06-09-2020, 02:16 AM
hi duncan,
the easiest thing is to start again.
the phoenix crank, other modern cranks are available. is purly a reliability thing. not power.
the high comp head is fine. but it does very little on its own.
i find on the seven its main advantage to a fast engine. is that the chamber flow over the valves is bigger. so it lets the gasses in and out quicker. but unless you do the rest of what the engine needs it gets a bit lost.
start from the bigining, the bill williams book is cheap and explains well for beginners. read the section on tuning engines.
so, to go faster. you want as much gas and air to move through the engine as quick as possible.
if you gas flow the engine to a high standard, thats lining up all the inlets and outlets to the block so there are no steps. you can take the tops of the guides. polish the ports. open the inlet and exhaust ports. it all helps gas flow. same as the high comp head, the chamber over the valves lets more gas in and out.
once you have that, you need to look at were you are going to use your revs.
i would suggest if a lack of speed is the problem, a modified trials cam to raise the revs is a must.
but again this wont work on its own.
its no good having a standard gearbox on a trials cam, when you change from first to second. the revs will fall of the cams range.
so one of your problems is likely to be a lack of the correct cam, and a close ratio gearbox.
the last thing, but very important, is a lightend flywheel. i find is a must to stay on a higher cam.
but buyer be ware.
my supersports is fast and all that. but you then have to live with the negative. it doesnt like slow speed. and is unhappy staying below a village speed limit.
im with the others, your carb may not be giving you the fuel supply the speed you want needs.
i find a good starting point for most people is.
5.25 rear axle.
close ratio gearbox.
trials cam.
a well ported block, matched to the exhaust.
a high comp head.
1 1/4 SU carb
a lightend flywheel.
is a good start for all, it should give 30+ BHP and an easy 65 mph.
but you need to do it all together, as each individual improvement helps each other. or are useless without each other.
after that you have to fine tune things.
good luck.
tony
the easiest thing is to start again.
the phoenix crank, other modern cranks are available. is purly a reliability thing. not power.
the high comp head is fine. but it does very little on its own.
i find on the seven its main advantage to a fast engine. is that the chamber flow over the valves is bigger. so it lets the gasses in and out quicker. but unless you do the rest of what the engine needs it gets a bit lost.
start from the bigining, the bill williams book is cheap and explains well for beginners. read the section on tuning engines.
so, to go faster. you want as much gas and air to move through the engine as quick as possible.
if you gas flow the engine to a high standard, thats lining up all the inlets and outlets to the block so there are no steps. you can take the tops of the guides. polish the ports. open the inlet and exhaust ports. it all helps gas flow. same as the high comp head, the chamber over the valves lets more gas in and out.
once you have that, you need to look at were you are going to use your revs.
i would suggest if a lack of speed is the problem, a modified trials cam to raise the revs is a must.
but again this wont work on its own.
its no good having a standard gearbox on a trials cam, when you change from first to second. the revs will fall of the cams range.
so one of your problems is likely to be a lack of the correct cam, and a close ratio gearbox.
the last thing, but very important, is a lightend flywheel. i find is a must to stay on a higher cam.
but buyer be ware.
my supersports is fast and all that. but you then have to live with the negative. it doesnt like slow speed. and is unhappy staying below a village speed limit.
im with the others, your carb may not be giving you the fuel supply the speed you want needs.
i find a good starting point for most people is.
5.25 rear axle.
close ratio gearbox.
trials cam.
a well ported block, matched to the exhaust.
a high comp head.
1 1/4 SU carb
a lightend flywheel.
is a good start for all, it should give 30+ BHP and an easy 65 mph.
but you need to do it all together, as each individual improvement helps each other. or are useless without each other.
after that you have to fine tune things.
good luck.
tony