Boost drop at high rpm.

[BOOSTD]

Can anyone tell me why the standard turbo looses boost when pushing 15psi at high rpm???

My Hybrid turbo is doing the same thing to a greater extent.

I'm thinking the waste gate actuator tension is not enough to hold the waste gate closed......

anyone had first hand experience with a HKS actuator or the like?

[JimX]

I put a HKS actuator on my turbo to help with holding boost. It's now set to a minimum of around 10psi or so, and maximum of 25+ (at a guess). It's got a thread on it so I can loosen it off as much as I want, but I set it to around 10psi to minimise the work that EBC has to do (set to 14psi).

The standard actuator is only rated to around 8psi I think. You should be able to get up to 12 or 14 out of it normally, but being as old as they are they tend to weaken with age. You could try throwing a bed spring on if you want to do it cheaply.

[Emre]

Restriction on the exhaust side is the main culprit.

Since you are using the standart-hybrid turbo, i'd say the exhaust housing is too small for the exhaust gasses generated at high boost and rpm.

The wastegate actuator could cause that as well, but since it's an HKS item, it generally means that it has a stiffer spring in place. If it's an adjustable item, play around with it.

[BOOSTD]

JimX: Bed spring sounds like a good test =)

Emre: My exhaust housing has a .81 A/R and 52mm outlet which is in no way restrictive. I have the standad actuator btw.

[Emre]

Fair enough, your first sentence led me to believe you have a very close to standart hybrid in place.

For WIW, i have the 1 bar HKS actuators in place and they don't budge open before it reaches 1 bar.

[Cubes]

I've always had a boost drop problem where if the EBC is set to manual mode it will drop boost. BUT on cold nights it may drop only 1psi where as on a normal day it will drop boost to around 12-13psi from be it 14psi, 15 psi or 16psi it doesn't matter it will still drop to the 12-13psi range.

I have fitted a VG30 BB Turbo that had what looked like a massive fat exhaust a/r compared to the RB20's standard turbo.

It made full boost around 4100rpm and still lost boost up top.

I tried both the VG30 actuator and the RB20 actuator which is really tight. With the RB20 Actuator you really have to put some weight behind it to pull it out. RB20's actuator is also a lot stronger than the RB25's actuator.

So yer.. I was stumped.. Still lost boost and the turbo was large.

Slapped the standard RB20 turbo back on as the car felt slower with the larger turbo on the street due to lag + the rb20 has no torque what so ever so it was horrible to drive. Worse than a 1.5ltr Pulsar.

[Emre]

The restriction can be any where in the exhaust, in the form of stock manifold, dump or a clogged up catalytic converter.

I used to have it quite severe with the stock turbos and having a little boost spike made the problem look worse. If set at 16 psi, my boost level used to peak at 18 psi and drop down to 14 psi up the top end. It never bothered me a great deal though, as i had a fat mid-range where the shaft speeds weren't a concern and ran friendlier boost levels near the redline.

Currently i have the 2530's in place with the HKS dumps and actuators and seems to hold the boost better. Still have a slight boost drop up the top, but this time i think it's being caused by the restriction on the intake, in the way of the stock cooler.

[Cubes]

Boostd.. Are you running an EBC?

I've got a Blitz SBC-ID which has two modes. Auto and Manual.

Auto mode learns the boost curve and in turn some how allows you to hold boost up top. BUT boost response isn't as crisp compared to manual mode as manual mode is a % of maximum boost. Manual mode flicks straight 15psi even on light throttle where as auto mode needs more acceleration and more time in the gear to hit the defined set boost level.

In turn Auto mode is pretty useless in first gear as most of the time you will only ever hit 13psi. Second gear is a little better and it hits 14.6psi as you go to click third. Third will flick straight to 15psi and hold it firm right to the rev cut of 7500rpm.

Fitting the EBC and setting it up in auto mode gained me around 14rwkw extra over the bleeder setup and or EBC mode in manual mode. BUT that being said the EBC in manual mode or the bleeder felt quicker accelerating away from a set of traffic lights and part throttle acceleration. Honestly when I fitted the ebc I was dissapointed as I expected an increase in boost response over the ebc. Was I wrong. The car felt a little slower and not as crisp. Even with the EBC in manual mode it didn't feel as crisp as the bleeder, but pretty close. Then again the bleeder was spiking to 17psi where as the ebc was on only 15psi. Strange thing is my boost guage never picked up the spike it was only when I had the ebc's handcontroller connected with the bleeder still operational did i notice it as the ebc has a peak hold function with its graphs etc.. If i were to do it again I would probably go the Apexi AVCR as i'm not totally happy with the blitz. I.e going up a hill and I decide to accelerate in fourth with rev's around 3000rpm boost will spike to 17psi and some times hit fuel cut.. So I use Manual mode as it will not spike.

[BOOSTD]

-Joel- yes i have a HKS EVC 3. has a auto setup function which maps the boost curve at stock boost. No sure but some have fuzzy logic 2. This obviously doesn't help my problem because it only happens at high boost. I think if i install a bleed valve and adjust to 15psi and then let my EBC learn the high boost curve it might help if it is a boost control problem.

Emre. I still have the stock exhuast manifold. It has been ported, but I don't think it would flow much more.

[Cubes]

Have you tried a RB20DET wastegate actuator?

It is a hell of a lot stiffer than the RB25/VG30 actuators that you can simply move by hand. The RB20 actuator is pretty hard to move unless you have a really good grip on it.

[BOOSTD]

I'll go to JMS tonight and have a look =)

[Cubes]

Clutching at straws, but it may help alleviate it.