MPI Turbo Viper ongoing Review.....

[Yamadog]

Is there a calculation chart to run backwards through the gearing to approximate crank HP?
stock at 70 track- approx crank 135
6.5#'s 125 track - should be about 241.25 seems high for 6.5# crank if I did the math correctly

70 x 1.93 = 135.1
125 x 1.93 = 241.25

 

[Studroes144]

I would think that with more hp, the percentage of power lost in drivetrain will grow.

 

[Srxspec]

Where are you getting the number of 125 hp to the track? That is not anywhere in the picture shown on the previous page.

Track HP vs engine HP, on our Dynojet 360 track dyno anyways, equals about 55% efficiency.

The mathematical equation I use to calculate engine HP from track HP is below.

Track HP / 0.55 = Crank horsepower

Box Stock SR Viper LTX has 73 hp to the track stock = 132.xx crank hp

Tom's SR Viper LTX set @ 5 psi had 98 hp to the track = 178.xx crank hp

Tom's SR Viper LTX set @ 6.5 psi had 110 hp to the track = 200.xx crank hp

Every engine or track dyno will read slightly different. We made 1 run at 7.5 psi that was 116 hp to the track (roughly 211 engine hp) and then we dialed the boost back down.

I can tell you that 5 psi of boost on an MPI kit will add approximately 56 crankshaft HP to the sled.

The other thing is, Tom did a very good job on installing his kit. He was not comfortable with the tune up, this is what I helped him with when we dynoed. Setting his waste gate properly and then setting his hi/low boost switch properly was worth 20 hp to the track from when he came here to when he left (I don't have the sheets in front of me, but I believe as he showed up he had 78 hp to the track on low boost previously and 90 or 93 hp to the track on his high boost setting, he also had a fair amount of lag), we picked up to the numbers you see on the previous page with tuning.

 

[TD Max]

I would think that with more hp, the percentage of power lost in drivetrain will grow.

My experience is through ownership of a chassis dyno but NOT directly related to snowmobiles.

My take on this is that:

1) There is a high parasitic loss in the powertrain and track be it gear, chain, track windage etc

2) The power loss through the gearcase track etc should remain relatively consistent regardless of HP

3) The power loss through the CVT could be variable, BUT if it were to increase significantly it would have to show up elsewhere as heat

Which leads us to:

4) The power loss cannot be considered a simple fixed "percentage" as some seem to feel

5) The only way to REALLY know is if you were to take test an engine on an engine dyno at 2 known HP ratings and then put into a sled and test again

Allen and I may come to a disagreement on this, but I still plan to use his clutch kit and/or machining

 

[Yamadog]

That is still impressive crank #'s at 7.5 #'s of boost you are gaining 10.54 hp per # of boost. which is well above what we were all going with based on earlier dyno numbers that put it closer to 9.5 hp / #. I think after the mess I got into I might want to finish my rear skid upgrade and load this thing up and get it out to South Dakota to someone who can properly set it up, clutch it and give me true dyno #'s at 9 & 12#'s of boost.

It sounds like for what I have in this thing now a few more$$$ could really get this thing on track.

 

[Yamadog]

Where are you getting the number of 125 hp to the track? That is not anywhere in the picture shown on the previous page.

Sorry Godd at math not at reading fuzzy pics on my cell phone. I liked the old site when you could clck on the pic and open it in another window.

Im going to PM you Srxspec

 

[MrSled]

Looks perfect on my phone..

 

[MrSled]

Here is more on the Dyno Runs: http://www.ty4stroke.com/threads/my-mpi-2014-viper-tuned-by-ulmer-racing.129639/

 

[Yamadog]

Looks perfect on my phone..

Sorry my phone was built by etch a sketch Still pretty healthy numbers for this motor

 

[Northern boy]

I thought I would write an update on the MPI Turbo install on the Viper. I have a little over 900 miles on it and I slowly raised the boost up to 6 lbs. Finally after some adjusting and some incredible service support from Matt at MPI the sled has settled in nicely. Its very quiet and smooth. Has a very nice mid range kick that surpasses any Apex that I have driven other then my Super Charged Apex

Fuel mileage is pretty steady at 12 MPG and have seen mid to high 11s to as good as 14 mpg depending on trail conditions and sustained speed at boost.

AFR numbers are 11.9 to 12.5 on full boost at WOT and it cruises in the 12s and on occasion with practically no throttle it may flash some 13s and low 14s..

Engine temps are steady at 167 thru the woods and long pulls on the grade it will get up around 180 deg. With this sled I would never let it sit and idle when chit chatting with your buds... it builds heat very fast and that could be death to any boosted sled.

I am not a big racer but I do like to play with the Radar Gun so as time permits I will post some numbers later in the season.

I have to admit, I was worried about boosting this sled... but I would do it again in a heartbeat.

If you have any questions or are looking for an installer and you are in my area, I can help you out. Mind you this is not a simple task installing but after you work thru some of the growing pains you find the importance of why things are moved and understand the kit some much more.

 

[Northern boy]

Hey guys,

I have done everything you have said to do, i installed an MPI turbo, we put in the clutch kit they said to put in , and changed the gears.
To 100MPH it pulls like a freight train, but that is where it stops and than I get slapped like a young girl by old Skidoos and Apex’s.
We are running old logging roads in Northern Ontario Canada, so a 15 mile straight stretch is pretty common. I thought I was going to kill everything with this beast, pretty disappointed, I road it for almost 1000 miles.
Any ideas?

 

[YamahaTim]

Hey guys,

I have done everything you have said to do, i installed an MPI turbo, we put in the clutch kit they said to put in , and changed the gears.
To 100MPH it pulls like a freight train, but that is where it stops and than I get slapped like a young girl by old Skidoos and Apex’s.
We are running old logging roads in Northern Ontario Canada, so a 15 mile straight stretch is pretty common. I thought I was going to kill everything with this beast, pretty disappointed, I road it for almost 1000 miles.
Any ideas?

Are you running the 8 DN belt. Mine did 111mph once and usually I would see 106mph. So still not a lake racer!

 

[MrSled]

Hey guys,

I have done everything you have said to do, i installed an MPI turbo, we put in the clutch kit they said to put in , and changed the gears.
To 100MPH it pulls like a freight train, but that is where it stops and than I get slapped like a young girl by old Skidoos and Apex’s.
We are running old logging roads in Northern Ontario Canada, so a 15 mile straight stretch is pretty common. I thought I was going to kill everything with this beast, pretty disappointed, I road it for almost 1000 miles.
Any ideas?

Looked for a cracked header..... machine secondary .....also really look over the install to be sure your brackets and all intact.

 

[yamahaguy]

Put some wheel kit(s) on the rear skid to help reduce drag. I have done this will all my previous sleds and wow what a huge difference 2 to 4 extra wheels makes with top end, gas mileage and not to mention slides last longer then normal.. I think track drag is often over looked. my 2 cents.

 

[Studroes144]

Put some wheel kit on the rear skid to help reduce drag. I have done this will all my previous sleds and wow what a huge difference 2 to 4 extra wheels makes with top end, gas mileage and not to mention slides last longer then normal.. I think track drag is often over looked. my 2 cents.

A lot of truth to that! Extra wheels and good slides are a great investment!