Advise Needed From Turbo Experts

[legend01]

Hi Guys

Been advised a couple of times now that my turbo is holding me back , engine is capable of more .Now for a while ive been resisting this notion its a fairly new garrett GT3040R the spec's on this turbo are turbine -wheel-60mm w/84 trim and a .82 housing.....Compressor-wheel 82mm w/56 trim and .70 ar.Been advised to uprate it to the garrett gt3540r this turbo has been updated to the new garrett GT3582R there's not a great deal of differance between these two turbo's gt3582 specs are ,turbine-Compressor wheel 82mm w/56 trim and 0.70 ar, turbine wheel 68mm w/84 trim but here im thinking of going to the 0.63 houseing

as you can see very little differance .

The engine is a built rb20det ,specs are rb25 crank, rb26 rods, aries 40thou oversized forged pistons.hks cams, ported head ,hks cam gears ,1mm oversized valves and all the bolt on goodies engine is making 306rwkw at the moment and I'm pretty happy with that .At UAS dyno day it made 250rwkw at 4250rpm and full boost by 3800rpm so the power is there but more than one tuner has said get rid of the turbo u need something bigger while thats fine and dandy to say get this turbo it will do the trick thats what I was told when I bought the gt3040 well now I'm being told something differant so I thought I'd throw this up here and get some advice on what poeple think would be a better turbo for my setup even been looking along the lines og the tdo6 .

cheers Peter

P.S did a search but not realy a lot of info on this power level with an rb20 ,well its an rb2.1 thanks

[BHDave]

what sort of boost are you running to make the 306? What happens if you add more? Has anyone determined that it's the turbine side thats limiting the set up? Have you played with turbine housings to see what effect it has?

I've seen your dyno sheet and, to be honest, it's pretty bloody impressive to have the midrange and top end you have considering the relatively low capacity and relatively large turbo (and turbine housing A/R). Personally i'd leave it, unless you are chasing a number.

[R31Nismoid]

Wow your turbo is as responsive as when its on RB25's, how much pre-load is used to get it like that?

edit - just looked @ your graph, whats 136km/h on your setup?

Anyways, how much power/response are you after exactly? Purpose of the car?

You kinda haven't really said, so sorta hard to look at what turbos might fit your requirements... without listing them

Also, how much boost was needed for 300rwkw/RB20? And was the 250rwkw with the same boost and thats the reason its holding back?

[legend01]

I'm running 23psi boost for that power level ,the tuner has said to me more boost made very little differance so he left it there but seeing as it was a fresh engine (1600klm) then he played it safe as I told him I'd be happy if it made the 300kw mark.

BHDave I played with smaller housings on earlier turbo's (cost me a small fortune) and consulted with a turbo builder who had done the mods to previous turbo's for me ,though he did originaly suggest the gt3540 he thought the gt3040 with the .82 rear housing would be enough so went on his advise.Dont get me wrong I'm real happy with the way it is atm I drive it around on low boost which is 13psi and its maken 240rwkw at that .

Reason im thinking more is I put alot of work into getting boost to come on as early as possible and in building a solid engine ,it has the running gear for alot more hp the trick is getting it ,im not doing it for numbers im doing it for myself to see what I can get out of it and still make an enjoyable car to drive

R31Nismoid I dont understand what you mean by pre-load ,I'll have to check the graphs when I get home for the power at 136klm's .(edit)Power at 136km/h is 280rwkw @ 5100rpm going of the dyno sheet.I have not set goal on power level since I made the 300rwkw mark except how much more is it capable of ,wasn't that long ago that 300kw was unheard of in an rb20 ,now there's quite a few pushing that mark so how much more can they go.The 250rwkw mark was on same boost level but at 4200rpm the 300rwkw at 6500rpm

I like using the car at the drags although I will be doing some track days with it .It has run an 11.7 at wsid but think I can better that yet.

I can build an engine and fully rebuild a car but I'm afraid undersatnding turbos atm is a little beyond me and how they flow so I'm trying to find a better solution and some more info on what is going to work best without going stupidly large turbo thats usless execpt on superhigh rev's it is still a weekend driven car,

cheers Peter

[BHDave]

I see where you are coming from re the bigger turbine in a smaller housing, you are trying to trade off any extra lag as a result of the larger rotating mass by having a smaller turbine housing to force it to spin up quicker.

It's the way i'd do it, despite knowing full well that high exhaust manifold pressure is the enemy.

Just consider you have the extra torque a bigger turbine can provide spinning up the same compressor so i don't think you will be stepping backward significantly in response even with the same sized turbine housing. The potential is there to choke at the top end with the small housing.

All i can suggest, if you decide to go ahead, is be prepared to step up on the turbine a/r.

[Adriano]

Are the rods stock rb26 ones? I probablt wouldnt go chasing heaps more power and risking the motor if they are.

[legend01]

Rods are stock Rb26 resized, shotpeened and hardened and balanced

[GTS20X]

Do you know what compression ratio you have with this engine