Not Holding Boost! Hks 2835 Pro S .87 A/r

[AngryRB]

I'll have a stab at this, its because the engine is outflowing the turbine and plus when there's no mufflers,cats etc the exhaust is sucking the flap open , like a venturi effect once things get hecktic in the mid to top end.  Bit with a boost controller and loading up the gate it helps close it for longer.. 

[hypergear]

During this this two years I've had two of those 2835 Pro-S in for repair, and they all appears to have an boost tapering problem.  One particular customer did manage to get it hold 20psi without boost tapper, and that is by overloading the actuator given 3mms of waste gating.  We did larger trimmed compressor wheel, as well as doing billet 76mm Garrett GTX comp wheel, it did not change that behaviour.

I found the boost tapper behaviour is common with internally gated Garrett GT30 turbines. I suspect it is due to the crop in the rear exducer blades. After replacing the exhaust wheel with one of our SAT models, the boost pressure held dead flat at 20psi with minimum actuator preload.

This is a pretty good example in earlier SAT developments. Replacing an GT30 turbine wheel with a older G3SAT turbine wheel nothing else's changed.:

 

[LaurelPWR]

This turbo I have is still different and much worse than anything else...
It didn't even hold 12psi of boost to 6500rpm and then dropping off sharply to 0psi... I've never seen a turbo do that

[hypergear]

never seen any turbos do that before. I assume its got a 4 inches metal induction pipe or something similar?

[AngryRB]

Is it possible the blow off valve in that position could cause the issue? 

[LaurelPWR]

never seen any turbos do that before. I assume its got a 4 inches metal induction pipe or something similar?

Yes it has a 4inch intake I the the z32 afm

[LaurelPWR]

Is it possible the blow off valve in that position could cause the issue? 

I've also wondered about that a fair bit but when I do my regular boost leak tests, I put 10-20psi more than my max boost through the system and nothing leaks...

BUT!!!
the problem now is not the boost drop, it's OVERBOOST Hahahahah seeing 30+psi in 2nd and 3rd gear midway through the rev range is just not making any sense and if I don't lift off throttle it would keep going .... Wtf my dudes

[LaurelPWR]

Basics tell us- If a turbo car is going to over boost, it will do it in higher gears as there's more load on the engine thus more concentrated/energetic exhaust charge to push the turbine....
Stumped as to why my car only make target boost in 4th but free boosts in 1st, 2nd & 3rd now

[nick_33]

Would it be worth taking off the actuator and seeing if you can open/close the wastegate freely?

It could be possible that since the initial problem the dump pipe may have moved and is stopping the wastegate from opening. For all you know it's possible it made no boost because it was stuck open.

Split dump pipes have the tendency to do this, I also had boost control issues with my split dump pipe. There are also many stories of the wastegate not fully opening causing overboosting.

[LaurelPWR]

Would it be worth taking off the actuator and seeing if you can open/close the wastegate freely?

It could be possible that since the initial problem the dump pipe may have moved and is stopping the wastegate from opening. For all you know it's possible it made no boost because it was stuck open.

Split dump pipes have the tendency to do this, I also had boost control issues with my split dump pipe. There are also many stories of the wastegate not fully opening causing overboosting.

We did in fact test the opening/closing of the flapper multiple times in the first weeks when it wasn't making boost and it was a-ok. There's no physical way the dump can move and the special 2835proS split dumps are a work of art with the way they are welded all the way to the flange etc.

[LaurelPWR]

While I was on the highway of said night that i noticed the "free boosting", I heard a "rattle & ting" type noise come from the engine bay around the turbo/dump area and from what I could hear over the loud highway driving noise it went nearly all the way to the back of the car...it sounded like a 10mm nut or something falling from the bay and flicking up under the car BUT I'm beginning to wonder if there was a restriction of some sort inside the exhaust and it's somehow cleared itself and flew out the back whilst cruising the m1 that night hahha

 

[CEF33Y]

Have you ever run without the boost controller connected? (just straight hose from cooler pipe to wastegate)

Reckon the boost controller could be playing up?

 

Surely nothing mechanical would make the boost go from tapering off at high rpm to overboosting, without noticing something major with the way it runs.

[LaurelPWR]

Have you ever run without the boost controller connected? (just straight hose from cooler pipe to wastegate)
Reckon the boost controller could be playing up?
 
Surely nothing mechanical would make the boost go from tapering off at high rpm to overboosting, without noticing something major with the way it runs.

Hey man yeah we did right at the beginning but I have not tried it now that its over boosting ... Will give it a whirl this weekend [emoji1362]

[chiksluvit]

While I was on the highway of said night that i noticed the "free boosting", I heard a "rattle & ting" type noise come from the engine bay around the turbo/dump area and from what I could hear over the loud highway driving noise it went nearly all the way to the back of the car...it sounded like a 10mm nut or something falling from the bay and flicking up under the car BUT I'm beginning to wonder if there was a restriction of some sort inside the exhaust and it's somehow cleared itself and flew out the back whilst cruising the m1 that night hahha
 

The rattle and ting could be your engine pinging due to overboost, but not related to the reason why it overboosted

[LaurelPWR]

The rattle and ting could be your engine pinging due to overboost, but not related to the reason why it overboosted

Haha nah dude.... Like I said, I was cruising when I heard the noise and it sounded like a small rock or 10mm socket tinging up under the car....

[chiksluvit]

lol sorry didn't see that bit, just visited the thread after a few rounds of drinks
Curious to know why too so Ive also been following this thread

[LaurelPWR]

So I ran the turbo off the actuator yesterday and it struggled to make 20-22psi (has 22psi springs in it)
So may be safe to say my boost control is playing up [emoji848]

[LaurelPWR]

One thing I don't think I've mentioned is that I had to rotate the housings and customise the actuator bracket before fitting the turbo...
Maybe one the housings isn't seating exactly perfectly...??
Or maybe the actuator isn't happy with its position in relation to the gate flapper..?

[89CAL]

One thing I don't think I've mentioned is that I had to rotate the housings and customise the actuator bracket before fitting the turbo...
Maybe one the housings isn't seating exactly perfectly...??
Or maybe the actuator isn't happy with its position in relation to the gate flapper..?

More detail?

[LaurelPWR]

More detail?

I'm not sure what else there is to say dude...
The turbo was a new HKS 2835 Pro S internally gated with an .87 a/r rear.
It's not a model specific kit for an rb or Jz or anything... Just a "universal" or "off he shelf" HKS turbo.
So I had to rotate the housings before fitting it. After rotating the housings the actuator didn't line up with the bracket so I re-drilled the holes and re mounted it where it needed to be to line up twitch the flapper linkage.
These are the only pics I can find of the turbo off the car. The first two (black background) are before any modification or rotating. The. There's a pic of the actuator after I re drilled it and then last two of ofer it was re mounted and housing rotated.