As a Greddy owner I have read multiple posts on this phenomenon of Boost Creep. From what I have read most people experiencing creep see boost higher than the anticipated pressures at higher rpms. This almost always associated with aftermarket exhaust systems and test pipes. Now you would think that if you lowered the back pressure the larger differential across the wastegate would allow more flow and promote the gate opening faster. So the only thing I can figure out is that the turbo is running more CFM due to the free flowing exhaust and the wastegate cannot flow enough and the result is more exhaust through the turbine wheel than desired. So I have come up with three solutions, one is to make the wastegate flow more by porting, two is to dump the wastegate side of the turbo to atmosphere and three is to run more boost.

Now I am very interested in the second and third option. Has anyone installed a better splitter to isolate the wastegate and turbine streams in the downpipe along with an exhaust dump? How loud is it / would think it is? As far as more boost is concerned we will see if I can get around to pulling the head this winter.

 

My guess on it is that the stock downpipe sucks a$$. I'm working on a new 3" one.

 

Great minds...... I've blamed all the boost creep issues of the greddy kit on the integrated system as well for the same reasons. HOWEVER... I have no personal experience w/ it.

I've been suggesting atmosphere dumping of the WG pipe since day one for this kit.

Porting crossed my mind but in comparison to open atmosphere its not even close or worth considering. I doubt you'll ever get caught by letting it dump out in the open. Cut the pipe off yourself and have someone weld the hole on the DP where it used to connect. If you want to be ghetto you can use one of those clamps assuming its not on a bend and it'd work fine.

NOW.... as for sound, it'll be the exact same as stock UNTIL you open the waste gate when you really get on the throttle hard, in which case it'll be a pipe straight from the turbo to the air...quite loud. Mine is done this way and it's pretty loud but the turbo itself does a good job of making it quieter, a N/A car is always a LOT louder of course then my car w/ straight pipes. I don't think you'd mind the sound issues, the beauty is when you need to be quiet just don't go past 5psi or so and your fine, once you go past that you get a nice hp boost.

-Greg

 

3" for the greddy kit???? What is it stock? 2.5? Seems that 2.5 would be just fine for less then 400hp which is plenty enough of a high limit on that greddy kit.

I guess a bigger dp would solve some issues but for the simple fix wouldn't a open dump to the atmosphere be better?????

Thoughts kev?

-G

 

The Greddy doesn't have a separate dump and down pipe that join up later. The wastegate is integral to the turbo. The back of the turbo is the only place they are split and then they both feed into the same down pipe. Makes dumping to atmosphere much harder.

 

The Greddy kit actually has a separate dump and wastegate pipes but IMHO the whole hting is not designed well. The problem is obviously made worst when you try to put a high flow exhaust on top of a high flowed engine AND kept a so low boost.

The dump on the greddy s2k turbo kit has 2 problems. The waste gate pipe is not long enough and there isn't any divider plate on the dump to separate the wastegate and turbo exhaust outlets. For the skylines gtr a lot of poeple noticed that the wastegate pipe needs to be at least 40cm long to prevent turbulence between the 2 exhaust paths. Anything shorter than this had been demonstrated to affect spool up and top end in the rb26dett. For the f20c, with larger volume and better flow, 40cm may not be long enough.

If I have a greddy kit, I would modify the dump pipe. I would weld a divider plate in the dump, extend the waste gate pipe and either vent it to the atmosphere or plumb it back to the main dump pipe futher down.

 

hmmmmm this sounds like a good idea, I may do it

 

i might try venting to the atmosphere later on this winter or early spring.. trying to extract a litle more power out of the car before i decide on whether to upgrade my set up

 

vent to atmosphere FTW

 

Change the wastegage to 44mm