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Working Out Compression Ratio.


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#1 merther

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Posted 15 August 2019 - 01:30 PM

Hi
Looking for advice on how to work out my compression ratio on engine build.
It's a 1293cc and pistons are flush to the top of the deck. Pistons have 8cc dish. It will use a bk450 head gasket.
I'm unsure how to work out what cc my cylinder head should be?
I want to aim for a 10:3 compression ratio.
Thankyou in advance

#2 Steve220

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Posted 15 August 2019 - 03:06 PM

Are you 100% sure they're flush? It makes a difference even if theres a thou or 2 there.

#3 Steve220

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Posted 15 August 2019 - 03:08 PM

If your deck height is 0, it'll be around 10.8:1 on a standard 21.4cc chamber head.

Edited by Steve220, 15 August 2019 - 03:09 PM.


#4 Cooperman

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Posted 15 August 2019 - 04:33 PM

If you do a search on here you will find the formulae you need.



#5 Rorf

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Posted 15 August 2019 - 05:10 PM

How much has been skimmed from the head. My 1293 with pistons slightly higher then the block has had the head skimmed 60 thou and not sure what the CR is but using normal high octane pump fuel it goes like a rocket. Slightly retarded to stop the pinking on heavy acceleration and sometimes it runs on when ignition switched off probably due to slight over fueling whilst off the throttle.






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