I have a 383 sbc efi and cop. 3582r turbos.
The engine doesn’t like to rev past 5200 or so.
The turbos have a .62 turbine housing and I’m starting to think they are choking the engine.
It feels like a soft rev limiter. I don’t stay in it cause I’m not sure what’s going on so it may still rev higher just at a snails pace.
Looking at the .82 or .106 ar housing
Any ideas?

 

You need to post up a lot more on the rest of the combo. This sounds like valve float to me, what is the head, cam and spring package? Is the turbo kit intercooled? How big is the intercooler? Its COP so is it carb with ignition control or EFI, if EFI what management system?

Those are a 62mm exducer correct? How much power are you making? If the hot side is choking changing the AR isn't going to fix this. How much boost are you running?

 

It’s a 383 sbc megasquirt 3pro,83lb injectors, solid rollers with the manufacturers recommend valve spring rate( don’t remember exactly). Air to air intercollegiate. Dart 2 sportsman heads about 9.5 to 1 compression. Using ls2 truck coils for COP. Yes 62 mm exducer
Never had it dynoed cause it hasn’t reved cleanly past 5200rpm.

 

I thought at first my spark wasn’t up to the demand. I’ve tried plugs, wires, changed dwell.
I’m only demanding 8lbs of boost. Car runs great till you try to rev it out.

 

I still think valve float. I would pull an exhaust valve spring and test it.

 

Measure your back pressure, and look at your rocker to valve stem pattern. One may point you in the right direction.

 

The cam is a custom grind from cam motion with 200lbs on seat and 550lbs open.

 

Start of boost is the easiest metric for choosing a turbine housing.
Pick the revs your engine should make max power - say 5,000.
Divide by 2.0 - 2.5 (answer = 2,000 - 2,500 rpm)
Accelerate at WOT in top gear up a hill (or on a dyno). Full boost should arrive around 2,000 - 2,500.

If you don't care about torque and want a bit more top end power you can go up a housing size - it will make more at 5,000 due to lower back pressure but won't boost till 2,500 or 3,000.

 

I think the housings are too small myself, but not necessarily causing the problem. You'll have to check the drive pressure to verify.

 

I finally got a pressure sensor on the exhaust.
Was recording 27lbs at 4800rpm with 10lbs of boost.
Might be slightly higher cause waste gate was opening.
That was also about 75% throttle.

 

With drive pressure being nearly three times the boost pressure, yeah there is restriction happening on the hot side.

 

Yeah, that's too much. I'd go to the 1.06's and hope its enough.

 

I have order the .82 ar housing. I’m hoping that will get me to 7000 rpm. If not I’ll order the 1.06 size.

Brendan

 

How did the bigger housings do?

 

This is twins right? So that's 27psi in bp on one turbo! WOW.

 

Dam,that is crazy,and at only 8psi in the intake. ?

 

Yeah, I guess I'll either be buying new housings or turbo's for the new mill if this is accurate!
Right now they are on a 350 and "feel" pretty good.

They are Magnum t70
T-70 65J
Compressor:
A/R 70 Air Inlet: 101.0 Air Outlet: 62.0 IND Wheel: 69.1 EXD Wheel: 91.0 Trim 58
Turbine:
A/R: 68 Inlet: T4 Discharge Outlet: V-Band Turbine Housing: (undivided) EXD Wheel: 64.5 IND Wheel: 74.2 Trim: 76

 

No one brought up ign timing, but low timing can give you some elevated drive pressures so that's something that should be looked at too.

 

These are in a pretty in a pretty good place on a 225-250 na hp engine as a single or 450-500 na hp as twins.

 

That's the goal. I think the 441 should make that N/A. We'll see when it finally hits the dyno!