Turbo Recommendation

[Darius]

I am debating on what turbo to upgrade to on my RB25 and am having a difficult time deciding on the GT35R (.82 A/R exh.) or if I need something a step larger?? I have mapped my power goals, but mapping flow seems like taking a stab in the dark. I'm looking for 600-650hp=450-485kW on a car used in drag racing and highway pulls.

The following modifications have been done:

Stock bore

Forged pistons (8.5:1 static compression)

GTR rods

Cometic head gasket

Block and head oiling/draining modifications

Port and polished head

Ferrea 1mm oversized valves

Tomei valve springs

HKS 256 8.8 mm cams

ARP fasteners everywhere

Stock hydraulic lifters (rev limit = 8400 rpm)

N1 oil pump

The intake side and fueling system are going to be upgraded accordingly.

Please don't flame me for asking a "which turbo" question because I have researched my ass off, but it just seems like standard practice to throw a 35R on and call it a day. Has anyone had experience with the GT40 vs the GT35R?

[discopotato03]

Its funny you should ask about GT40's vs GT3582R's because that exact debate is going on at a few boards in the US .

If you are really serious about the 600-650 wheel Hp and if your are prepared to go to the trouble and expense to do it properly then the GT4088R would be my choise . Before that though I think I would be putting the money into an RB26 because the head and inlet manifold is a better basis to start with . The hydraulic buckets in an R33 type RB25 engine are all about being quiet and maintenance free so really far from the best thing in your application . Also better cam profiles are available for RB26 heads than R33 25's .

Geoff Raicer from FullRace Motorsport makes arguably the best turbo exhaust manifolds money can buy and they'll bolt onto RB25 and RB26 heads . They've had a lot to do with Garretts GT4088R turbo and their trademark is being able to fit largish turbos to engines without having that innitial large turbo feel real world . You would also benefit from his personal experience because he likes the GTR's drive train enough to graft it into an S14 (US 240 SX which he calls R14) , he's no stranger to RB26's and PROPERLY designed twin scroll turbo systems . I suggest you search the FullRace Motorsport website and it has a forum at thar site .

Yours is not going to be a cheap build so I hope you have a healthy budget for it .

Cheers A .

[The Mafia]

Just looking at the engine mods - The GTR rods definately won't hold that kind of power. You'll need stronger rods. The GTR rods are only rumoured to hold about 350rwkw until they bend \ break.

So I assume its go a smaller turbo or rebuilt the engine with stronger internals.

[GeeTR]

Its the stock rod bolts i thought that limit output, with the ARP he could be OK. Would def look at bigger cams, and those Turbonetics GTK turbos look pretty promising

Manual or Auto?

[Darius]

Its the stock rod bolts i thought that limit output, with the ARP he could be OK. Would def look at bigger cams, and those Turbonetics GTK turbos look pretty promising

Manual or Auto?

Right on. I'm not worried about the rods at all. I've seen RB26's pushing 600hp daily and have not had rod issues. I've read the RB25 destruction thread and most blow because of rings or ring lands at about 500hp due to ill tuning.

LOL it is funny that you mention full-race because I'm fully aware of their product, but the $2300 price tag makes me flinch. That is a lot of money to spend when I could find someone to build me a custom manifold for about half the price and it would be close to equal-length. I'm very serious about the power level as it has been my goal from the beginning of the swap/build. I know the lifters are the weak point, but I don't think I should have to rev a 2.5L turbo motor above 8000 rpms to make 650 hp. I might end up getting the Full-Race manifold if my tax return is large enough.

I can't look at bigger cams because I'm not going to pull the head again to machine the head to fit the higher lift cams. I will simply have to live with what I have and make 650 with that.

Thanks for the informative responses discopotato and GeeTR.

[discopotato03]

Yes they are costly but then not all manifolds are created equally . For the dough you get thick walled stainless pipe , like that used in nuclear power station cooling systems , and a properly designed and fabricated merged collector . If you ask he'll tell you that its equal pressure drop over the six individual runners thats important not just equal length .

Sad fact of life is you build won't be a budget one and if lifting the head off is an issue then you may be aiming too high . For the power you want I think you should be looking into components that will do the job easily enough rather than those that could be not up to the task . Don't forget your asking for more than double the advertised ponies the original RB26 put out and production engines can only take so much . This is why I said I'd start with an RB26 because they got all the factory goodies std so they make a far better basis for high power capacity . Plenty of people have paint themselves into corners attempting to get high outputs from RB25's and the outcome is always the same . "I wish I'd started with an RB26" at least the head/inlet system anyway .

Something else to think about , particularly if FR's manifold is too costly for you , is using the RB26's twin parallel turbos . Good bolt on ones are easy enough to get and they eliminate the external gate issues you have with large twin scroll singles .

A pair of 2530's or similar with reworked std manifolds/good dumps/properly modified head/suitable cams should get close to the ask , using the greatest number of std or std replacemebt components . Wherever possible factory engineering generally makes the most cost effective upgrade because it was mass produced and benefits from economies of scale . Custom bits kill your budget because the labor costs involved .

Anyhow its your call , I'd just hate to see you get the power and blow the thing to smithereens . No money and a pile of scrap .

A .

[NYTSKY]

GT2835 for response.Will see about 290-300rwkw at 20psi.

Or GT3082 for power.Will see over 300rwkw.

I have 250rwkw in mine and its plenty for a street car.

[The Mafia]

GT2835 for response.Will see about 290-300rwkw at 20psi.

Or GT3082 for power.Will see over 300rwkw.

I have 250rwkw in mine and its plenty for a street car.

a 2835 won't see 300rwkw at 20psi.

a 3037 will, but defnately not a 2835.

[SLY33]

a 2835 won't see 300rwkw at 20psi.

a 3037 will, but defnately not a 2835.

it would, but first you have to get it to hold 20psi thru the top end not so easy.

Have you looked at the new turbonetics or is your choice narrowed down between the garretts?

BTW, machining the heads for cam clearance, cant that be done with the head on?

[gtst25]

a 2835 won't see 300rwkw at 20psi.

a 3037 will, but defnately not a 2835.

Yep Grepin was getting 312rwkw - 2835 with the larger exhaust housing.

Cheers

Edited September 22, 2007 by gtst25

[Dale FZ1]

I'd suspect that a 2835 of that spec would be at the maximum of its capabilities, and that the suggested 3037 would just do it a lot easier with better turbine efficiency (read ability to flow the mass-volume required). I don't think I would use the GT28 based turbine if chasing up around 300rwkW, even if it was the HKS variety.

In the end, the max flow number is one thing - but the delivery and response characteristics are another. At least there are options, but the story remains the same. Be sure of the required outcome and size accordingly.

Back on thread, if you're chasing 450rwkW, then it's going to be a completely different situation. Adrian's suggestion about the RB26 top end and twin 2530s in the right spec is pretty good. And it is a proven combination with the advantage of solid lifters. For sustained rpm over 8000, the reliability of hydraulics would have to be suspect in my books. Nothing is ever absolute, just saying that for high rpm solids are better suited than hydraulics. Obviously Nissan's engineers thought so too.

If punters are getting there with a GT35 then it should work for you too. There is some good information on bimmer forums too, with the advantage that they are turbocharging 6 cylinders of similar size/spec as the Nissan engine. Again, what works for them should work for you too.

Edited September 23, 2007 by Dale FZ1

[wolverine]

dale, the HKS2835proS has a 56mm turbine so is more similar to the (old?!) GT3071WG version than anything else but of course it has the HKS turbine housing which seems to make it work well but i agree with your sentiment about its size.

[discopotato03]

Just to quantify , far better cam profiles available for the non hydraulic bucket RB heads plus springs etc etc . The RB26 head also happens to have the matching stud patterns for the highest performance factory manifolds available which is important where budget is a big issue .

I was going to suggest 26 internals in a 25DE block but deleted that because if aftermarket rods and pistons are needed then might as well plonk the 26 top on an RB30 block . There really is no cheap way to make the power from an RB 6 , I really think the 26 head is the solution and the more cubic inches you can put under it the less revs you'll need to get the ponies .

I wouldn't waste time and money on an R33 RB25 head because the valve train wont hack the sort of valve actuation necessary to make the engine breathe in and out . You really need that 26 head and all 3 manifolds .

Cheers A .

[Darius]

Thanks to everyone for the good discussion! I think there might be a little confusion on the engine part of it though. I live in the States, so in this current project I am stuck with an R33 RB25DET with the modifications listed above. The machine work has already been done on the block and head and I have no intentions of changing heads at this point. The next project will have to be the 26/30 hybrid. I have sunk almost $10,000 into the swap (S14) and upgrades so far and am not afraid to spend the money to accomplish my goal. I never considered twin charging simply because I see most guys with RB26's going to a large single setup to reduce plumbing headaches and avoid paying for two new/larger turbos. The full-race manifold is looking more appealing every day, as long as I can keep my A/C because you can't be a baller unless you have huge hp AND ice-cold air! hahaha jk

OK so say the exhaust manifold is going to be Full-Race and obviously a large single turbo. Garrett has been my focus because I can get them for the least amount of money and they can still get my to my power goal. Frankly, I don't think a GT30 will have the top end capacity to flow enough air for my power goals. I have not looked at Turbonetics much but I'll check out their line. I have looked at Holset and Borg-Warner turbos, but have read here on SAU that they're better for diesel than gasoline engines. ?? Maybe someone can brief me on why that is.

[WHITER33GTS-T]

I have twin T3/T4s on my RB25 and that makes 399rwkw on 17psi and reving to 8000rpm.

What about a T04Z or T51R???

[R31Nismoid]

Yeah, but you have to look at it from driveability point of view at some point.

You go from 200rwkw (6000rpm) to 325rwkw (6500rpm), where it climbs over the next 2000rpm.

Pretty tight and sharp powerband. And with a stock geared car, you'd have to hit the limiter each time to get a decent run onto the next gear.

With a suited turbo to the job an increase of the power band by around 1500rpm is not out of the books at all.

Giving 3500rpm of good power, and comes in a bit more progressive.

A GT30 series wont get you there, GT35 should do it. 450kw (not rwkw) remember