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GM Performance Parts LS3 Engine Build Part 3 - Late Crate Update

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By Richard Holdener, Photography by Richard Holdener

The success of this project can be traced directly back to our starting point. Right out of the box, the GMPP LS3 crate motor is an impressive little small-block. Think about how cool it would have been to have an all-aluminum small-block that pumped 492 hp and 484 lb-ft of torque. Now toss in the fact that said small-block would idle with 20-plus inches of vacuum, deliver as much as 25 miles per gallon on the freeway, and run flawlessly for 100,000 miles or more. The modern LS motor is a real thing of beauty and makes for one heck of a starting point for even wilder buildups. We demonstrated this by replacing the factory heads and cam in the LS3 with ported heads from GMPP and a healthy Comp Xtreme Energy hydraulic roller cam. With these simple bolt-ons, the power jumped to 569 hp and 522 lb-ft of torque. The next upgrade came in the form of a 417 stroker assembly from Demon Engines. The additional displacement combined with a FAST LSXR intake improved the output of our LS3 to 608 hp and 570 lb-ft of torque. This was now officially one serious small-block, especially when you remember the all-aluminum construction (less weight is the same as more power).

Having performed all the major upgrades on our normally aspirated motor, we were left with only one of two options: nitrous oxide or boost. Not to discount the impressive nature of the former, we chose the latter. There is only one thing better than a modified LS stroker, and that is a modified LS stroker on boost. Luckily for LS enthusiasts, their responsiveness to normally aspirated bolt-ons carries over to blowers and turbos.

You just haven't lived until you've been behind the wheel of a supercharged or turbocharged LS Camaro, GTO, or muscle car. Knowing this, we decided to live a little and subject our very own modified GMPP crate motor to some boost. Rather than go the usual route and run a centrifugal or twin-screw supercharger (that comes next), we opted to test a turbo. We liked the turbo option since the exhaust-driven impeller all but eliminated the parasitic losses associated with driving a supercharger. To the average enthusiast, this means a turbo will offer more horsepower per pound of boost than any other form of forced induction. The trade-off for this efficiency is that the turbo will not offer the same boost response as a positive-displacement blower, but the stroker already had more than enough low-speed power.

Equipped with flat-top pistons from Probe Racing, our 417 stroker was sporting a compression ratio just a hair more than 11.0:1. A turbo motor can be run at this compression ratio but would require careful attention to the timing curve and/or use of octane booster. Rather than reduce the boost, run octane booster, or lose power from retarded timing, we opted to drop the static compression ratio. Though we were committed to using the flat-top pistons, we found another way to drop the compression on our 417 stroker. The cure came from Procomp Motorsport. Not only did Procomp offer dedicated LS3 head castings in both as-cast and CNC form, but the company also offered a version with dramatically larger combustion chambers. Where the typical LS3 chambers measure 70 cc, the big-chamber, CNC-ported LS3 heads from Procomp featured chambers that checked in at a whopping 81 cc. The 11cc increase in chamber volume dropped the static compression ratio of our LS3 stroker down to 9.9:1 compression-much more boost friendly than the 11.1:1 produced by the GMPP heads. Thanks to a little love rub by the flow experts at Dr. J's Performance, the flow rates offered by the Procomp heads exceeded 360 cfm. The basic difference in performance between the Procomp and GMPP heads would be the drop in static compression.

By Richard Holdener
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