Ever since I installed the turbochargers on my LT1, the power band has been limited to 5500 max RPM. The engine just falls flat on its face when it reaches 5500 rpm.
No sputtering, no misfires, AFR looks fine, timing wont help it... it just stops pulling.

Current setup is a stock stroke LT1 with 6.00" rods, stock-ish aluminum heads, Comp XFI 224/224 cam on a 113* LSA
Compression ratio is 9.4:1, running pump fuel and water/meth injection, AFR is 10.8-11.0 at 16 psi and 24* timing.
Turbos are Garrett 60-1 compressors on a 0.82 AR T3 housing with a "stage 3" wheel.
I have 2.5" downpipes with cutouts.

Before the turbos, that engine was spinning to 6200-6300 rpm NA and on nitrous with a similar cam. As soon as I installed the turbos the powerband was limited to 5500 rpm...

Are my turbines what's limiting the max RPM? I would really like to be able to shift it past 6000 rpm.

 

I would say they are small, but a back pressure check would give you some useful info. Could also be valve springs, or a combination of the two.

 

I don't think it's the valve springs. Last fall I replaced my old springs (was running them for arround 5-6 years) with a set of new Comp springs which have a higher spring rate and it did not help at all.
Springs are Comp 914-16. 165 lbs on the seat and 365 lbs open.

 

Wow. Lots of spring.

The DP's are small, but shouldn't stop from pulling.

What are your plugs gapped at?

 

NGK BR7EFS gapped at 0.030" right now. It has an LTCC box running LS2 coils.

 

Does it act the same with the cutouts open and closed?

 

Yes.
The downpipe and exhaust system are mandrel bent 2.5" pipes. The cutouts are 3-4' downstream from the turbine and I'm running Magnaflow mufflers.

 

I've been reading on the stage 3 vs stage 5 T3 turbines, and it seems the stage 5 (T350) turbine flows a lot more air.
Does the stage 5 wheel fit in my current housing or does it have to be changed also?

 

I would measure the back pressure pre-turbine before I started changing parts. I think your turbos are sized OK, so I personally don't think that's your problem. a BP reading will tell the tale though.

 

Ok, I'll try to figure out a way to measure back pressure pre-turbine.

 

tap a small 1/8NPT hole and install a normal boost gauge. Use copper tubing for the first couple feet then you can couple that with regular nylon tubing.

I've seen people post up some pretty slick setups for that.

 

Thanks!!

 

I would coil several feet of copper tubing to help pull the heat out of it.