Gt4294 On A Rb25?

[KB240RB]

Im gonna be building up my RB25 soon and im looking into my turbo options. I want a solid 700-750whp after its all done. Maybe more if it makes it. The turbo ive been looking at is the GT4294. Ive found it as low as $1000 in the states. Its the journal bearing version. How well would this turbo work out on the RB25 using a Divided 1.15 Housing on a Divided Manifold?

[R34GTFOUR]

not well at all unless you want to rev it to 10-11k rpm, thats a very large turbo for a small displacement engine.

A garrett T04Z would be a better choice, it still wouldnt be "responsive" but no set-up will be if you want that much power out of a 2.5L engine.

[KB240RB]

There not terribly different in size. The t04z is a 67mm and the 4294 is a 71mm. Why would you think you would need 11krpm? T04z is rated for 750hp and the 4294 is rated to 850hp. Plotting the compressor map, the 2.5L would be at the very top and end of the map of the t04z. But with the 4294 it's right in the middle showing 75% effeciency at 750hp. It's also well within the surge line of the 4294. I know it'll be laggy but it seems to be pretty matched for a 8500rpm powerband with the 2.5L.

[R31Nismoid]

ugh journal bearing on a turbo that large?

I take it the car is a dyno pony?

[KB240RB]

Nevermind guys. Sorry I asked.

[juggernaut1]

How would a twin scroll 4088 fit in between those two.

I see they use this turbo on the leading time attack car in the UK at the moment which is a 2 litre subaru.....but they do spin it to 10500 rpm.

Edited December 2, 2009 by juggernaut1

[KB240RB]

4088 is pretty close to a to4z.

[juggernaut1]

OK that makes sense because the car that won superlap this year was a stroked EVO and that had a twin scroll HKS TO4Z on a full-race divided manifold.

Edited December 2, 2009 by juggernaut1

[R31Nismoid]

Nevermind guys. Sorry I asked.

I just don't understand mate why you would build a motor to hold 500rwkw.

And then use a $1000 turbo.

That holds very little logic mate unless its just for dyno comps or something.

[juggernaut1]

Nismoid....KB is from US so his hp figures will be a little higher than our equivalents assuming he is quoting dynojet target hp numbers.

[KB240RB]

It's for whatever I see fit. Street driving, dyno, highway, maybe 1/4. I'm not looking to set records. Just make the power that feels good to me. I had 600hp in my s13 and that didn't feel like enough for me. Now I have a rb in my s14 and want to go for more. I don't need to compete with people. As far as the journal bearing thing. There way cheaper to replace if something happens. For a street car I don't see the need to spend 2k on a turbo when so many others are available. I'd rather use the extra cash on a nitrous kit.

[Lithium]

Have you considered going for a big nasty Holset turbo? I reckon a GT4294 would be pretty seriously laggy on an RB25.... I could see it being more annoying during lag than it is fun once you get past the lag. An HX52 may prove to be a bit less laggy, not to mention just as cheap - if not cheaper

[bradsm87]

It's DEFINATELY DEFINATELY worth paying the extra for a new GTX4294R. It's obviously ball bearing and has the brand new "GTX-R" compressor wheel. it'll spool quicker than a GT4294 and make a heap more power and be efficient at a bigger boost range. It's the bee's knees.

Don't forget to get a high quality split pulse exhaust manifold with either twin wastegates or a single wastegate as long as there is a splitter in the manifold sealing against the wastegate.

[KB240RB]

Ive read a little about the GTX turbos. Newly designed billet compressor wheel and dual ball bearing. Ive heard them costing ALOT though. Well over the normal GT4294R. Im waiting to see tests of them. What do you guys think the GT4294 with a 1.05 Divided Housing and Divided Manifold would hit 20psi at? Ive seen the 3.0L Supra guys have 20psi @ 4600-4800rpm. I couldnt see it being but a 500-600rpm difference on a 2.5L.

[KB240RB]

Just so you guys know, im not some baller with tons of cash to blow. Im an automotive detailer just trying to spend what i can to make as much power as i can. $2k-$3k turbos isnt gonna happen. There are other areas of the engine ill have to use that money for. I do everything in my garage with only help from my father when i need a hand with something heavy. My goal is to build an engine with everything working together as they should to make some impressive figures and show some people how to build something proper on your own. Money always buys the best things but you can still do something impressive without being the best.

[R31Nismoid]

What sort of motor do you have built?

Because one to handle that kind of power... means the turbo is going to be less than 10% of the overall cost of the parts from the motor to diff.

[Dale FZ1]

Why would you think you would need 11krpm?

I know it'll be laggy but it seems to be pretty matched for a 8500rpm powerband with the 2.5L.

Ive seen the 3.0L Supra guys have 20psi @ 4600-4800rpm. I couldnt see it being but a 500-600rpm difference on a 2.5L.

There are other areas of the engine ill have to use that money for. I do everything in my garage with only help from my father when i need a hand with something heavy. My goal is to build an engine with everything working together as they should to make some impressive figures and show some people how to build something proper on your own.

Looking at the whole picture Kev, I’ll suggest that there is nothing inherently wrong with chasing 700hp. Use it how you see fit, too.

If you’re accepting that the minimum engine rpm you’ll hit 20psi (is that what you calculate your RB25 will require to hit the power target?) is 5500rpm, then by rights you’d want to extend the upper rpm ceiling to avoid ending up with a fairly narrow and difficult to use torque range. You’d have to be prepared to buzz the engine harder than 8500, which would lead me to ask two questions

1. Have you looked at the gearing and final drive ratios for your road speed targets? If so, what do you reckon is likely to work with this powerhouse?

2. What reciprocating components would you use in the engine itself?

I have no issue with whether you use a plain bearing spec turbo, more that the powertrain is configured as a whole.

Given that the BMW boys have achieved some pretty good results Stateside, it’d be interesting to see what/how they do it. Typically the route seems to follow cubic inches via the M3 platform, but I think the 2.5 litre 6 cyl seems to run hard too.

[PM-R33]

I'm confused. You say you have built an engine to support 700-750whp, that's around the 550rwkw mark. Now a lot of us here understand the costs involved and required to build an engine to handle that much power. Considering you havn't used a stroker kit or a 3L bottom end, that RB25 would have to be built to very high standards. I for one can't see an engine built to handle that power relibably with all supporting mods for say under 20 grand by a workshop. Hell im probably way off, even 30 grand.

Now i realise in the states your dyno's read a bit different to ours, but even still, for a 500rwkw engine you are still talking big dollars.

So my question is, if in fact you have built an incredible engine to handle that power well, why can't you spend an extra $1k-$2k on a proper turbo to go with the setup?

Or, is the engine not as big of a dollar engine, which brings me to my next question, what is the specs of the motor? Are you sure it can handle over 500rwkw?

Not having a go at you mate, but when i see some one talking about a big dollar, high horespower build, and then start saying they want a cheap turbo for around $1000 to make the power they say the engine can handle, i start to question it. Hell if i had an engine with that kind of potential, i would be looking at top dollar latest technology turbo's over the $3k mark.

Edited December 2, 2009 by PM-R33

[Lithium]

^ Did you read his last post? I have met people who have set out to do things like what he is aiming to do, and achieved them - though as said, the 2.5litre thing could prove very restrictive in all but making the peak power level....

KB240B - one of the misleading things about comparing where full boost is reached between a 2.5 litre and a 3litre is that the engine displacement and as such, the natural non boosted torque is already 20% higher. With the 3litre you could have a LAGGIER turbo than what the GT4294 on an RB25 would be and still have the same power delivery. If it had the same amount of lag, it would smoke the RB25 for power delivery. Given the RB25 would give 500-600rpm in terms of lag, it would end up as a completely different beast in terms of peaky power.

[PM-R33]

Yes i did read his post. You aint going to build a 500rwkw engine in your garage as an automotive detailer. However for the sake of the argument let's say he is, and he has all the machinary and equipment to do the job and balance everything perfectly, build the head perfectly and build it to rev above 8000rpm all day every day, therefore so there is zero labour costs.

In parts alone, not including the turbo, i can easily count up over 15k.

-fuel system to support 500+rwkw, ignition system, clutch

-rods, pistons, new crank, oil pump, harmonic balancer, bearings/seals

-valves, springs, cams, full engine gasket kit

-intercooler to flow that much power, exhaust manifold, gate, custom dump, intake manifold, custom pipework

Thats just a handful i've quickly thought of, missed tonnes of shit, not to mention all the little costs that we all know add up to a few hundred or thousand. Havnt included any machining or balancing or assembly costs.

Honestly i just don't see on a build to make a 500+rwkw car, to be arguing over the cost of a turbo when you are talking that much money.

Hell there are guys on these forums who's engines have cost them well into the 30+k mark and they probably did most of the stuff themselves, engine removal etc.

Maybe it's just me, and if so, ill stay out of it. I just can't get my head around being in a situation like this, building such a high horsepower engine, and then asking peoples opinion on a turbo because you can get it cheap and don't want to spend a little bit more on a turbo that will do the job so much better.

Edited December 2, 2009 by PM-R33