M8 Performance
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We use the .468 RS with good results.
Thats the great thing about the 4V M8 heads. You dont need nearly the same amount of lift on the M8 as you do on a TC to get the same power.
I'm running .569" lift cam on mine, where the RS468 is running .470" lift and getting about the same power.
I'm running .569" lift cam on mine, where the RS468 is running .470" lift and getting about the same power.
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841 Posts
alot of debate on 4valve vs 2 valve heads..the advantage of the 4valve falls off on the higher rpms, basically comes down to swirl in the chamber,
lets look at 2 heads that flow the same cfm, 1 being 4 valve the other being 2 valve, they difference will be port velocity between the 2 heads
4 valve has smaller ports and in theory should reach velocity quicker where as the 2 valve needs more rpm to get velocity up,
problem on the 4valve is that the ports begin to tumble into the chamber where as a 2valve can swirl, steps are being taken with off setting valve sizes in the 4 valve head to help promote swirl though
also m8s (imo) have too much cylinder head, they flow way more than they need to for even the larger m8s, so they pick up well with higher lift cams
however i will say ( and again imo) because the heads are so big, cam companies are putting smaller duration cams in and really screwing with exhaust durations to help draw out upper rpm power, and the fact that alot of exhauat companies are making smaller than even stock headers to try to offset the large head on the m8 and help give it more torque, all this is bad for the quy who wants real power
best thing you can do with an m8, make it into a 140ci or bigger, have a pipe made with a header of 2inch and have a cam made with more reasonable durations, like 250 on both intake and exhaust along with .550 lift or so
once you get all the m8 parts working together and sized correctly, you will have a monster on your hands
lets look at 2 heads that flow the same cfm, 1 being 4 valve the other being 2 valve, they difference will be port velocity between the 2 heads
4 valve has smaller ports and in theory should reach velocity quicker where as the 2 valve needs more rpm to get velocity up,
problem on the 4valve is that the ports begin to tumble into the chamber where as a 2valve can swirl, steps are being taken with off setting valve sizes in the 4 valve head to help promote swirl though
also m8s (imo) have too much cylinder head, they flow way more than they need to for even the larger m8s, so they pick up well with higher lift cams
however i will say ( and again imo) because the heads are so big, cam companies are putting smaller duration cams in and really screwing with exhaust durations to help draw out upper rpm power, and the fact that alot of exhauat companies are making smaller than even stock headers to try to offset the large head on the m8 and help give it more torque, all this is bad for the quy who wants real power
best thing you can do with an m8, make it into a 140ci or bigger, have a pipe made with a header of 2inch and have a cam made with more reasonable durations, like 250 on both intake and exhaust along with .550 lift or so
once you get all the m8 parts working together and sized correctly, you will have a monster on your hands
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1,382 Posts
6500 rpm isn't high rpm in a race motor, but, the issue lies more with chamber shape, as a 4 valve motor should be a pent roof and not a hemi or semi-hemi design. A good 4 valve head would be a shallow pent roof with little included valve angle, and a center spark plug. Compression would be a flat top piston and piston height would be what determined compression ratio, not a high dome piston. But, that shallow pent roof would make the heads taller to contain the rocker gear and valves standing up, which makes a packaging problem in a motorcycle engine..
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841 Posts
rpm and what is concidered high rpm is debatable, as rpm is not a good way to look at what is high in the rev range but rather engine stroke and piston speed, just by the numbers a 2.25 inch stroke at 12,000 rpm will have the same piston speed as a 4.5 inch stroke at 6000 rpms, and piston speed is the limiting factor along with acceleration rates, which gets into long vs short rod to stroke ratios...and ultimately piston speed is what draws on the ports
Just had a D&D Fat Cat installed on my bike. Looks like a beast of a pipe. :nod
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