Alcoa Ansen domed pistons for a '56 265 engine

I have a set of pistons that are what the title says. There is a number 40 cast in the inside bottom of them. How do I know if that's forty over or what does it mean?

 

Stock bore 3.750 + .040 = 3.790 - a few .001’s for clearance.
Measure them 90* to the pin bore and below the ring lands.

Pictures would be nice, it won’t help with the size, we just like to see them.

 

Here is a pic of them

 

Alcoa forged the blanks and Ansen did the machining on them. Looking at them I suspect they are about 12-1 compression, maybe even a bit higher. Not a lot of demand (I’d say less than zero) for 12-1 265 pistons but cleaned up they would make cool garage art.

 

I'm actually going to use them in my 265 and run E85 with them.

 

Wow, didn’t see that coming. Sounds like an interesting project, keep us informed.

 

Yeah I'm using them along with a Comp Cams 285B-6 solid lifter cam.

 

Do you have any idea what size rings these make take as in 1/16", 1/16" & 3/16" or???

 

Chevrolet originally used 5/64 and 3/16 but I don’t know what Ansen machined their pistons for. They’re most likely 5/64 but you can measure with a decent ruler to make sure.

 

I'd use Jo-blocks or feeler gauges.....

 

That should stir your soul when it idles! That cam is gonna be rowdy in a 265.

 

I'll have my engine guy check them for me.

 

Yes sir it'll sure hit pretty hard. I originally bought it for a 283 I was gonna build for my '55 but the block turned out to not be good so I got the 265.

 

Looking at those pistons I'd guess the rings are 1/16 1/16 3/16. Pretty common back then.

 

That's what I was thinking also but someone said they could be 5/64", 5/64", & 3/16".

 

And they could be since that's a popular option,but I think it looks like the two upper rings are thinner than 5/64.

 

And the smart thing to do is measure them so he gets the right rings instead of going by what you or anyone else thinks they look like.

 

They could be 1/16 but I think 5/64 was still pretty common in that era. I believe it wasn’t until the ‘70’s when race pistons started using 1/16 compression rings and Chevy was still using 5/64 into the 1970’s.

 

I'm not just gonna buy any ring set until I know what they are. I appreciate the reply.

 

I have the original pistons from my engine. I will pull one of the rings off of one of them and check thwir fit.

 

Well, obviously.

 

The point of my comments is that a ring set for a
3.750 +.040 bore could be hard to find. Chevrolet used 5/64 compression rings on the early SBC’s but the suggestion was made that Ansen may have machined their pistons for 1/16. I believe it was later that 1/16 came into use and if I understand your comment you want to check the original rings from your 265. You can take a top ring off one of the original pistons and use it as a gauge to verify what ring set will fit your Ansen pistons.
You don’t want to buy a scarce HTF ring set that won’t work with your forged pistons.

 

Is Egge still in business????...
They might have ring sets for the 265 +.040" pistons....