Project Street-Max GMC Sierra

Part 3: Our Duramax Picks Up 50 HP

Diesel Power Magazine, November 2011 Issue


If you’ve been keeping up with our Street-Max series, you know we rebuilt the Allison six-speed in “Project Street-Max, Part 1” (Sept. ’11) and picked up 220 hp in “Project Street-Max, Part 2” (Oct. ’11), thanks to EFILive tuning. In this installment, we’re adding head studs and an aftermarket turbo to our ’06 Sierra. And just as we’ve done in the past, we’re once again adding the supporting modifications necessary to maximize the truck’s horsepower. For utmost flow, a 4-inch downpipe will replace the factory piece, and for ultimate longevity, a complete EGR delete (which does away with the EGR valve and cooler) will be installed.



(While we had the turbo and intake plumbing removed, Knoles installed a complete EGR delete kit. The system does away with the EGR valve and cooler and requires some modifying of the passenger-side up-pipe (cutting the EGR cooling tube and welding it shut), or installing an LB7 up-pipe in its place. The EGR delete we installed was manufactured by All Season Diesel Performance but was purchased from Danville Performance)

Under the hood, things are starting to look a little more modified. Here, you can see the

The folks at Knoles Performance Solutions in Petersburg, Illinois, performed all the work and got started by removing the factory turbo and downpipe. Because the truck only had 50,000 miles on it and no head gasket issues to date, we decided to thread in a set of ARP head studs one at a time. Once all the fasteners were torqued down, a Fleece Performance Cheetah turbo was bolted on, and we headed back to Randall’s Performance looking to break the 500hp mark on its chassis dyno. Stay tuned, as we’ll be adding a modified CP3 injection pump, larger injector nozzles, and going after 600 hp in the future.

Project Street-Max
Past Modifications
Part 1, Sept. ’11

  • Air intake: K&N with Amsoil dry filter
  • Exhaust: 4-inch MagnaFlow single exit (stock downpipe)
  • Fuel System: AirDog 100-gph
  • Transmission: Sun Coast GMax 6-pac, 1058 converter

Part 2, Oct. ’11

  • Fuel pressure relief valve: Shim kit
  • EGR: Blocker plate
  • PCV: Reroute kit
  • Tuning: EFILive via Fleece Performance ECM and DSP5 switch

Current Modifications:

  • Turbo: 68mm Fleece Performance Cheetah turbocharger
  • Exhaust: HX40 downpipe
  • Emissions System: Full EGR delete
  • Engine Modifications: Head studs

Part 3, Parts List (labor not included):





Cheetah turbocharger

Fleece Performance

68mm Garrett-based VNT (with HX40 outlet, a $200 option)


HX40 downpipe

Fleece Performance

Increased exhaust flow for turbo


Full EGR delete

Danville Performance

Complete deletion of EGR system (valve and cooler) Supplied by All Season Diesel


Head studs


Increased clamping force on heads


Total Price $3,741

Using the same Fleece Performance extreme tune (created via EFILive) as last time, the turbo gained us exactly 50 hp—and blew past the 500-rwhp mark with ease. To make the truck build the same 36 psi of boost it sees on the street (with a maximum recommended boost of 42 psi for the Cheetah), a 30-percent load was used on the SuperFlow dyno at Randall’s Performance. To date, we’ve added 270 hp at the wheels to our ’06 LBZ-powered GMC with bolt-on modifications. Thanks to Fleece Performance’s retention of the factory variable nozzle technology on its Cheetah, spool-up wasn’t sacrificed at the expense of more power. We also noticed a substantial reduction in exhaust gas temperature, and the turbo was able to completely clean up all the smoke we’d previously seen while running the extreme tune. And last but not least, the exhaust note the truck emits now is downright wicked.

Stock Horsepower: 254 hp at 3,000 rpm
Tuned Horsepower: 475 hp at 3,000 rpm
Current Horsepower: 525 hp at 3,200 rpm

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