Rb25de

[lammy426]

just a little question,i have an rb25de with 10:1 compression,how thick has the headgasket/spacer got to be to lower the comp to 8:1,or a formula to work it out,many thanks john

[SKiT_R31]

dont decomp it with a spacer, it ruins the squash, loses you power with minimal benefit for knock resistance. With tech these days, you should be able to make the same power with the higher compression as with lower compression, befrore you need forgies. You'll make more power from stock management, or with aftermarket management and a good tuner you can make just allmost as much power as the stock internals can handle anyway - and a decomp wont make that any better, it will just hit you with the same n/a squash issues (which arent ideal for boost) combined with making less power per psi due to the lower compression.

that said, the answer to your question, you need decompression plate (i think 0.7mm) and 2 standard head gaskets, which will drop you to about 8:1 (which is too low for a 25 anyway, as normal rb25dets are 9:1) thats a 1.7mm increase.

you'd be better off with a copper headgasket, thicker than standard (1mm) at ~ 1.8mm, its a bit of decompression, puts you closer to the rb25det stock compression, combine it with some colder plugs (7's or somthing) and it will be spot on.

[lammy426]

dont decomp it with a spacer, it ruins the squash, loses you power with minimal benefit for knock resistance. With tech these days, you should be able to make the same power with the higher compression as with lower compression, befrore you need forgies. You'll make more power from stock management, or with aftermarket management and a good tuner you can make just allmost as much power as the stock internals can handle anyway - and a decomp wont make that any better, it will just hit you with the same n/a squash issues (which arent ideal for boost) combined with making less power per psi due to the lower compression.

that said, the answer to your question, you need decompression plate (i think 0.7mm) and 2 standard head gaskets, which will drop you to about 8:1 (which is too low for a 25 anyway, as normal rb25dets are 9:1) thats a 1.7mm increase.

you'd be better off with a copper headgasket, thicker than standard (1mm) at ~ 1.8mm, its a bit of decompression, puts you closer to the rb25det stock compression, combine it with some colder plugs (7's or somthing) and it will be spot on.

i'm at 378bhp atf at the moment at 10.13psi boost and i've fitted meth/water injection and hoping for 400bhp+ when i get it mapped at 12psi boost.i have another rb25de engine i was thinking of lowering the comp to 8:1 and big turbo to push the rb25de to the limit,has anyone tried doing this,thanks in advance john

[SKiT_R31]

whats the specs on your water meth injection? I've been looking into it, using a siemens methonol injector and a microtech MF-1 Microfueler ecu, cheap as chips.

if you've got the engine out of the car, why dont you just change the slugs? Dish in higher power applications is a big plus, and if your after big power, it would make sense, you might be eble to get some 25det or 26dett pistons, or for lower comp - even 30e pistons would be better...

anyway, i reckon you'll be able to get some good numbers out of it, im assuming its an r32 rb25de?

[lammy426]

whats the specs on your water meth injection? I've been looking into it, using a siemens methonol injector and a microtech MF-1 Microfueler ecu, cheap as chips.

if you've got the engine out of the car, why dont you just change the slugs? Dish in higher power applications is a big plus, and if your after big power, it would make sense, you might be eble to get some 25det or 26dett pistons, or for lower comp - even 30e pistons would be better...

anyway, i reckon you'll be able to get some good numbers out of it, im assuming its an r32 rb25de?

its a devilsown 150psi pump with 1gph nozzle pre turbo and a 3gph pre throttlebody set to inject at 6psi boost,it works well but i'm only on the 1st washertank of meth/water and i have to use about 3 tanks to clear all the carbon out of the engine,then i'll get it remapped.its my spare engine i wanted to lower the comp on and get it ready for when this one fails and its an r33 rb25de,and i suppose i want to keep to standard internals because over here(england)lots said don't bother putting a turbo on it you'll never get any power,i have already proved them wrong and just want to do it a bit more

[G0DZLR]

what else have you done to that motor? how long has it been running at 10PSI? quite interested as i have done the turbo conversion on my RB25DE (1994) just running stock gear, no aftermarket stuff...

[lammy426]

what else have you done to that motor? how long has it been running at 10PSI? quite interested as i have done the turbo conversion on my RB25DE (1994) just running stock gear, no aftermarket stuff...

pfc,480cc injectors,255litre fuel pump,fmic,25 row oilcooler,fpr,coldairbox with feed pipe,splitfires,good plugs,turbo elbow/downpipe 3" upto 3'75 to 4.5" tailpipe all xs power,decat,r32 gtr clutch,kenlowe electric fan and modified plenum but you have already seen this in the sticky on gts+t its been at 10psi about a year and 8.5psi for 1.5 years before that, i think alot of power comes from cold intake i know shawny as the same mods without the plenum and he's 50bhp atf down and i put it down to all that intercooler pipe over an hot engine, and i have done a oildrain mod

Edited March 30, 2009 by lammy426

[clip14]

there are members of my car club pushing 310rwkw (400hp at the wheels - not at the flywheel) on stock compression rb25de in a street/drift car. also a competitor in d1nz running a rb25de+t at the same power levels in competitive drifting.

set up right, you can run the high compression and put out lots of power. just get the tune right and dont skimp on supporting mods.

[lammy426]

there are members of my car club pushing 310rwkw (400hp at the wheels - not at the flywheel) on stock compression rb25de in a street/drift car. also a competitor in d1nz running a rb25de+t at the same power levels in competitive drifting.

set up right, you can run the high compression and put out lots of power. just get the tune right and dont skimp on supporting mods.

thats great to know,how can i contact them i'd like to discuss mods with them,are they on this site or do you have an email address i just want to get the most out of it ,400atw is great i want some of that,many thanks john

[clip14]

tiger white is the name of the drifter who runs a rb25de+t.

he has a few videos on youtube and you may be able to google some information about his set up.

[lammy426]

tiger white is the name of the drifter who runs a rb25de+t.

he has a few videos on youtube and you may be able to google some information about his set up.

the info i've found so far its 346wbhp but that will do me for now,just got to find out what boost he is at to get 30 bhp more than me ,most of his mods are the same except turbo