Horsepower Road Blocks: Duramax LB7

Published in the June 2009 Issue June 2009 News, Duramax

While a relatively new entry into the light duty diesel market, the Duramax line of engines have made a huge impact over the past few years in the performance market.

The Duramax 6.6 liter engine first appeared in the GMC and Chevrolet pickups in 2001. For the first four years, this engine (named LB7) remained unchanged and proved to be a sound offering. During that time, there were a few minor changes that needed to be made, but all and all the engine held up quite well considering it was a ground-up new design.

In 2004.5 the engine was updated to the
LLY and in 2005 it became the LBZ. The latest version, the LMM, appeared in 2007.5 and remains the current design. Our series covered the horsepower road blocks for the LBZ engines in the second part of this series. So, for this final installment, we opted to go back to the original LB7 for the receipts.

Making 500 Horsepower

Achieving 500 horsepower is pretty easy to do with a Duramax but there are a few supporting components that cannot handle the additional power. The 300 horsepower factory-rated engine and powertrain were not designed for 500 horsepower. So, as soon as the horses start increasing, the Allison transmission starts having issues.

"At the 450 to 500 horsepower mark, if the transmission is holding up, it won't for very long. Having the entire transmission rebuilt with upgraded clutches, valve body and torque converter will ensure that the power gets to the ground and not the pocket book," says Jim Jones, owner of Texas Performance Diesel.

Not having to worry about powertrain issues, the builder can focus on engine. Intakes and exhaust systems are a must. The factory didn't design the engine with this much horsepower, so the factory intake must be replaced with a good breathing intake and the exhaust needs to be upgraded to a 4-inch system.

To get the fuel into the engine doesn't require major overhaul, thanks to the common rail injection system. So it is a matter of programming and tuning to get the power or rather the fuel into it. A good EFI Live custom tune, PPE Hot Plus 2 or the TTS Extreme programmers can be tweeked to get 500 horsepower to the ground. To keep the CP3 (the high pressure fuel pump) fueled, an upgraded lift pump (the low pressure fuel pump) needs to be upgraded to flow the required volume.

For a daily-driven 500 horsepower road warrior, the turbo charger needs to be upgraded to a GT4088R or a GT4094R which is somewhere between a 64 to a 68 mm charger. This will supply the required air and keep the backpressure in check.

Making 750 Horsepower

This is the point of no return the for LB7's. How the tuner programmed the vehicle and how the owner operates the vehicle will determine if the rods can support 750 horsepower and for how long. Most whom we have talked to (and my personal opinion) say to absolutely change the rods if you want 750 horsepower or more (probably safer to do it around 700 hp).

While in the motor there are a few components to look at upgrading as well. Connected to the rods are the pistons. There are many good aftermarket pistons and each has its strengths and weaknesses. Make sure and discuss your objectives with each manufacture and see what they would recommend for your project. When it comes to compression, they will leave it up to you and your engine builder. "We have actually been seeing a trend of people lowering the compression of their high horsepower engines, but not to what most people would think," says Chad Remakel from Empire Diesel Performance. "Ten years ago, heck, even five years ago, most engines were being lowered down to between 12:1 to 14:1, but the recent trend with these engines is to lower it down to between 15:1 to 16.5:1."

Once the pistons and rods have been chosen, the next major item to think about is the cam. The factory cam can and will work in a 750 horsepower application. But there are few better times to think about sending the cam out and have a regrind done. This is especially important when trying to reach higher horsepower goals later.

While the cam helps valve lift, porting and polishing the cylinder heads can help reduce boost pressure, increase flow and reduce EGT's; which all equate to higher horsepower. "Our Stage 1 CNC Ported Heads really offer a good increase in flow and are a great option for the budget-conscious racer and the 750 horsepower range," says Guy Tripp owner of SoCal Diesel.

When reassembling the engine, make sure you add head studs, because with this much power, the cylinders are experiencing tremendous pressures and without sufficient clamping, the heads will lift. Helping add to that lift is the amount of fuel. At 750 horsepower, upgrading to 20- or 30-percent-over injectors is necessary. "It is important anytime you deal with aftermarket injectors but especially important with Duramax injectors to have them balanced, any time you upgrade or change the sizes," says Remakel.

Feeding the injectors a modified CP3 or twin CP3's are necessary. This teamed with a good lift pump will provide for a bullet proof setup and ensure that the truck won't fall on its face or die three-quarters of the way down the track. "That's never a good feeling and one I have experienced too many times," laughs Jones.

More fuel means that more air is necessary. A well-designed 2.6 aftermarket turbocharger can get you to 750 horsepower, but at that level, driveability does suffer with a single turbo. Adding a stout twin setup will yield a better all-around driver.

Making 1,000 Horsepower

A good stout bottom end is needed to handle this amount of power. Upgraded rods and aftermarket pistons are needed to effectively achieve 1,000 horsepower without worrying about burning through a piston.

At this level, a good cam with increased lift is necessary to open the valves as far as possible to let the tremendous air flow needed to support 1,000 horsepower. "Tuning can play the biggest role in a 1,000 horsepower engine that lasts versus an 800 horsepower engine that doesn't," says Remakel. "If everything is running right, these motors will last and hold together at this power level, but if you are not running right, kiss the motor goodbye."

Tuning was consistently pointed to as the key and probably single biggest factor in reaching 1,000 horsepower safely and consistently. The injectors that the process is controlling will be 50 to 60 percent over stock, which is a tremendous amount of fuel. Dual CP3's are necessary to support that much flow.

Keeping up with the air flow necessary, a high flowing 70mm, 72mm or a well-tuned 74mm single can get you there. For trucks that are on the road or built for drag racing, twins are the best way to achieve this power level.

To keep the EGTs cool at this power level is extremely important. Running a good water/methanol system with multiple nozzles or adding nitrous will help keep EGTs under control, but monitoring them should always be in the back of the driver's mind.

"For anyone wanting to go extreme, we are putting a 9.8L twin screw blower that is fed by two parallel 74mm turbochargers; that will make some power," laughs Remakel.



Empire Diesel Performance



Socal Diesel



Texas Performance Diesel


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