750/810 race gearing

hei zedders,

my GPZ750 racer project (formerly "650/750 vintage road racer" )is proceeding. not much to show for now, mainly dismantling, making "to do" lists and ordering parts.

Would like to order now front and rear sprockets for the 520 conversion I'll be doing, would love to hear what people who road race these things use.

Already got a set of AFAM 520 15 & 16 fronts sprockets, thought about 36-37-38 rears.

Too low, too high?

Thanks

TG

Even though I ride a 1000 heres my experience: I have a 15 tooth front,39 tooth rear (stock).I went to a 42 tooth rear and the bike got off the line like a madman but was running a lot of revs at cruising speed.I went to a 36 tooth rear and it had good top end but not much low end.So Im back 15 front/39 rear.I guess the Kawi engineers know better than me.I would try 15/37 on your bike and see how it runs.bjbj

thanks hoc,

tried to have a go at the gearing calculator www.gearingcommander.com/ but there's no GPZ750 in the data base and the kz750 (twin) shows a strange 13:33 final drive. is that stock on a 4-cyl KZ750?

will have to enter the data myself i guess,

TG

My KZ650 is 16/42 I believe.

The manual shows that the KZ750 had a 33/13(2.54) final drive ratio. I just plugged in all the transmission values into the calculator, shows a 225km/h top speed at 10000RPM in 5th gear. That's identical to your lowest ratio of 15/38.

If you go with your suggested ratios your top speed at 10,000RPM will range from 225 with 15/38 to 252 with 16/36. That's if you have the power to get there .

I think there is a kz 750 four in the gearing commander. I guess for your situation I would kinda figure out how fast you want to go. If you want to go 115 put the gearing in there that gets the top speed to 115. I dont guess you'll be using a whole lot of low end power. But I guess it would depend on your riding/racing style.

T_Dub wrote:

The manual shows that the KZ750 had a 33/13(2.54) final drive ratio. I just plugged in all the transmission values into the calculator, shows a 225km/h top speed at 10000RPM in 5th gear. That's identical to your lowest ratio of 15/38.

If you go with your suggested ratios your top speed at 10,000RPM will range from 225 with 15/38 to 252 with 16/36. That's if you have the power to get there .

my 60rwhp 500 racer goes up to 200kmh/120mph, so if I'll get anywhere near the 90rwhp i want from the 810, 230-240 should be doable.

Another checkpoint for me is one of our tracks that has a speed trap. It's not on the main straight but the open classers still get up to 180kmh in 4th,

Will try to enter this data to see what gearing produces these numbers. big question is if the 810 will still breath well @ 10,000, will have to build the motor before...

Any dynos graphs/results from tuned 810's out there? That could help.

Thompson, it's all out road racing so style is WOT most of the time!

TG

My zed has run 82hp, I have the printout but will have to figure out how to load it on here!!!

My bike well pull 17/40 gearing no problem. I think it would pull 17/38 too. I like the 17/40 though.

Mark

Mark what sort of top end do you get with that gearing?

Turboguzzi,

If you are roadracing then you are going to have gear your bike specifically for each track. I would suggest gearing the bike to attain 90-95% of max revs in whatever gear you happen to be in at the fastest part of any particular track. Most bikes achieve peak hp at about 90-95% of redline, and it will also give you a little margin for drafting or tailwinds. Always worked for me.

mjg15 wrote:

Turboguzzi,

If you are roadracing then you are going to have gear your bike specifically for each track. I would suggest gearing the bike to attain 90-95% of max revs in whatever gear you happen to be in at the fastest part of any particular track. Most bikes achieve peak hp at about 90-95% of redline, and it will also give you a little margin for drafting or tailwinds. Always worked for me.

Thanks mjg and all,

Been vintage road racing for a few years now so quite used to swapping sprockets for the right gearing, was only trying to start at least with the right range.

Thanks for the info, it will help fine tune the calculator, will let you know what i end. will try to stick with a 16 front as a basic starting point for lower overall weight.

TG