Compression height Q...

[hardtimes]

Anyone explain the 'text book' definition of how to determine compression height, used to determine piston useage ?

[Ronnie]

Its here

https://www.uempistons.com/installat...stallation.pdf

R

[Walt Dupont--Me.]

My computer won't open Ronnie's reply but the compression distance is from the middle of the wrist pin to the top edge piston. Walt

[G.M.]

Deck height is the distance at the top of the stroke the piston is above or below the top surface of the block. TDC is located with a dial indicator. G.M.

[Ronnie]

Here it is Walt

[Fordors]

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Compression height will also be dependent on stroke and/or rod length.

[bbrocksr]

Originally Posted by Fordors

Compression height will also be dependent on stroke and/or rod length.

I think were getting two different measurements mixed up.
Compression height is the distance from the center of the pin to the top of the piston as shown in Ronnies picture.
Deck height is the distance form the top of the piston to the top of the block which can be change with rod length and crank stroke.
Bill

[Ronnie]

Deck height can be pos or neg measurement from deck.

R

[Fordors]

Originally Posted by bbrocksr

I think were getting two different measurements mixed up.
Compression height is the distance from the center of the pin to the top of the piston as shown in Ronnies picture.
Deck height is the distance form the top of the piston to the top of the block which can be change with rod length and crank stroke.
Bill

I made no mention of deck height. If you compare a '49 Ford piston to a '49 Merc piston there is a difference in compression height as the Merc has a 1/4" longer stroke. They both fit the stock 3.1875 bore but only one works with a particular crank. If you were to stroke the Merc another 1/8" the comp. ht. must change again.
If one were to build an engine for a particular purpose and desired to change the rod length by adding length for example the comp. ht. is reduced, even though displacement remains the same.
No dispute from me with Ronnie's picture, I'm just stating the many factors involved in establishing compression height.

[hardtimes]

Originally Posted by Ronnie

Its here

https://www.uempistons.com/installat...stallation.pdf

R

Wow, that says it all ! Thanks much for sharing that site / info !

[JWL]

I guess nobody is going to answer the original question----to determine the piston compression height required you must measure the center-to-center distances of the rods and the crank and measure the cylinder block from centerline of main housings to the gasket deck. Add or subtract the desired deck height and do the math. Simple but important. In some examples of competition engines I have used different compression height from right to left banks.

[Chuck Sea/Tac]

Originally Posted by JWL

I guess nobody is going to answer the original question----to determine the piston compression height required you must measure the center-to-center distances of the rods and the crank and measure the cylinder block from centerline of main housings to the gasket deck. Add or subtract the desired deck height and do the math. Simple but important. In some examples of competition engines I have used different compression height from right to left banks.

That's amazing, everyone read it wrong, including me. Had to read it twice, to figure out what was going on!