Titanium Valve Train: A Solution to 928 Timing Belt Woes?

     We decided to use titanium valves & valve train components to increase horsepower and timing belt reliability in street/track engines. By reducing the mass of the valve train, the loads on the entire timing mechanism are reduced. A significant part of that reduction results from the ability to use lighter valve spring pressures. One of the biggest enemies of timing belt durability is the “snatching loads” that result from the constant acceleration and de-acceleration of the engine and the valve train. These extreme loads that cause belt stretch and fatigue are significantly reduced and I am confident that timing belt reliability will be greatly enhanced. This change mitigates a critical obstacle to running reliably at higher rpm’s.

     The biggest drawback to this approach is the cost, and although it is not cheap it may not exceed the cost of using original Porsche parts to do the same level of modification. It is my sincere hope that it will save 928 racers and open track competitors from the occasional engine failure and therefore represent a very good investment. That’s exactly how I am looking at the investment for the track cars that I am building.

     We have consulted with the top people at Del West, the world’s leading manufacturer of titanium valves for Formula 1, Winston Cup, Indy Car, Indy Racing League, LeMans, etc. We are using their valves in the engines that are now being built, and they are the finest available. They have assured me that these valves are as durable for this intended usage as stainless steel valves, with two provisions. They do not anticipate any issues with durability, heat cycling, metal fatigue, etc. There are two areas that need to be addressed to ensure my goals for the service life of the valve: wear of the tip of the valve, and the valve seat itself. The tip is easy, you use a lash cap if it is indeed needed, standard practice. The seating area of the valve will be plasma sprayed with a cerametallic coating that will prevent erosion of the valve face. Del West is already using this process on areas of the valve now, this solution has been proven effective on applications that are more severe than any that we are likely to subject them to. We are using beryllium-copper valve seats on the 928 Developments heads, this will probably mitigate the problem greatly, the plasma treatment will eliminate it entirely. As is the case with our application of plasma spray material to the camshafts, this is the leading edge of technology and it provides answers that traditional techniques do not provide.

     Critics of titanium valves will maintain that titanium is not a suitable material for a street/track engine’s valves. They expound that race engines are torn down after every race (often not true), and the titanium valves are thrown away with every rebuild. They don’t know the actual reasons for the valves being replaced, they just conclude that it must be because of an inherent weakness in the material and therefore the valves are not suitable for any other application. Nothing could be further from actuality.

     Allow me to quote David Reher, of Reher-Morrison Racing engines (one of the top drag race engine builders in the country) in Tech Talk Article 2, National Dragster magazine in 2001. David states “ Yes, titanium valves are more expensive initially than steel valves, but they dramatically increase valvespring life and significantly reduce the chances of valvetrain failure.” “We performed a back-to-back comparison test between stainless valves in a 555ci bracket racing Rat motor… With steel valves, the engine made 920 horsepower at 7,000 rpm, but the power curve dropped at 7,200 rpm. We pulled the heads, swapped the valves, and had the engine running on the dyno again 90 minutes later. Withy titanium valves, the engine had the same power at 7,000 rpm. At 7,200 rpm it was up 20 horsepower, and it maintained that output to 7,800 rpm. Best of all, after two years of racing and hundreds of runs, this engine hasn’t broken a valve spring.”

     The race engine shop that I work out of builds and maintains a great many different race engines that use titanium valves, and these engines will go an entire season with the same valves. In the case of sprint cars, they may well see 30+ race events with multiple sessions per event on the titanium valves and they are completely reliable. Let’s also cite the use of titanium valves in the 24 hour endurance cars as an example. Over 10,000,000 cycles in the course of one racing event, with torturous sustained loads and temperatures, this is an application that demands ultimate reliability . The equivalent of some 10,000 street miles, perhaps more. Ferrari, Honda and Yamaha are now using titanium valves in their production street engines, and we must conclude that the alloying of this material now gives it the longevity required.

     What is the weight savings of titanium in the valve train? The stock S-4 intake valve weighs 65 grams and the exhaust 64 grams. The titanium intake valve weighs 42 grams and the exhaust 40 grams. That is a weight savings of about 35%, significant. When you combine that with the lesser weight of the titanium retainer it will be close to 40%. We are also building some solid lifter combinations with lightweight buckets that will lower the mass of the reciprocating valve train components even more, so there will be a 50% loss in weight as compared to the original components with their oil filled hydraulic lifters. Cutting that weight in half is really going to yield benefits, and I think that we can get there. Remember, titanium will yield power and reliability in many different areas of the 928 engine.