[Rb26] Which Compression Ratio With 1.3Mm Head Gasket?

[Behind Horizon]

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

[KiwiRS4T]

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?

[Piggaz]

Need deck height and cc of the pistons. Without that no one can tell you.

[Behind Horizon]

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): 86.500mm
Piston Style: Dome, with no valve reliefs
Piston Material: Forged aluminum
Compression Distance (in): 1.193 in.
Piston Head Volume (cc): -16.20cc

Check 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

[Behind Horizon]

No one?

[KiwiRS4T]

I gave you the answer - get the 9:1 pistons. The rest is unnecessary detail!

  On 19/08/2013 at 6:22 PM, Behind Horizon said:

No one?

[Behind Horizon]

  On 19/08/2013 at 6:33 PM, KiwiRS4T said:

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....

[Shoujiki]

I calculate it to 9.01:1 with the assumption of cylinder head volume of 63cc and 0mm deck clearance.

[BenR]

26 has 70cc chambers.

[KiwiRS4T]

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.

[Shoujiki]

^ 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