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EBC - Can you alter boost levels at different RPM's?

Robo's

By Robo's,
in Engines & Forced Induction

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Robo's Mentor

Robo's

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Guys thanks for the discussion.

As stated in my first post, i am running a adjustable HKS actuator. I have tensioned it up and we saw a peak of 17.8psi on the dyno in the middle (around 4300rpm). It then slowly drops off as revs rise and severly drops off over the 6000rpm range. It bottomed out at too 12.5psi.

So possibly there can be no boost leak as the i am using no boost controller and only one hose from the intercooler to the actuator which is tight as buggery and has been changed.

I have come to the conclusion that the 2530 is too small for the Rb25. I have compared the 2 side by side and there is only millimetres difference in size. I would still doubt whether a 2535 would hold the same boost up high and i am willing to experiment in this.

If i can gain an extra 1psi up high i would try. At the moment know more boost can be added as the standard computer is holding me back.

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SLY33 Mentor

SLY33

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hey guys, ive had a 2530 on my car for some time and had the same problem as robos. ive tried everything that had been suggested here and you just cant get the boost to hold. Im no turbo expert so i cant tell you exactly why this happens, yet from what ive heard the turbo is too small to support the amount of air required by the rb25 to maintain the boost levels. I also said in a post ages ago that i had also concluded that its too small for an rb25, but then thats all subjective really. The car was damn fast even with boost dropping off, running repeatable 12.5's at 115mph with 2.1 60footers, considering such a small turbo.

so saying its too small depends on what you want out of it. For most street applications id still say its a great upgrade, providing stomper torque that hits hard early.

in your case robos, 12.5psi is slightly lower than what mine dropped off too, but only by about 0.5psi or so. If you ask me its not worth chasing a little extra boost, as you are obviously wanting a good strong top end, get a larger turbo and do it much easier because the 2530 will never give you a big kick up top! its just too small. Even tho the 2535 may only be mm bigger on visual inspection, see what results people have got, i know there is at least 1 user on here with a nice 240rwkw from a 2535.

cubes, i will answer your question to nacho, the turbo is simply too small for the rb25, hence why whatever boost control method u choose to use, it wont change that fact. throw it on an rb20 however and see a great top end, pulling madly as far as 8000rpm (i have been in an r32 with this setup, and the turbo behaves completely different up top)

cheers.

PS robos: look into a GT-RS!

SLY33 Mentor

SLY33

Posted
Posted

hey guys, ive had a 2530 on my car for some time and had the same problem as robos. ive tried everything that had been suggested here and you just cant get the boost to hold. the turbo is too small to support the amount of air required by the rb25 to maintain the boost levels. (so Nacho, there is your answer to Cubes) I also said in a post ages ago that i had also concluded that its too small for an rb25, but then thats all subjective really. The car was damn fast even with boost dropping off, running repeatable 12.5's at 115mph with 2.1 60footers, considering such a small turbo.

so saying its too small depends on what you want out of it. For most street applications id still say its a great upgrade, providing stomper torque that hits hard early.

in your case robos, 12.5psi is slightly lower than what mine dropped off too, but only by about 0.5psi or so. If you ask me its not worth chasing a little extra boost, as you are obviously wanting a good strong top end, get a larger turbo and do it much easier because the 2530 will never give you a big kick up top! its just too small. Even tho the 2535 may only be mm bigger on visual inspection, see what results people have got, i know there is at least 1 user on here with a nice 240rwkw from a 2535.

so the turbo is simply too small for the rb25, hence why whatever boost control method u choose to use, it wont change that fact. throw it on an rb20 however and see a great top end, pulling madly as far as 8000rpm (i have been in an r32 with this setup, and the turbo behaves completely different up top)

cheers.

PS robos: look into a GT-RS!

Cubes Grand Master

Cubes

Posted
Posted

Sorry to bring it up again but I've been doing some investigating. :rofl:

I really don't like simple 'No it doesn't work' answers. I like to know why, what and where.

When I don't understand and others can't explain why with detail that answers, questions it frustrates me.

Robo,

I've since found a compressor map that is apparently almost identical to the HKS2530.

The 2530 pretty much max's out with a PR of 2 and ~30lb/s of air which is ~320hp.

The old golden rule of the HKS turbo's being conservative by approximately 15% would push the power up to approximately 370hp.

220rwkw + 60-65rwkw drivetrain loss = 280kw = ~370hp. Fairly close.

370hp = ~33.6lb/s of air.

The RB25 with a VE of 90% & 17psi uses approximately 30lb/s of air at 5500rpm.

By 6000rpm it is using ~33lb/s worth of air, over this and boost theoretically should start to drop off and airflow will plateau. Which it appears to do so. :rofl:

If you drop the VE to 85% at 7000rpm (which is where it is most likely at) you have an airflow of 33lb/s at 12psi.

The figures appear to be too coincidental.

But... Always a BUT.. I still have a question unanswered.

It doesn't explain how boost will shoot through the roof if you manually hold the wastegate shut.

A little off the track but i'll mention it anyway.

Increasing the exhaust a/r improves VE due to less backpressure and improved cylinder filling. This then reduces the boost required for the same airflow.

Lower boost = a denser charge as the air is cooler.

A denser charge contains more oxygen which is where the power comes from.

Even though you are running a lower boost with a larger exhaust a/r (Improved VE = less restriction = less boost required) my understanding is now that once you reach the turbo's flow limit the airflow will plateau and boost will drop accordingly. Power should then flatten out.

The VE Figures are guestimates.

A VERY VERY good example of this is this RB25 that underwent a RB30DET conversion. The Turbo was a GT30. Look what happens to the top end when the turbo's airflow limit is reached.

Airflow plateau's and I'm about to send a PM to find out if boost was actually dropping. No doubt it was. :cheers:

If I'm wrong with the above please let me know, bit of a silly statement really as I'm sure you will. :)

Cubes Grand Master

Cubes

Posted
Posted

Just to note... 33lb/s of air on the rb20 is around 7500rpm with 17psi. So you should see a little boost drop by 8000rpm on the rb20.

Drop boost to 15psi by 8000rpm and that too is 33lb/s of air.

Thats providing the cams are setup to provide sufficient airflow at that rpm.

Generally with the rb20t the VE will drop over 7000rpm which will allow the boost to be held. So you probably wont notice anything.

Which suggests why the 2530 is well known for how well it works with the rb20t.

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