Feedback - 24/50 vs 21/41 gearing (Stock Tune Only)

[number1kyster]

What speed did you get with tune, 24/50, stock I got 113.??

So top speed with the 24/50 is around 113? I can run that now, stock, with my 21/41 gearing. I would imagine when tuned, they run out of gear super fast!

 

[Turboflash]

So top speed with the 24/50 is around 113? I can run that now, stock, with my 21/41 gearing. I would imagine when tuned, they run out of gear super fast!

Cat gear chart shows 24/50 = 115 MPH @ 8800 RPM. 118 @ 9000.
IMO, gearing is a personal preference thing. When I think about what gear to run, I ask myself what type of riding do I do most? Tight, corner-to-corner, long-straight, loose snow, hardpack, ice. How many speed runs will I do? I think about track speed. If I gear up, I'm trying to turn track faster (at any given RPM), thereby decreasing torque on track = less spinning. If I gear down, that makes it easier for the engine to spin the track. So where is the sweet spot for me between too low, too high, and just right?

 

[74Nitro]

It's nice having the extra 600 rpm's of RPM that a tuned turbo four stroke enables.(9000 up to 9600) No other sled can do that. It is why we can run such low gearing and still achieve great top speeds.
A 2 ratio in a 800 or 850 sled won't even be in the ball park. They come with much higher gearing from the factory to achieve speeds over 100 mph as their power peak is around 8000rpm and they have no over-rev. (assuming same size track drivers)

 

[Crossfire12]

You really over rev that far, why not gear up a little, just asking? Gotta be hard on belts over reving to 9600, no

 

[74Nitro]

You really over rev that far, why not gear up a little, just asking? Gotta be hard on belts over reving to 9600, no

I did gear up to 24/48 from 24/50 recently.
As long as the secondary isn't at the end of its travel, I don't see how it is hard on the belt.
Remember, it isn't all that often that that I am at these speeds. But it is there when I need it.

 

[Crossfire12]

Curious if you got full shift, I’m interested in lowering my gears from 21/41, how fast did you get 24/50 over reving

 

[74Nitro]

Curious if you got full shift, I’m interested in lowering my gears from 21/41, how fast did you get 24/50 over reving

Not entirely an apples to apples comparison because u r running cat clutches... .?
Also, I was using the slightly longer 8dn belt which I understand takes away 3 mph on top.
However, with 24/50, and 8dn I could gps 113 at 9600.
I never did observe what the speed was before revs started climbing past 9000, but I would hazard a guess of 4 mph less

 

[74Nitro]

I do know that I gained 3 mph by reducing the bottom sprocket by 2 teeth

 

[Turboflash]

It's nice having the extra 600 rpm's of RPM that a tuned turbo four stroke enables.(9000 up to 9600) No other sled can do that. It is why we can run such low gearing and still achieve great top speeds.
A 2 ratio in a 800 or 850 sled won't even be in the ball park. They come with much higher gearing from the factory to achieve speeds over 100 mph as their power peak is around 8000rpm and they have no over-rev. (assuming same size track drivers)

Wow, 9600? What tune are you running that goes up that far? Whichever one you have, have you seen the dyno horsepower curve showing it's "healthy" to run it up there? For example, my Stage 3 PEFI tune (280HP) peaks at about 8800. (See attached files). By the time it gets to 9200, it's already down 10 HP. I would guess at 9600 it's down 25 HP and bumping the rev limiter. I would not deliberately run it up there as resonance and harmonics can come into play. The engine (w balance shaft as designed by Yamaha) wasn't designed to run at 9600. Can it? Probably. Should you? I don't think so. No different than trying to run an 8000 RPM 2 stroke at 8600. Can it run at 8600, probably. Is it good for it, probably not. Maybe you've altered the internals of your engine so it likes it up there? Just gear it taller if you're up there allot.

 

[74Nitro]

Wow, 9600? What tune are you running that goes up that far? Whichever one you have, have you seen the dyno horsepower curve showing it's "healthy" to run it up there? For example, my Stage 3 PEFI tune (280HP) peaks at about 8800. (See attached files). By the time it gets to 9200, it's already down 10 HP. I would guess at 9600 it's down 25 HP and bumping the rev limiter. I would not deliberately run it up there as resonance and harmonics can come into play. The engine (w balance shaft as designed by Yamaha) wasn't designed to run at 9600. Can it? Probably. Should you? I don't think so. No different than trying to run an 8000 RPM 2 stroke at 8600. Can it run at 8600, probably. Is it good for it, probably not. Maybe you've altered the internals of your engine so it likes it up there? Just gear it taller if you're up there allot.

As I stated, I don't spend much time up there.
The sled is clutched for 88-9000.
It doesn't really matter if the power falls off, it still has oodles to pull through.
TD tunes.
And yes, I have popped it off the Rev limiter a few times.

 

[74Nitro]

As I stated, I don't spend much time up there.
The sled is clutched for 88-9000.
It doesn't really matter if the power falls off, it still has oodles to pull through.
TD tunes.
And yes, I have popped it off the Rev limiter a few times.

Two strokes power band falls off like a cliff.
Garbage.

 

[STAIN]

What chain with 24-48 gear?

 

[Byam]

What chain with 24-48 gear?

92

 

[74Nitro]

What chain with 24-48 gear?

Same as 24/50 fit, but not much adjustment left.

 

[Turboflash]

Same as 24/50 fit, but not much adjustment left.

If you want to recify that situation, there is a 2 pitch shorter chain available from Cat (not sure about Yamaha). So, 90 pitch 13 wide is 2602-760 and 15 wide is 2602-840.