boost falling off at high rpm (internal gate t28)

[BlackZenkiS14]

Ok, so i have an OEM ball bearing T28 from a late model S14 SR on my blacktop. Stock manifold, stock internal wastegate actuator, and Greddy Profec-B boost controller.

I have it set to run at 17psi, but it starts falling off around 6k and is barely at 12psi or so by redline. I want to hold 17psi til redline (running meth/water also).

Can i fix this with an HKS actuator? Or external wastegate? Or is this something inherent of this small turbo and the only fix is going bigger?

[ultimateirving]

I think that turbo runs out of breath at the higher RPMS with that much boost..

[e1_griego]

It's something inherent to the turbo.

[HipHopHippo]

exhaust leak maybe?

[jr_ss]

You're asking too much of it and pushing the turbo too hard as it is...Those things run out of steam at 14psi and blow nothing but hot air after that. It's designed for response and linear power, not peak and is going to fall off regardless. Upgrade to the S15 Spec R or a larger turbo.

[Mikester]

^^What he said^^

Kyle, I still have my APEXi BB turbine w/lines from Okinawa sitting on the bench if you're interested in an upgrade. It will make 300-320 like butter... or 370-380 to the wheels full-out... It was originally made to plug & play with S14/15 SR's... PM or give me a call if you're interested~

[BlackZenkiS14]

Well the plan is GTX2867R, but was trying to figure out whether or not I could et what I wanted out of this turbo for the season. Might just have to stick it out and upgrade over the winter.

Mike shoot me price and pics, if its silly cheap I might bite

[fliprayzin240sx]

Wastegate is probably getting overwhelmed by the exhaust flow. Getting a stiffer/adjustable internal wastegate should fix it.

[BlackZenkiS14]

Originally Posted by fliprayzin240sx

Wastegate is probably getting overwhelmed by the exhaust flow. Getting a stiffer/adjustable internal wastegate should fix it.

Think external gate would get it done better?

[Mikester]

Originally Posted by BlackZenkiS14

Well the plan is GTX2867R, but was trying to figure out whether or not I could et what I wanted out of this turbo for the season. Might just have to stick it out and upgrade over the winter.

Mike shoot me price and pics, if its silly cheap I might bite

Kyle, it's an awesome turbine... Depends on your view of 'silly cheap' lol..

If you are looking to pay anything less than 700, then no it's not.

However, here is my dyno from Okinawa... Stock valvetrain, appropriate mods, 17psi boost:



The black line is the boost...

Originally Posted by BlackZenkiS14

Think external gate would get it done better?

^^Absolutely!^^ 'cept it gets a bit on the loud side

[Croustibat]

Originally Posted by jr_ss

You're asking too much of it and pushing the turbo too hard as it is...Those things run out of steam at 14psi and blow nothing but hot air after that. It's designed for response and linear power, not peak and is going to fall off regardless.

I absolutely agree on this. Nothing the OP can do, the turbo is giving out everything hes got. These turbos can do 20psi... but on smaller engines.

Originally Posted by jr_ss

Upgrade to the S15 Spec R or a larger turbo.

The S15 spec R turbo is exactly the same one. Bigger ones are found on sunny/pulsar GTIR sr20, but they are a pain and a half to adapt.

@OP> Just get a gt2871r. There is a reason everyone uses one : it does the job perfectly and is an easy fit.

gtx2867r is a very good choice too, although a bit more costy. Check the gtx2867r thread, lately we posted 2 "extreme" examples of what you can get out of one. The vid and graphs i provided were for torque more than power ( twinscroll flange and mani), someone else posted graphs for a pure power build. "mine" got a max of approx 440hp , the other one was in the 480 range . The difference is that the first made 100more HP at 3000rpm

[jr_ss]

Originally Posted by Croustibat

The S15 spec R turbo is exactly the same one. Bigger ones are found on sunny/pulsar GTIR sr20, but they are a pain and a half to adapt.

@OP> Just get a gt2871r. There is a reason everyone uses one : it does the job perfectly and is an easy fit.

I disagree. The S15 turbo is capable of more boost and with more boost comes more power. However, he does need something bigger for sure.

[BlackZenkiS14]

The s15 turbo is near identical to what i have now, if I'm gonna do a bigger turbo, I'm gonna make it worth it. 2871 at the very least, but would really rather have the new gtx2867

[Croustibat]

Originally Posted by jr_ss

I disagree. The S15 turbo is capable of more boost and with more boost comes more power. However, he does need something bigger for sure.

You can disagree all day long, they have the exact same specs, so they perform the same ...

[ultimateirving]

Originally Posted by BlackZenkiS14

The s15 turbo is near identical to what i have now, if I'm gonna do a bigger turbo, I'm gonna make it worth it. 2871 at the very least, but would really rather have the new gtx2867

Get a 2871r since u posting in the thread with all ur updates lol..

[BlackZenkiS14]

Originally Posted by ultimateirving

Get a 2871r since u posting in the thread with all ur updates lol..

Lol whoops, busted. Its the most informative thread on these engines on this whole forum lol

[cotbu]

His problem is probably not the turbo, but his setup.
As the s14 t28 is similar to the s15 turbo aside from materials and ball bearing CHRA. The s15 gt2560r can hold 17psi till red line, so why is his boost falling to 12psi by 6000rpm. It's not because the turbo is pumping hot air, it's not because it's not ball bearing, or the iconel wheel. I do know if he swaps to one of the turbos listed he will still have the same problem, just might not be as apparent. He probably won't be able to hold 20psi till red line.

I actually thought you had a 2871r while reading this thread!!!!

[BlackZenkiS14]

Well, I'm all ears, where do you think my setup is failing me?

S14 t28
Freddy intake
Greddy fmic
Greddy profecB
740cc injectors
Jwt tune
Jwt s3 cams
Z32 maf
Meth/water injection
Oem exhaust manifold with new gaskets

[Mikester]

Originally Posted by BlackZenkiS14

Well, I'm all ears, where do you think my setup is failing me?

S14 t28
Freddy intake
Greddy fmic
Greddy profecB
740cc injectors
Jwt tune
Jwt s3 cams
Z32 maf
Meth/water injection
Oem exhaust manifold with new gaskets

Right there

Your turbine is too small to hold 1.15bar (17psi) of boost to redline. Other than that, you have all the right stuff from inlet to exhaust tip to be able to hold boost throughout.

[ultimateirving]

Originally Posted by Mikester

Right there

Your turbine is too small to hold 1.15bar (17psi) of boost to redline. Other than that, you have all the right stuff from inlet to exhaust tip to be able to hold boost throughout.

YUP, see first reply to thread.

[cotbu]

Wrong!
Waste gate and boost controller settings most likely.
If your waste gate is adjustable? try setting it to 13.5- or 14psi. I don't know what your settings are for boost control, but read the manual. You might even have a warning setting that decreases boost when you reach the over boost setting. All I know is the t28 can do 18psi till red line on an sr20.

Estimation for when you go gtx2867 or gt2871 350HP @ 20psi on a dynojet accept it!

[BlackZenkiS14]

Well its the original Greddy Profec B, so there isnt a bunch of weird electronic settings with it. Just Balance, Low, and High.

[jr_ss]

Originally Posted by Croustibat

You can disagree all day long, they have the exact same specs, so they perform the same ...

They may have the same specs, but one can boost higher than the other because of different materials, which still means more air flow. No sense in arguing semantics though, you say tomato, I say tomoto...

Originally Posted by cotbu

Wrong!
Waste gate and boost controller settings most likely.
If your waste gate is adjustable? try setting it to 13.5- or 14psi. I don't know what your settings are for boost control, but read the manual. You might even have a warning setting that decreases boost when you reach the over boost setting. All I know is the t28 can do 18psi till red line on an sr20.

Estimation for when you go gtx2867 or gt2871 350HP @ 20psi on a dynojet accept it!

Regardless of EBC settings, or adjustable wastegates, his motor is just out flowing the small turbo plain and simple. He's on the backside of the compressor graph and it's not flowing enough to keep up with the demand, hence the fall off of power. He MAY be able to squeeze slightly more out of it, by controlling the gate a bit better, but it's not going to get him where he wants it.

[cotbu]

Your saying he's approaching surge, right?
Not with the s3's! He's loosing way to much boost before red line. If he turns the boost down and he has the same problem/ or it goes away, what does that tell us?

[Mikester]

^^It tells us that his turbine is only capable of holding 'so much' boost to redline. Had the very same issue with my old T25... Yes I know- smaller turbine; but same effect- just more of a dramatic dropoff for me. If I turned the boost down to 10-11psi, it would hold all the way thru.

I don't normally disagree with you... but I'm sticking to my guns this time

Kyle, your EBC is one of the best ever made... Miss my old Profec to this day!

[jr_ss]

No, I'm saying he's approaching the choke line, which explains what's going on with his car.

The S3's aren't helping his case any. They are better suited to a 2871R or equivalent turbo, that make flow a decent amount of CFM's. His turbo just can't keep up with the demand.

[cotbu]

Originally Posted by Mikester

^^It tells us that his turbine is only capable of holding 'so much' boost to redline. Had the very same issue with my old T25... Yes I know- smaller turbine; but same effect- just more of a dramatic dropoff for me. If I turned the boost down to 10-11psi, it would hold all the way thru.

I don't normally disagree with you... but I'm sticking to my guns this time

Kyle, your EBC is one of the best ever made... Miss my old Profec to this day!

1st part uh uh
2nd part nothing wrong with it just the setting could be an issue. Like the switch for external or internal WG or

Originally Posted by jr_ss

No, I'm saying he's approaching the choke line, which explains what's going on with his car.

The S3's aren't helping his case any. They are better suited to a 2871R or equivalent turbo, that make flow a decent amount of CFM's. His turbo just can't keep up with the demand.

I can see him choking this turbo, but that's not what is describe in this thread. I've seen choking and it when the compressor will not flow anymore, he's loosing boost before red line. Now granted if he's only using part throttle and this happens I'd agree, but he would have to do a WOT/PEDAL to the floor pull or dyno for me to concur. I don't think he's doing the pull correctly now!

ps those s3's aren't shifting that power band from 3k-9k

[cotbu]

Before we get heated I'd like to suggest that we pull up dyno's of gt2871r or any turbo where the boost falls off! Now are all these poor setups the result of choking?
There was a thread about boost drop off somewhere.
I do love a good debate even when I loose!

[Tom N]

I know there's slight differences between the S15 t28 spec r and the S14 t28 but it doesnt seem right for the S14 t28 to drop off to 12psi at 6k. I have a spec r t28 and it will hold 17psi over 7k. Make sure you don't have something wrong with the internal gate. Could be getting blown open.

[BlackZenkiS14]

I'll go out tonight and do a few pulls and log some results and see what I get.

But it hold boost fine at 6k rpm, but lowers to less than 1bar by 7.5k

But cotbu, it's been about 5 years since I set up the boost controller lol, but I remember setting those switches properly when I did.