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Rb25 Gt2876 15Psi At 4800?

Stargate

By Stargate,
in Engines & Forced Induction

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Stargate Contributor

Stargate

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Hey guys,

when driving in 3rd gear, standing on the throttle at 60 does virtually nothing. At around 4k, the turbo is sitting on around 10psi. Once you come onto around 4800-5k, it hits 15psi hard (cant believe the difference in power between 10 and 15psi). Any ideas why it boosts so late? Has been like this since I changed the turbo but having looked through the dyno results pages - noticed that most turbos are on full boost by 3000, with the larger turbos around 3.5k. Any ideas?

Mods are as follows:

Nistune ECU

Standard Bottom End

Standard Head Minus Tighe 264 8.5 Cams with Adjustable Gears

Gt2876 with 12psi actuator bleed to 15psi

Stock Cooler and Piping

4" intake pipe to Standard AFM

Standard Manifold

Standard Dump Pipe with 3" Exhaust (Highflow cat and Cannon Only)

I can do a bit of a test drive with a video cam and post up the boost guage and tacho if needed or if it helps.

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https://www.sau.com.au/forums/topic/352235-rb25-gt2876-15psi-at-4800/
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JonnoHR31 Grand Master

JonnoHR31

Posted
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first test would be to pull the vac line off the actuator and plug it up and see when you hit your target boost then, but make sure you back off straight away as with everything working it'll free boost.

Stargate Contributor

Stargate

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Posted (edited)

first test would be to pull the vac line off the actuator and plug it up and see when you hit your target boost then, but make sure you back off straight away as with everything working it'll free boost.

I have done this accidently before - roughly the same boost pattern.

Thanks Captain

Found it on GCG, seems like another new name/combo, Garrett really are getting over the top!

What housings did you get with it?

Garrett Turbo: http://turbobygarret...6R_705330_2.htm

However, this was designed to go onto an sr manifold. So I took it back to MTQ and got a t3 housing - unsure of ratio. The turbo bolts to standard dump pipe so it may be a direct replacement rear housing for this turbo.No machining was needed to fit it to the turbo. I believe the compressor ratio was 0.86

Edited by Stargate
GTScotT Grand Master

GTScotT

Posted
Posted

It will be the fact the 2876 has a cropped gt30 exhaust wheel, and the exhaust housing is to suit an uncropped wheel. MTQ should know better.

True?!

I always thought it was a 2871 GTRS with a 76mm front wheel... How sure are you that it is the cropped GT30 rear wheel?

If this was the case, we could use this CHRA to build 2835 variants. Simply have GCG redo it with a 71mm front wheel to make a 2835 spec CHRA or even build a GTX2835.

The only issue will be the exhaust housings, the OP6 would probably be the easiest way to go.

bradsm87 Proficient

bradsm87

Posted
Posted (edited)

The GT2876R has a 53mm turbine wheel, same as the GT2860RS and GT2871R. It is a TERRIBLE mismatch of turbine to compressor. U get no more than the power of a GT2871 R but the lag of a GT3076R. Even garrett state on their web site that it's not for normal performance applications:

* Best suited for unique applications such as asymmetric turbo installations

* Not recommended for general performance applications

You're really gonna get HUGE gains from a GT2835 or GTX3071R or GT3076R. The GTX3071R would be my pick.

Edited by bradsm87
simpletool Mentor

simpletool

Posted
Posted

Yep, it'd be the same as the HKS 2540. That was completely replaced by the GTRS, same peak power with better spool.

Anyway, it's meant to be for small engines running big boost with a T25 footprint. This isn't the only problem as you would expect boost still well under 4000rpm with a 2876 on an RB25. You should get 1 bar around 3500rpm in 4th with a 3071, even lower with 2871 (GTRS).

Stargate Contributor

Stargate

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Did you do the cams and turbo at the same time?

Check your timing and adjustable cam gears.

Timing is spot on with the gears set to 0.

The GT2876R has a 53mm turbine wheel, same as the GT2860RS and GT2871R. It is a TERRIBLE mismatch of turbine to compressor. U get no more than the power of a GT2871 R but the lag of a GT3076R. Even garrett state on their web site that it's not for normal performance applications:

* Best suited for unique applications such as asymmetric turbo installations

* Not recommended for general performance applications

You're really gonna get HUGE gains from a GT2835 or GTX3071R or GT3076R. The GTX3071R would be my pick.

I would really like to get the gtx3071r but since I am attempting to sell the vehicle, I dont really want to spend money on it. Not to mention changing manifolds, piping, exhaust etc.

Yep, it'd be the same as the HKS 2540. That was completely replaced by the GTRS, same peak power with better spool.

Anyway, it's meant to be for small engines running big boost with a T25 footprint. This isn't the only problem as you would expect boost still well under 4000rpm with a 2876 on an RB25. You should get 1 bar around 3500rpm in 4th with a 3071, even lower with 2871 (GTRS).

Hmmm, well as mentioned it comes onto 15psi in second around 70km/h at roughly 4.5-4.8k revs. Breaks traction coming onto boost in first and second, but its very hard to launch (as you could imagine). Kinda fun to drive though.

Considering selling for 8k now, just so I can get my gtr. From what ive heard above, about $2-$3k worth of mods and it will go quite nicely. Shoot me offers via pm if interested...

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

It will be the fact the 2876 has a cropped gt30 exhaust wheel, and the exhaust housing is to suit an uncropped wheel. MTQ should know better.

Indeed this is why I asked about the turbo itself, I'd be very suspect about it.

Have the gate held shut and test it, but the likely scenario is as above.

Stargate Contributor

Stargate

Posted
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Indeed this is why I asked about the turbo itself, I'd be very suspect about it.

ive had this turbo on the car for around 9 months so im sure any warranties (if any) are well and truely void. I suppose I could pull it off and get MTQ to check it out and fix it, but i'm sure it will cost me a few $$$.

Stargate Contributor

Stargate

Posted
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Well it wont be under warranty if there is nothing wrong with it... Which there technically isn't by the sound of it

well,ive shot mtq sydney an email asking them is there is any option for a cropped t3 housing with the nissan 6 bolt dump. If not, what option(s) are avaliable for exhaust wheels to suit my housing.

Stargate Contributor

Stargate

Posted
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first test would be to pull the vac line off the actuator and plug it up and see when you hit your target boost then, but make sure you back off straight away as with everything working it'll free boost.

I have tested this a few months ago, but will do again tonight just to confirm. No change in boost speed.

Dobz Experienced

Dobz

Posted
Posted

+1 for thinking there's something up with that turbo.

I had a genuine gt2876 with a .86 rear housing on an stock rb20 once and i was hitting 18psi just before 4500rpm, so an rb25 hitting full boost at 4800rpm with the same turbo doesn't sound right.

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