Please keep in mind that vintage big bore kits were never intended for road racing. To put 70-73mm size sleeves in a factory cylinder bank the bore breaks right through the casting. That both reduces strength in the cylinder bank and seriously affects the cooling capacity of the system. So your engine is capable of producing more power but has much less cooling capacity than the original 736 design. In drag racing this is not such a big deal as power is used for such a short time. And on the street during normal riding there is little time at a high enough work load on a motor to heat it up enough to be a major problem, other than being stuck in traffic on a hot day.
But road racing puts a major workload on the motor for say 15-20 minutes. That will severely stress the cooling capacity. I have several big bore cylinders/ motors and have real concerns for street use , never mind road racing.
Big bore motors have been used for road racing, but it's not hard to blow one up. Running methanol, for example, is likely a major reason the T-rex bikes have survived. Methanol has a major cooling effect.
Things that would likely help a big bore motor in the cooling department:
Antifriction coated piston shirts.
Ceramic coated piston tops/combustion chambers.
A big honking oil cooler.
Use one of the billet big bore cylinder blocks that Mike Rieck custom designed and had made. These blocks have MUCH more cooling capacity than even the factory 736 version at 1000cc plus bores. Top shelf stuff, but unsure whether your class rules allow aftermarket cylinder blocks. That is the way I would go if I wanted a big bore engine in a road racing application.
Mechanically, I know Mike Rieck spent a ridiculous amount of time carefully preparing my golden rods for my 1000cc motor. They were way out of balance and the rod bolts needed both replacement and modification to fit properly. I'm quite certain that he would have loved to throw them in the display only antique pile and put a pair of bombproof Carrillo rods in. Mike was kind enough to handle my insistence that the motor stay as old school as possible. Thanks Mike. If my motor was for anything resembling road race use and it's associated heat loading, Mike would have gotten his way in a second with the Carrillo rods.
I know you are in a time crunch, but I think you would be better served by at least getting a set of Carrillo or other high end set of steel rods for that motor. I have a feeling it will save you time wise on both ends. Old golden rods are easy to sell anyway. Plus if you have a set of great rods on a nicely done crank, you are well on your way to swapping in a more sane piston/cylinder set set up for road race use. Remember Pops Yoshimura was adamant about not going beyond 850cc on a road race engine. We do more today, better technology and all, but something to consider with your old tech big bore.
I'd just hate to see you assemble a rare big bore motor that could let go on you in short order at the track.
I'd seriously consider something like an oil temp gauge hooked to an alarm buzzer if things get out of hand fast you might have more chance to pull back if need be.
George
