How many RPMs?

D

Dryslick13

New member
If I go up on the rear gear 2 teeth, how many rpm will I gain? Currently hitting just below 5800 and want to gain 200-300 more. This is with #35 gears, if that makes a difference.
 
If you are running a LO206 your rpm will be limited to 6100 rpm ( usually closer to 6050). Generally you will gain 100 rpm per added rear sprocket tooth.
 
Yes, it is for a LO206. So the 2 teeth should get me spot on. Not getting on the limiter on the long straits. Also wanted a little more grunt off our 2 hairpin turns. New to all this. Never sprint raced before and trying to get the kart sorted before our 1st race. Thanks for the info Flash.
 
Dryslick13 said:
If I go up on the rear gear 2 teeth, how many rpm will I gain? Currently hitting just below 5800 and want to gain 200-300 more. This is with #35 gears, if that makes a difference.
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In the 4 – 1 gear range, if you add 2 teeth, you have to pick up at least 200 RPM, (or very near) to be going the same speed. It changes as the gear ratios go up and down. While 2 teeth may help you off the turns, it also means you have to turn more rpm or you're going slower on the top.

Depending on where you are on the HP curve, you may not gain that 200 RPM. The down slope on the horsepower curve at that RPM can be very steep.

Unless you're geared completely wrong, the only way to pick up 200 – 300 RPM is with more horsepower on the high-end. Tuning can help. A little leaner can help, but only if you're a little rich now.

It's called tuning, and tuning is tough! (Al Nunley)
 
If Dryslick is running an LO206 engine package then tuning would be severely limited and changing the jets to run richer or leaner isn't allowed. Best way to get the rpms you are looking for is to experiment with several gear ratios or ask someone running in your class for a recommended ratio. Check your bearings for wear, brakes for a dragging pad and the straightness of the chassis. Anyone of them can increase drag and rob you of rpm.
 
Often times the fastest lap times are achieved by being on the rev limiter for a while before you get to the end of the straight a way. This may be for a considerable distance. It sure as heck gets you through a tight infield faster. Don't be afraid to try adding 2 teeth but then try adding 1 or 2 more on top of that.
Every track is different.
 
Jimbo,??? you say being on the rev limiter is OK... I've wondered about this... won't that wear on the electronics ??
 
We touch the limiter at the end of our longest straight, it won't hurt the coil. It simply switches the primary and dumps to ground. Riding the limiter too long will load the cylinder with unburnt raw mixture, just touching it gives max RPM, thus track speed.
 
It won't hurt the electronics at all. The kid kart motors are on the rev limiter almost all the time. They are on the limiter more than they are off.
 
^ Absolutely.

Our kid kart JRLO206 was on the rev limiter leaving the grid and sounded like a popcorn popper the entire race. Ran it 23 races constantly against the rev limiter and NO failures whatsoever. (Albeit at 4100 rather than 6100 max.)




-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
26 years of service to the karting industry
765-339-4407
bcarlson@CarlsonMotorsports.com
 
Dryslick, GJMS has very long straights with a couple of tighter corners. IMO working at keeping up the speed fast through the slowest sections will allow less teeth on the rear which will benefit your over all lap times more than reaching the rev limiter on the straights. Gear for the stop watch. If you have a Mychron study the "Time" spent at peak power and work the set up that maintains peak power for the most "Time" in a lap.
You being new to sprint racing IMO the "spot on" gear ratio will be changing as you learn the limit of how fast a kart can go through the slow sections.
Good Luck,
Rodney Ebersole
 
No data aquisition tools. Just have lap timer and tach. Those 3 sharp turns are tricky combined with the long straits. What is a decent time at GJMS? We are running a 6" wide Buris tire. Need to get new wheels for the wider Duro tire, but waiting to see what they do for next season before I spend more money on wheels and tires.
 
Ran it 23 races constantly against the rev limiter and NO failures whatsoever. (Albeit at 4100 rather than 6100 max.)
[/QUOTE]
does that mean that the clutch is set at 4100 RPM? I wonder what the dyno would say about where the peak torque is on that engine.
 
alvin l nunley said:
Ran it 23 races constantly against the rev limiter and NO failures whatsoever. (Albeit at 4100 rather than 6100 max.)
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does that mean that the clutch is set at 4100 RPM? I wonder what the dyno would say about where the peak torque is on that engine.[/QUOTE]

Al,
The rev limiter on the JRLO206 is at 4100 rpm (MAX!!) You can't set the clutch up at peak rpm, you set it up at peak torque. We oval raced with our kid kart and the engine was against the rev limiter leaving the grid area....so....we really never needed the clutch once the kart entered the track.
 
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