Preparing A High Mileage 6.0 To Go Turbo Part 1

JSRP's Craig Poust is going to takes us on a trip to install twin turbos in this 2004 GMC HD. We'll start in this article by putting a hotter street tune on it and see where that takes us. All images from screenshots.

JSRP’s Craig Poust is going to takes us on a trip to install twin turbos in this 2004 GMC HD. We’ll start in this article by putting a hotter street tune on it and see where that takes us. All images from screenshots.

Craig Poust, the owner of Justin Sane Racing Products, has bowed to the desires of some of his customers and fans and picked up a 2004 GMC 2500 HD (basically a Chevy Silverado) so he can teach us how to get it to deliver more power. We’re doing a series of articles to follow along with him as he goes through the process of installing the turbo or turbos and performing the upgrades required to take advantage of them. We’re going to start with performing some easy modifications to the factory ECM tune that will drop more than a second of the truck’s quarter mile time.

How to Select a Viable LS Engine at the Junkyard

This is the first build Craig has done where he didn’t get a high mileage LS engine from the junkyard. The GMC HD he bought from a friend did have more than 300,000 miles on the engine though. Buying a reliable high mileage engine, especially one that you can’t hear run at a junkyard can be an iffy proposition as you know.

Craig says that if this area under the valve covers on high mileage engines is this color, the rings should be in good shape and you can go with the motor.

Craig says that if this area under the valve covers on high mileage engines is this color, the rings should be in good shape and you can go with the motor.

Craig tells us what to look for in a high mileage engine, LS or otherwise, whether it’s coming out of a junkyard wreck or in a vehicle you’re looking at buying.  The first thing to do is to pull the valve cover. Take a look inside between the valves. If you see sludge, take a pass. If not, look closer. If the floor of the heads are a nice golden color, you can be pretty sure the rings are in good shape. If you get a puff of smoke when starting, well, valve seals are pretty easy to change.  Of course, if you already have the LS or are buying a new one, this isn’t something to worry about.

Adjusting the ECM Tune to Drop Up to a Second off the Elapsed Time

The GMC has a bone stock 6.0 LS.

The GMC has a bone stock 6.0 LS.

Stock tunes are designed to deliver a combination of power and economy. The problem with that is they are pretty much exclusive; you can’t have great performance and great economy. Craig started his project by doing a few test passes on the street near his house where’s he’s marked off a quarter mile. Stage and mash was how he did this and it resulted in an ET of 16.5 seconds and a top end of 89 MPH.

For ECM mods all you need is a laptop and the right software. The cable t pug into the diagnostic port comes with the software.

For ECM mods all you need is a laptop and the right software. The cable to pug into the diagnostic port comes with the software.

Then he went to work on the ECM. First he modified the torque and transmission settings in the computer some, not too much. That dropped almost two tenths of a second off his ET. Next came modifying the timing tables. These are normally pretty mild from the factory, again to maximize economy while delivering somewhat acceptable performance. Without locking up the converter, he tweaked the torque management settings even more. This netted another drop of two tenths of a second. He decided not to mess with the mixture settings because the truck didn’t come with a wideband sensor in the exhaust.

The only nod to performance the original owner of this truck made was this K&N cold air intake.

The only nod to performance the original owner of this truck made was this K&N cold air intake.

While these adjustments only netted him a total of three tenths of a second, he was using stock tires that were badly in need of replacement. Plus, he was on a cold country road at the beginning of winter. Craig is sure that if he’d had good tires and a track, these mods would have dropped his ET into the low-to-mid 15-second range.  Also, he wasn’t locking up the converter when he was doing this. He would just sit at idle and mash the throttle to the floor.

These modifications to the engine and transmission management can most easily be carried out with Haltech software and your laptop. Next we’ll look at how to modify the exhaust manifold(s) for turbo(s) and install wastegates.

About the author

Mike Aguilar

Mike has been wrenching on cars since the early 1970s when he worked at his dad's auto repair shop. By the age of 14 Mike had built his first performance suspension, and by 16 he had built, and was racing cars in several sanctioned events in the San Francisco bay area.
Read My Articles

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