When you want that little bit of extra power, performance, and peace of mind where do you look? Pro tuners looking to squeeze everything they can out of a Harley leave no stone unturned, and one place they go to here—don’t laugh—is the gaskets used to assemble that engine. Honestly. Specifically, it’s the head gaskets, but it doesn’t stop there. Every gasket is important—more important than you’d think.
We recently watched as the guys at Speed’s Performance Plus screwed together another one of the hot-rod V-twins they’re known for, and right out on the bench (right along with the big-bore cylinders and pistons, the cams and gear drive, the custom-ported heads, and everything else that would go in and on this engine) there was a full set of Cometic gaskets. And the guys were going through that gasket pack carefully, picking and choosing, just as if they were choosing the lift of the camshafts. Asked what was up here Jason Hanson, the SPP tech assembling this particular motor, said that over the 16 years they’ve been on the road the Speed’s team has used Cometic gaskets exclusively and told us why. From an average cam swap, to curing a rocker-box or primary leak to putting together a high-end engine build like this one they’ve always used Cometic, and they’re not alone in that choice. Cometic gaskets are an exclusive NASCAR performance product, and those Cup Car engines, it’s safe to say, are stressed just a little more than the average Harley-Davidson. But as important as that quality is, with Cometic’s MLS (Multi-Layer Steel) technology for the head gaskets, with the AFM (Aluminum Foam Material) gaskets used in elsewhere in the engine, and with the rubber-coated spring steel gaskets for rocker boxes and more, the quality is beyond question.
But it was more than simply quality that brought Speed’s to Cometic and all that MLS, AFM, spring-steel and the rest. As it turns out all those gaskets, and all that sealing technology, is offered in a wide array of sizes and thicknesses, and it was that which had Jason going through the gasket pack just as carefully as he had chosen anything else that went into that engine.
“Generally, we’ll use the standard-thickness base gasket,” Jason explains. “But as for the head gaskets we’ll choose the thickness there according to the cylinder head design and the design and size of the combustion chamber.” And a small difference in thickness can make a big difference in performance and power. Those MLS head gaskets are available in thicknesses ranging from .030 of an inch all the way up to .050 of an inch and beyond, all the way up to a .120, useful for some stroker applications. And each has its place. Engine builders differ on their choices here, too, some believing that the thicker gasket allows the engine to run a little cooler. Others swear by slightly thinner gaskets for the improved compression and performance. As a rule of thumb, depending on piston dome shape and combustion chamber size, each .010-inch reduction in gasket thickness can be good for one point of compression ratio. Give or take. And if you’re going the other way, if you’re trying to drop the compression level a bit to accommodate a turbocharger, for instance, Cometic’s got the head gaskets for that. Varying gasket thicknesses can come in handy in other ways, as well. In certain situations and parts combinations it might be necessary to run a thicker base gasket along with a thicker head gasket, situations where the parts matchup might put the open valves just that little bit too close to the piston tops. To a certain degree that clearance can be adjusted with the gaskets.
Here’s another way a properly chosen gasket can help build power. Years ago Wayne Hanson, Jason’s dad and SPP’s founder, began using custom Cometic exhaust port gaskets, solid replacements for the standard H-D mesh gasket. “And this becomes really important with high-end cylinder heads that have been carefully ported,” Jason explains. Tightening a pipe down against a standard, run-of-the-mill mesh gasket squeezes and deforms that ordinary gasket to the point where it actually protrudes into the port disrupting the flow. A small point? Perhaps, if you’re willing to give away a few horsepower simply by using the wrong gasket.
Gaskets might not sound like a path to performance, but they sure can be. Depending on what else is done during an engine build, the performance increase from properly chosen gaskets can be significant. Why leave any power on the table when it’s so easy not to?
Speed’s Performance Plus
(605) 695-1401 – MN
(605) 695-2272 – SD
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