Rb25 Rebuild

[HKS-R33]

Hey, im currently building an rb25 and i was wondering what compression ratio i would have if I'm running CP pistons that give 8.5:1 compression ratio and use a tomei 1.2mm head gasket.

The tomei website says that by using the 1.2mm headgasket, it drops an rb25's comp ratio to 8.6:1.

I have been searching and i couldn't find a proper answer.

Any help would be appreciated.

Mike.

[STATUS]

really depends how much the machine shop decks the head and block, usually with both decked a 1.2mm head gasket will bring you back (close) to std comp.

[HKS-R33]

How much would you have to deck the head and block to get it close enough to standard comp with a 1.2mm head gasket.

Also, would i be better off aiming for around 8.5:1 or 9:1 comp ratio?

Thanks, Mike.

[discopotato03]

I think the way to go is at least 9.0 to 1 CR if not a little higher ie 9.3 .

You have a golden opportunity to fit slightly larger exhaust valves which you can buy in direct fit form - as in dimensionally the same as std hydraulic R33 RB25 except for the 0.5mm over size head .

The std exhaust valve seats in the head are just opened up a little internally .

Big bore twin cam RB heads are a bit short on exhaust valve and port size probably because of the late 80's thinking that went into their design .

I'd aim for the slightly higher CR and exhaust valves to make the engine breathe better and make good power without having to resort to high boost to make the torque .

Cheers A .

[STATUS]

^^ i agree that bumping the comp is a good idea, but what turbo are you running MIKE? as this is a prime factor in determining comp ratio.

[R31Nismoid]

Yeah up the comp.

This isnt 1995 anymore, fuel is a lot better and can handle more over what it was designed for back then with the 98's of today.

With all the ethanol fuels coming in and so on its only getting better.

[HKS-R33]

Thanks for all of your input guys. Im running a GT35R with a .82 Ex Housing. I am using a Tial 44mm Wastegate. I am definately going to be putting bigger exhaust valves in it. How big should i go and where can i get them?

Also, how much power would i be able to get out of the standard camshafts before id need to upgrade.

I was expecting to have to lower the comp because of the big boost that i will be running. If i wanted to keep the comp at 9:1, what combo of pistons and head gasket would i have to run.

Im also contemplating whether to go metal head gasket or o-ring the block and use the oem nissan one.

[HKS-R33]

Does anyone know if i o-ring my block do i just use the standard head gasket?