i think its the a/r size, stall speed, and gear

 

do you have the wastegate referenced at the turbo or did you say somewhere else? Sorry finals kicked my *** today so reading isn't my strong point right now

 

What size charge piping are you running?

 

N20 is your friend for your rear mount turbo setup like MY99TAWS6 suggested. very common for the import crowd.

or

add a supercharger to the mix .

or

swap in a BBC 540"++ and call it a day.

 

I would say its the combo of the large 3" exhaust leading to the turbo, 1.06 AR, and T6 flange all working against you big time! Simply not enough exhaust velocity to get that turbine moving, thats why when you pulled the vac line to the WG, you're still left with 5psi. If you look at anyone's cross over pipes on a front mounted turbo setup they are 2"-2 1/4" Look at it like blowing air through a straw with your mouth, vs a foot long piece of garden hose. The straw's air stream will for sure have more velocity.
I would recommend doing 2.25-2.5" exhaust from the Y to the turbo first, then get a smaller AR for the hotside on a t4.

 

It is plumbed back to the intake manifold.

 

2.5" from turbo to the intercooler, then " to the TB.

 

I went turb to get away from the no2 I had. My thinking is if I was going to juice the turbo, I would save myself the headace and just run a 300 or 400 shot. No juicing it is a way to mask over the problem in my mind.

My next build will be a 440+ LSX.

 

I went with the 3" for the expected 1000+crankhp I am trying to make. It would be easy to change the housing first.

I am going to messure the exhaust back pressure first then decide if I can tolorate a smaller AR. I am realy thinking of going to a tangent housing and a turbo valve. I am thinking this is the best thing to do, but I might lower the turbine housing ar a little to if I am not making much back pressure.

 

That 88mm seems to be common turbo for the mustang guys and they usually have less cid, I would look into what ther variables are with your turbo compared to what they run. I'm guessing but I wouldn't be surprised if the T6 mount and the A/R like mentioned earlier just aren't giving you the velocity.

What your experienceing sounds similiar to a problem I had many years ago on a 1.8 Miata. GT2540 bb turbo (good for 450rwhp) wouldn't build boost with a .86 exhaust, installed a .68 and it was like I was running a totally different turbo, built boost easily in any gear.

 

yeah, im running a t6 85mm with 2 1/2" hot piping on 383ci. but my a/r is .96 and i had the opposite problem you are having. i couldnt stop over boost! i ended up adding a second wastegate

 

I am pretty sure the large AR housing is the problem. I am going to do a few checks before I change it out though. I am going to pull the air filter off and see what happens. I have the largest KN filter I could buy that would fit right on the turbo inlet. But when I do go on boost that thing is screaming. It sounds like a massive air leak but I had already pressurized the system and looked for leaks, and when I was on the dyno, the dyno operator went around the car loking for leaks and the source of the noise and he said it was coming from the air filter. His dyno is in a pit with ramps to it so you can walk around the dyno and under the car. Pretty cool the way he has it set up and it makes it easy to tie it all down. Any ways, should you be able to hear the air going into the air filter that loud? i can here it while in the car on an open street with the widows down or up. It sounds like the blow off valve does when it opens, but not a momentary blow but a constant blowing sound while under boost like a very bad leak. Like I said I fixed all the leaks and we looked for the source of the noise while o the dyno and verified I had no leaks, and the sound is from the air going threw the air filter.

I am going to remove it and see what happens. Even if that fixes the low boost problem I am still going to temparaily install two pressure transducers, one in the cold air piping right at the discharge of the turbo and one somewere in the exhaust piping, not sure were yet. That way I can wire them up to my HP Tuners and record the pressure threw a full run. Once I have that data I will know if I can go to a lower AR housing or if I need to get a tangent housing with the same AR and use one of those turbo valve flanges. The housings should be about the same price but the turbo valve and its controls are not cheap. I would like to take care of this with as little money as possible. I realy like the idea of the turbo valve, it should make the car build boost real fast and it should make it a monster ride even on the street.

 

You have compressor surge. It's not a leak. Be careful or you will blow up your turbo. It may be the t-6 housing. It may be be another part of the turbo ( comp wheel to big etc). Whatever it is your turbo is unbalanced for your setup and is definitely surging. I know how you feel. I'm going through the same damn thing. Finding out why it's doing it is trial and error. It may or may not be as simple as switching to a t4 housing.

 

I played the video clip you sent me to. It sounds just like that. So from what I understand about turbo surge looking at Garretts maps and reading their web sight, there is not enough exhaust flow threw the turbine section to keep the compressor spooled, or another way to put it is the turbine can is not making enough power to turn the compressor because of the low exhaust velocity. The compressor wants to stop due to the load.

So the culprit to this is the turbine housing is sized too large for this setup. So I need to get a smaller turbine housing to correct this problem. I think I am going to get a tangent housing this time just in case I decide to do the turbo valve thing. So with this in mind, what size housing should I get for it?

 

or move the turbo up front

 

no can do.

 

pretty hard to believe a t6 88mm turbo would surge on an 408 cu in engine.

Reducing stall size will cause more lag.

 

Do you think going to a smaller ar turbine housing will get rid of the low boost issue? Or maybe the turbo valving and housing like you did will fix it? I hear turbo surge all the time on our Industrial emgines at work and the noise is not like that, it is a steady blowing sound coming from the air cleaner that sounds like a leak.

 

Either your T6 housing is to big or your turbine is to big. Or both. Your compressor is pumping a higher volume of air than the engine can accept at that given rpm. Whatever rpm 5psi comes on at. I went up 2 turbine sizes and 1 A/R size and now i'm surging. When the wheel and backside were smaller everything was cool. What size turbine wheel are you running? A smaller turbine would be good. But you'll have to get the turbo rebalanced etc. A T4 housing would be easier. Does anyone know how much more air a T6 will flow compared to a T4 of the same A/R? Ask around to find someone with a similar turbo/motor setup to yours. Your turbine wheel may be to big. Some times a smaller turbine and housing are good. You may need a little more back pressure. For some reason your current setup is to efficient down low and flowing to much air.

If you was on the dyno and at 5psi continued to keep reving while surging two things would happen. At some rpm eventually it will clear up. The other is you would be putting a lot of strain on the turbine shaft and the compressor hurting the turbo. Eventually it will blow up. If you spray on the stall and a little bit after the launch that will get you up to the higher rpms faster where it may clear the surge.

 

Did you pressurize your piping trough the turbo inlet? I've seen where the turbo housing itself will sometimes leak.

I think you are fighting an unknown leak vs anything else. That turbo should spool on your setup. I'm able to spool an 80mm 1.25 a/r 87mm turbine without using the quickspool valve just fine. It's a T4 setup though but I would think they would be similar depending on turbine size. What size is your turbine anyways?