.]

I pulled the heads off a 327 which is a 250 HP Powerglide engine and found these pistons.
I was told they were 10 or 11 to 1 high compression pistons.
They are obviously replacements as they are marked 0.040 and TC260R.

Can anyone give me some information or comments on the pistons?
Thanks.

[John H.]

Re: Piston identification.

I pulled the heads off a 327 which is a 250 HP Powerglide engine and found these pistons.
I was told they were 10 or 11 to 1 high compression pistons.
They are obviously replacements as they are marked 0.040 and TC260R.

Can anyone give me some information or comments on the pistons?
Thanks.

Bruce -

Those appear to be the 11:1 pistons used in 327 SHP engines (340/350/360/365/375hp).

[Clem Z.]

Re: Piston identification.

I pulled the heads off a 327 which is a 250 HP Powerglide engine and found these pistons.
I was told they were 10 or 11 to 1 high compression pistons.
They are obviously replacements as they are marked 0.040 and TC260R.

Can anyone give me some information or comments on the pistons?
Thanks.

my guess the "R" means right side of the engine. what is on the pistons in the other bank ???

[Joe L.]

Re: Piston identification.

I pulled the heads off a 327 which is a 250 HP Powerglide engine and found these pistons.
I was told they were 10 or 11 to 1 high compression pistons.
They are obviously replacements as they are marked 0.040 and TC260R.

Can anyone give me some information or comments on the pistons?
Thanks.

Bruce-----


These are "11:1" pistons. However, that's with 62-64 cc combustion chambers. If your car has the original 59 cc GM #3795896 heads, these pistons will produce somewhat higher compression (although likely close to a REAL 11:1). If composition type gaskets are used and the heads were not previously milled, you might be in the 10.5:1 REAL CR range.

The correct pistons for your application are flat top style with 4 valve reliefs.

[Bruce B.]

Re: Piston identification.

Clem,
Thanks for the education, the pistons on the other bank are marked with a "L".
I am not an engine guy but it is nice to get this type of information and expand my limited knowledge.

[Bruce B.]

Re: Piston identification.

Joe,
Thank you also for the info.
My 340 HP engine also has these pistons and the compression ratio is called out as 11.25 : 1 . Would that compression be due to the smaller combustion chamber heads?

[Joe L.]

Re: Piston identification.

Joe,
Thank you also for the info.
My 340 HP engine also has these pistons and the compression ratio is called out as 11.25 : 1 . Would that compression be due to the smaller combustion chamber heads?

Bruce-----


The 340 HP used 62 cc heads. The 11.25:1 rating was used for SHP small blocks from 1962 through 1964. It dropped to 11.0:1 for 1965 with little else affecting compression ratio changed. I think it was likely just an on-paper "specification revision" to bring the advertised compression ratio closer to reality.

[Duke W.]

Re: Piston identification.

Joe,
Thank you also for the info.
My 340 HP engine also has these pistons and the compression ratio is called out as 11.25 : 1 . Would that compression be due to the smaller combustion chamber heads?

Typical Flint "as-built" engine CRs are a half point lower than advertised due to decks being higher than nominal. The only way to compute the true CR of a specific engine is to take all the relevent measurements and run them through a CR calculator.

340 and 360 HP engines were double gasketed from Flint beginning during the '62 model run. This dropped CR about another half-a-point, so most of the actuals were no more than 10.5:1 as built.

Duke

[Clem Z.]

Re: Piston identification.

I pulled the heads off a 327 which is a 250 HP Powerglide engine and found these pistons.
I was told they were 10 or 11 to 1 high compression pistons.
They are obviously replacements as they are marked 0.040 and TC260R.

Can anyone give me some information or comments on the pistons?
Thanks.

if you plan on reusing these pistons i would remove all the sharp edges from the machine work. your second picture show after the tops were machined they left a lot of burrs that could get hot and cause pre ignition

[Bruce B.]

Re: Piston identification.

Clem, John and Joe;
In the first posted picture at the 5 o'clock position you can see what appears to be a spot where a valve hit the piston top. This is cylinder #3 and it looks like it was done by the exhaust valve. There are similar small dings on all pistons at the exhaust valve positions.
But obviously this could not happen the way the engine is assembled now.
Could it be possible that someone originally put the pistons in 180 degrees out and this situation occured?
This engine came in an old 62 Corvette which I modified years ago and the engine has been sitting for 5 or 6 years. I pulled the heads off recently as I need an engine to put my modified Hilborn setup on. With these pistons and a cam which would deliver a good vacuum signal it would be perfect for my application.
Currently with my stock 340 HP engine I don't get a good quality vacuum signal. Therefore I have been tuning using a alpha-n program which is based on throttle position. Since the Hilborn has 2.0625" butterflys I do not use much throttle and it has been difficult to tune. With good vacuum I could use a MAP program and it should work much better.
I have put about 900 miles on the current setup and it is a blast to drive.

More info, when I took the heads off the head gasket was a steel 0.027"+- thick gasket.