Better Turbo For Built Rb25Det

[radianation]

I've been told that I have a turbo that is a bit too large for my (mostly) built RB25DET because it doesn't produce power until higher in the curve. Can anybody give me some additional opinions and insights on the comparison between a Bullseye Power S362 .70 A/R and a Garret GT35R .82 A/R? It looks like the S362 (what I currently have) doesn't really start producing power until the RB is out of RPMs. I'm only hitting around 421 rwhp with this turbo, but I would like to hit 550rwhp.

Any help is appreciated. I'm looking for the ideal turbo choice for this engine. I plan on doing road racing...

[zebra]

Isnt the S362 a 700hp turbo?

for a circuit Rb25 I would go either a T67-25G/TD06-25G or a Gt3076.

[PM-R33]

Just before every one jumps onto you, in Australia we call it "circuit racing".

When us Australians hear "road racing" we assume illegal street racing and every one will start going off at you and you won't understand why

Given that you guys in the US now have direct access to the new range of Garrett turbo's I would definetely try the new GTX3076. It won't do your 550rwp, but for a circuit setup in a light S chassis I think it would be a fantastic setup.

[radianation]

Yes, I definitely do *not* mean illegal street racing. I have been doing auto-x for a few years to get a better understanding of my car, and I'm looking to do some HPDE track days this coming year for fun and hopefully get into the sport competitively within 2-3 years once I have more experience.

My original power goal was around 550rwhp, and while the car drives absolutely fantastic right now.... I think that hitting that goal is more of a personal challenge. I'd love to find a turbo that has the best of both worlds. I'm going to do some research on the turbos you have recommended.

And yes, that S362 is very capable of making the power (I've seen it on a 2JZ), but it seems the RB doesn't flow enough to get me where I need to go with this turbo?

[Lithium]

You ran yours on a Dyno Dynamics eh? Most of the results from people in US seem to be from Dynojets and Dynapacks which read quite a bit higher than Mustang and Dyno Dynamics dynos - how does the car actually feel power wise? Wouldn't be surprised if you threw it on a Dynojet and found you are actually near 500whp... there are people who have done that power on mildish RB25s on Dynojets with GT35Rs.

[radianation]

Yep. I am aware of the differences in numbers, but since I've always had tuning done on Dyno Dynamics I want to stick to that as my benchmark. The car feels great, but I think it could be better. I have a hard time comparing it to anything? I have a 370z nismo that has a lot more torque feeling, but no high end power.

[R31Nismoid]

definitely the GTX3076seems like the perfect choice.

400rwkw is a lot of turbo for a 25rwd car even with the best setup.

the 3076 on paper looks to be 340rwkw on pump... so around 450rwhp which would work nice as you have the lighter car.

what will happen though is you'll have so much more response and power range it would almost certainly be faster.

also to consider such a change in setup will also mean suspension and other alterations to get the most out so it might not be faster 'out of the box' so to speak as a laggy-ish 700hp turbo to a much nicer 600hp(approx) will be quite a change.

[radianation]

Suspension work is getting there, but not complete. Coilovers, polyurethane bushings, sway bars, ruca, tension rods, etc. upgraded the brakes and wheels/tires too. Not 100% where I want it, but it handles great and I can drive it with the throttle mostly at auto-x (obviously not for circuit racing hehe)

I just need to be able to find a GTX3076 with a cover?? Looks like Garret assumes you'll use your existing one?

***edit** I found the housings. I see you buy them separate.

Edited December 16, 2010 by radianation

[bradsm87]

What cams do you have? If the answer is stock, 550hp at the wheels is a bit excessive.

[radianation]

421.3 HP / 314.16 KW @ 20 PSI 93 octane pump gas

RB25DET (R33 Series 2) powered S14 240sx

Wiseco 20 over forged pistons

Eagle Rods

ACL bearings

ARP studs

Cometic HG

Tomei Poncams 256 8.5

Tomei adjustable exhaust camwheel

Bullseye S362 Turbo

Custom 3" Exhaust

Greddy Intake w/Q45 TB

Lovefab Exhaust manifold

HKS GT-II 60mm wastegate

HKS SSQV BOV

LS2 Truck Coil Conversion

Denso 850cc Injectors

Nismo FPR

Walbro 255lph pump

300zx Fuel Filter

AEM EMS

and More...

Edited December 16, 2010 by radianation

[zebra]

Ok, So you wil need a bigger fuel pump or a 2nd wal-fail

3" exhaust will be starting to hold you back at this point, so look into a 3.5"

But something is not right for a turbo that size to be at 20psi and only be making 314rwkws

For eg, 20psi using a Gt35R would be making 340-350rwkws on a DD dyno

Oh and before some noob says he should run 98 octane fuel, the YANK 93 MON fuel would be like our 100 RON

[radianation]

See, that's what I'm scratching my head about. The concept of the different turbo is only one suggestion. Other things we've discussed is upgrading the valve springs and trying to get a higher redline? Maybe running E85 fuel conversion?

This is kind of a newbie question and I'm sad to ask it, but if I go to a 3.5" exhaust should I match that with the exhaust housing on the turbo? Looks like the housing I was going to choose had a 3" vband out.

BTW - Fuel seems to be there right now with no signs of slowing down anytime soon?

Edited December 16, 2010 by radianation

[zebra]

Just run a reducer to the 3" V-band.

and Yeah valve springs may help as it could be valve floating and thats killing the power.

Do you have a dyno sheet handy?

[radianation]

We did notice at the top end from pull to pull that there would be a weird random dip in power? We couldn't figure it out because there didn't seem to be any mechanical issues or problems with fuel / AFR etc.

Edited December 16, 2010 by radianation

[zebra]

The dip does look like valve float, but cant be 100% sure, but the lower boost setting doesnt have it which tells me it is. Have you tried pumping more boost into it?

The chart shows a decent gain from 17-18psi to 20

[radianation]

With the inconsistency we couldn't really get a solid grasp on how much timing we could put at it, and thus didn't push too hard. Turning up the boost ... might be able to get 1-2 psi more while on the 93 gas here before it gets a little suspect.

[R31Nismoid]

If it is a 700hp turbo, you need closer to 22-24psi to really get it hoofing along.

But i still think going smaller would be better, there is so much more "meat" on the graph to gain.

Sounds honestly like you don't have the setup for 550rwhp/400rwkw anyway, so a peg back in power and a gain in response would be a win-win.

I also think you have exhaust size issues. Drop it from before the CAT, although it's 3", it might show some gains and then thats where you can point the finger. Could also be valve float but doesn't seem so at this stage.

[radianation]

Can you give me a little more input why you think I don't have the setup for 550rwhp? This has been a 3 year project and I'm committed to my goal. Thanks.

[bradsm87]

A Garrett GTX3076R would be the go. That should crack about 480 rear wheel horsepower and come on to boost earlier than that.

[radianation]

I appreciate all of this advice. As of right now, my research list for next step upgrades includes:

• Supertech or Tomei Valve springs
• GTX3076R .82 vs GT35R .82 (leaning towards new GTX)
• 85-88mm exhaust upgrade

If I'm leaving anything critical off to help improve the performance of the car while getting me closer to my goal please toss it out there for me. I suppose I could live with hitting 550rwhp on a DynoJet once we're all said and done... lol