Good questions!
The rear engine runs less compression so that the front engine is always the "lead" engine. As mentioned in the build somewhere, this is how Larry Forstall, the bike's original builder designed it and I'm confident to continue to run with it. We could also adjust the ignition timing etc and do the same thing, just to take the edge off the rear engine. When the engines were apart, we learned that the front and rear cylinder heads were different thicknesses, in the future we will likely shave the rear to match and have equal compression, but again at this stage, I'll just keep it as is...it works.
Although a lot of attention is spent on adjusting the carbs and cables, the engines will never be 100% synchronized. However, I believe that when they are both at full throttle, they are very close. When they are at partial throttle as I shift gears and roll into 5th, if they are not fully synchronized, I believe that one is simply pulling the other, the stronger pulls the weaker. There may be some inefficiency that transfers into heat, again now resolved by the coupler’s oil bath, but I don’t think the engines are actually battling each other to death.
Many multi-engine cars and bikes have quickly reduced themselves to expensive shrapnel, some before ever making it onto the salt, there is a lot of discussion surrounding timing the two engines so that they will work together. Some say one engine needs to be timed a few degrees out from the other using ignition or valve timing, even crank phasing. The concern is that the power pulses are going to pound the engines to the point where parts break, which is fairly catastrophic in our case at 11,000 rpm. I think this is more of an issue when the crankshafts are joined together, which is not our case. Both of the Double’s transmission output shafts are coupled together. I believe that the gear train in both transmissions absorbs the crankshaft’s power pulses. I’ve been told that my transmissions are going to fail, I’m confident that they are robust, considering the abuse that early GSXR’s around the world are still enjoying on the track. Regardless, I take my time changing gears and back off the throttle as both transmissions are shifted together.
I’ve proven that Larry’s original design works and Richard has worked out the weak links.
unk Looks like an entertaining project for sure.
