Horsepower Vs. Weight

[racerrad8]

So, with the recent question about horsepower gains of installing the RPM exhaust over stock and the light-hearted gains posted, it did get me thinking.

Even if I had a dyno, some of the gains cannot be measured with the dyno. Those gains are Horsepower Vs. Weight.

Yes, the dyno will give you the engine output to the rear wheel, but what about reducing weight and the rear wheel has less weight to propel. So, I started doing some reading on this subject which is covered widely on the internet.

But lets talk FJ specifics numbers. I picked the 89-90 FJ1200W model for the calculations from this data table: https://www.motorcyclespecs.co.za/model/yamaha/yamaha_fj1200%20%2089.htm

Rear Wheel Horse Power - 112.5
Wet Curb Weight            - 571

By dividing the weight by the horsepower, I was able to determine the amount of horsepower for each pound of weight. (Power to Weight Ratio)

X=Weight/Horsepower     X=571/112.5     X=5.1 Power to Weight ratio.

I then took the weight reduction of 22 pounds by removing the stock exhaust system and installing the RPM Exhaust.

571-22= 549 pounds

X=Weight/Horsepower     X=549/112.5     X=4.9 Power to Weight ratio.

So, if we take the original weight and apply the new Power to Weight ratio, we come up with the horsepower gain by reducing the overall weight.

571/4.9=116.5 Horsepower

New Horsepower - 116.5
O.E. Horsepower - 112.5

So, the net gain of just bolting on the RPM Exhaust system over the stock system is 4 horsepower just in weight reduction.

Hopefully someday someone will post the actual horsepower improvements of the engine output to the rear wheel. That number can then be combined with the 4hp gain of the simple weight reduction.

Randy - RPM

[ZOA NOM]

That's some nerd shit right there! Nice!

[Old Rider]

This is why i always ride with almost  emty gastank !  now from jokes to guns i wonder how much horsepower i will get if i polish and port the head on the fj?

[Pat Conlon]

All things kept equal, not much...
You would be better served by unshrouding the valves.

[giantkiller]

So if I have 163 hp.and I shaved off about 42lb. How much horse power do I have now... I guess it doesn't matter I weigh 264lbs

[giantkiller]

Some day I'll get one of your exhaust systems. Just don't have any spare cash right now.

[ZOA NOM]

Ive heard 10lbs = 1hp, so you're up 4.2hp.

[racerrad8]

So if I have 163 hp.and I shaved off about 42lb. How much horse power do I have now... I guess it doesn't matter I weigh 264lbs

Original weight 571 - 42 = 529

O.E Weight    571/163 = 3.5 power to weight ratio
Light Weight  529/163 = 3.24 power to weight ratio


Now, divide the original curb weight by the new PTW ratio.

571/3.24 = 176.23 horsepower with the bike weight reduction listed

Randy - RPM

[racerrad8]

Ive heard 10lbs = 1hp, so you're up 4.2hp.

Buddy, you have to do the math...

Randy - RPM

[ZOA NOM]

Ive heard 10lbs = 1hp, so you're up 4.2hp.

Buddy, you have to do the math...

Randy - RPM

Of course you do.