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Piston And Head Gasket Choice For My Rb25 Neo

Abo Bob

By Abo Bob,
in Engines & Forced Induction

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Abo Bob Grand Master

Abo Bob

Posted
Posted

1. If I get 86.5mm pistons to suit a GTR and use a stock head gasket will I get 8.5:1 compression ratio or does this require the GTR crank?

2. Will I be getting the lower compression ratio by increasing the distance to the top of the bore when the piston is fully up? If so I might as well be using RB25 pistons and 1.6mm metal head gasket because the squish areas are still having their effectiveness reduced right?

I'm thinking either Wiseco or Arias at this stage.

3. I've heard the NEO RB25 has GTR rods. Can anyone confirm?

4. How thick is the stock head gasket?

5. If I haven't got it right yet - how do I go about lowering the compression ratio to about 8.5-8.6 without wrecking the squish areas?

6. Do people think I will notice if I drop the CR to 8.2 instead?

7. I read elsewhere on here that dropping 0.5 in CR will require an increase of 0.2 in boost to get the same power. Is this true?

Thanks.

infected flow Rising Star

infected flow

Posted
Posted
1. If I get 86.5mm pistons to suit a GTR and use a stock head gasket will I get 8.5:1 compression ratio or does this require the GTR crank?

2. Will I be getting the lower compression ratio by increasing the distance to the top of the bore when the piston is fully up?  If so I might as well be using RB25 pistons and 1.6mm metal head gasket because the squish areas are still having their effectiveness reduced right?

I'm thinking either Wiseco or Arias at this stage.

3. I've heard the NEO RB25 has GTR rods.  Can anyone confirm?

4. How thick is the stock head gasket?

5. If I haven't got it right yet - how do I go about lowering the compression ratio to about 8.5-8.6 without wrecking the squish areas?

6. Do people think I will notice if I drop the CR to 8.2 instead?

7. I read elsewhere on here that dropping 0.5 in CR will require an increase of 0.2 in boost to get the same power.  Is this true?

Thanks.

why do u want lower compression...?

standard head gasket 1.2mm

rods are not gtr this is confirmed!

also the head and block will need a shave so that will also change compression.

u will notice a big difference dropping compression to 8.5

my compression is 8.9 and u can still notice the difference in response.

:D;):)

ed Grand Master

ed

Posted
Posted (edited)

You lower comp ratio with just gasket.

here is some charts from tomei

http://www.tomei-p.co.jp/_2003web-catalogu...B25_gasket.html

EDIT: personally, I would rebuild to 9:1 comp and get the ECU re-tuned since you are only chasing 250rwkw.

Edited by ed
Sydneykid Grand Master

Sydneykid

Posted
Posted
I want to lower the compression to please my tuner.

Tell your tuner the Gibson GTR's ran 9.4 to 1, and that was 12+ years ago. ECU's have improved immensely since then. Lowering compression ratio is very old hat and low tech, tell him to get out the of the 80's.

:) cheers :D

Abo Bob Grand Master

Abo Bob

Posted
  • Author
Posted

I appreciate that the answer you are giving is the best one for the situation but without writing an essay about the comprimises I have to make I can't get my entire situation across.

Therefore I am asking some specific questions so I can make the best of my situation. Changing my tuner is something I'd like to do but I still need to find out the answers to the abovementioned questions. I know there are people here who know the answers, just hoping they might be able to help me.

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