273 Pistons Question Commando or Not

[Hyper_pak]

Fabo Family:
I have a set of 273 pistons and rods. I have been told all 273's have 4 valve notches. My question is how do I tell high compression from low or standard compression? I don't have a 273 to install them in to check deck height. Any ideas? Is there a casting number inside the piston? Thanks!

 

[grumpuscreature]

If the pistons have 4 valve notches they are low comp. The Commando pistons have a definite dome shape. Helen Keller could see them....

 

[BillGrissom]

Ditto. I have both. My Commando pistons are kind of messed up though. Should have spent more time freeing them. The HiPo pistons have a higher ridge in the center, which is very obvious viewed from the side. I also understand that left bank and right bank ones are different, meaning the pin is not in the exact center. Some racers swapped them L & R for better performance (which probably starts some arguments).

 

[OldmanRick]

This is supposed to be a factory hipo 273 piston.......

 

[grumpuscreature]

Here's Egge Machine's version...

 

[Rocky_JS]

If Std bore 2 notch hi-po, 4 notch low-po. however if they are aftermarket replacement piston all bets are off as far as compression. I have a set of 4 notch .030's that calc out to 10:1, and a set of .040 that I haven't checked yet.

 

[Hyper_pak]

Dang it! Thanks guys.

 

[rumblefish360]

Oh ya! That was a set of four ACE's fellas!
Nice work!

 

[pishta]

I remember mine as having 2 valve reliefs and a dome which had flats on it.
Uh...just like these ! And those pins are thinwalled light compared to the 4 valve relief lower pistons, probably to offset the weight of the taller domes piston.

These were credited to this site, dont know who's......