Ideola's Interactive Compression Ratio Calculator

[ideola]

Have you ever asked any of these questions?

• If I resurface my block by .xxx", how much CR will I gain?
• What Cometic gasket should I use to achieve x.x:1 CR?
• What combination of NA head and 931 pistons will yield a usable result?
• What displacement and CR can I expect with a stroker setup?

I've just completed version 1.0 of an online interactive compression ratio calculator, which will provide answers to these and many other related questions.

I've been wanting to build one of these for some time. Finally got some down-time this holiday season to work on it. (The current version is pre-loaded with 924 2.0L parameters, but should be usable for 924S/944/968 applications provided you know the critical dimensions).
Ideola's Compression Ratio Calculator

Features

• Includes 14 user-selectable profiles based on known-good OEM and custom configurations (for 924 2.0L)
• Ability to switch from metric to standard (for those of us with machinists who prefer working in thousandths rather than mm).
• Definitions for all of the parameters
• The three most commonly (and easily) modified parameters are highlighted in bright blue: deck height (changed by milling the block); cylinder bore (changed by going to oversized pistons); and head gasket thickness (changed by using thicker or thinner Cometic MLS gaskets)

Notes

• Where possible, pre-loaded values are based on OEM or manufacturer specs.
• Several specs are not published by Porsche, so I have done my best to "back into" those numbers based on my own observations, measurements, info distilled from this forum, comparisons to known aftermarket configurations, and a whole lot of number crunching.
• Block deck height is not published anywhere, but is an absolutely critical number for determining CR. Most blocks I've measured are between 230mm and 232mm. My presumption is that the factory original spec is 232mm.
• Head volume of the 931 head is presumed to be 19.5mm based on recent measurements by RC and by my head machinist.
• Piston dish volumes are "backed-into" calculations I've made based on OEM published CR, known compression height of the piston, and the presumed values for deck height and head volume listed above.
• OEM head gasket thickness is presumed to be .046". The calculator is pre-loaded with all of the available thicknesses from Cometic.
• The calculator is currently hard-coded for 4 cylinder engines, which really only impacts the calculated displacement. I am considering a future expansion of the tool to include profiles for 911, 944, 928, etc., at which time I will make the number of cylinders a definable parameter.

Take a look and let me know what you think. Suggestions and constructive feedback are welcomed!

[Gawernator]

Wow. Thanks!

[iplagolf]

A guy's tires won't stand up by them self in another thread, and now this...Either I need another drink or I've had one too many! I should have kept the Yugo...

[iplagolf]

My last post should have been in green, but I don't know how to do it...

[ideola]

Originally Posted by iplagolf

my last post should have been in green, but i don't know how to do it...

There y'go!

[iplagolf]

I do some really stupid stuff some times...I like to have fun...I poke more fun at myself than I would at any one else. After I posted here, I thought, damn, I hope this guy doesn't think I'm this huge ass. But I still don't know what you're talk'n about. After the tires that won't stand up on their own...Who could make this stuff up...My friends Jack, Bud and any liquor first name you can think of, are laugh'n are a##'s off. Life is good!!!

[ideola]

Originally Posted by iplagolf

My friends Jack, Bud and any liquor first name you can think of, are laugh'n are a##'s off. Life is good!!!

Indeed!