Lets Playyy, Find That Restriction!

[ST240]

Here's my ride:

RB25DE/30 Stock intake manifold/TB

Precision 6262 (~GT35R for arguments sake ) .58 T4 hot side

Tubular mani to 3" straight pipe

Same side entry vertical flow intercooler (omfg read below)

2,5" intake piping

z32

740cc

I'm having an issue where during a pull, nistune shows load index tapering off while boost is staying constant as well as timing/afrs. It is literally flat until 5500 rpm at which point it starts tapering off. It was REALLY bad, going from 75 to 61 with boost at 14 psi. l swapped my piece of shit horizonal flow, same side entry intercooler for a vertical flow one, and without chaning anything, a log showed it going from 86-75 with boost building to 16 psi. While this is a major improvement (the car feels awesome in comparison!) I still feel as if it is running out of puff at the top end. Could it be the stock intake mani/TB? I thought they were good to 300 rwkw and i dont think im there yet really. Has anyone else noticed this kind of thing?

Any info would be appreciated!

Edited July 15, 2011 by ST240

[NYTSKY]

A 3L with a .58 housing? Way to small IMO.

[NYTSKY]

DP

[The Mafia]

.58 T4 hot side

lol you think thats not too small for a GT35 sized turbo, and 3.0L motor?

Time to sell up and buy a Holden my friend.

[StealthX]

Choked to the max. I'm guess your ignition timing is abnormally retarded too?

Can you buy replacement housings for precision turbos as easy as Garrett ones?

[ST240]

Choked to the max. I'm guess your ignition timing is abnormally retarded too?

Can you buy replacement housings for precision turbos as easy as Garrett ones?

Running 16* at full boost so not too bad. Yeah you can, but i might be better off swapping the turbo all said and done. FFS. Just bought that thing.

You guys really think its the rear end in the turbo eh? Nothing intake related?

[Simon-S14]

it's defo the rear housing. that's tiny. EGT's would be thro the roof

[bubba]

Won't be stock intake mani and throttlebody unless you've left a rag in there somewhere. With the same head, RB20 manifold and throttlebody, pair of 2540's at 22psi we saw 365rwkw.

Not sure on exhaust housing specs of that turbo but I've had a small turbo on a 3L and when it choked up it nosed over hard (250-90hp in 1000rpm)

[Rolls]

Must be really hard to starve off detonation with a tiny hot side like that. Does it make full boost by 2k and then dive over at 5k?

How physically big is the hotside though, is it comparable to a GT35 or is it bigger?

Edited July 31, 2011 by Rolls

[ST240]

No my EGTs are fine. 800-900 in full boost?

No knock. No it spools by 3500-4000 and kinda dies off around 5500. The more i think about it the more i do agree with you guys that it is the hotside. The turbine is 62mm, which is also the size of the compressor. Which doesnt add up because it does feel kinda laggy somewhat. Unless my tune is way out.

Kinda wish id gone gt35r or gt30r. Not too much data on this turbo at all.

Edited August 15, 2011 by ST240

[Rolls]

The more i think about it the more i do agree with you guys that it is the hotside.

It is 100% the hotside, there is no doubt about it, eg what everyone in this thread has said.

Also 900c is very hot imo, should be more like 750c max. Change the rear of the turbo and it will fix all your issues, it is completely mismatched!

Edited August 15, 2011 by Rolls

[Simon-S14]

900 egt is way beyond normal. too hot.

must be choking like a bitch. its laggy cause the tuner probably cant put ANY timing into it without inducing detonation

Edited August 15, 2011 by Simon-S14

[R31Nismoid]

Yeah exactly, its getting so hot and causing so much stress you cant put any timing into it as a result. 700hp+ of turbo with a rear end capable of probably 400hp max... Not going to end well.

You need at least a .82 sized A/R, even a 1.06 would be fine (when talking GT35)

Will depend what options you have from precision but anything inbetween there as it also depends on how the A/R is calculated as the housings wont be the same as Garrett I'm assuming.

Maybe ask Precision what housing they have that is between a Garrett .82 and 1.06

That would probably be the best choice.

[FineLine]

You'll blow the arse off a 35r at 900 degrees mate. trust me I know.

[GTScotT]

What exhaust manifold have you got?

If its a cheapy maybe you can get it cheaply moded to T3 and get a Kando Dynamic T67. Cheap and easy way out, otherwise if its an expensive manifold I would try get another T4 frame turbo.

[ST240]

Thanks a ton guys.. Youve been a great help. I'll definately be looking into my options. Apparently I can get a twin scroll T4 .86 . Ive got a fairly good manifold on it; twinscroll but not true twin scroll with two gates . Ah its gotta be better than fully undivided .

Btw I am the tuner. And Ive been monitoring knock and there is none. But I am being conservative with my timing numbers.

Edited August 16, 2011 by ST240

[Harey]

My understanding is the twin scroll housings are roughly one size larger than the single scroll variants.

So 0.82 single scroll is roughly equal to 1.06 Twin Scroll.

So a 0.86 twin scroll might still be too small for a 3.0L, as it would equate to somewhere around a 0.7 single scroll which is too small.

I would recommend either a 0.8X single scroll or a 1.06 twinscroll.

[ST240]

Really? If that is indeed true, all I can find online is a choice between .82 and .86 divided. Id really like to try the divided one out but not if its more like a .68

[The Mafia]

you need a divided manifold for a divided rear housing or you are wasting your time.

Just get the 0.82. Anything smaller will be too restrictive.

[ST240]

Like i said I have a divided manifold with the appropriate runners in each port. What I lack is dual wastegates.

On a separate note, I was told by the precision guys that a .82 T3 open housing flows the same as between a .58 and .68 T4 open housing. Can anyone confirm? Sounds quite dubious.They also told me they dont offer any larger turbines because they "feel you should be moving to a 6265 if youre flowing that much". Lol. Guess the GT35R with a 1.06 is a silly idea then .

Edited August 17, 2011 by ST240