Not making top speed

[Bill Hooper]

Hello,

I have two 2017 Sidewinders. One is an LTX and the other an STX. There is no difference between them as I swapped the track out on the STX for the same one I have on the LTX, which is a 1.25" Ripsaw 2 with studs. Both have the same gearing, both have had the primary and secondary clutches built with the same Thunder Products Clutching kit (weights, glide washers, springs) plus all new rollers in the primary and secondary's for both sleds. Sleds are identical as far as I can tell. Pressure tested the boost system to make sure there were no leaks. Tested to 15psi and both sleds lose 5 lbs in 10 seconds, approximately. Both have had the red fuel return line elbow drilled out to 5/32" to fix the fuel return issue.

Problem - Sled 1 hits 8800-8900 rpm at WOT, holds the RPM, but only hits about 100mph give or take a couple. Feels like it runs perfectly, just low top speed. Sled 2 hits 8700 but them immediately sinks back to about 8200 to 8300, but it hits 112 mph pretty consistently. Both were tested on the same section of trail, same conditions, at exactly the same time.

I am stumped. I have no idea why this is. My next step was going to be to install a boost gauge on both and see if both really are hitting ~10 psi and holding it. Both sleds feel perfectly good, HUGE acceleration, very smooth running, just one hits the RPM but not the speed and the other hits the speed but not the rpm.

Can anyone help me here?

Thanks!

Bill

 

[74Nitro]

Did you buy them new? Maybe one is tuned.
Same belts?

 

[Bill Hooper]

I've owned them since 2018 and 2019. Both have exactly the same belts. Neither is tuned.

BIll

 

[MrSled]

how many miles on each of them?

 

[blevis213]

Did you reach out to thunder. They're good guys they'll help you.

 

[1nc 2000]

My 17 would do this also when stock.
Even with the stock clutching.
Mine would pull the 112 speed when rpms were at 8800 or at 8400.
Never figured out and exact reason for rpm drop other than high intake temps causing computer to back off rpms.
After switching out primary clutch and tune never seen rpm drop like that any more.
Intercooler plugged with snow and ice?

 

[74Nitro]

Have you verified each speedo with a gps speed app on your phone. Are the speed sensors properly secured to chaincase, they are known to come loose and fall off.

 

[Bill Hooper]

how many miles on each of them?

Mr. Sled - Sled 1 that hits the rpm but not the speed has 11,000 miles. Sled 2 that hits the speed but not the rpm has 5,000 miles.

 

[Bill Hooper]

My 17 would do this also when stock.
Even with the stock clutching.
Mine would pull the 112 speed when rpms were at 8800 or at 8400.
Never figured out and exact reason for rpm drop other than high intake temps causing computer to back off rpms.
After switching out primary clutch and tune never seen rpm drop like that any more.
Intercooler plugged with snow and ice?

Both sleds were confirmed completely clear of snow and ice in the intercooler area.

 

[Bill Hooper]

Have you verified each speedo with a gps speed app on your phone. Are the speed sensors properly secured to chaincase, they are known to come loose and fall off.

I have not verified via GPS. I could try to do that on the next ride. Speed sensor on both sleds appear to be attached.

Bill

 

[MrSled]

Mr. Sled - Sled 1 that hits the rpm but not the speed has 11,000 miles. Sled 2 that hits the speed but not the rpm has 5,000 miles.

So one sled is tighter and one sled is loose, or one sled makes more HP then the other , if you adjusted the clutching so they they both run at the same RPM at WOT, you should see closer speeds.. just my thought.

 

[Bill Hooper]

So one sled is tighter and one sled is loose, or one sled makes more HP then the other , if you adjusted the clutching so they they both run at the same RPM at WOT, you should see closer speeds.. just my thought.

Mr. Sled - My goal was to the the sled that made the speed but not the RPM, was to get its RPM UP to where it should be thus increasing its speed. For the other sled that makes the rpm but NOT the speed, figure out why its so slow and bring its speed up equal to the other sled.

Bill

 

[MrSled]

Mr. Sled - My goal was to the the sled that made the speed but not the RPM, was to get its RPM UP to where it should be thus increasing its speed. For the other sled that makes the rpm but NOT the speed, figure out why its so slow and bring its speed up equal to the other sled.

Bill

but is the faster sled running at the ideal RPM and the slower is over reving? loading it heaver would make it work hard to make speed if it has the HP to pull it.

 

[Bill Hooper]

I did a pressure test on both sleds and found that if I pressure up to 15 lbs and stop, I lose 1 lb every 2 seconds, so I lose 5 lbs in 10 seconds. That doesn't seem like a lot to me ... am I wrong? Is losing 5 lbs in 10 seconds excessive? Seems like any loss is made up at the wastegate and so boost would stay the same.

Bill

 

[MrSled]

I did a pressure test on both sleds and found that if I pressure up to 15 lbs and stop, I lose 1 lb every 2 seconds, so I lose 5 lbs in 10 seconds. That doesn't seem like a lot to me ... am I wrong? Is losing 5 lbs in 10 seconds excessive? Seems like any loss is made up at the wastegate and so boost would stay the same.

Bill

That sounds excessive to me.. @Srxspec