Vetal

iTrader: (3)

What can be done, beside switching to larger turbo? I have 383ci with 68mm turbo (TC78), and want to help it breathe keeping this turbo.
Would things like a) better intercooler b) larger wastegate help choked engine to produce more power? I read somewhere that guys did put second wastegate to help breathe when they were turbo limited too

onfire

iTrader: (17)

The turbine size is the killer. Best fix is replace the turbo. Budget bandaid would be to find the largest ar turbine housing made and install it to relieve some back pressure.

Shownomercy

iTrader: (1)

Curious on this as well, is there a larger ar housing for the 7675 PT units?

Orr89rocz

iTrader: (13)

More gate and largest/least restrictive down pipe exhaust system you can get. Neck that 3" dp up to 4" as soon as you can and if possible depending on your space requirements

JoeNova

The biggest thing you can do with what you have is go conservative on the cam, absolutely no overlap. Also, it may sound crazy, but put the turbo as far away from the engine as you can. With a small cam and long hotside, you'll be effectively reducing the CFM that both the turbine and the compressor need to flow, putting them both in a better efficiency range and you can actually make more power this way, but you'll lose spool time (which won't be a problem with that turbo on a 383 no matter how you slice it).

We actually made more power on a rear mount stroked Windsor than we did when it was mounted right in front of the engine with a coated and wrapped hotside. The exhaust cools before it gets to the turbo, effectively reducing the amount of CFM that is being pushed through the turbine. This typically only helps if your turbine is the main restriction and not your compressor.

The smaller cam will have this benefit for both the turbine and compressor.

Also, run the largest downpipe you can fit.

Vetal

iTrader: (3)

But what about simplest things first, like larger wastegate, would it help?
Also I already have better intercooler lying, I'm trying to understand whether it will help too

Shownomercy

iTrader: (1)

Didn't you get an answer on that...?
https://ls1tech.com/forums/forced-in...es-help-7.html

Vetal

iTrader: (3)

opinions divided a bit on wastegates. And we didn't discuss how intercooler affects power

chiaj144

iTrader: (4)

I can tell you 100% for sure the wastegate has nothing to do with backpressure. I had a 38mm wastegate on my sled this year. Backpressure was through the roof. It was so high it was blowing the wastegate open at 1 psi or so with a 9lb spring in it. I measured close to 15lbs at zero psi. The gate would open, I could make more boost and the backpressure would still increase with the gate open. All I was doing was over spinning the turbo and moving out of its efficiency range. I ended up having a defective exhaust housing. I don't know if it was not machined properly or labelled wrong but as soon as I changed it backpressure dropped and the sled made power.
If your inter cooler has significant pressure drop swapping it out will help a bit. What kind of pressure drop do you have?

Vetal

iTrader: (3)

Drop wasn't huge, but it was around 4psi still

20psiofevil

Cooling the exhaust gas could help. I wouldn't worry about the compressor much, you can always add a huge shot of methanol if need be or a2w ic.

stevieturbo

Depending on how much boost you're running, 4psi could be considered huge.

If 40psi, then 4psi is 10%

If you're only running 14psi, then that's 29%. Huge by any standards

If you have a major restriction imposed by the turbo, then clearly you need to optimise everything else. Your IC should have almost zero restriction, and be very efficient at cooling

w/g will make no difference. If your current gate was too small, you would lose control of boost as load increases. You dont mention that happening ?

It would still be worth finding how much pre-turbine pressure there is though so you can find a good balance. Likewise turbo speed would be interesting to know, to determine if you are ringing the life out of it, and again find a sweet spot.

Then with that data try and select a camshaft to work around the inefficiencies.

It would also help determine whether more boost less timing, or less boost more timing is the best way to go ( or spend some time on a dyno )

Vetal

iTrader: (3)

I cannot understand why people keep saying "loose control of boost", "boost creep" etc. Turbo is small and restrictive, it means it cannot produce anymore boost, it means no boost creep can ever possibly happen even

stevieturbo

hence why I also said it would be a good idea to monitor turbo speed, just to see if you are spinning the nuts off it.