Materion has confirmed that it is now supplying its AMC 4632 hypereutectic aluminium-silicon alloy for use as a MotoGP piston material. Unlike its SupremEX alloys this is not an MMC, so it is legal for use in MotoGP engines.
It is manufactured using a proprietary powder metallurgy method that refines the microstructure and provides enhanced mechanical properties over the 2618 and 4032 aluminium alloys from which racing pistons are commonly forged or billet-machined. In particular, it aids in piston weight reduction and improves stability at elevated temperatures.
In the past we have reported that a Husqvarna MX2 250 cc four-stroke single campaigned by the REVO Seven team benefited from the use of Materion’s PerforMet bronze alloy for its valve guides and its SupremEX MMC for its valve spring retainers. Retainer weight was reduced from the 7.9 g of the stock steel items to 4.3 g, which was the basis for an increase from 14,500 to 15,300 rpm before the onset of valve float.
This year the REVO Seven Kawasaki UK team is contesting the 250SX AMA Monster Energy Supercross Championship using Kawasaki KX250 250 cc four-stroke singles developed by MXology, a new company formed by Scott Bredda and Mark Yates. These engines have SupremEX spring retainers and con rod, PerforMet valve seats and guides, a ToughMet small-end bearing, a 4632 piston and in the latter stages of development is a PerforMet piston ring.
Meanwhile, Materion has revealed the result of endurance testing by Cosworth of a 2.3 litre Ford EcoBoost I4 turbo engine fitted with SupremEX con rods and pistons, PerforMet valve seats and guides, and ToughMet copper-nickel-tin alloy small-end bushings, as described in RET 124 (February/March 2020). There was initially the use of PerforMet piston rings but Materion’s Dave Krus said, “There was an issue with the durability of the ring coating – since solved – so we used the OE rings in the durability portion of testing.”
The use of Materion materials allowed the piston pin to be shortened and the stock steel ring groove insert to be abandoned. In addition, the top ring groove was set closer to the crown, reducing crevice volume by 58.2%, while this shorter MMC piston offered an 18% reduction in weight over stock. The rod was 3.3% longer to compensate for the shorter piston yet 40% lighter than stock. In total, the Materion piston-pin-rod package saved 31.6% over the stock component assembly weight.
In addition to the saving in reciprocating weight was a potential saving in rotating weight, as it was calculated that Cosworth had the potential to take 718 g out of the crankshaft in view of the revised counterbalance requirement. Krus reported, “There was an increase in vibration when they removed the [stock] balance shaft, but less than one might expect. The out of balance when the Materion components were installed and the balance shaft removed was slightly lower than that of a 2.0 litre EcoBoost I4 engine, which is sold without a balance shaft. Of course, removing the balance shaft reduces friction.”
In view of the testing programme, Krus admitted, “We didn’t see all of the efficiency gain we thought we would. For example, everyone expected that the reduction in crevice volume would result in significant efficiency gain.
“However, we found that most of the improvement we got in efficiency was through reduction of friction consistent with the reduction in reciprocating mass. One possible explanation, which we did not have time to verify, is that the location of the injector, the injection profile and the design of the bowl in the crown is effective in minimising fuel going into the crevice.”
Cosworth carried out a 150-hour accelerated wear test, at the conclusion of which there was no dimensional change to the internal components, aside from a 1-2 micron recess in the valve seats, which is less than would otherwise have been expected. Krus noted that more than 96 of the 150 hours were run at WOT – “it’s really a brutal test”.
One snag was a little fretting on the [stock] main bearing but, Krus noted, “That was because it was designed to fit into a steel big end ,whereas the aluminium big end expands more. An appropriate bearing could be designed to overcome that drawback though.”
He added, “The thing that most impressed the Cosworth test engineers was how well the aluminium MMC rod stood up to its task. Through those 150 hours of testing, Cosworth saw how well these components worked and [as previously reported in RET] they have used the technology for the Gordon Murray Automotive T50 [naturally aspirated 4.0 litre] V12. That is a 12,000 rpm engine, and they chose our material specifically because of its higher fatigue strength at temperature and higher stiffness, which allows you to make a very light and very stiff piston.”
Krus was also able to report that Materion is working with Advanced Sleeve on liner development, a well-known race con rod specialist, various race piston specialists and Total Seal on ring development. Indeed, Total Seal has already provided customers with rings made from PerforMet, which is much more conductive than chrome steel and so takes more heat out of the piston. “So that material is finally commercialised in the race engine sphere and working,” Krus concluded.