How close to piston-valve interference does the increase in valve lift beget? Since the camshafts are gear-driven there's little possibility that the cam drive will fail as a chain or belt drive system could, but is there a possibility that interference could occur by over revving the motor into valve float?
We are going to set the piston-to-valve clearance distance when we design the chamber. We know the cam lift, and we know what rocker ratio we want to use, and we will be setting a valve angle and a chamber shape. So, once we have these parameters all decided, we can set a chamber depth which allows the necessary valve-to-piston clearance around the TDC area, so that the standard pistons may be used without clash. This is part of the design plan.
You see, since we are in full control of nearly all the parameters in this head, we do not have to perform gymnastics to fit things into some already existing design and casting that is basically set in stone. We can make it any way we want. And we will.
Regarding valve float, while this is always possible with a serious over-rev, our Ace valve spring package is high performance with advanced beehive springs and lightweight hardware that has excellent control over the valve and the spring harmonics and damping. It is the same basic package that has been successfully proven for years in our other Fireball engines, and has been reliable at over 6500rpm in those engines, and has shown perfect reliability and longevity for over 50k miles so far in those engines. So, we have a very good handle on the control of the valves, and it is not a worrisome problem in my mind. Never broke or lost any valve spring, or dropped or bent any valves, in any Fireball yet.
A few things we have planned for the package, and will be discussed for implementation in the design are:
New valve angle: The standard UCE valve angle is 26 degrees for each valve, 52 degrees included angle. This is relatively old architecture, and the more modern and efficient designs will use lower angles(such as 23, or 18, or 15 degrees, etc). This allows a more compact and efficient chamber for better combustion efficiency, allowing higher compression ratio, less ignition advance, faster burn, etc. However, it also can limit valve size a bit more, so a decision between valve size and valve angle need to be weighed, as well as how the port flow will work with the new valve angle. These all mesh in together, and we don't have a final decision on these details as of yet.
Valve size: We plan a bigger intake valve, and possibly a smaller exhaust valve to make room for it. This entails moving the intake valve guide and port inboard a little bit, which is no problem since we are designing the whole thing from scratch anyway.
Combustion Chamber size and shape: We plan a modern efficient compact(around 50cc) combustion chamber which optimizes flow and also allows higher compression ratio and more efficient burn for more power overall. Looking at somewhere between 9.5:1 and 10:1, depending on piston type and displacement. This will be a single spark plug chamber design.
Intake port: We cannot move the intake entry location from where it is, because we need the standard intake system to be able to bolt up, so that will remain where it is. However, we will port the head with the right shape to work with the new valve angle and the existing entry location, and the largest cross sectional area that is efficient with the existing intake system. Aiming at around 200+ cfm peak flow, with a nice fat low lift flow profile too.
Exhaust port: We are going to work with the smaller exhaust valve and a high efficiency exhaust port to utilize the exit speeds for best scavenging using a smaller valve and port, to allow us to use a larger intake valve and port. This maximizes torque, especially in the critical midrange rpms. Will bolt up with the standard exhaust header, the normal way.
Rockers: We will machine a mounting system for an entirely different rocker design on this head than the stock type. The stock rockers will not be used. The design will include a high ratio full-roller type rocker system, which will provide the maximum valve lift that we can fit with the valve springs that we use in our Ace Fireball packages(about .500" lift max). Ratio rockers also have the effect of extending the effective valve duration for increased rpm range, even though the actual numeric "seat to seat" duration is not actually increased., but everything between is lifted higher for longer. So, we get more duration and a LOT more lift with the same stock cams, which gives the performance increase we want, but saves money on not having to buy cams.
I realize that all these features will sound like a lot of money, but we have taken this into account, and we will be using available parts that do not need to be custom made, and are reasonably priced, so we can put the money in the machining of the head, and the parts and hardware are greatly reduced in cost compared to the custom parts we had to have made before, and all the hand porting and welding up chambers and lots of time on the various machines. So, this "should" come out in a very reasonable price range, not too different than what the hand-done head mods cost before, and give a lot more features and benefits in the package. It makes sense.