Definitive 903cc piston deck clearance...?

Matt Zerega

It's about passion, not practicality.
Good day, All. I'm in the process of building an offset bored 903 turbo motor using a bare block I procured (I don't have the factory pistons, and I'll be using custom pistons). I can't find the factory piston-crown-to-block-deck clearance spec...which is critical to properly specifying compression height on my custom pistons, in order to achieve desired static compression when the motor is all buttoned up.

Here's what I understand thus far about stock 903cc engine specs:
  • 65mm O.D. piston
  • 68mm stroke
  • 110mm rod length
  • 24.3cc chamber volume
  • 30.75mm piston compression height
  • 1.14mm assumed head gasket compressed thickness
So...at 9.5:1 math suggests that the stock pistons set -0.41mm below the deck surface

Anybody know where I can find the stock 903cc spec for deck clearance? I'd rather not rely entirely on my assumptions and math.
 
Last edited:

lezesig1

expatriot
Hello Matt,

On your behalf, I just posed this question to a long time and well known 903 engine builder.
Unfortunately, I did not receive the dimensional answer you were hoping for.

Their answer is "it depends". They further explained the myriad of available dome shapes,
compression ratios, head types, head materials, and so on.

Feel free to PM me direct if you would like the contact info for the company I spoke with.

lezesig
72 spi
 
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