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Discussion Starter #1
I have been running an old Pt88 on my 370ci. On full boost which I believe is 22-23 psi, I have run 8.9 @ 153 at 3900# race weight. The turbo kit is the standard flipped truck manifolds with 2.5" merged into a T4 .96 A/R exh housing. I purchased a T6 1.00 exh housing for it. The current plan is to saw off the T4 flange, spread the merge and weld on the T6 flange.

The new T6 1.00 housing has a 5" flange (as opposed to the 4" on the T4 .96 housing) but I am using the same exh wheel. Currently the DP is mandrel bent 4" from the turbo all the way to the back. Now there will be a 5" 45* off the turbo (about 1.5-2 ft) then necking down to the 4" right before the 90* that goes thru the kmember and out the back.

What can I realistically expect to gain from this? Is it even worth the effort to cram in the new T6 housing since I am not changing the exhaust wheel? Will it help build more boost or just build it faster?

Here's what it looks like now.
 

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Its gonna gelp some but the wheel is still the ultimate restriction. Dont spread the merge out. Cut the old flange off and slide the T6 flange over it till it stops, weld it on there and then make some small fill plates if theres a gap. Let the merge extend into the inlet of the new housing. Theres not much difference in the A/r so there wont be alot of gain there but the T6 will gain some over the T4. if your still having backpressure issues after that.... Theres always clipping the wheel which works pretty well on that wheel. Ive done it before.
 

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A T6 housing has a ton of extra cross section at the flange. If you extend the merge pipe into the mouth of the housing you eliminate this extra area. A sudden increase in the area such as exit the merge into the housing can cause turbulence and a loss of velocity. Extending the pipe past the flange into the housing till it touches will keep the velocity higher right up to the scroll entrance. This works especially well on smaller ci engines with big T6 stuff. Look at what Tial did with tje Vband exhaust housings. This does the same thing.

Clipping a wheel is where they cut back the tips of the turbine blabes so the wheel can flow more exhaust. Its measured in degrees off the center of the shaft. Usually a 5 or 10 degree clip. Its an old school trick but it works.
 

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Discussion Starter #5
A T6 housing has a ton of extra cross section at the flange. If you extend the merge pipe into the mouth of the housing you eliminate this extra area. A sudden increase in the area such as exit the merge into the housing can cause turbulence and a loss of velocity. Extending the pipe past the flange into the housing till it touches will keep the velocity higher right up to the scroll entrance. This works especially well on smaller ci engines with big T6 stuff. Look at what Tial did with tje Vband exhaust housings. This does the same thing.

Clipping a wheel is where they cut back the tips of the turbine blabes so the wheel can flow more exhaust. Its measured in degrees off the center of the shaft. Usually a 5 or 10 degree clip. Its an old school trick but it works.
That ton of extra cross section is why I bought the bigger housing. Extending the pipe to the scroll seems like I'd be right back to where I am now with the T4, no?

That clipping thing sounds good though.
 

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No you bought the bigger housing for the bigger cross section at the scroll entrance. Thats where you needed more area. A T4 housing that was 1.25 or 1.44 would have done the same thing, increased the area at what i call the nozzle point. The flange area of the T4 isnt whats choking that turbo nor is it the scroll entrance really. Its the wheel itself anyway.
 

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I have been running an old Pt88 on my 370ci. On full boost which I believe is 22-23 psi, I have run 8.9 @ 153 at 3900# race weight. The turbo kit is the standard flipped truck manifolds with 2.5" merged into a T4 .96 A/R exh housing. I purchased a T6 1.00 exh housing for it. The current plan is to saw off the T4 flange, spread the merge and weld on the T6 flange.

The new T6 1.00 housing has a 5" flange (as opposed to the 4" on the T4 .96 housing) but I am using the same exh wheel. Currently the DP is mandrel bent 4" from the turbo all the way to the back. Now there will be a 5" 45* off the turbo (about 1.5-2 ft) then necking down to the 4" right before the 90* that goes thru the kmember and out the back.

What can I realistically expect to gain from this? Is it even worth the effort to cram in the new T6 housing since I am not changing the exhaust wheel? Will it help build more boost or just build it faster?

Here's what it looks like now.
I would go with your original plan with the T6. You will see a pretty decent gain from this upgrade. Yes your still working with the same turbine but that turbine can support close to 1500hp. We have a local gut that did the same change (except with a sbf) and went form running 9.0's to 8.7's because of his backpressure issue we then did a compressor wheel upgrade and now he's running 8.teen's. There is a quite a difference from going to the T6 .96 over the T4 .96. Trust me its worth it. Also go with 4" right of the turbo no need for the 5".
 

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Discussion Starter #8
Could I achieve the same gains by going to a larger AR T4 and larger turbine wheel? I didn't realize how large this T6 housing was. I have very limited space as seen here.

Here is how much space I have behind the exh housing with the cover on it.



I have less space in front.

The T6 housing is slightly larger than the T4 with the cover. No way that I will be able to cover the T6 without moving the radiator further forward. That's a major struggle with these gen 4 fbodies.
 

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You could achieve bigger better gains going that way imo.
 

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Have you logged turbine inlet pressure. How much boost have you run?

What intercooler do you have one the car?
 

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Clipping a wheel is where they cut back the tips of the turbine blabes so the wheel can flow more exhaust. Its measured in degrees off the center of the shaft. Usually a 5 or 10 degree clip. Its an old school trick but it works.
Thats what I call research and development
 

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Discussion Starter #12
Have you logged turbine inlet pressure. How much boost have you run?

What intercooler do you have one the car?
Haven't logged back pressure but I think it's around 2:1 right now. Takes 45 psi + a 6 psi spring to hold the gate shut and it makes a max of 22-23 psi.

Intercooler is huge. 24X12X6 core with 3.5" in and out.
 

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Thats what I call research and development
Nah... I didnt come up with it nor take credit for it. A 4g63 mitsu guy told me about it at a dyno day i attended when i had my 2.3 ford. Was seeing 68 psi of drive pressure for 32-33 pounds of boost with the holset turbo i had. Did a 10 degree clip and dropped it 16-18 psi iirc. Lost 500 rpm on spoolup though.
 

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Discussion Starter #14 (Edited)
I had a good conversation with Chris (TURBONOVA70) this afternoon. Although I understand that the larger exhaust housing will help knock down some of the back pressure and make a little more power, without doing both ends, it wont be worth it. By the time that I get done modifying both ends of this turbo, I'll end up spending close to as much as an entirely new turbo would cost me and I'll just have a pile of parts left over. I'm better off selling my turbo as is, and using the cash to put towards the new turbo. I'm not too proud to admit that I try to play this game on a pretty tight budget so I gotta stretch every dollar for all it's worth. So for now, I'm going to get her up and running until I have the cash to buy the bigger better turbo down the road.

Thanks to those that have contributed to this thread. I appreciate all the help.
 

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Is there a larger turbine wheeled T4 based turbo around that would be a straight bolt on that would reduce the back pressure as much if not more than changing the PT88 to a T6 rear?
 

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The garrett Gt4718, aka 4788, is a T4 based turbo that has a turbine wheel that is roughly 11mm bigger than yours. You have 4 housing options that are T4. .96, 1.08, 1.23, and 1.44. Its compressor moves 20 lb/min more than the PT88.

Borg Warner has the S488. standard wheel is 96mm with 92mm and 87 optional that are bigger than yours. There is a T4 1.10 housing available. I rhink you can get it with the 96.... I know you can with the other two. its compressor flows 15 lb/min more than the PT88
 
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