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Rb25/30 Cr On 98

MRHD66

By MRHD66,
in Engines & Forced Induction

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XKLABA Grand Master

XKLABA

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Hi mate, 9.5 CR is fine just can't run big boost, it's mostly in the tune anyway, if you have a united servo down there they will have premium 100 soon if not already, the servo around the corner from me said they are all getting it weather that's true or not is a different story, and maybe even E85

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XKLABA Grand Master

XKLABA

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30psi with 9.3 CR, got a link I would be interested to see that one and what mods he has done, I know there is a guy on here with a built 2.6 engine with 9.3 running a little over 20 psi on 98, but then your dymanic comp ratio would change the amount of boost your can run also, with big cams creating lots of overlap and reducing the effective stroke will reduce the DCR

so you might have 9.3 static comp ratio but then have big overlap and reduce the DCR to ( and this is just a guess for discussion sake ) 7.5-1

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MRHD66 Rising Star

MRHD66

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here is link http://www.skylinesaustralia.com/forums/topic/395232-394kw-1994-r33-gtst-act/ he said he has run up to 30 psi

yes i dynamic CR is less with big cams ( every cam changes it)

was thinking of running camtech 268 dur ,9mm lift in (with VCT) and 272dur 10.4mm lift

and yes for my HD

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R32Abuser Mentor

R32Abuser

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Depends on so many different factors. It's easy to say "He did this with this turbo, pistons etc." and it was OK...doesn't mean YOUR build will be EXACTLY the same and also be fine.

E.g. My RB25/30DET, Static 9:1 CR (there abouts), 256/8.5mm Tomei Cams, 18PSI @3500-4000RPM. Pretty much copied Cubes' RB30 build. However, the thing wanted to ping its head off on BP98. More so than normal and definately not like Cubes' RB30.

Chased our tails (tuner and I) for a little while...Eventually, chucked some more fuel into it, pulled some timing and it was all good. Sacrificed a small amount of power for some reliability. However, the thing is definately more sensitive to knocking than the run of the mill RB.

If it were me, I'd be going E85 just for the sake of it.

Is it going to be a build for a road or track car?

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R32Abuser Mentor

R32Abuser

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Hmmm from an initial glance, there isnt that many servos (is there any???) that run E85 around your area anyway! Could always buy it by the barrel since the car isn't going to be a "daily" driver.

Worst case scenario, tune for 98 and see what you can get away with. If you're having issues with the thing knocking and you're not happy with the power/torque, chuck the juice at it!

If it were me, depending on your turbo choice, I'd be keeping it to 9:1 on 98...

Edited by R32Abuser
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MRHD66 Rising Star

MRHD66

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Hmmm from an initial glance, there isnt that many servos (is there any???) that run E85 around your area anyway! Could always buy it by the barrel since the car isn't going to be a "daily" driver.

Worst case scenario, tune for 98 and see what you can get away with. If you're having issues with the thing knocking and you're not happy with the power/torque, chuck the juice at it!

If it were me, depending on your turbo choice, I'd be keeping it to 9:1 on 98...

smaller turbo more cr ?
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R32Abuser Mentor

R32Abuser

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Im not sure what you're trying to ask in the above post...

As a very general statement: The smaller turbo you run, the higher the EGT's will be and thus increase the sensitivity of the setup to knocking (apples with apples of course!). Run a higher Static/dynamic CR and you will only make the problem worse.

Edited by R32Abuser
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MRHD66 Rising Star

MRHD66

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Im not sure what you're trying to ask in the above post...

As a very general statement: The smaller turbo you run, the higher the EGT's will be and thus increase the sensitivity of the setup to knocking (apples with apples of course!). Run a higher Static/dynamic CR and you will only make the problem worse.

I mean when the turbo size gets bigger the cr should digress?
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Shoota_77 Veteran

Shoota_77

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Now I'm confused...

The turbo you use won't change your comp ratio. Comp ratio is a mechanical thing only modified by structural changes to head shape, piston shape, deck height, etc.

If what you're asking is "When you put on a bigger turbo will it cause comp ratio issues (pinging)" then yes, correct. The higher the static comp ratio, generally the less boost you can pump in without detonation issues. Unless of course you up the type of juice you're using to overcome these issues (100+ octane or E85 which is a more stable fuel under high compression). Sometimes the shape of the piston and combustion chamber can affect this too. Sharp edges that get super hot can cause pre combustion too.

Is that what you're getting at?

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XRATED Veteran

XRATED

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Maybe get back to why you want to run so much static CR? On a 25/30 a few points more CR isn't noticeable... I've had a 25/30 around 8.4:1 and it was noticeably torque-ier than the 25 bottom end it replaced. New pistons took the same motor up to 9.4:1 and there was very little.... if any difference.

Generally, a smaller turbo will make more heat, require more boost and create more back pressure/egt for the same hp...

At the end of the day, what would you like from your car? how much hp will get you there? what turbo is best matched to your engine for the power goal?

The turbo selection will make the biggest difference difference to your power delivery and potential. The old school NA v8 3C's (cams/compression/carbies) have a much smaller affect on power delivery/potential of RB's than you might think.

Cheers

Justin

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MRHD66 Rising Star

MRHD66

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Maybe get back to why you want to run so much static CR? On a 25/30 a few points more CR isn't noticeable... I've had a 25/30 around 8.4:1 and it was noticeably torque-ier than the 25 bottom end it replaced. New pistons took the same motor up to 9.4:1 and there was very little.... if any difference.

Generally, a smaller turbo will make more heat, require more boost and create more back pressure/egt for the same hp...

At the end of the day, what would you like from your car? how much hp will get you there? what turbo is best matched to your engine for the power goal?

The turbo selection will make the biggest difference difference to your power delivery and potential. The old school NA v8 3C's (cams/compression/carbies) have a much smaller affect on power delivery/potential of RB's than you might think.

Cheers

Justin

to get it to have better off boost RESPONCE
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