Cams or smaller turbo?

[robbie2883]

soooo...here's my setup...rb25 built with eagle rods and wisco pistons. 8-1 compression. stock cams, greddy intake and IC. top hat t4 divided manifold with tial 44mm WG and gt3582r running an 82ar turbine housing and 3" turbo back exhaust running at 15 psi for now. i just got the turbo on a couple months ago and have it pretty well street tuned. i am not happy at all with the spool up. like 4500-5000 it reaches full spool. i am trying to figure out it's in the tune...or if i should look at some 264 cams or just sell the turbo and go with a gtx series 3076? my goals are only 500ish..... input please? and thanks!!!

[Cjmartz2k]

500 at the wheels? I guess you could get that if you pushed the hell out of a GT3076, but if you want response most of all, I assume you aren't drag racing? Don't worry about the numbers if that's the case. If it's at the motor, GT3076 can make that easy with great spool. Oh yeah, more boost. 15psi isn't enough.

That being said, what gear are those spool numbers in? If 4th, that's a bit slow for that turbo, but I'd guess the tune is the problem. Cams wouldn't help much, and might hurt if you ditch VCT.

[RustspecS13]

Theres a vid linked some where here in the rb forum of a RB25 making pretty much exactly 500whp with a GT3076, a GTX3076 would do it assuming every thing else is also done right.

~Alex

[robbie2883]

500 at the wheels? I guess you could get that if you pushed the hell out of a GT3076, but if you want response most of all, I assume you aren't drag racing? Don't worry about the numbers if that's the case. If it's at the motor, GT3076 can make that easy with great spool. Oh yeah, more boost. 15psi isn't enough.

That being said, what gear are those spool numbers in? If 4th, that's a bit slow for that turbo, but I'd guess the tune is the problem. Cams wouldn't help much, and might hurt if you ditch VCT.

GTX not GT. the new GTX3076 is supposed to be capable of 650 at the crank which is what my current turbo is capable of. oh and that's in 2nd gear (top of 3rd is around 110mph and i don't go that fast on the street)...i drop low in the boost curve when shifting to 3rd as well and it take a little bit to get going again. and yeah....i know more boost to make the 500...but it's not going to spool any faster at 20-22 than it does right now. i'd love to be able to fix this with the tune...i just don't see how timing can be that far off and that's the only thing i can think to make her spool any faster.

[boostedh23a1]

You need to get this data on a dyno or via ems to get accurate/consistant values. I am looing for about 550-600whp on my rb26 and am trying to figure out what turbo I wanna run too. my buddy has a gt3071 on his mr2 and i just dont see something like that working on a rb26 but hey im a tard...

[RRRRB]

if you only want 500whp id downgrade to a 3076R or a precision 5857.. i made about 490whp on 25psi with my 3076r.. i have a Divided T4 housing for that turbo too if you ever need one..

I got board with the 30R so im upgrading to a 6766

[robbie2883]

no to make the change....got the timing squared away...and still have more to play with and put a avcr on there. the avcr made a huge difference over the hallman mbc

spools fast and should have no problem making the power i want.

[RRRRB]

yeah with a 1.06 T4 divided turine housing i was getting 25psi by 3800-4200 on my 3076r

[ItzGenX]

That thing should be spooled to 1 bar by 4-4.2k or so. Is the turbine housing also divided? If so, a single wastegate on the manifold meeting at a Y joint can cause cross pulsing with the exhaust energy and induces more lag. 8:1 compression is also low, especially for a short stroke motor. With that low of a compression, you don't have much power off boost (more power = more exhaust energy). Low amounts of exhaust energy off boost means you'll have to wait longer to get the gas volume needed to reach positive boost pressure. Cams can help, but ultimately, your compression ratio is still lower than average. The upside is that you can run more boost without exploding, but it comes at the expense of response and off boost power.

[boostedh23a1]

You think the gt3076 on a divided t4 manifold and housing would do 550whp on pump gas?

[robbie2883]

You think the gt3076 on a divided t4 manifold and housing would do 550whp on pump gas?

the GTX can. but doubt the GT could

[boostedh23a1]

Hmmm wonder if a small gtx35 twin scroll t4 would be better and not push it to the limits.

[ItzGenX]

The smallest t4 twin scroll housing for gt35 turbines are. 86 ar and a rare find since it was casted by garrett in small numbers. The next one up will be the atp casted housing with a 1.06 ar that I have on my gtx35. I couldn't find any other twin scroll t4 housing that fit a gt35 turbine. All of the smaller housings are t3 or undivided t4.

[boostedh23a1]

anyone running the GTX3076 on a divided t4?

[robbie2883]

the divided housing is NOT as big a deal as the divided manifold...i am not saying you won't make any gains over a non divided housing, but again...the main benefits come from the manifold design.

[Darius]

The gains of a divided manifold housing are minimal for what is charged by fabricators. You are better off going with a less expensive combined exhaust manifold collector and running a quick-spool valve on your divided inlet turbo housing. It saves you a wastegate and exhaust routing complications as well.

http://www.youtube.com/watch?v=_KNLKVgg8po

[Bluefire]

Your compression ratio is the problem... an 8:1 compression ratio setup is designed to allow for high boost levels. This results in poor low end response but high hp numbers up top. Cams might help a little, but not by much. You would be better off getting cam gears and trying to shift the powerband lower, sacrificing top end power. As for the turbo, switching to twin scroll will help spoolup only slightly, but not enough to make a big difference. Your better off with a smaller turbine housing or smaller a/r.