<U>Situation</U>
Greddy Si Turbo Kit boost level at 6.5 psi without IC stock no Boost Controller
Greddy Si Turbo Kit boost level at 5.5 psi with IC stock no Boost Controller

<U>Discussions</U>
The wastegate spring in the internal wastegate is 6.5 psi. With the pressure drop from the Intercooler, you go from 6.5 to 5.5, understood. so the wastegate reads 5.5 psi from the Intake Manifold. The wastegate should not open and provide more pressure until 6.5 psi is reached.

The greddy should output 6.5 without an IC, but the turbo should output ~7.5psi with an IC, so once the pressure drop happens, it is becomes 6.5psi going into the Intake Manifold.

With Other turbo kits and custom turbo kits, the wastegate does not open until the psi in the intake manifold(or any point after the IC, pressure drop) matches or exceeds the spring rate, correct?

This happens to almost everybody i know of that has a Greddy Turbo kit with IC, and no Boost controller. I know that i can use a boost controller to raise the psi.
it doesn't make sense, and it seems that nobody else has questioned this before, from my research.

Thanks and please help me out
-deepsi


[Modified by DeepSi, 6:57 PM 10/15/2002]

 

from my understanding as it was explained to me in other forums was that to consider the flow of the pipes without the IC...5.5 psi. now consider the same flow with the IC in place...4.5psi. the IC slows down the flow to cool it thus causing an "obstruction" to the flow from the turbo to the intake manifold.

 

I'm a little confused as to exactly what you are getting at here. Are you confused why boost drops 1 psi after adding an IC? If so, that's just plain ol pressure drop that all ICs cause.

If you are asking why the WG isn't opening at 6.5psi anymore, which it's supposed to, it's because of where the boost reference is located on the stock Greddy kits (and most stock internal WG setups). The WG gets its reference from the compressor housing, which is before the IC. The 1psi pressure drop happens AFTER the IC, so the WG still sees 6.5psi not 5.5psi.

The way to remedy that is to move the WG boost reference do the charge piping after the IC or in the intake manifold. I know you mentioned the manifold in your post, but you were mentioning it like it's using that as a reference right out of the box (which it's not - you would have to move the reference from the housing to the manifold).

Now, if you are saying that when people move the WG reference from the comrpessor housing to the IM it STILL opens at 5.5psi and not 6.5psi then I have no clue why it would be doing that.

In either case I would put a MBC on it regardless, since they help the turbo spool faster anyways. So you can't go wrong IMO.

If I'm missing something, please feel free to correct me and elaborate.

- Slater

 

sorry if this is confusing, but i really dont know how to word it otherwise.
I understand that and understand the pressure drop caused by the Intercooler

The Greddy SOHC turbo kits uses the Compressor house for the vacuum source for the wastegate
the Greddy DOHC turbo kit uses a vacuum source from the back of the manifold for the wastegate.

exactly, that is my question/problem people just fix it by using a MBC/EBC, and i know it will fix it, but WHY IS IT DOING THAT?????

 

Ah, I got ya.

I was not aware the DOHC kits referenced boost from the mani - I was under the impression they referenced boost from the compressor housing like the SOHC kits.

Hmmm...I have no clue why it would not be opening corretly. 6.5psi is 6.5psi, regardless as to where it's being sourced from. If the WG is set to open @ 6.5 and it is reading a 6.5psi signal (from the manifold) there's no reason it shouldn't be opening until 6.5psi.

Just out of curiousity - did you remove the intake restrictor on your DOHC kit?

- Slater

 

The intake "restrictor" is only on the GSR versions, not the Si versions of the greddy kit. Yeah, the refernce boost for the GSR/Si kits come from the intake manifold, unlike the SOHC kits.

Anybody????

-deepsi

 

ttt

 

Well, if the boost source for the WG is on the manifold and not the compressor housing, then in theory, it should still only open at 6.5psi or whereever it is normally set. I have no idea why the WG would open sooner with an IC in place so long as it's still reading the same boost.

 

Atleast people understand my point now , sorry if it was unclear ealier, but now we need some answers

 

who has actually seen 6.5psi without the intercooler? my tial wastegate spring is rated to .3bar and without any boost control when I first hooked it up I could only see .2-.25bar max and thats reading pressure from the intake manifold. now, 10 months later, I can see .3bar. is it possible a wastegate spring takes time to break in?

 

the wg spring does take al ittle time to get worn in. The more you wear on it up and down the better it will react to what spring level itwas designed jusy my 2 cents.

I think when the spring is new it has the tendancy to give a little lower rating not much but little lower.

 

Yeah but the turbo kit i bought was used (2 months), and people still record the 5.5 psi. But that is a excellent reason, and i might be statisfied with that answer