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Mower Building / Setup Help => Driveline => Topic started by: jerry55 on March 18, 2014, 08:55:31 PM

Title: pully size
Post by: jerry55 on March 18, 2014, 08:55:31 PM
Pulley sizes for 12 hp sportsmen..  with 13" tires, 700 trans with 12 hp built engine
Title: Re: pully size
Post by: cycloneracer on March 18, 2014, 09:02:12 PM
Need some info.   


Tire size.

Transaxle?   Transmission?    Which one??

What has been done to engine?


Do some searching in the driveline section.   
Title: Re: pully size
Post by: jerry55 on March 19, 2014, 07:20:07 AM
Need some info.   


Tire size.
Transaxle?   Transmission?    Which one??

What has been done to engine? 


Do some searching in the driveline section.   
   Tires  Are 13"..  transmission is a 700 peerless & the engine is a 12 hp briggs flatty that's modified.
Title: Re: pully size
Post by: cycloneracer on March 19, 2014, 08:10:55 AM
You want to overdrive the transmission.

I ran a 6" on front to a 4" on the transmission.    But that was with 16" rear tires.    You could run the same, you would just need to run different gears on the transmission and axle.

A lot of racers run George H's setup.   8" on transmission and 5-6" on the transmission.

Check out the stickys in the driveline section.
Title: Re: pully size
Post by: jerry55 on March 19, 2014, 09:32:34 AM
Need some info.   


Tire size. 13"

Transaxle?   Transmission?    Which one??   700 peerless

What has been done to engine?  12 hp built


Do some searching in the driveline section.   
Title: Re: pully size
Post by: westcoast racer on April 15, 2014, 12:01:32 PM
Can anyone answer me this (George maybe)?  What is better to run when it comes to pulleys and why?  6-3.5/4, 7-5, or 8-6?

Is it better to keep the pulleys 1:1 and the transmission 1:1 and then get the final ratio with sprockets?

Does having a larger pulley on the engine increase torque?  Is that harder on the gear box (700)?

I know that the smaller you go on pulley sizes the greater the chance for the belt to slip.
Title: Re: pully size
Post by: Jeff McKelroy on April 15, 2014, 05:01:32 PM
"Does having a larger pulley on the engine increase torque?  Is that harder on the gear box (700)?"

By over-driving the transmission, you will lose a small amount of horsepower to the transmission, but you get to keep the torque.

You most likely don't want 1:1 anything.  Not only can you damage the transmission, your engine's power curve will not be in tune to the track.

The most "popular" pulley set-up is the 8x5 scenario, however, if you have the resources, I would recommend purchasing the true A-Belt pulleys from EC, that is, both the 8 and 6 inch engine pulleys, and the 4 and 5 inch transmission pulleys, and experiment.

As far as chain and sprockets go, I have to say that depends. What power does your engine make and where?  How big is your track? How tight are the turns, how does your mower handle on the inside/middle/outside lanes? This just takes experience unfortunately, and experience will cost you a few sprocket sets.  Might I suggest the Quick-change sprocket kit from EC, and a 12 and 42 sprocket to start with...
Title: Re: pully size
Post by: PJG56 on April 15, 2014, 07:24:30 PM
Whats your target rpm range and track size?





Title: Re: pully size
Post by: westcoast racer on April 16, 2014, 12:23:13 PM
Track is 1/8 mile.  125 ft staights and 45 ft inside radius corners.  I currently run an Oppy twin with about 25 hp with the simple mods I did.  Engine turns about 5200 rpm max.  I have 6" engine pulley, 4" transmission, 3rd gear is 25/25 and a 15 and 42 sprocket.  I have 8" rims with 16" tall tires.  I run about a 6:1 final on this track.  Works well but if I had more torque could I would like to get closer to a 5:1 final. 

Would having an 8" engine pulley with a 6" transmission give me more torque?

Title: Re: pully size
Post by: Jeff McKelroy on April 16, 2014, 02:33:36 PM
Track is 1/8 mile.  125 ft staights and 45 ft inside radius corners.  I currently run an Oppy twin with about 25 hp with the simple mods I did.  Engine turns about 5200 rpm max.  I have 6" engine pulley, 4" transmission, 3rd gear is 25/25 and a 15 and 42 sprocket.  I have 8" rims with 16" tall tires.  I run about a 6:1 final on this track.  Works well but if I had more torque could I would like to get closer to a 5:1 final.  

Would having an 8" engine pulley with a 6" transmission give me more torque?



You would get better pull out of the turns with the 8X5 combination.  You're actually lugging it pretty good there. Depending on the cam, I found 6.5625:1 to be a good ratio for my opposed.  I was a bit weird with my gearing.  Because I had the torque, I wanted a bigger transmission sprocket to slow the chain down, so my gear combo was 16/56.  Now, you will hear all kinds of arguments that 3.5:1 is 3.5:1 is 3.5:1, and that's fine, BUT it did change the way the mower pulled, but made no difference on top speed.  And my chain lasted longer between services. Assuming a 48.86" rollout, you would still achieve roughly 36 MPH on the track.   :twocents:
Title: Re: pully size
Post by: PJG56 on April 16, 2014, 06:13:34 PM
Just to muddy the waters, i also run an oppy, i gear mine for 6500 and sometimes approach 6900 depending on the track .We use 8 engine 4 tranny 6"tires with 40.75 roll out,10 thooth on tranny/ 44 on axle final ratio 6.6/1