some 09 stuff from yami site KINDA

[morrisond]

Yes, personally i do care about acceleration in the first 0-5m. I live in Ontario and half our trails are very tight and twisty with 20-30 m straight aways. You need that grunt to launch out of the corners and pop the front over the big holes, it's why the 4 strokes are so much better than 2 strokes on our trails as at low rpm 4 strokes make an lot more torque. The trails are so tight that the only way you would be in the power band the majority of the time on an small displacement high rpm engine is if was geared so that the top end was only 60-70mph, if not you would run out of "straightaway" before you got in the right RPM zone for max power.

On the the torque vs. RPM argument riddle me this. You are going full out on an lake on glare ice at say 110 mph. You get off the trail and get in some powder(say 12 inches), in this case the engine with more torque will be able to maintain speed better as the CVT won't be able to shift low enough to compensate for the lack of torque. Am I wrong?

 

[Alatalo]

If the choice is a multi-cylinder, high-rpm, smaller cc engine vs. a few-cylinder, low-rpm, bigger cc engine, I would pick the multi-cylinder, high-rpm, small cc thing any day (assuming same horsepower and primary gear in the high rpm case). Though, my reasons have got very little to do with the torque vs. horsepower discussion...

I think this is basically the same for most of the people who prefer the 4 cylinder motor. It sounds cool.

No, my reasons have got very little to do with the sound (a high-revving triple like the Aprilia MotoGP bike that was around in 2003-2004 generates a quite nice tune...). My reasons are based on some of the things that Laban and Tork have already been on to; the most efficient way to get a good power to weight ratio is NOT to build a few-cylinder, low-revving, big cc engine.
If this discussion is about a future RX-1/Apex engine, I for sure hope that Yamaha will base the new engine on something like the existing generation R1. I will be very disappointed if they offer a triple based on a combustion chamber design from the beginning of the motocross fourstroke era (that five valve design does nothing good for BMEP or rpm...).

The same is ABSOLUTELY true about a snowmobile and CVT. Max acceleration occurs at the Torque peak. NOT THE HP PEAK.

Then, why is my FX Nytro tuned for peak hp rpm during acceleration and not only at top speed...? Why are the snocrossers tuning their clutches to pull peak hp rpm out of the corners...? And why are the dragracers tuning their clutches to follow the pipe temperature dependent peak hp rpm...?

 

[QCRider]

Anyway, does a high-revving & low-torque engine necessarily have a narrow powerband ?

Show me one that doesn't.

Why is is that a high-revving/low-torque engine like the Phazer does rather well from the start but has a weak top-end ?

Compared to what? Compared to an old early 90's Indy 500, which was also about 80 HP it's probably pretty slow out of the hole and has relatively the same top speed...

Then there's some additional questions that one might want to think about when it comes to power just at the time when the clutch engages. First of all, can you really use it all that well on a snowmobile ?
Do you really care that much about the acceleration the first 0-5m (from standstill) unless you're racing ?[/quote]

Why do you stop at 5 mph? I personally find acceleration the most fun part of snowmobiling. Top speed is not really that big of a deal to me, but taking a sharp corner at 10 - 30 MPH and accelerating hard to the next one does.

Bottom line is this. A broad torque band is a good thing. High torque at relative high clutch RPM is a VERY good thing. High horsepower is good no matter how it comes, but it is better when accompanied by high torque.

Given all of this and the fact that high revving engines will necessarily be more expensive to build and continually operate in a more stressful manner, I still prefer no gear reduction.

One thing that still is out there about reduction gears is that at some point they are going to start to fail. We don't change the oil in them as far as I know, right? There is still a maintenance factor to them, and I am surprised we haven't started to read about it here yet.

 

[Laban]

On the the torque vs. RPM argument riddle me this. You are going full out on an lake on glare ice at say 110 mph. You get off the trail and get in some powder(say 12 inches), in this case the engine with more torque will be able to maintain speed better as the CVT won't be able to shift low enough to compensate for the lack of torque. Am I wrong?

You are wrong. Think about it, what happens with the rpm of the engine when you go out in the powder and hit full throttle ?

As Alatalo said, the CVT would adjust itself to where you get the most hp.

 

[Laban]

Anyway, does a high-revving & low-torque engine necessarily have a narrow powerband ?

Show me one that doesn't.

The Apex, Phazer ?

Broad powerband is not necessarily lots of hp at low rpm's you know.

Compared to what? Compared to an old early 90's Indy 500, which was also about 80 HP it's probably pretty slow out of the hole and has relatively the same top speed...

I doubt it. i'd say that it was the opposite. Though there are of course some differences in the suspension, track and so forth that makes things a bit difficult to compare.

Why do you stop at 5 mph? I personally find acceleration the most fun part of snowmobiling. Top speed is not really that big of a deal to me, but taking a sharp corner at 10 - 30 MPH and accelerating hard to the next one does.

How long do you think it takes for the CVT to reach the optimal rpm range ? Acceleration is done at peak hp and the CVT will reach that rpm rather quickly.

Bottom line is this. A broad torque band is a good thing. High torque at relative high clutch RPM is a VERY good thing. High horsepower is good no matter how it comes, but it is better when accompanied by high torque.

A broad powerband is always good but you usually tune a engine for peak hp or a broad powerband. The new Ski Doo engine is a great example of this, detuned for a broad powerband. Probably because they'll use it in utility vehicles, and i'm also guessing to avoid competing to much with their own 2-stroke machines.

Given all of this and the fact that high revving engines will necessarily be more expensive to build and continually operate in a more stressful manner, I still prefer no gear reduction.

I'm not so sure that they would be more expensive. I don't see why Yamaha would have built their cheapest snowmobile the way they did if that was the case.

 

[ltfrebac]

Infinite Range CVT? This is where your assumption may be wrong. An snowmobile transmission is infinite between it's starting ratio and ending ratio. But it's does have an starting ratio and ending ratio. With more torque you can have an higher lower ratio(meaning less torque multiplication) to achieve the same rate of acceleration giving you more gear on top.

At 80 mph, the CVT just can't shift down enough to multiply the torque enough to compensate for an lack of, in an High RPM engine low torque, it doesn't have the range.

Your comparison of an 19,000 rpm 900 Hp F1 engine vs an 3,000 RPM 500 HP truck engine is not valid as they are not the same HP, the point many of us have been trying to make.

In F1 the old turbo motors of the 80's had much greater acceleration as they had more torque, but similar HP to today.

An modern analagy would be Lemans Racing. The Audi Diesel makes about 650hp and 800 lbs of Torque, absoultely crushing the F1 based racers that have similar HP but much lesser torque. Audi can run larger gears, giving up not that much in accel(limited by traction anyways - just like sleds) but still accelerating faster than the F1 based cars, but crushing them on top by I think 20MPH from an press release I read the other day.

No, the Audi Diesel is crushing its competitors because of its execellent fuel comsumption which means more time on the track, and less time filling up fuel in the pits.

 

[MT RX1 Mountain Man]

What's a torque? LMFAO
This post went a whole nother direction!

 

[SLEDSTART]

lets get it back on track...
Looks like the 09's will be on the Site this Friday at 3:00 AM eastern time.

 

[QCRider]

Let's just hope for 160 hp plus, no matter how they get there.

 

[Laban]

I'm with the people that wants to keep the seating position of the Apex. Could perhaps be a little bit more rider-forward but not much.

 

[QCRider]

I totally agree with you there Laban!!

 

[Tork]

just to clear up a point others have made (and I screwed up on it too LOL)

I think there is zero weight penalty for the 4 cylinder engines gear reduction. (duh, I didnt put 2 and 2 together sooner)

If I remember correctly, the RS 3 cylinder uses a counter rotating weighted balance shaft as it is not inherently a smooth motor.
I am suspecting the Nytro likely has this too.

If I am correct, the 4 cylinder gear reduction weight would be basically offset by the weighted balance shaft on the 3 cylinder that the 4 cylinder does not require.

Now if I am wrong, well there you have it I have made a complete fool out of myself once again LOL

 

[Ike]

I´m hoping for weight loss on Yami´s + some new hp on all of them etc. LOL Yep. I know. I want it all, factory turbo on the 4-cylinder with the cost of an Phazer...

Been breathing too long 2-stroke fumes I guess.

Ike

 

[QCRider]

I really don't care that much about the weight in the DBII chassis. It's fine. I can understand for the ditch banger crowd that less weight would be good in the FX Chassis though. Simply adding power to the Apex will work for me and I don't think 165-170 is too much to ask.

 

[SLEDSTART]

I really don't care that much about the weight in the DBII chassis. It's fine. I can understand for the ditch banger crowd that less weight would be good in the FX Chassis though. Simply adding power to the Apex will work for me and I don't think 165-170 is too much to ask.

I agree on asking for the 165-170 HP range...
QC...I notice your still riding an 05 like I am. Have you had much seat time on the new riding position? I am thinking of picking up a 06 Apex in trade for my SRX plus some cash and have the 05 as my back up. I'm wondering what your opinion is on the 06 and newer as far as riding position. I'm thinking of waitin to see what comes out this friday but there are some great deals on 06's and 07's out there and you save a ton by letting somone else take the hit. Especially with the miles I have been putting on this year!

Thanks,
Snowdog