Top End Boost Drop On Gt2530 Equipped Rb20

[femno]

Hey guys,

Got a quick question.

We were on the dyno the other night with my mates 32, we upped the boost from 1.1bar (strong, flatline 1.1 with no dropoff) to 1.4bar had a nice increase in torque and power (around 220kw) but, after boost ramps up nicely to 1.4, it slowly drops all the way to 1.1 by redline. Its as if the turbo is running out of puff.

Currently running a HKS 2530 63T with 0.64 housing, Tomei 260 cams (timing unknown at this point, but EX looks to be retarded for nice midrange judging by the CAS), HKS Adjustable actuator adjusted to achieve 1.4 bar with no bleed off, PowerFC. We previously had a mech bleed valve with actautor set to 1bar, did the same thing.

After viewing plenty of RB20 dyno sheets it seems common that people have boost drop across the revrange, so im betting on an EBC but just thought id get some input cos theyre not exactly cheap.

Must we run a EBC to control the boost? Im doubting it but could it be the cam timing affecting the boost so dramatically? Should we '0' the cams? Theyre the only other thing untouched.

Cheers!

Mat.

[_Ryan_]

I dont know much, just curious, but did i read correctly, that when the wastegate is adjusted the issue goes away? ", HKS Adjustable actuator adjusted to achieve 1.4 bar with no bleed off,"

i paid under 100$ for a hks EVC 4

[femno]

The actuator is adjusted to give 1.4, what I mean is that the signal hose is connected directly from the comp cover to the actuator with nothing in-line. With this setup we still have the boost dropping.

[bcozican]

i have nearly exact same setup (but with hks 264 cams and nistune) and have the exact same prob running just a boost T conttroller drops 2lb over 6700 peak from 18psi to 16 psi

tuner etc said if it worries me EBC would be the fix

[femno]

Ah well thats what I wanted to hear, after power peaks fairly early, its like someone switches the power off lol, the more you rev the less it pulls!

[Strik3r]

could also be a restriction in the exhaust or in the intake. Either can cause pressure loss like your describing.

[femno]

Exhaust consists of a Long split front/dump, so long it joins at the cat, straight from japan, ultra-flow cat, and super dragger with resonator replaced for pipe.

Intake is a brand new PWR cooler, Apexi suction kit suit z32.

So i think all of that should be fine.

[bcozican]

outta interest what rpm peak power at ?? mines higher than most ive seen obv due to cams and not alot of timing in there

6600 / 6700 peak for mine 264 in / ex hks cams

wot diff does 260 tomei's get ? gather quicker spooling as less duration?

[femno]

From what I remember its around 6000, dont quote me though.

If you have adjustable cam gears then you should able to dial up the cams so as they bring the power on quicker, make the most of the cams you have.

[Russman]

EBC it is then ey Mat! Not much time before Superlap!

[Equinox]

Easy way to work out if it's the boost controller or not is to watch the wastegate flap on the dyno while the boost begins to drop.

If the flap is opening more as the boost drops then the wastegate or boost controller is the issue however if the flap stays constant or even begins to close then I'd say the compressor is simply out of flow.

6000+RPM on an RB20 with a GT2530 is getting very close to the end of the compressor map.

[Russman]

Easy way to work out if it's the boost controller or not is to watch the wastegate flap on the dyno while the boost begins to drop.

If the flap is opening more as the boost drops then the wastegate or boost controller is the issue however if the flap stays constant or even begins to close then I'd say the compressor is simply out of flow.

6000+RPM on an RB20 with a GT2530 is getting very close to the end of the compressor map.

Good advice. thanks.

[benz_200t]

sorry for hijacking ur thread.

i have seen many sr20's running GT2835.

would this suit the RB20?

[Ricochet]

mate youve done what i wanna do,

same engine mod ideas,

hows it all goin for ya apart from the above problem???

[Russman]

Don't know much about GT2835's.

I'm gunna stick with this turbo coz it's great... providing I can get it to hold boost above 6500rpm

Engine is great. on 14psi for the last 3.5yrs that I've owned it and I've given it absolute curry every time I take it to the track. It loves it. 7900rpm all the time.

I've just bought a AVC-R and I think we're tuning tonight. We'll post up how it goes.

[bcozican]

running 2835 would be like running a garrett 2871r - 3071r wouldnt it ? would make the power but larger exhaust housing would prob at the the rb20's classic lag problems ??

i run the above setup too ... car used basically track only... friggin good setup.. not too laggy except for small motokana tracks but anything else as said when on boost it holds right to limiter all day everyday and is very smooth

^^^^ let me know the results

[abu]

I was going to tell you to go with a GIZZMO MS-IBC Russel but it seems it's to late now. I will have a look at my dyno graph from when I had my R32 tuned, was running HKS actuator with a AVCR but slightly different turbo, HKS2535 which is just a step up from what your running but same rear housing from memory so would be pretty close

From memory my turbo held power up to around 7200rpm but don't have the graph with me, will check when I get back. I remember putting a little extra per load on the actuator which helped boost controll but over all it wasn't the best

My AVCR spiked and ran like crap no matter how much we played with it

[femno]

Cheers all for the help.

The AVC-R is a good unit, we were able to obtain a dead flat horizontal boost pressure with one of these boost controllers on a 3071R equipped SR (pretty hard hitting turbo), so hopefully, we can achieve the same on the RB20 with a good combo of preload and AVC-R settings.

Will let you all know how we go with it.

[Roy]

Grab a 2530 and look in the exhaust housing. The volute of the housing is tiny, Now put your hand over the exhaust at 6,000rpm and feel the air coming out. When you get so much back pressure in the exhaust housing perhaps its limiting the engines ability to hold boost at high rpm/cfm ?!?!?!??!

I dont know what that all means but a consideration

[Equinox]

The HKS GT2530 is nearly identical to the Garrett GT2860RS.

Calculating the airflow of an RB20 at 1.4bar (assmuming 90% VE @ redline) results in approximately 43lb/min.

If you have a look at the compressor map of the GT2860RS you will see that 42lb/min at a pressure ratio of 2.4 is outside the compressor's rated operating region:

If you recalculate the airflow assuming boost of only 1.1bar, then at 8000rpm the engine is demanding 37lb/min of air. This is right on the max end of the compressor's map.

I'd say this is the problem man. The compressor is simply too small, and the boost is bleeding back to the region where the compressor is efficient at that rpm; 1.1bar.

Edited March 20, 2009 by Equinox