we had my car on the dyno and running off the wastegate the car was making 8psi but once installing the manual controller it will not go any higher in boost quick run down on the setup 331 (9.6:1) 210cc heads with precision PT70 turbo .81 AR, built TH400 4k stall,precision 46mm W/G and Tial 50mm BOV, the car spools very quick and maintains boost fine no spikes like you would think if you had a large boost leak, now the wastegate is springed for 13.5 and when on the dyno its wide open dumping exhaust wouldnt this be closed if the turbo was running out of gas with only 8psi ive checked the car up and down for leaks and have not found anything major that i havent already corrected, once i finish some suspension work im gonna try to make a run without the wastegate vacuum line hooked up to see if it will build more boost but precision and a local turbo shop is telling me the turbos to small for the setup and to go 76 or 88mm because they think 8psi is all the turbo will make with my setup now ive seen 70mm turbos on 331 making way more then 8psi and then the guys at the tunning shop are blaming it on a leak so im trying to figure the best way to find the problem without shot gunning a 2000$ turbo at the car. i bought the turbo from a shop who changed the wheel to an S trim wheel i believe but only used it for tuning on a dyno then went larger for high boost so im wondering if they changed somethings that hurting the turbo?

 

If the wastegate is open at 8.5 psi on the dyno and you have 13.5psi springs in it your gate isn't working right. That turbo is a little small but the gate shouldn't open up until it meets the spring pressure. You have the gate referenced right? and to what?

 

look up this guys build ( 4Jenna ) hes got a combo close to yours and he was running 15 psi

 

the springs are small medium large groves in the precision wastegate straight from precision but the wastegate when it was mounted is on a seperate pipe off the t4 flange collector area not in the cross over pipe like it should be i need to relocate it like precision recomends a 45 off the cross over pipe..if i pull the vacuum line off the gate it shouldnt matter spring tention right because it will take the wastegate out of the loop.

 

You didn't list cam and intake but I'm assuming if you have 210cc heads and a 4k stall that you rev that 331 pretty high. This says to me that the turbo is too small. A .81 T4 of any kind is pretty small. How much power do you think your engine makes N/A?

If you disconnect all lines from the wastegate and it is still opening it is because the backpressure is so high it is acting on the 46mm gate surface area to push it open.

 

The cams a comp cam 600/610 Lift 112 lobe separation I spin it to 6500 nothing majorly high running a Holley systemax intake manifold, so I either need to mount a camera to watch the wastegate to see if it's opening still after pulling the line off the wastegate or put it back on the dyno to test,

 

I'd say your engine makes at least 410Hp. This is too much for a .81 housing. You need the .96. Your oversized wastegate is hurting you also. A 38mm gate would get pushed open a little later due to the fact that the backpressure is acting on a smaller surface.

The compressor is too small for 13.5psi also. That would be around 800Hp. Changing to a T76 with a .96 would be best.

 

I'd bet you're just pushing the gate open with exhaust backpressure. Probably fairly restrictive with a .81 T4 exhaust. Also, I ran one of my ebay GT45's by itself a couple times and it (with about a 70mm compressor) was capable of 10psi on my 406.

 

i was thinking that back pressure might be an issue when i bought the turbo but now that you say something about pushing the gate open i realized this weekend while driving the car the wastegate flutters even when its not making boost if im on it half throttle and back out you will here it flutter and im not sure if thats normal why would it be opening without boost.