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Originally Posted by PaulDriver
This is still true of injected engines, but since the fuel is injected directly into the cylinder, it dosn't take nearly as much time to heat the cylinder and vaporise the gasoline, thus the real benefit of feul injection, reduced emmisions.
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Actually, all EFI systems I've seen inject the gas into the intake air stream, not directly into the cylinder. Most seemed to be set up so the gasoline droplets hit the backside of the intake valve, so, yes, cylinder heat to vaporize the gas - and you get to use heat of vaporization to keep the intake valve cooler. Of course, the heat problem is not the intake but the exhaust. Oh - and I think the EFI "pulses" (as opposed to the MFI metered stream) helps with vaporization as well.
There
are engines that inject fuel directly into the cylinder - they're called diesels.
Oh - an 'L' head! Cool! You may be able to improve efficiency a bit by increasing compression (those motors were built for really bad gas). You won't be able to do much of this because it's a side valve, so there's a lot of combustion area that isn't directly over the piston. I
think these motors had the exhaust valves dumping into a common manifold. You can increase performance by replacing this with individual pipes, even if they're not tuned headers. I've never worked on one (bike guy) but have dealt with side valve engines...