Stock 4th gen 4.8 and 862 heads. Just a tick stage 2 ls1 turbo cam. And truck intake. It has a borg Warner turbo. That we got from someone with nopaper work but was told it is a 76 75. 76mm comp and 75 turbine. 1.10 ar t6 divided inlet. 60 mm Watergate. Running holley efi. Once we got to around 20 psi we barely can get it to go higher. 22 psi on the dome made around 19 20 psi. And 30.5 psi on the dome only made 22.5 to 23ish psi waste gate has a 7oai spring init. Made 750 hp at 22 psi and 15.5 degrees on e85. We expected a little more at that boost level. We didn't want to go higher on timing but may need a little more.. But I've seen people running s475 well passed 22 psi which doesn't seem they are having issues doing. Should this turbo be running out of steam or do I have a problem. Wastegate etc. Main problem is we wanted to get to 25 psi but couldnt.

 

No expert here, but a 60mm wastegate might be a tad much. No matter what spring you run that is a lot of area for pressure to blow open.

 

I have seen the china intercoolers become a restriction at higher levels

 

 

What do the data logs show?

 

Not busting anyone's chops, but this seems like another situation a few datalogged sensors would let you know where you're at. An inexpensive couple pressure transducers and measure back pressure and pre-intercooler pressure. That's what is so nice about the ease with which our EFI systems collect data. Good luck with your ride!

 

Yea we are in the process of adding some more pressure sensor to get some exhaust pressure reading and intercooler readings. It was also 50 to 60 degrees ambient air and intake charge at the throttle body was around 85 to 90 degrees. Has a nice treadstone intercooler. Yea we were already considering doing two small wastegates instead of one big one. The exhaust side is realy setup bad. We didnt know and have learned since we had the hotside built. 2.5 inch crossover way to much. Then into a 3 inch single pipe which would seem to dilute the air even more making it move slow Into a divided turbine housing t6 so huge t6 inlet with a big pipe feeding it and the divided part of the housing im sure is creating some crazy turbulence. Should of been 2 to 2.25 inch cross over never merged and kept seperate into the housing with two waste gates. But Then to 1.10 ar with the 75. So this car has to small a turbine exducer and to big everything else. This car is laggy building boost at the line and on the street. But seems to be maxing the 75mm turbine exducer out. So uptop it has alot of pressure. Bad pressure balance accross motor. Plus huge waste gate thats easily cracked open due to surface area. I feel like just redoing the hot side and maybe sending turbo off to get a more match turbine setup will do alot for this setup. But the car is getting a forged 6.0 soon so we will see then what we do or change. I just wanted to see if other people were thinking the same and from what yall already said yall were thinking the same as I was. Too big of a wasye gate. To small turbine setup have no idea why they built it so small with such a huge t6 divided inlet. Any more thoughts or advice on hot side or ways to improve this please tell. I love to learn from others experience and etc. on the dyno pull it didn't even build boost to 5300 rpm fyi

 

we aren't logging any exhaust pressure or anything. Just regular iat and at the intake. Which were around 90 degrees and about 60 degree ambient I believe I can't remember exactly. I will put more detail when we get back to the computer with the logs. But we def need to start logging more stuff to get a bigger picture of whats going on. But from what i can see it laggy foesnt build boost till around 5300. And we are having trouble making more than 22psi and I maxed the dome pressure out to 31.2 since we only had a 3 bar dome pressure sensor. So back pressure seems to be a issue after motor stsrt making power and having more exhaust it must be building lots of exhaust pressure and we can't keep that 60mm waste gate shut. Ill get back asap as soon as we can get more detailed info and a bigger picture. But from the looks of it theres probably alot of cars that could be making more power much essier just properly setting up the turbo setup.

 

i have never seen a 7675 with a 1.10 ar t6 flange, is that right?

 

 

The 83mm Borg warner turbine is actually measured by the inducer. The exducer is 75mm.
The 83mm wheel should never be used in the T6 housing. It leaves too much dead space in the housing.


I made 42 PSI on my S475/87 1.10 T4 on a 5.3 when my gate failed.
Change your wastegate spring to help fight against backpressure. It can help you rule out the wastegate as the source of the issue.

 

no way you have a 75mm turbine on a t6 turbo.
you need a stiffer spring.
you need more timing than that at that boost level.

have fun

 

thats what I was told. By the dude i bought it from. Also I've never measures it or removed it to see the part number on the turbine wheel. But yea I never could find it but he said it s 76 mm with a 75 turbine thats all I got. He said it was close to 1100 dollars when he got it. I'm wanting to take it off and take the turbine housing off to measure it.

 

I mentioned s475 as in other have used them only thing I can see thats comparable and they had no problem going much higher in boost. But im kinda wondering what it realy is now I wanna measure it.

 

post up some pics we can help you id it.

 

I haven't wanted to put a bigger spring in since I have it being controlled by dome pressure through holley. It shouldn't need a strong spring the air pressure is keeping shut plus the spring pressure. I know people running very small springs and rely on some pressure alone almost. But also thats doesn't mean it's correct and they may have less exhaust pressure. Also I've seen two lost where they say the measurement is taken at the inducer but I've read a borg Warner spec sheet that specifically stated 83mm at the exducer. So I'm confused what to believe now

 

I ran a precision 66 on my 5.3 and it worked perfectly, boost was on a rope! But I also never ran a lightweight spring, never had any reason to run less then 15 psi.

Agree, check the plugs and get on the keyboard! I also don't think he mentioned what he's spinning it to, but he may be cutting it short for peak power with a 23x cam in a 4.8L.