Overboosting (not Stock )

[Packy]

Ok a quick but technical question for you guys out there that do know something about skylines.

Has any of you had a problem with overboosting on an external gated RB25??? The reason i ask is because it is the problem I'm having right now.

Mods are as listed:-

GT35/40R turbo

custom manifold

tial 38mm wastegate

plazmamann inlet manifold

550cc injectors

040 fuel pump

wolf 3d V4+ ecu

hybrid intercooler (genuine)

2.5inch intercooler piping

Now i'm wondering if anyone has had this problem with the engine/turbo wanting to keep making boost. The tial gate is spose to have a 1bar spring in it. You can hear it opening (screamer pipe) though the boost isn't dropping or flattening out. Do i need a bigger wastegate, as in 48mm or new manifold or what??? As with no boost controller (straight off the wastegate spring) we were getting 1.2bar at 4500rpm with only 68percent throttle. Haven't had it at 100percent throttle yet, as the engine hasn't been built for anything above 1.2bar.

Anyone have any sensible suggestions???????

[saliya]

Ok a quick but technical question for you guys out there that do know something about skylines.

Now i'm wondering if anyone has had this problem with the engine/turbo wanting to keep making boost. The tial gate is spose to have a 1bar spring in it. You can hear it opening (screamer pipe) though the boost isn't dropping or flattening out. Do i need a bigger wastegate, as in 48mm or new manifold or what??? As with no boost controller (straight off the wastegate spring) we were getting 1.2bar at 4500rpm with only 68percent throttle. Haven't had it at 100percent throttle yet, as the engine hasn't been built for anything above 1.2bar.

Anyone have any sensible suggestions???????

If the gate is opening, but it's not restricting boost, it's not letting enough gas out. This could be from a number of common reasons:

* pressure signal isn't in the right place

For most external gates you need to supply the pressure signal at the middle (not top) fitting. Disconnect anything

you have going to the top and try with the middle only.

* pressure signal isn't getting to gate

Tee a gauge into the line and check that there's pressure when the manifold is seeing pressure.

* gate spring isn't what you think it is

Using a hand-pump and gauge, supply pressure to the fitting. Make sure the gate opens at the right pressure.

* gate isn't big enough

Try removing the gate and bolting the screamer pipe on directly to where the gate goes. This is almost equivalent

to having the gate open all the time. If you still can't hold boost down, the wastegate piping isn't big enough

(highly unlikely, but possible). If you _can_ hold boost down, either the gate is too small or it is faulty.

* gate is faulty

Maybe the gate isn't opening fully? Check that it opens fully when you test it with the hand pump.

* manifold gauge is wrong

Check that the boost you're seeing is in fact what is there by using a known-good gauge.

Regards,

Saliya

[Packy]

pressure signal is in the right place...same as you say.

I will be taking the gate off and checking with a hand pump.

There is no restriction/problems with the line to the wastegate.

We had the dyno psi gauge, the avcr pressure gauge and the wolf pressure gauge all reading 18psi.

But yeah, I was going to pull the wastegate off and check the spring tension anyway. I'm just hoping its big enough and the manifold doesn't need to be modified.

Thanks for the help Saliya.

[T04GTR]

the manifold is the issue.

you need a bigger wastegate.it simply cant flow enough air.

a simple test is to drive it with the gate removed or no spring in it. if it makes any boost then its 100%the gates to small.

i had the sam problem. till my garrett 42mm had a date with the die drinder hehe

[phee]

Yes. My external wastegate diaphgram had a hole in it so it wasn't releasing pressure, has cost 9k in damage and counting.

[Packy]

yeah might leave the wastegate off, after i pull it off to check the spring.

Phee....not good, did it happen on the dyno??

[phee]

No, happened on the way home from my b'day dinner back in May

[R31Nismoid]

http://www.skylinesaustralia.com/forums/in...=43638&st=0

[Packy]

phee...bugger

R31nismoid....hmmm i must have missed that when i did a search..sorry.....but helpful nonetheless !!!

thanks

Packy

[R31Nismoid]

Its in the sticky thread dude

You dont even need to search

[Packy]

haha ah well, i'm blind as well....

just took the gate off, damn its in a bad place

measured it, its a 35mm gate.....so maybe i should be buying a 38mm or 45mm.

[Packy]

Well found out why the wastegate was not bleeding off enough gas. The diaphram was folded over and therefor was not allowing the gate to open. Was a simple fix, we also put a 10psi spring in to help. Cost me $60 to get done/fixed from a performance workshop. Which was about an hours work for the guy.

[phee]

Well done. Wish I had found my problem as easy as that... oh well!!