Scatter,

I think the number to watch when you hit the dyno is the ET from the start of the run to peak hp. We use the two units called torque and horsepower and reducing rotating mass will increase your rw torque and horsepower but what those numbers don't show you is how much quicker you get to a given rpm that has more power than the one before it.

Looking at it that way, even if you only gain a couple of hp, if you are getting to to your shift point markedly quicker even under load, you could theoretically gain more speed than your new hp numbers would indicate.

Later

 

Ok so what your tellin me is launch in third on the button![img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img]

 

While a 20lb lighter axle is significant in terms of overall weight, don't confuse that with rotational mass. Rotating mass is strongly dependent on the distance the mass is located from the axis of rotation. Since all of the mass of an axle is so close to the axis of rotation it takes much more weight to affect the overall rotating mass. Unlike wheels. tire, sprocket, and chains that have their mass located furhter from the axis of rotation.

Rotating mass is defined as the moment of intertia I=mr^2 where m=mass and r =radius from the axis of rotation. As you can see from the equation the radius plays a big role.

 

Oh yeah, I will be installing my new Chromolly tubing axle with Yamaha hubs, sprocket hub, and disck brake and 520 conversion kit this month. What is really cool about the Chromolly tubing is it is strong enough to maintain stock width for the serious duners but I will be shaving also around 20 lbs of rotating mass with everything taken into account, including my new 8" Yamaha rims. I am first and formost a duner and I often show my friends the underside of my quad (Like you Scatter). It would only be worse if I had to make my rearend narrower........that didn't come out right.[img]i/expressions/face-icon-small-disgusted.gif[/img]

I am looking forward to some gains on the hill though. I think the axle is costing me around $500 all set up. The bad thing is I have to run a Yamaha carrier so a new swingarm is coming with the setup. I will be around $1000 by the time I install the chain conversion and powdercoat the axle and new swingarm.

BTW, stock width helps maintain the sleeper M/O I love to portray. My DS looks pretty much stock. The new 8" wheels will start tipping somebody off though. Scatter, I am curious to see how your 25" tires act. I bet they will look killer!

Later[img]i/expressions/face-icon-small-happy.gif[/img]

 

DSengineer,

Awsome info! Thanks for the formula! That makes perfect sense.[img]i/expressions/face-icon-small-happy.gif[/img]

Ron

 

I was told once that it was for every 25LBS reduced a gain of 1 HP , does that sound true??

 

Very well said! ..... or as we say on Sunday morning...AMEN!

 

from my experience, that is probably a little conservative..

222

 

How conservative??

 

First off we need to define the 25lbs in question. Are we talking dead weight or rotating mass? Big difference. You can't simply define rotating mass in lbs.