120mph on “Dream-o-meter” = ?

I hear ya I think we are on the same page... but do you think that my track was slipping 15mph or so faster than I was traveling or do you think the configuration or measurement is just off?
 
Both. Speedo's aren't exact and you lose from slipping.

Had an 03 RX1 that would role out at 115 mph in 1000 on hard pack. Felt like no slip great bite. Radar showed 96/97 every run. I could watch the speedo drop back to 100 ish almost instantly after getting off the throttle then coast down from there.

Air gets very heavy. 120 mph is hard to do in perfect conditions with a stock sled that has been prepped for speed runs.

opsled
 
In my experience with my viper over the years the speedo reads approximatly 14% high versus radar guns. So assuming the same for you would mean that 120MPH/1.14=105.26MPH. The other gentlemen are right about the track spin on anything but ice with picks. I have commonly actually felt a slight acceleration for a moment when going an indicated 100 mph while letting off the throttle for a second and the speedo drops at least 10mph in the right conditions. You can only figure out what potential top speed could be with rpm not current mph. Below is the way to calculate potential top speed with any gearing and other known driveline information.

Size of track drive sprocket - Viper - 9 tooth x 2.52" pitch track = 22.68" Diameter
22.68"/12 to convert to feet = 1.89' 1.89'/5280 feet in a mile to covert to fraction of a mile = 0.000358
0.000358 x 60 (Converts RPMs to Revolutions per Hour) = 0.0248
0.0248 x 8600RPM (top nominal stock pipe shift speed RPM) = 184.728 MPH
182.728 x 22/38 (Stock Viper Gearing) = 106.95 MPH theoretical top speed at 1 to 1 clutch shiftout. Some overdrive is possible but not as efficiant as 1 to 1 or very likely.
106.95 MPH x 1.14 for dreamometer reading would be 121.92.

You could change any of these perameters to get a the potential top speed.

Having said all this 120 MPH on the speedo is very high for a stock viper. The highest I have ever seen on mine is 122 MPH in perfect conditions (Hardpacked very icy back road with just a small dusting of snow for lubrication). Most of the time an indicated 117 to 118 MPH is about it. My viper has had some pretty good trail porting work done to it and ALOT of clutch time spent. I beleive either yours is indeed modified (most likely ported) or someone has changed you track driver from 9 tooth to 8 tooth. This would most likely have been done to accommidate studs in a 1.25" tall track. You may want to count the teeth on your track drive sprocket to be sure. If it is an 8 tooth driver your real speed calculation would be as simple as 120MPH/1.14=105.26 105.26 x 8/9 = 93.57 MPH This is as long as nobody ground any teeth off the speed sensor on the clutch side of the cross shaft which is a trick to get the speedo more accurate.
 
All I can hope is one day I have a tenth of the knowledge some of you have on this site (opsled & bornyamaha). I appreciate everyone’s responses on this. The sled isn’t studded however it has a new track so it may have been in the past. I will have to count the teeth I appreciate the suggestion. I must say the sled really runs it may have more under its skin than I know. Wish I had more knowledge to know what I have.
 
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opsled said:
You don't know. You can calculate what speeds should be at certain RPM's and certain shift positions in the CVT system but there are no indicators of exactly where the shift position is at any certain time. Only approximate calculations can be done with RPM and they could be way off. To many variables.

Speed is counted off drive axle so if the math has been done correctly by the manufacturer and nothing on the sled has been altered speed should read correctly if there are no traction issues.

opsled
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Thanks, that was really my point from the beginning :) Just use a GPS and be done with it ;)
 
mmordan said:
All I can hope is one day I have a tenth of the knowledge some of you have on this site (opsled & bornyamaha). I appreciate everyone’s responses on this. The sled isn’t studded however it has a new track so it may have been in the past. I will have to count the teeth I appreciate the suggestion. I must say the sled really runs it may have more under its skin than I know. Wish I had more knowledge to know what I have.
Click to expand...

I'm guessing we live close to each other so I may be able to help you figure out what you have. PM me if you like.
 
I would think the term slippage and spin are different. Think of this when the track applies force to the snow the snow is soft and gives a bit %15 means every 10 feet your tracked pushed the snow a foot and a half backwards. Its more an issue of what your applying the force to soft snow.
 
kart74 said:
When I ran my viper on asphalt the speedo would say 130 and it was 116 actual
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An asphalt track has a lower profile than most trail snow tracks which would factor into the lower actual speed.


Think about it like this. Your drivers are the wheel on your car and the track is the tire. Lower profile tires will decrease your actual speed but the speedo won't know so it reports as though you still have the factory tires.

opsled

PS, 116 is moving great for a stock Viper. You are dialed in good. Congrats.
 
Ha! I wish it was stock. It was piped, and not dialed in well at all. Only did it a couple times, but needed alot more suspension work to get it right
 
BornYamaha said:
In my experience with my viper over the years the speedo reads approximatly 14% high versus radar guns. So assuming the same for you would mean that 120MPH/1.14=105.26MPH. The other gentlemen are right about the track spin on anything but ice with picks. I have commonly actually felt a slight acceleration for a moment when going an indicated 100 mph while letting off the throttle for a second and the speedo drops at least 10mph in the right conditions. You can only figure out what potential top speed could be with rpm not current mph. Below is the way to calculate potential top speed with any gearing and other known driveline information.

Size of track drive sprocket - Viper - 9 tooth x 2.52" pitch track = 22.68" Diameter
22.68"/12 to convert to feet = 1.89' 1.89'/5280 feet in a mile to covert to fraction of a mile = 0.000358
0.000358 x 60 (Converts RPMs to Revolutions per Hour) = 0.0248
0.0248 x 8600RPM (top nominal stock pipe shift speed RPM) = 184.728 MPH
182.728 x 22/38 (Stock Viper Gearing) = 106.95 MPH theoretical top speed at 1 to 1 clutch shiftout. Some overdrive is possible but not as efficiant as 1 to 1 or very likely.
106.95 MPH x 1.14 for dreamometer reading would be 121.92.

You could change any of these perameters to get a the potential top speed.

Having said all this 120 MPH on the speedo is very high for a stock viper. The highest I have ever seen on mine is 122 MPH in perfect conditions (Hardpacked very icy back road with just a small dusting of snow for lubrication). Most of the time an indicated 117 to 118 MPH is about it. My viper has had some pretty good trail porting work done to it and ALOT of clutch time spent. I beleive either yours is indeed modified (most likely ported) or someone has changed you track driver from 9 tooth to 8 tooth. This would most likely have been done to accommidate studs in a 1.25" tall track. You may want to count the teeth on your track drive sprocket to be sure. If it is an 8 tooth driver your real speed calculation would be as simple as 120MPH/1.14=105.26 105.26 x 8/9 = 93.57 MPH This is as long as nobody ground any teeth off the speed sensor on the clutch side of the cross shaft which is a trick to get the speedo more accurate.
Click to expand...

Just checked it is a 9 tooth track drive... So from what you said this would imply the there has been some work done to the engine to boost performance? I took someone else’s advice and downloaded a GPS speedometer app so hopefully it works up north because our snow by my house is in water form. I don’t think my wife will let me do any grass drags lol... Next time I have her out I will try to get a top speed reading on the GPS. Thanks for the advice everyone!
 
tomseal6 said:
Do you know what RPMs you were at. Can be calculated
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Hey so I originally replied with an estimate on the RPMs and was off... Was up north again on the same trail and decided to try a run at top speed again. I hit 121mph this time and was sure to watch the tach. It was steady at 9000rpm. From what I’ve seen on here 8600 is the mark to shoot for. My question is how will that effect my performance? The sled pulls great up to the top and has great throttle response. I just don’t want to over-rev and hurt the motor? Is there better performance to still be had with some clutch work? Where do I go from here?
 
It should definitly pull harder around 8600. The conditions can make a big difference in the shift speed. The less load, (very icy road or trail like you may have been on to acheive that speed or very fluffy snow, spinning alot), can raise your RPMs quite a bit higher than you may want. A warm day with sticky snow can bring it below where you want. The engine power on cold vs warm days will have an effect as well. I try to aim for 8500 to 8600 all the time and I can definitly feel the acceleration tail off if I start getting past 8700. Having said this I can tell you that there have been several days that I have been close to the 9000 rpm area most of the day if I am on it hard. If you set it up to be at 8600 on those days then if you get a really warm day with heavy snow you might be down to 8100 to 8200 and that seems worse. It may be worthwhile for you to add some weight to your primary weights and experiment a little. If you don't want to be changing things all the time for different conditions (been there done that) it is best to find a happy medium. With your top speed I would just make small changes. Not sure how well you accellerate (It can be a very different thing than top speed) but with the top end numbers you have it must be running pretty good.

You can run all day at 9000 rpm. It won't hurt the motor.
 
I was riding on a hard packed seasonal road/trail so the conditions were great. Temps were in the mid to low 20’s. The sled pulls out of the hole and all the way through the power band up to the top very well I would say. My dad was riding with me
on his Apex and we both hit WOT a few times on some straights and he wasn’t pulling a gap on me. We also traded sleds for a bit and the Apex didn’t feel any faster from going 40 to WOT. It felt a little faster out of the hole but it isn’t studded and was hard to get it to hook good (very torquey). Next time I get out with home we will have to line em up. I don’t have pipes s10mike. Clutching to me is a foreign thing I’ve never even seen a clutch apart. I’ve done rebuilds on 2 strokes (top end) but never touched a clutch. Kinda scares me, plus I don’t have a puller or anything (read you can do it on the sled without one) but I’m afraid to tear it apart with the sled running so good. Will dropping the RPMs lower my top speed?
 
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Kind of almost makes me wonder if it could be a big bore and or at least ported and you don't know it.

Sent from my SM-G930V using Tapatalk
 
From my 9000 plus miles of seat time on my old 700 Viper that would probably be 106-108 mph. They mostly get real whacko close to 100 and beyond.

A couple times I had a reference with a buddy riding alongside with a GPS device. One time I was seeing 111-112, GPS was 102.....highest I ever saw on the speedo was 125, GPS said 113.....had a strong tail wind at my back on a lake.
 
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BornYamaha said:
Kind of almost makes me wonder if it could be a big bore and or at least ported and you don't know it.

Sent from my SM-G930V using Tapatalk
Click to expand...


I plan on pulling the head this summer and doing the Opticool gasket. Do you or anybody know the stock cylinder diameter vs the big bore? Someone else had mentioned possible port work being done... How do I check for this? What do I look for? I’m not a mechanic but have turned a few wrenches... any help would be awesome, thanks guys!
 
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