As GPI customers and GPI builds have become a force to reckon with in the naturally aspirated racing scene, we could not help but notice the lack of shelf piston options geared towards this environment. Staying true to our name, we contacted our friends at Diamond Pistons to set about designing a new piston. We have enjoyed great success working with Diamond Pistons on our Drop-In Piston Series available for the Gen V LT engines and had no doubt we had chosen the right partners for this project.
With the LS3 platform growing in age, it has found its way into the hands of people who really want to go fast and push the bar a little further. While we have made great achievements and strides within the stock bottom-end arena, not everyone is wanting to stay stock bottom-end forever. There are many options out there when it comes to dished and flat top pistons but not so much with dome options. So, we set about creating a max-effort, high compression piston that caters to the naturally aspirated guys and gals.
CREATING THE MOLD
The process started by taking a LS3 cylinder head and creating a mold of the combustion chamber – this would be the foundation of the dome.
We needed plenty of valve relief for what we were wanting to achieve but needed to maintain as much effective volume as possible. Even with a significant valve relief, we were able to end at an effective volume of +8.3cc! Combining this volume with some milling will allow us to reach compression ratios of 15.0:1 and greater with relative ease. This was not so easily achievable with current shelf piston offerings. However, we did not stop at just high compression ratios – these pistons are loaded with features designed for max effort, naturally aspirated builds.
Although it differs among manufacturers, we see many aftermarket pistons with valve reliefs measuring from .150” to .175”. Knowing we needed as much relief as possible to accommodate the most aggressive of setups, including large solid-roller combinations, this piston is equipped with a massive .200” valve relief for both intake and exhaust, designed for 15° LS3 heads. Also included, is a cutout for the LS3 combustion chamber quench pad. The intake relief is ready for a maximum of a 2.180” valve, and the exhaust a maximum of 1.600” valve.
We decided not to include the standard moly skirt coating on this piston. Rather, we wanted to leave this option open for the end-user to decide, as many will utilize specialized coatings such as abradable coating options from Line2Line. The choice of coating is significant and should be geared towards the overall design of the build.
Lateral gas ports in the top ring groove are included standard with these pistons. This allows for maximum ring seal for racers, whether running a vacuum pump or not.
Aiming to reduce ring drag, these pistons are supplied with a 1-1-2 ring pack produced by Mahle Motorsports. This is an exceptional ring package that offers lower drag than the standard 1.2-1.2-3 that you will find in many shelf pistons.
These pistons are designed for a standard 6.125” rod, allowing for the use of our GPI/Compstar connecting rods, the Callie’s Ultra I/H Beam Series rods, or even the Ultra Enforcer Series by Callie’s. They utilize a .927 pin that is included in the package, and the underside of the piston has had lightening completed to remove mass.
As you can see, there is a lot of engineering that has gone into this piston and we’re excited to offer it as a shelf piston, exclusively available through GPI and its affiliate dealers. This is an utterly amazing custom piston, available at a shelf piston price.
Compression Ratio calculated using a stock LS3 head and .040” 4.085” head gasket.
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