Does any one know where I can find a1977 Yamaha DT400 Porting template?
I just had it bored two over and figured mite as well port it if I can find a template.
Any info would be appreciated
Deciding on porting specs is both easy and hard.
EASY - raising the exhaust port puts more power emphasis on high RPM but ironically is also reducing the trapped volume of the engine which is truly its "size" which is why doing that reduces the low RPM power.
HARD - beyond raising the exhaust a certain amount you have to also raise the transfers and it takes a computer program to tell you what your peak power RPM is and lets you virtually change the port durations till it shows what you want. see Relation of Port Timing to Peak RPM
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