As long time W-Body specialists, Overkill Motorsports is proud to be a premier tuner for the GM LS4. Having the 5.3 LS4 V8 under the hood is the pinnacle of the W-Body platform and we're here to make it even better. From improving power output, to improving transmission life expectancy, fixing driveability dislikes, and perhaps even a little MPG improvement, your LS4 will feel much more responsive, and more fun to drive, whether you're an enthusiast car owner or consider yourself a normal car owner.

Will: Whether you have a new or old transmission, the Overkill transmission control revisions will help improve your transmission's life expectancy by fixing the tuning issues that create first gear shuddering and slip/bump, reducing torque converter lockup stress, and can lower fluid temperature. Overkill tuning can also disable 4-cylinder mode, which fixes the majority of oil burning on older LS4 engines. Lastly I focus on improving items that other tunes won't, such as improving throttle response, improving transmission shift behaviour, and can provide tuning for all grades of gasoline plus E85 using the optional flex fuel conversion kit.

  • Gains of 10-15 wheel horsepower anticipated on typical setups
  • Tuning available for 87, 89 mid grade and 91/93 premium gas available
  • Stronger mid-range torque off the line and stronger 2nd gear acceleration
  • Torque management smartly revised to eliminate power limitation
  • YOU'LL LOVE AN OVERKILLED TRANSMISSION! Completely revised shift behaviour at part throttle, less bogging, 6000rpm 2-3 upshifts
  • Overkill exclusive Transmission fluid pressure management reduces fluid temperatures, reduces shuddering and slip/bump, improves life expectancy!
  • Displacement On Demand in 4th gear highway only, can be fully disabled on request for oil burning or exhaust sound issues
  • Improved MPG possible, more consistent MPG tank to tank
  • Revised cooling fan operation for stock thermostat, fans stay on at Key off for 1 minute as required
  • Speed limiter removal
  • A/C Compressor shutoff at heavy throttle to recapture lost horsepower
  • Reduced Traction Control intervention
  • P0420 removed for high flow cat converters
  • Buick Super owners, we're the only one providing mail order LS4 tuning for your Buick!

Autocal Handheld: The best way for us to provide LS4 tuning for you is through our Autocal handheld system. The Autocal handheld allows you to take the handheld to the vehicle, read the factory file, upload our Overkill tunes and provide scan data, with no laptop required. Backed by a powerful tuning software, I'm able to offer a full featured Overkill tune with tuning support available for cam upgrades, forced induction, throttle body swaps, transmission gear ratio swaps and E85 flex fuel conversion. Return to stock calibration whenever you want, apply updates and retunes easily through email with us and Overkill retuning is available at no charge for as long as you own your LS4.

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Want a great deal? Of course you do. Purchase your Autocal handheld tune and add our flex fuel retrofit kit for $150 extra, saving $70. Since tuning is required for the flex fuel kit, its a perfect combo to add lots of performance to your LS4!
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Module Reflash: The least expensive Overkill tune delivery is with a computer module reflash. When you send in your existing computer modules, Overkill tuning is programmed directly onto the modules and then shipped back to you. This offers the very distinct advantage of price! It's the cheapest LS4 tune you'll find on the market. Its also a very detailed tune, full of features and benefits. Keep in mind that you'll need to send in your modules again for any revisions. This is ideal for someone who has simple modifications or is completely factory and wants the benefits of an Overkill tune. Modules are programmed and reshipped within 2 business days of receiving your computer modules.


Overkill tuning is available if you already have an Intune or Trinity device and you want to step up from the preloaded tunes to something more customized to your LS4. Overkill tune files are provided through email which can then be uploaded to your Diablo device and flashed into your LS4 just like the Diablo preloaded tunes. Purchase price will include Overkill tune files plus no charge revisions for new modifications as needed for as long as you own your LS4.

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Overkill tuning is available if you already have an HP Tuner suite. I can provide you with Overkill tuning files to flash into your LS4 plus ongoing support and revisions for new modifications, including tuning support for cam upgrades, forced induction, throttle body swaps, transmission gear ratio swaps and E85 flex fuel conversion. If you wish to purchase an HPTuner suite please email, overkill Motorsport is an authorized reseller.

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The LS4 can be enabled for E85 flex fuel use with out retrofit kit. This kit installs a sensor into the fuel supply system that accurately measures the ethanol % in the fuel coming from your gas tank. Once installed and tuned for, you'll be able to fill up with E85 ethanol, or gasoline, or any mixture of, and the computer will know the correct air/fuel ratios to target.

Kit includes a genuine GM fuel content sensor from another application, high quality black anodized AN fittings for the fuel line connections, and a custom, professionally made wiring harness that requires no cutting or permanent alterations to connect the sensor into your vehicle's wiring harness. Anticipate gains of 10-15 wheel horsepower over 93 octane gasoline, and more over 87 octane.

**Note** Flex Fuel Tuning isn't available with all tuning methods. An Overkill flex fuel tune is available with all Autocal purchases or computer send in tunes, available on 05-06 and 08-09 but not 2007 with HPTuners, and not available any years with Diablosport.

It is a popular option to upgrade to the flex fuel injectors off of a late model GM 6.0 pickup truck platform, part number 12613412. These can be had cheap if you know the right sources and are advertised at 50#. While appealing due to their price, I do not recommend them for the LS4 platform, for a few reasons:
  • No Projected Tip, Different Spray Pattern - A significant performance benefit of the factory injector design is lost with these more traditional injectors. The fuel injector spray on a projected tip gets sprayed at the roofline of the intake port, while these have a recessed spray port. A difference in spray pattern comes as a result...The factory Bosch injectors have a spray pattern that is angled upwards, giving it a more direct shot through the intake port, rather than spraying at the port floor. While fuel injectors have lived fine for a long time spraying at a poor angle, the performance benefit of the factory projected tip design is lost, and you may notice a difference in start up performance in particular as a result
  • They're not 50# - After adapting these into other platforms, it's with certainty that these aren't 50# injectors as the tuning in their factory application suggests. They tune closer to 40#. While this is a fine flow rate for flex fuel application, don't let it be suggested that their "50#" rating is a benefit over our 39# offering above.
  • Taller, O-rings aren't right sized - They're taller than the factory injectors and should be used with spacers to space up the factory fuel rail. Also, and I've never seen this mention, the lower O-rings are a narrower outer diameter than factory, meaning it's possible to see vacuum leaks where the injector slides into the intake manifold orifice, because the Oring isn't as wide to seal against the walls as the factory injector Oring. It still seems to seal ok, as long as its orientation is perfectly straight in the orifice bore, but it's a word of caution.
    • If you must find a less expensive solution to our 39# injectors, using part number 5184085AC on ebay, you can find the factory 32# fuel injectors from a 2011+ Chrysler Pentastar V6. They're the same line of Bosch fuel injectors as the factory LS4, and 32# is adequate to flow for E85 with bolt on only modifications. They're currently running around $90 for a set of 6, and $15 per extra injector, making a total of $120. Alternately, our 39# injectors are an ideal offering, and available for purchase above.