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Discussion Starter · #1 ·
The information is still slowly flowing in.

It seems the LLY compressor is very close to operating on the choke line.
Basically this is defined as a compressor wheel speed that creates sonic velocities. The end result is little or no added flow, popping silicone boots, excessive drive pressures, and higher compressor discharge temperatures. Sharply higher.

This leads to the heat soaked CAC, hotter intake plenum temps (thinner oxygen), reduced power, overly advanced timing, and as explained in earlier articles, excessive CAC heat discharge in front of the radiator...

I really hope people start to understand this. It is the fundamental danger of using excess boost, and undersized compressors, in combination.

I believe that the turbo, with a stock intake, enters choke with stock boost levels, at 5000 ft when IAT reaches 150 degrees. Or sea level with a cold air intake, around 28 psi. The increase in compressor discharge temps goes balistic, going from 400 to 550 in the span of only 4 psi at the upper boost range. Or if IAT increases.

With the frequency that some people report overheat as altitude increases, explained by movement to higher compression ratios on the compressor map. WIth no other changes, overheat begins when the choke area is entered, just by climbing higher to lower atmospheric pressure.

This now should serve as explanation why those with larger aftermarket compressors do not have the same issues (as a general rule). Choke requires worse conditions for larger compressors; either more boost, higher altitude, increased IAT or a combination.

Our compressor is too small, as is the CAC plumbing. With high IAT, 3 psi is lost in the CAC plumbing, forcing the compressor to higher rpm to overcome the added resistance. This puts the compressor in choke sooner. Reducing these sources of resistance will help get the most out of the turbo.

For the cage squirrels reading this, there should also be 10 or 20 HP made available by replacing the CAC plumbing with 3" plumbing. (LB7 already has it). With larger plumbing, the compressor will run around 10,000 rpm slower for the same plenum boost produced. Longevity:Thumbup:
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