Race Engine Building - Speed Parts Upgrade

There's nothing new here, just a company I recently revisited after a long period of absence in my engine building program. This came about when I recently needed a distributor for a small-block Ford that I was putting on the dyno on a Sunday. Guess what? My local speed shop was closed and its owner was off racing! Anyway, a friend of mine had a brand-new, billet-body PerTronix Flame-Thrower, with a coil, ready to use on his own engine. He asked if the PerTronix brand was OK, and I assured him that the company's products were satisfactory.

I realized that it had been some 10 years since I had built a PerTronix ignited engine. When I opened the box, I saw a really nice billet unit. An Internet check showed that the distributor went for a typical street price of less than $220. The engine that needed it was a cam test unit that was expected to run strong and clean past the 8,000-rpm mark. In fact, the Flame Thrower got the job done, firing 0.045-inch plug gaps to 8,200, which was the absolute redline on the test engine. In all, a nice piece at a nice price.

Even a novice engine builder is aware that excess reciprocating mass within the engine is not good-but at what point is any mass excess? The absolutely correct engineering answer is "anything more than zero." Having zero reciprocating mass is impossible, so what we are looking for is as little as possible. In the real world, super-light pistons are expensive, as it takes a lot of intricate machining and time to whittle out those last few grams. This means that accepting the best compromise between light and cost-effective is in our best interest.

Like most pro engine builders, I am always on the lookout for a stout piston that is both light and affordable. Well, it looks as if Mahle (pronounced "Molly") has just set a new standard in combining low mass and low cost. I have had the experience of helping and dyno testing with three engine builds using these pistons-and I like what I see on the dyno. But more to the point, they have some features that contribute to both overall weight and power.

First, the weight aspect. The photos on the next page show a forging that is designed to place metal where it does the most to contribute toward strength for the least amount used. The pin bosses are the most obvious point of difference from a typical off-the-shelf performance piston. Note that the pin bosses are closer together. This allows a wristpin about 1/4-inch shorter than the normal short pin so often used by a regular piston. The regular wall pin that comes with these pistons is almost as light as the lightweight pins we see in other pistons.

Then there are the rings. Here, these Mahle pistons come with rings, and they aren't the regular 1/16-1/16-3/16, D-wall performance rings commonly used. Now, I may have thrown in an unfamiliar term here. "D-wall" is the standard radial depth used by many piston/ring manufacturers. It is the bore diameter divided by 22. For a typical bore of 4.03, this results in a ring with a radial width of about 0.183 inch.

With the Mahle pistons, the rings are 1.5 mm, 1.5 mm, 3.0 mm in width (0.59 inch, 0.59 inch, 0.118 inch). Although they are only a couple of thousandths thinner than their "inch" counterparts, the rings themselves are not the normal D-wall rings. Instead, they are made to an alternative Mahle spec that calls for a significantly shallower radial depth of 0.155 for the top ring and 0.165 for the second ring. This makes them 5 percent lighter than the inch equivalent, and the static wall loading is less. This means less ring drag on the bores but just as much dynamic pressure loading (especially necessary for the top compression ring) to seal everything. In all, it's a nice piston package and well worth checking out before you build your next engine.