Maintenance & Technical > KX500 Original
Port timing
kwakman:
is anyone staggering there port timing? i.e. opening rear boost ports 1deg before transfers so as to purge the exhaust gas from cyl as this helps get more fresh charge in as the exhaust gas at top of cylinder is the hardest to get moving...
stewart:
i thought the bigg port timing numbers lost bottem end power lots of comprsion and timing helped it some but not as much as getting the power from modest compersoin and less port timing with some retard igntion for over rev ,,i think the stagger timing has been deserted not enough differance
stroke.n.smoke:
When I measured up my stock '01 cylinder and made a port map of it I got these numbers (all numbers with the pv open) add 5 degrees to port opening with pv closed and take 10 degrees off the duration with it closed...
ex port opens 90 degrees ATDC
ex port duration 180 degrees.
Transfer ports open 117 degrees ATDC and has 126 degrees duration. I can't remember what base gasket was in there, but wasn't anything out of the ordinary. When I measured the squish it was at least .070" but not much of a squish band at all. Plus or minus a couple degrees since I'm not an expert at this. Also, all the transfer port heights are the same including the rear boost port.
Just for comparison my RZ 350 twin uses this for port timing
ex opens 83 degrees ATDC
ex duration 194 degrees (I have seen them at 202 degrees duration) But with 114opens/132duration transfers.
I also try to use a squish band of 55% of the bore. On the 350 it would equal 17.5mm wide which is increased from 10mm wide for the stock head. Also the squish band is recut at 1degree more than the top of the piston, approx 14 degrees. (dome top) Which leaves me a little confused with the KX 500's flat top piston, what do you do to the squish band?
kwakman:
All im saying is that the transfers are open the shortest duration for all years and ex ports are open the longest. the 86 has higher compression than all other years so my plan is to raise the transfers to give more port time and to closer match the ex port timing and maybe lose a little compression to increase my top end, along with a platinum pipe. the 86 has bags of low and middle and i want to trade it for top end as it runs flat up top even with retarded ignition timing.what duration should i be aiming for on the transfers to move the power up the rpm band? Im thinking 124 to 126 but i will listen to your thoughts before doing it.................... :-P
kwakman:
I'm still here....... :-P
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