his setup is doing that now.
I don't think a larger gate will help down below either, but he has to try something.

 

Rather than have them independent of each other what if you made them sequential? Have the one on the hot side be the primary one and only when that one is fully opened have the one on the cold side start regulating boost?

 

has anyone thought that the real issue is in the description. The is a compound system, the turbo is compressing the air, in effect causing the blower to see more air than it would without the turbo in front of it. I am not 100% sure on how to fix the issue, possibly lower the turbo boost? Smaller turbo? Dunno

 

Here is where huge amounts of money can be spend on R&Ding stuff.
I think a 1lb or 0 lb pulley, and 5psi turbo set up and see if you can controll it to 15psi,.
Compound has a built in glitch that I think will be hard to over come. The more air the blower sees the more exhaust flow/speed of that exhaust. Spining the turbo faster. so you vent more how much that going to be the hang up and need to have a HUGE hole to slow the turbo wheel down.. Sooner or later one air supply must be taken out of the loop.
I think a 2.5inch cutout on the exhaust would open the exhuast up enough to slow it down but not sure.
The turbo needs alot of flow to get the wheel up to speed, but not near that much to keep it spinning. And the blower sucking air is making the wheel spin easier, so now it will take even less exhaust flow to keep it spinning.
The chicken or the egg, we fishing yet.
I am sure Kyle will figure it out, once he gets the other gate hooked up and sees if that helps kill the exhaust flow.

 

No, I mean over speed as in turbo fins "transform" in to miniature flat missiles and attack their most hated enemy... the housing.....

 

Thanks for the input guys, but I really believe the problem right now really lies in the LARGE turbine side this turbo has. I didn't have near the boost creep problem with the small P-trim turbo I had on this thing the first go around, it's only been with the new turbo with a much bigger 96mm, 1.36 a/r exhaust turbine. I think the problem is that with it having so much size and flow though it, it has a ton of power to turn the relatively small compressor wheel easily.

It takes a little while for it to get up to speed, but once it does, it doesn't take much to really work it hard and the back pressure isn't very high pre-turbo, so the WG just isn't able to bleed off the excess flow with such low back pressure. After all this turbo was designed for a large diesel and doesn't even begin to work well till about 25psi I think the second WG will do the trick, but don't have time to put it on yet. A week or two and I will get it fix, I'm sure.

 

Why did you switch to bigger turbo?

 

Because the the small exhaust of the MP T76 was chocking the crap out of the blower. The S475 is about the same size compressor (76mm vs 75mm), it just has a MUCH larger exhaust turbine and housing. I thought I would gain a lot with a much free-yer flowing exhaust. I think It will, just got to get the boost level controllable with the WG so I can start tuning on it it and dialing it in. I'm driving it all the time right now, just have to watch the boost gauge once I get into second, and back off the gas when it nears 15psi or so,

 

You just need 2 bigger wastegates vented to the atmosphere.We've run that turbo at 8psi before and at 12-14psi made around 800rwhp.

Also on compound boost app's the blower needs to be pulleys down -lower boost- to make it more efficient.

For the Cobra we did.It hit over 1k hp but was tuned down to 800hp for the street.Been 3-4 years and the car is still on the road on the stock motor.

 

On a compound setup would it have not been easier to have the supercharger feed the turbo? Since the supercharger is limited to the engine RPM and the turbo's only limit is air flow. Wouldn't that have been easier to work into a compund setup