Last month, the most extensive modification to date was performed on our ’06 GMC Sierra 2500HD—fortifying the Allison transmission with Sun Coast parts. This month, we put the built Allison to work and set our sights on gaining more than 200 hp, thanks to an extreme EFILive tune from Fleece Performance Engineering. But in order to get the most out of the custom tuning, a few changes were in store for Project Street-Max.
First and foremost, an AirDog system was added to guarantee the CP3 would be supplied consistent fuel pressure. Next, a fuel pressure relief valve shim kit was installed to ensure the higher rail pressure (commanded by the tune) could be maintained under wide-open throttle. Then, the 6.6L’s intake tract was cleaned up thanks to an exhaust gas recirculation blocker plate and positive crankcase ventilation re-route kit.
Be sure to check out the tuned LBZ’s new dyno numbers below, and tune in next month to see what an aftermarket turbo gains us.
(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
Fuel Pressure Relief Valve: Shim kit
EGR: Blocker plate
Tuning: EFILive via Fleece Performance ECM and DSP5 switch
• Head studs
• Aftermarket turbo
• Aftermarket downpipe
|Parts List (labor not included):
|Extreme hp package
||ECM, DSP5, EGR blocker, fuel rail shim
||Reroutes blow-by to atmosphere
||100-gph flow rate
Fuel Rail Valve Shim Kit
There are three 0.020-inch-thick shims included in all FPRV shim kits, and the nut serves as the separating tool. Removal of the glow plug controller assembly (on the driver-side firewall) gains you access to the FPRV, which is removed, disassembled, outfitted with the supplied shims, and carefully reassembled.
The FPRV is the safety mechanism that’s built into the high-pressure common-rail (HPCR) system to prevent overpressure. When big tunes are loaded, they command high pressures and fuel flow rates, which can cause the FPRV to pop off more often than at lower pressures and fuel rates. This weakens the FPRV spring and will eventually cause the FPRV to pop off at working pressures instead of spikes (the infamous P1093 code is a typical symptom of a weak spring). The shims will still allow the relief to operate yet maintain rail pressure when commanded.
Back on Randall’s Performance and Accessory’s load-cell dyno (and with a 25 percent load being applied), the first Fleece Performance extreme tune yielded 455 hp and 852 lb-ft. Looking at the torque curve, you can see that ramping up timing at higher engine speeds led to peak torque occurring at 2,700 rpm. This keeps low-rpm cylinder pressure from getting out of hand (too much timing down low can actually crack pistons). The higher rpm timing advance, peak boost of 28 psi (on the dyno), and 425 hp on tap from 2,600 rpm to 3,500 rpm makes for a very safe yet fun tune on the street.
With a timing bump added to the extreme tune (32 degrees BTDC vs. 27 degrees), we picked up 20 hp. The truck now sees 33 psi of boost on the street, cooler EGT, and rail pressure never drops below 24,500 psi (validating the importance of adding the AirDog and shimming the FPRV). Keep in mind that we’re running 35-inch-tall mud-terrains, which may have hampered our numbers a little. With the stock wheels and tires on the truck, we might’ve seen 500 hp. Overall, we added 221 hp and 382 lb-ft with just a tune. Next, we’ll see what an aftermarket variable-geometry turbo can do.
Stock Horsepower: 254 hp at 3,000 rpm
Current Horsepower: 475 hp at 3,000 rpm
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