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High Oil Pressure for a 340 - What's Your Problem?

Son of Lester
Cpl. Cole Crewes,
Camp Lejeune, NC: I read the article on the Lester Scruggs 404 stroker and thought it would be a great addition to my '02 GMC Sierra 2500HD 4X4 with the LQ4. I would like to keep the fuel injection and change the bore to 4.060 to squeeze out a little more low-end power. Do you think it's a good idea? Should I keep my stock intake manifold with the stock heads? What size injectors will I need?

Jeff Smith: First of all, Cole-it's always a pleasure to hear from our men and women in the service and especially from Marines. The additional cubic inches with a bigger bore would be beneficial to adding torque. The iron block should accommodate the 0.060-inch overbore without difficulty, although it would be a good idea to have the block sonic-checked first. A minimum of 0.200-inch wall thickness after boring is preferable, but slightly under that is acceptable since you're not trying to make huge power. I'd suggest finding a spare 6.0L short-block to perform the work. That way, you could keep your truck running while you build the new engine. Then you can sell your original short-block after the new motor is in the truck. I found SRP and Mahle pistons available for your application. Both of these pistons require an aftermarket connecting rod because they use a smaller 0.927-inch wristpin versus the stock-diameter wristpin. This will unfortunately add to the cost of your buildup. The SRP piston is a 4.065-inch-bore piston (PN 279592). The Mahle pistons are an excellent choice-they're what we used in our Lester Scruggs motor-and come with pistons, pins, locks, and a complete ring package. The Mahle package PN is L922314065F04 and costs $626.95 from Summit Racing. These pistons are designed to be used with a stock stroke and 6.125-inch connecting rods. We used Scat rods in our engine. Keep in mind that these changes will require balancing the engine. Look for a piston and rod package that is no heavier than the stock bob weight. If the piston and rod package is heavier, it will require adding Mallory metal to the crank that could add $200 or more to the cost of normal balancing.

I'd suggest retaining the stock truck manifold and the LQ4 heads. It's also possible to squeeze more power out of the engine with a little work to the stock heads. West Coast Racing Cylinder Heads (WCRCH) has an excellent CNC porting process for the stock 6.0L heads that adds quite a bit of power without having to purchase new cylinder heads. On our 404ci LS engine test, the WCRCH-ported 6.0L heads were worth 24 lb-ft and 29 hp over the stock 6.0L heads. Headers would also be a wise investment to improve exhaust flow. We found a set of 15/8-inch direct replacement shorty headers from JBA (PN 1850S-1JT titanium coated) that would work. A low restriction after-cat-style exhaust would also be a good idea again to allow the engine to make as much torque as possible.

You didn't ask about a camshaft, but if you're going to improve the power a little with some tuned-up heads, a mild cam would also be a good idea. The original LQ4 camshaft specs out at 196/207 degrees of duration at 0.050-inch tappet lift, with 0.467/.0479 inch of valve lift with a lobe-separation angle of 116 degrees. The mildest cam would be the '02 to '04 405HP LS6 factory cam (PN 12565308, $264.95 from Scoggin-Dickey). Before you drop the cash, try looking on the Internet for a used LS6 camshaft. The LS6 specs out at 204/218 degrees of duration at 0.050 with 0.555/551-inch lift with a lobe-separation angle of 117.5 degrees. This adds 8 degrees of intake and 11 degrees of exhaust duration along with 0.088/ 0.072 inch of additional valve lift. This cam lift and duration bump, along with the mods to the heads, plus the exhaust will no doubt require some tuning to wide-open throttle fuel and spark curves and also the part-throttle areas. This should probably be left to a professional tuner, so it might be wise to find this person first before ordering any parts. He might be able to point you in the right direction from a parts combination standpoint and he will already have the tune-up in his repertoire of EFI maps.

As for injector size, my buddy Kurt Urban at Urban Performance tells me the LQ4 engines used two different injector sizes ranging between 24 and 28 pounds per hour (lb/hr). The LQ9 engines with higher horsepower ratings used the 28-lb/hr injector. Urban says that with the mild enhancements you are planning, the stock injectors should be big enough to feed 400 hp.

More Info
Kurt Urban Performance;
Commerce, MI; 248/345-8169; kurturbanperformance.com

Mahle Motorsports; Fletcher, NC; 888/255-1942; mahlemotorsports.com

Scoggin-Dickey Parts Center; Lubbock, TX; 800/456-0211; sdparts.com

Sportsman Racing Pistons (SRP); Huntington Beach, CA; 714/373-5530; jepistons.com

West Coast Racing Cylinder Heads; Reseda, CA; 818/705-5454; proheads.com

CC Quickies
You might remember Keith Anderson's Viper as the late-model class winner at last year's Real Street Eliminator event at the Car Craft Summer Nationals. Keith recently took his Viper down to Texas for a couple of fun weekends. He ran the car at the dragstrip, pulling down an impressive 10.76 at 133 mph and then impressed the crowd with a 190.0-mph run in the standing mile. Yahoo!

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