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Street Race Truck More... The Toolbox

Approved Upgrades for the GM Crate 602/604


All right, you’ve got your new 602 or 604 crate motor sitting there ready for race season. You’ve heard all the guys talk about what their motor is putting out, now it’s time to get that out of yours. So, it’s time to crack that puppy open, right? Wrong. Per the regs, you can’t alter the original assembly unless approved. So here are a few tips and tricks to help massage a few extra ponies out of that beast, without getting disqualified for the season.

Perhaps the easiest and simplest is swapping out the spark plugs. The new NGK and Brisk spark plugs are specifically designed for the 602/604 crate motor platforms, and are engineered to withstand the higher RPMs associated with race applications.

Next up is running the right carburetor. Making the right choice when it comes to carbs could mean the difference between having a winning car, and not. Using the formula found here we can do some calculations to figure out a rough estimate. Most 604 motors will go into “valve float” around 6800 RPM. So for the sake of argument, you could use 6200 RPM as a max. Willys Carbs has an option specifically designed for the 604. Based on a 750 CFM body, it is capable of flowing up to 900 CFM.

Believe it or not, your oil is also a major factor in pulling as much power out of your motor as possible. Products like the Lucas High Performance line of motor oils were designed to not only run cooler (up to 40°F cooler), but have also has been proven to stave off fuel dilution longer than other oils.

One more thing to keep in mind; word amongst the racers is that the OEM timing mark may vary from motor to motor. It is a good idea to locate your TDC (Top Dead Center) independently and mark it. Once you have marked it, it also might not hurt to add a timing tape like the one shown for finer control.

Last but not least, don’t forget about all the accessories you have at your disposal. KRC Serpentine Drive kits can help reduce pulley drag substantially, freeing up valuable horsepower. Don’t just focus on the engine of your racer either. Low drag Teflon bearings in the rearend will make your car roll easier, and limiting or eliminating brake drag will also help.

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