dannyum89

JE/SRP Forged Pistons Flat Top +.030 1.125 C.H. 10.8:1 with 64cc head
As the title states, what does it mean?

Colin91Z

C.H. or Compression Height. It's the distance from the middle of the wrist pin to the top of the piston.

dannyum89

Okay...

Colin91Z

I'll take that to mean you're still not sure what I mean, maybe this will help

http://www.rosspistons.com/custom_co...ion_height.php

dannyum89

I understood what you said but why would they even mention that? Whatever. I was just curious.

Z95m6

Probably because depending upon the rod you're running its going to determine how far in or out of the hole the piston is.

OldSStroker

If you wanted the piston top to be even with the deck (Zero Deck) you could solve for Compresion Height (CH) this way.

CH = (Deck Height)-(stroke/2)-(rod length)

Stock SBC deck height is 9.025, so for Zero Deck on stock engine:

CH = (9.025)-(3.48/2)-(5.70)

CH = 1.585

Or for a 383 (3.75 stroke) with 6.0 rods and a 9.00 deck height:

CH = (9.000)-(3.75/2)-(6.00)

CH = 1.125

You could adjust block deck height or CH to get the piston out of or down into the bore.

Colin91Z

I was only trying to help you, no need to give me the "whatever" treatment

If you don't want help, don't ask questions.

OldSStroker

Bad day at the ranch, Hoss?

Z95m6

I don't think Colin was out of line, he was just trying to be helpful like always.

Colin91Z

No sir, I just didn't take too kindly to his comments...since I was only trying to help him

SStrokerAce

Yeah I don't think he got WHY they would mention that spec, rather than just read thru the catalog to find the rod and stroke you want. Some of us shop for pistons that way, I use the CH to get all the rest of the specs dead nuts.

Bret

rskrause

Yeah, changing the CH is by far the easiest way put the piston where you want it if your combo is in any way an oddball. It's much easier and cheaper to get a "custom" piston made with the pin bore moved up or down ten or twenty thousandths than a set of custom rods or an offset ground crank.

Another technique is available if you are using copper gaskets - they are readily available in a wide range of thicknesses. Obviously, they don't move the piston but using a different thickness gasket will change the relationship of the head to the piston crown. They are readily available from ~0.020"-.120" and they are also very strong. So why don't more people use them? They leak fluid. Seepage isn't a big problem on a race car, and high boost drag cars are usually run dry anyway. but they really aren't suitable for the street. I wonder if some of the newer coated designs (like the Titan ACS) would suffer from this? Of course, conventional gaskets are also available in a (smaller) range of thicknesses. So that can be the easiest option if you just need make a small adjustment.

Colin: the "whatever" would have annoyed me to. Welcome to the miserable ***** club, I am the founder.

Rich

Colin91Z

Thanks man

SStrokerAce

Rich, the ICS are pretty trick stuff.... moving the deck too much is going to make you work a little harder to get the manifold to fit though.

Bret