The development of valve train components seems to be one of the trickiest parts of the engine. Everything needs to work together in harmony, like a fine Swiss watch. For example, if you increase the weight of the valves, you need to increase the spring pressures. If you increase the spring pressures, you have to be careful how you have done that, or the added weight of each coil will also increase the reciprocating weight of the entire assembly, possibly requiring more spring. If you want to increase the performance of the camshaft, you need to watch the velocity, acceleration and jerk curves of the new valve action to make sure you have enough spring to keep the components in control.
So, just add more spring, right? Wrong! One of the biggest battles in releasing harnessed horsepower in a high-performance engine is friction. A stiffer spring adds more friction - or resistance - to the valve train which robs horsepower. So, we're looking for the ultimate balance between increased performance, reduced friction and extended durability. The valve train needs to be as light as possible so that the springs can have the least amount of pressure necessary to control the valves at their peak of motion. This is one of the most complex design aspects of a racing engine. One that is so complex that, even with the best prediction software, most true race engine development centers still use devices like a Spintron to measure actual valve trains in motion.
I have seen many cases of bad combinations of valves, springs and cams destroy very expensive engines. Years back, I used valve springs that came with the camshafts I ordered that were supposed to be the right spring. All the springs broke, causing complete engine failure. As if the race engine parts I was using weren't expensive enough, the repairs cost more than 3x what the original engine cost to build. It wasn't worth the money for the added 2~3hp at the peak of the power curve. For that reason, when it comes to valve train components, particularly cams and springs, I use extreme caution. If you'll note, all of the engines described in these pages us completely stock valve trains (cams, valves, springs, reatiners, guides & seats). That's not to say we're not experimenting with other parts, but we haven't found the perfect balance yet.
This quest for balance is what has led the push for Titanium in vale train components. Some of the first parts made from Titanium were the valve spring retainers. These seemed like a an easy part with little concern. However, what was found over time is Titanium is a soft material that doesn't like to be under compression. It has a tendancy to be easily disformed under continued use. So, the retainers were wearing out more rapidly than steel. None the less, they were also 1/3 the weight of steel and engine builders were accepting this trade-off. Later, there have been coatings and heat treatments that have prolonged their life considerably, putting a squash to those concerns. Pictured here is a Titanium retainer with Titanium Nitride (TiN) coating for extra wear resistance.
Several years ago, we tried using some larger (+1.0mm) Stainless intake valves made by Kibblewhite Performance. The results were terrible as the bikes wouldn't even run clean enough to make a good pull. When we were trying to diagnose the problem, we eventually pulled th heads and put our old heads with all stock valve train back on and that was the when we achieved one of the best runs ever. I assumed I opened the ports too much until 4 years later I was looking at the backside shape of the valves compared to stock and discovered that the "tulip" shape was way too large on the Kibblewhite valves. I sent them back to Kibblewhite to have them reshaped to "stock". They were unable to get them exactly as I requested, but with the shape they were able to deliver, we were able to achieve a 14.9hp improvement. In otherwords, the incorrect shape cost us 14.9hp with every other part of the engine being the same as the original test. This just goes to show, it doesn't take much in a small engine like this to really kill the power.
Although the +1.0mm oversized Stainless intake valves did net us a decent horspower increase, they were heavier than stick valves. This led us down the path of trying to lighten the valve train as much as possible to work withing the stock valve spring capabilities. I contacted all of the top names in Titanium valves; Del West, Ferrea, Stealth and Xceldyne. Xceldyne came back with the most reasonable quote and was the easiest to work with. I sent them drawings, they came back with recommended changes, we agreed and they delivered parts that were "too print" in the time they stated for the price they stated. It doesn't get much better than that.
Back to the topic of parts working together, once we made the switch to Titanium, we needed to match the guides and seats to that material. The OEM steel seats and valve guides do not interact well with Titanium. Therefore, we needed to have new parts made to accompany the valves. The seats were made from Berryllium Copper, which has very good heat transfer properties to help remove the heat from the Titanium valves, as well as extremely good wear characteristics aganst the Titanium. The valve guides were made of a bronze alloy that also has great wear and lubricity properties when run against Titanium. This will help with longevity of the guides and prevent galling an stiction of the valve in the guide under extreme conditions. I was also able to designthe guides to the exact shape I wanted for the best flow on the port. We haven't run the engine with these parts yet, but are looking forward to the results.
In an effort to provide a lower-cost solution to the big valve upgrade, I tried again to have more stainless steel valves made. First, I went to a company called REV. Their first batch of valves came back close to what I provided in the drawing. Some of their attention to detail was not as good as I had hoped, but the valves were for the most part what I had asked for. I then received a 2nd set that was, for whatever reason, way off from print. The valve margin (the thickness of the head) was way too big and the dish in the heads was more like a crater. I couldn't understand it. How could they make such a mistake? I provided a blueprint. I sent those valves back and REV has been unable to provide valves like the 1st batch since.
In then tried Ferrea Racing Components. I sent the same blueprint and they said they could make the valves no problem. Over a month later, they sent the valves to the wrong address. I was running out of time, so I had the valves redirected to my machinist to cut the valve seats. I had no indication that I should check the valves as Ferrea was a company that is well known in the racing industry for top-notch valves. My machinist received the valves, cut the seats like he was asked (did a perfect job I might add) and sent everything back to me. Once I received the package and looked at the valves, I was besides myself to see that Ferrea had made the same mistake as REV. The valves had an enormous margin and the dish in th ehead took up the entire head of the valve (increasing the volume of the combustion chamber, which loses compression).
That wasn't the worst of it. Ferrea uses the overall length of the valve, from head to lash tip, as their control dimension. Since they made the margin too thick, the valves were really too short. In other words, the stem no stuck into the spring side of the head less. This changes the spring preload ("Installed Height") causing more pressure on the spring and reducing the amount of travel before coil bind. My machinist didn't even catch the length error with the valves, so all the heads (I was doing 3 engines in one shot) were cut so the valve stems stuck up in the spring sode the correct height. In turn, this caused the seats to be cut deeper into the combustion chambers, shrouding the valves more and losing even more compression.
Ferrea acted as if they wanted to make it right, but once agin provided vales that were incorrect length. Zeke Urrutia, one of the owners of Ferrea, spent more time feeding me marketing BS about who his company works with and how good they are, than trying to remedy his errors. His error cost us thousands of dollars in cylinder heads, valves, machine work, porting, wasted trips to the shop, missed test days and a missed race day. I willl not only never be doing business with Ferrea, but cannot recommend them to anyone else. It's too bad, they used to have my utmost respect. Now, if I can steer anyone away from doing business with them, I will. Unfortunatley, I am still at a loss for who can make a good custom stainless steel valve for our little engines.