Power to Weight Ratio: Four Stoke vs. Two Stroke

christopher · Oct 28, 2014

Ahh yes, the ETERNAL never ending debate of Power to Weight ratios for 2 strokes vs. 4 strokes.

=====

2015 Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 150 (sea level)

Power to weight ratio = 3.28lbs per HP

(I list this just for base comparison, NO ONE is going to seriously ride a normally aspirated 4S Yamaha Viper in the mountains, while the overwhelming majority of 2S riders do ride without a turbo. I am trying to honestly compare apples to apples here..and I make NO argument that a boosted 2S will win every time until its engine fails from the added stress while the 4S runs for another 15-20K miles)

Yamaha Viper 162
Wet weight = 595lbs
Horsepower 125 (sea level)

Power to weight ratio = 4.76lbs per HP

Yamaha Viper 162 with OEM Turbo 6lbs Boost
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 180

Power to weight ratio = 3.38lbs per HP

Now lets take these two sleds up into the mountains and ride them at

6,000ft.
Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 123

Power to weight ratio = 4.00lbs per HP

8,000ft
Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 114

Power to weight ratio = 4.32lbs per HP

What happens is that just as soon as we get into some real world riding in the mountains the 4S is suddenly able to hold it's own. Of course, if the 2S rider boosts his engine, then he clearly wins the day. But I think the honest reality is that "the overwhelming majority" of 2S riders do not invest the money in a turbo or supercharger, whereas its just the opposite for 4S mountain riders.

Doesn't mean a 4S will EVER compete against a 2S on WEIGHT, but they can compete pretty well in a general sense on the Power to Weight Ratio.

And.
If we begin to raise the boost levels up a bit, as SO MANY of our 4S riders do, then the numbers really being to shine.

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 200
Power to weight ratio = 3.05lbs per HP

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 225
Power to weight ratio = 2.71lbs per HP

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 250
Power to weight ratio = 2.44lbs per HP

Dartos · Oct 28, 2014

So you are indicating the OEM turbo builds boost to an absolute pressure, not a prescribed boost above ambient pressure? If the boost is above ambient pressure, it too will loose horsepower with a gain in altitude, but you already knew that, just pointing it out for the rest of the class.

(Also all your examples at the bottom have 6 lbs of boost)

christopher · Oct 28, 2014

Sorry for not catching the copy and paste on the boost levels.
Just corrected that.

Deep Powder Guy · Oct 28, 2014

christopher said:
Ahh yes, the ETERNAL never ending debate of Power to Weight ratios for 2 strokes vs. 4 strokes.

=====

2015 Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 150 (sea level)

Power to weight ratio = 3.28lbs per HP

(I list this just for base comparison, NO ONE is going to seriously ride a normally aspirated 4S Yamaha Viper in the mountains, while the overwhelming majority of 2S riders do ride without a turbo. I am trying to honestly compare apples to apples here..and I make NO argument that a boosted 2S will win every time until its engine fails from the added stress while the 4S runs for another 15-20K miles)

Yamaha Viper 162
Wet weight = 595lbs
Horsepower 125 (sea level)

Power to weight ratio = 4.76lbs per HP

Yamaha Viper 162 with OEM Turbo 6lbs Boost
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 180

Power to weight ratio = 3.38lbs per HP

Now lets take these two sleds up into the mountains and ride them at

6,000ft.
Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 123

Power to weight ratio = 4.00lbs per HP

8,000ft
Polaris Pro 162 800 RMK
Wet Weight 493lbs
Horsepower 114

Power to weight ratio = 4.32lbs per HP

What happens is that just as soon as we get into some real world riding in the mountains the 4S is suddenly able to hold it's own. Of course, if the 2S rider boosts his engine, then he clearly wins the day. But I think the honest reality is that "the overwhelming majority" of 2S riders do not invest the money in a turbo or supercharger, whereas its just the opposite for 4S mountain riders.

Doesn't mean a 4S will EVER compete against a 2S on WEIGHT, but they can compete pretty well in a general sense on the Power to Weight Ratio.

And.
If we begin to raise the boost levels up a bit, as SO MANY of our 4S riders do, then the numbers really being to shine.

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 200
Power to weight ratio = 3.05lbs per HP

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 225
Power to weight ratio = 2.71lbs per HP

Yamaha Viper 162
Wet weight = 610lbs (15lbs added for turbo)
Horsepower 250
Power to weight ratio = 2.44lbs per HP

That is certainly one way to look at it......For the type of riding I do "peak hp" enters into the equation only when I'm climbing something steep even than there's always more hp (turbos) than most will ever use......I'm more about the " torque curve " mid range especially for boondocking & tree riding in and out of the throttle BRAP BRAP BRAP .... From what I hear the Vipers "mid-range torque" is good and really responsive perhaps nots as snappy as a 2S but pretty darn good from what here.....Clutch Setup playing a hug factor.

Weight on the other hand always feels heavier at lower speeds vs higher speeds...To Yamaha credit they do a great job with getting the center of gravity spot on to make the weight almost disappear.

DPG

christopher · Oct 28, 2014

That's an interesting point on the torque curve.
Will need to do a little hunting to find some dyno tested in graphic form that can be posted for comparison

tt m1000 · Oct 28, 2014

I thought the rmk was like 147hp? +-

Ride steep and deep!!

bholmlate · Oct 28, 2014

Yes Christopher
I am not sure what the point of this thread is other then to get every 2s guy into the Yamaha forum to say how wrong you are and the viper will never be able to compete on a level playing field with the 2s Dont get me wrong i own a 4s and the viper looks like a great sled as well. All you are really doing here is showing how you can use statistics to prove anything you want as long as you ignore anything that goes against what you are trying to prove.

DPG brings up a good point with the torque curve because torque is the force that gets you moving. in tight tree or any area you start and stop a lot it would an advantage to have a torque monster which 4s often are

christopher · Oct 28, 2014

tt m1000 said:
I thought the rmk was like 147hp? +-

Ride steep and deep!!

They are "claiming" 160 for the new 2015 HO.

christopher · Oct 28, 2014

bholmlate said:
Yes Christopher
I am not sure what the point of this thread is other then to get every 2s guy into the Yamaha forum to say how wrong you are and the viper will never be able to compete on a level playing field with the 2s Dont get me wrong i own a 4s and the viper looks like a great sled as well. All you are really doing here is showing how you can use statistics to prove anything you want as long as you ignore anything that goes against what you are trying to prove.

DPG brings up a good point with the torque curve because torque is the force that gets you moving. in tight tree or any area you start and stop a lot it would an advantage to have a torque monster which 4s often are

This thread evolved out of another thread where a member was claiming that 2S sleds ALWAYS win on the Power to Weight ratios, and its simply not true.

As for the Torque.
Right now I don't know the answer, but I will start hunting for some Dyno graphs so we can see...

BigFish BC · Oct 28, 2014

christopher said:
They are "claiming" 160 for the new 2015 HO.

that only comes in the short track axis

christopher · Oct 28, 2014

BigFish BC said:
that only comes in the short track axis

well then, I stand corrected.
Let me go back and recompute the numbers at 150hp instead of 160!

Deep Powder Guy · Oct 28, 2014

I'm confident the Vipers mid range torque will be very good especially if you keep the flipper engaged with the rpm so your alway in the sweet spot of the power band.....Best way to do this is watch the tach not the speedo.

DPG

Toolbag · Oct 29, 2014

So explain to me why you allow for a turbo to be added to one sled and not the other? You can turbo up a Pro just as easily as you can turbo up a Viper. Comparing a turbo sled to a non turbo sled and claiming apples to apples is disengenuous at best...

I think what needs to be done, if this comparison is to be at all valid, is to use a turbo 2s when comparing to a turbo 4s. Of course that would ruin your power to wieght argument wouldn't it?

christopher · Oct 29, 2014

Go back and read what I said.
A boosted 2S wins hands down!
I thought I was VERY CLEAR on that.

My point was that the overwhelming majority if 2S mountain riders do NOT use a turbo, while it is just the opposite for 4S mountain riders. The majority of them DO use a boosted sled.

Out if 1,000 Pro RMKs on the mountain, would even 10% of them be Turboed?

Out if 1,000 Vipers on the mountain, would even 25% of them be non-Turboed??

Mountaintech · Oct 29, 2014

Comparing 2 stroke torque to 4 stroke torque is like jumping out of gaspot pickup and into a turbo diesel!

turbo800 · Oct 29, 2014

christopher said:
That's an interesting point on the torque curve.
Will need to do a little hunting to find some dyno tested in graphic form that can be posted for comparison

Not sure if it matters or not, but CAT's claiming 135HP out of the 7000 vs the Viper @ 125HP listed above.

I've heard the Viper regularly dynos at 130-132HP...

TRUEBLUEMAX · Oct 29, 2014

Toolbag said:
So explain to me why you allow for a turbo to be added to one sled and not the other? You can turbo up a Pro just as easily as you can turbo up a Viper. Comparing a turbo sled to a non turbo sled and claiming apples to apples is disengenuous at best...

I think what needs to be done, if this comparison is to be at all valid, is to use a turbo 2s when comparing to a turbo 4s. Of course that would ruin your power to wieght argument wouldn't it?

Show me a $2000 turbo upgrade for a two stroke that doesn't void the warranty. No such thing. That's why there will be a lot of turbo Vipers and not many turbo smokers

stingray719 · Oct 29, 2014

christopher said:
That's an interesting point on the torque curve.
Will need to do a little hunting to find some dyno tested in graphic form that can be posted for comparison

Check any stock or turbo dyno charts on the Viper, its not a torque "curve" as it is almost level across. That is what got me to sell the M8 and buy the Viper.

christopher · Oct 29, 2014

turbo800 said:
Not sure if it matters or not, but CAT's claiming 135HP out of the 7000 vs the Viper @ 125HP listed above.

I've heard the Viper regularly dynos at 130-132HP...

I have asked MPI for some of their Dyno results from all the testing they did this year. Hopefully they can share some of their testing results for Aspirated and Boosted sleds.

christopher · Oct 29, 2014

TRUEBLUEMAX said:
Show me a $2000 turbo upgrade for a two stroke that doesn't void the warranty. No such thing. That's why there will be a lot of turbo Vipers and not many turbo smokers

Speaking with NO real firsthand knowlege here.

Are there any legitimate mass produced 2S Turbo kits for $2,500 on the market??

The MPI Turbo option on Snowchecked Vipers is an absolute STEAL in the industry.

Power to Weight Ratio: Four Stoke vs. Two Stroke

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