Jump to content
SAU Community

Recommended Posts

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.

Link to comment
https://www.sau.com.au/forums/topic/352235-rb25-gt2876-15psi-at-4800/
Share on other sites

  • Replies 47
  • Created
  • Last Reply

Top Posters In This Topic

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.

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

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.

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

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).

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...

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.

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 $$$.

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.

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.

+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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Power is fed to the ECU when the ignition switch is switched to IGN, at terminal 58. That same wire also connects to the ECCS relay to provide both the coil power and the contact side. When the ECU sees power at 58 it switches 16 to earth, which pulls the ECCS relay on, which feeds main power into the ECU and also to a bunch of other things. None of this is directly involved in the fuel pump - it just has to happen first. The ECU will pull terminal 18 to earth when it wants the fuel pump to run. This allows the fuel pump relay to pull in, which switches power on into the rest of the fuel pump control equipment. The fuel pump control regulator is controlled from terminal 104 on the ECU and is switched high or low depending on whether the ECU thinks the pump needs to run high or low. (I don't know which way around that is, and it really doesn't matter right now). The fuel pump control reg is really just a resistor that controls how the power through the pump goes to earth. Either straight to earth, or via the resistor. This part doesn't matter much to us today. The power to the fuel pump relay comes from one of the switched wires from the IGN switch and fusebox that is not shown off to the left of this page. That power runs the fuel pump relay coil and a number of other engine peripherals. Those peripherals don't really matter. All that matters is that there should be power available at the relay when the key is in the right position. At least - I think it's switched. If it's not switched, then power will be there all the time. Either way, if you don't have power there when you need it (ie, key on) then it won't work. The input-output switching side of the relay gains its power from a line similar (but not the same as) the one that feeds the ECU. SO I presume that is switched. Again, if there is not power there when you need it, then you have to look upstream. And... the upshot of all that? There is no "ground" at the fuel pump relay. Where you say: and say that pin 1 Black/Pink is ground, that is not true. The ECU trigger is AF73, is black/pink, and is the "ground". When the ECU says it is. The Blue/White wire is the "constant" 12V to power the relay's coil. And when I say "constant", I mean it may well only be on when the key is on. As I said above. So, when the ECU says not to be running the pump (which is any time after about 3s of switching on, with no crank signal or engine speed yet), then you should see 12V at both 1 and 2. Because the 12V will be all the way up to the ECU terminal 18, waiting to be switched to ground. When the ECU switches the fuel pump on, then AF73 should go to ~0V, having been switched to ground and the voltage drop now occurring over the relay coil. 3 & 5 are easy. 5 is the other "constant" 12V, that may or may not be constant but will very much want to be there when the key is on. Same as above. 3 goes to the pump. There should never be 12V visible at 3 unless the relay is pulled in. As to where the immobiliser might have been spliced into all this.... It will either have to be on wire AF70 or AF71, whichever is most accessible near the alarm. Given that all those wires run from the engine bay fusebox or the ECU, via the driver's area to the rear of the car, it could really be either. AF70 will be the same colour from the appropriate fuse all the way to the pump. If it has been cut and is dangling, you should be able to see that  in that area somewhere. Same with AF71.   You really should be able to force the pump to run. Just jump 12V onto AF72 and it should go. That will prove that the pump itself is willing to go along with you when you sort out the upstream. You really should be able to force the fuel pump relay on. Just short AF73 to earth when the key is on. If the pump runs, then the relay is fine, and all the power up to both inputs on the relay is fine. If it doesn't run (and given that you checked the relay itself actually works) then one or both of AF70 and AF71 are not bringing power to the game.
    • @PranK can you elaborate further on the Colorlock Dye? The website has a lot of options. I'm sure you've done all the research. I have old genuine leather seats that I have bought various refurbing creams and such, but never a dye. Any info on how long it lasts? Does it wash out? Is it a hassle? What product do I actually need? Am I just buying this kit and following the steps the page advises or something else? https://www.colourlockaustralia.com.au/colourlock-leather-repair-kit-dye.html
    • These going to fit over the big brakes? I'd be reeeeeeeeaaaall hesitant to believe so.
    • The leather work properly stunned me. Again, I am thankful that the leather was in such good condition. I'm not sure what the indent is at the top of the passenger seat. Like somebody was sitting in it with a golf ball between their shoulders. The wheels are more grey than silver now and missing a lot of gloss.  Here's one with nice silver wheels.
    • It's amazing how well the works on the leather seats. Looks mint. Looking forward to see how you go with the wheels. They do suit the car! Gutter rash is easy to fix, but I'm curious about getting the colour done.
×
×
  • Create New...