A little horsepower trivia.

We all mix horsepower numbers left and right. So many different ways to look at it. SAE vs STD vs DIN vs whatever the manufacturers use to measure crank power.

How does all of that compare?

Here is a very simplistic comparison that helps puttingthings in perspective:

197hp (crank) come out to about 174hp (sae on a dynojet 250)

That's a ratio of 0.883 - some refer to that as 12% loss from transmission & co although I would caution to jump to that conclusion as we have really no idea how our dyno equipment compares to that of manufacturers.

Anyway, using 0.883 as an over- simplistic conversion between crank and wheel power, a bike making 190 (sae) hp at the wheel would have to make about 215 hp at the crank.

Do the same math for the recent 202(sae) hp and the engine would have to be rated 229 hp at the crank from the factory.

Doing some internal engine work like ported heads or different cams I can easily see how this engine can make the suggested 250 hp and more at the crank.

Makes sense? Simply Apples and Oranges...

OK, here is my question: Why do we measure at the wheel when it seems there are so many variables to distract from a real number on any two dynos. Is it the same variable disparities (spellchck) at the crank when measuring HP/TQ? How do you measure HP/TQ at the crank? Ive always wanted to know this Thanks.

What's amazing is that you create more horsepower by adding more air, getting the expended combustion gases out a little faster, fuel management adjustments and basically leaving the engine alone.

I don't like all the different horsepower terms thrown around, it's just bench racing mumbo jumbo to me. BUT I do appreciate knowing what's actually being produced at the crank. There are lot's of varibles once the power transfers out of crankshaft, so what happens then I guess is good to know too.

Anyway it's a good discussion to be had over a cup of Java or a bottle of Beer.

Then like you mentioned before, getting an accurate reading depends on who's Dyno you use and what Brand of Dyno it is.

Theohiomike wrote:
OK, here is my question: Why do we measure at the wheel when it seems there are so many variables to distract from a real number on any two dynos. Is it the same variable disparities (spellchck) at the crank when measuring HP/TQ? How do you measure HP/TQ at the crank? Ive always wanted to know this Thanks.

Hey Mike, I worked at a large manufacturer who took power producing motors(electric) or engines and connected the dyno directly to the end of the crankshafts with a coupler. Once the engine/motor was started, they would apply the dyno braking mechanisim to the engine to stop it under a load to get actual horsepower figures.

Yeah but! but! isn't it the rear wheel horse power that really counts?

I would think its all about what you can put down on the pavement.

maxout wrote:
Yeah but! but! isn't it the rear wheel horse power that really counts?


One overlooked thing here has been torque (even by myself with these "bike night" dyno sessions). I messed up by not getting the initial torque numbers/curve, so theoretically a HP loss could actually be a overall power gain if the torque was increased in the mid RPM range and tapered off up high. Changing the rear tire may have cost me some HP... but it also may have increased the torque number.

Torque is what moves the bike. My future dyno sessions will have this information (otherwise it's kind of a pointless dyno run)*

*except watching the "gawddarn did that just lay down a hunnert an' eighty two horsepair" reaction from the Harley dudes and walking away with $50 gift certificates that keep the Missus happy with my continued participation in bike nights.

maxout wrote:
Yeah but! but! isn't it the rear wheel horse power that really counts?

I would think its all about what you can put down on the pavement.

for the most part i agree, BUT using numbers @ the crank will allow considering the feasibility of different drivetrains (for instance, chain or belt drives) which could give better transfer efficiency to your traction surface...



this is a discussion that could go on forever, but we could start a pool for best-guesses as to a timeline for a gen2 chainDrive conversion kit to come to market

So which would be best? for transferring power to the wheel? Chains are the weaker than Driveshafts? But Chain drive is easier to change ratios. Yamaha spent a LOT of research and dyno runs proving the current driveshaft design to handle the awesome power, after having destroyed the older VMax driveshaft and gearing during testing of the Gen2.

So, the only way to change the ratio of the current Gen2 will be making new gear sets. I used to work in R&D designing very large gear sets (Lufkin Industries) and I DO mean LARGE! I wonder if I might convince them to make me a smaller ratio set? I bet they would...bet it'd cost about ten thousand. LOL!

sfcrick wrote:
So which would be best? for transferring power to the wheel? Chains are the weaker than Driveshafts?

IMHO
i don't believe strength was the issue @ hand...

chains can be(and HAVE been) made to transfer thousands of horsepower... these have better efficiency because :
1. you are not changing the direction of force @ least twice
2. there is much less rotating mass (typically)

Yamaha researched with focus groups and the result was
"don't f%#ck with the legend"...

i for one LOVE the almost zero maintenance of a shaft, and i will gladly sacrifice some HP & torque for that reason...

A shaft is also contained within a housing (of some fashion), so it would be alot less likely to cut the operator in half if there were a catastrophic failure.

Well if its $10,000 lets do it.. If we can drop the gearing by 1000 rpm to get more tQ and take off speed I am all for it. I will put in $10,000 and sell them for $500 each. Twenty sold and all the rest are profit. Thats what I am talking about. Sign me up!!!

This with FX speed eliminater and velocity stacks and there will be no excuses for not being in the 8"s