Need help to speed thing up

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Need help to speed thing up

Postby 23t » Fri Feb 12, 2010 6:45 pm

Need some help with gear ratio and finding a top speed.

Here's what the setup is now,
@6500 rpm
20" tall tire
13.65 to 1 rear ratio
This is my max top speed 46mph.

Anyone tell me what the top speed should be by installing a 8.1 gear ratio?


Thanks, Daryl
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Re: Need help to speed thing up

Postby greenracing » Sat Feb 13, 2010 12:10 pm

I don't think you're going 46 mph now...

The formula is:

MPH = (RPM x TireHeight) / (Gear x 336.135)

At 6500rpm, a 20" tire and 13.65 gear that comes out to 28.3mph.

An 8.1 gear would give you 47.7 mph.


Perry
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Re: Need help to speed thing up

Postby 23t » Sat Feb 13, 2010 2:19 pm

Thanks Perry! The et slips tell me 46 mph!!

That's the formula I was using and 28mph is what I come up with the 13.65 too!!
Stock gears are 13.65 according my manual specs. and I want to install the 8.1 to pick up some more speed like 10 to 15 mph.

Perry, it could be the clutch ratio throwing this off. With clutch fully engaged @6500rpm, the ratio on the clutch is 0.8 to 1. I guess I should have paid more attention in math class. :roll:
This looks like it going to be one of those trial and error deals! :shock:
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Re: Need help to speed thing up

Postby greenracing » Sun Feb 14, 2010 9:19 am

Yeah - I remembered last night that you're running a snowmobile clutch, so it's probably in overdrive...

If you use:

ClutchRatio = (RPM x TireHeight) / (MPH x 336.135 x RearGear)

The 46mph comes out to a 0.62:1 clutch ratio

If you add that back in to:

MPH = (RPM x TireHeight) / (RearGear x ClutchRatio x 336.135)

an 8.1 gear would give you 79.5 mph.


Of course the snowmobile clutch reacts to torque, so if you gear up the rear end too much, it may not open up to .6 anymore, which is going to slow it down. When you're dealing with that, it is going to take some trial and error...


Is Heidi going to let you go 80mph on that thing??? :o :o
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Re: Need help to speed thing up

Postby 23t » Sun Feb 14, 2010 10:09 am

That gives me some idea anyway. Wow, I'm going to need to think this over. 80 mph? :shock: That would be a little more a repectable et! 8) And I can work with any torque issues. 8) Just wondering how the cart will react when I bring front wheels back down at that speed. That could be interesting! :shock:

Think I'm going to give them a try anyway, I can go back to the stock gears if needed.

It would of been a good idea to have you PM me on this!
Ahh, I'm not worried about Heidi, I'll just tell her the clocks messed up or something must have blew across the finishline. :wink:

By the way, anyone have a good used jr. dragster chute? Seriously!

Thanks Perry
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Re: Need help to speed thing up

Postby 23t » Sun Feb 14, 2010 5:19 pm

wheelzman wrote:Daryl I'm tellin' ya that 80 MPH on the connecting road is gonna net ya a ticket. I don't care how tight you an the local constable are!!!!!! :lol: :lol: :lol:


:lol: :lol: :lol: :lol: Your probably right Wheelz. At 50 I got a break, at 80 they might lose their sense of humor. :lol: :lol:
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Re: Need help to speed thing up

Postby CraftyGirl » Sun Feb 14, 2010 5:27 pm

greenracing wrote:Is Heidi going to let you go 80mph on that thing??? :o :o


Do I want him to go 80 on that thing? NO! 60 maybe, but not 80! :shock:
Anyone know a good insurance agent? Or maybe I should be looking for a good shrink for him instead. :lol:
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Re: Need help to speed thing up

Postby CraftyGirl » Sun Feb 14, 2010 8:44 pm

Jack, I believe you are right about that one! :wink:
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