Topic: Pulley Ratio

[ericsrv]

This is a just suppose..... Let's say I've got a lowered Craftsmen, 12 hp, I'm  running a 4.25" pulley on the crank, I'm running a 4.25" on the lower jackshaft pulley, presently I've got a 5.25" on the top of the jackshaft, and a 4.5" on the Foote trans. I've got 18" tires and the only mod was to lock the rear end and the gears are in an oil bath vs grease. If I change the upper jackshaft pulley to a 7.5", would that be the same as changing the crank pulley to 7.5"  Also, what might be a good ratio to work towards for good torque out of the turns,(remember I'm running a "Road Course" type event) MOWERCROSS!!!

[Big Mike]

if you plan on racing this on a road i dont think help can be given.

[ericsrv]

Not on the road, dah .... It is a timed event (See www.kilmr.webs.com) We're on grass, have straights AND right hand turns! This is a driver event,  not just to see who gets to the left hand turn first. Need some help on simple ratios going thru a jackshaft.   

[Burwell555]

it depends entirely on what kind of RPMs the motor is turning or you are willing to turn it, how long the track sections are such as short straights or long, how tight of a turn you have to recover from, such as hairpin and wide sweeper, and what you prefer as a driver. Example, do you want explosive bottom end or want to get passed and take forever to get it wound up and then hope to be able to run someone down then get by them at the other end of the straight....Since 99% of us around here "see who gets to the left hand turn first" as you put it, you are liable to be on your own with an attitude like that...just sayin. If it was as simple as that to win races, everyone would be national champions.

[Toadworks]

Ratio=driven/drive. Multiply all the rtios together and you'll have your final drive ratio


Your example

bottom of jackshaft (driven) / Crank pulley (drive)
4.25/4.25=1

top of jack (driven) / bottom of jack (drive)
5.25/4.25=1.24

trans input (driven) / top of jack (drive)
4.5/5.25=0.86

so to get final
1*1.24*0.86*gear ratio from trans

Since I have no idea what each gear is in your trans I can't tell you what your final drive is, but the pulley setup you currently have is almost a 1:1 through the pulleys.

[Big Mike]

i had to go threw this ratio thing i run a jack shaft but you get through it and it will cost you some $$ if you dont think about it right.

[ericsrv]

I appreciate the info on ratios. Guess what I was trying to say didn,t come out the way I intended. Hope I didn't offend anyone.