Behind Horizon Posted August 18, 2013 Share Posted August 18, 2013 (edited) Hello, I intend using a 1.3mm metal head gasket with CP 86.5mm 8.5:1 pistons in my RB26. Can you let me know which compression ratio I will have with a standard non skimmed head? All the compression ratio calculators are asking for data which I couldn't find, hence me asking here. Just want to make sure that the compression ratio won't drop too much as I already bought the head gasket but not the CP pistons. Would you therefore recommend running 9.0:1 pistons or 8.5:1? Installed GT2860-5 turbos already. Thanks! Edited August 18, 2013 by Behind Horizon Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/ Share on other sites More sharing options...
KiwiRS4T Posted August 18, 2013 Share Posted August 18, 2013 Piston selection is going to make more difference than your choice of head gasket - why would you not be using the higher compression pistons?. Should have bought the pistons before choosing head gasket. Presumably you can return the head gasket if it is not suitable. What compression ratio do you want and what fuel will you be using? Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6975501 Share on other sites More sharing options...
Piggaz Posted August 18, 2013 Share Posted August 18, 2013 Need deck height and cc of the pistons. Without that no one can tell you. Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6975526 Share on other sites More sharing options...
Behind Horizon Posted August 18, 2013 Author Share Posted August 18, 2013 (edited) The cometic head gasket I have came together with a RB26 complete engine gasket kit from which I used already half of the gaskets.Hence I can't return the head gasket and would like to use it.CP piston data SC7310:Bore (in): 3.406 in.Bore (mm): 86.500mmPiston Style: Dome, with no valve reliefsPiston Material: Forged aluminumCompression Distance (in): 1.193 in.Piston Head Volume (cc): -16.20ccCheck the attachment for other data.I couldn't find data for the deck height so I assume it must be close to original with these pistons as their compression ratio is 8.5:1? Edited August 18, 2013 by Behind Horizon Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6975575 Share on other sites More sharing options...
Behind Horizon Posted August 19, 2013 Author Share Posted August 19, 2013 No one? Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6977182 Share on other sites More sharing options...
KiwiRS4T Posted August 19, 2013 Share Posted August 19, 2013 I gave you the answer - get the 9:1 pistons. The rest is unnecessary detail! No one? Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6977183 Share on other sites More sharing options...
Behind Horizon Posted August 20, 2013 Author Share Posted August 20, 2013 I gave you the answer - get the 9:1 pistons. The rest is unnecessary detail! I am still interested to know what kind of compression ratio I would have with the 8.5 pistons.... Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6978752 Share on other sites More sharing options...
Shoujiki Posted August 20, 2013 Share Posted August 20, 2013 I calculate it to 9.01:1 with the assumption of cylinder head volume of 63cc and 0mm deck clearance. Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6978775 Share on other sites More sharing options...
BenR Posted August 20, 2013 Share Posted August 20, 2013 26 has 70cc chambers. Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6978798 Share on other sites More sharing options...
KiwiRS4T Posted August 20, 2013 Share Posted August 20, 2013 Still think you're complicating things unnecessarily. If there is nothing strange about your build you would expect 8.5:1 pistons to give you a CR of 8.5:1 and 9.0:1 would give you 9.0:1. In fact there may well be a small variance but I defy anyone to calculate it - you will have to measure it when the pistons are installed. Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6978800 Share on other sites More sharing options...
Shoujiki Posted August 20, 2013 Share Posted August 20, 2013 (edited) ^ I looked it up, and most people that actually real world tested it said 63 +/- 1.5cc. But for the sake of calculation, using 70cc spits out 8.02:1. Again with 0mm deck clearance. Edited August 20, 2013 by Shoujiki Link to comment https://www.sau.com.au/forums/topic/430467-rb26-which-compression-ratio-with-13mm-head-gasket/#findComment-6978881 Share on other sites More sharing options...
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