33bhp Dyno Resutls

Originally Posted by BanditPat

For restriction purposes the law states that the bike needs to be 25kw(33bhp) at the back wheel. Hence why my bike is stated at 45bhp at the crank and 33 at the back wheel.

How did someone find the crank number? TBH never take notice of any Dyno number but the back wheel as any other is made up...

Yes, your point about crank power based on rear wheel power is valid. I think we have both stated that the only way to get the correct crank output is to measure it at source.

Woops, meant to edit the last post... Here is my added bit:-

Also why would you care what the Crank power is? You only feel the power at the back wheel so the only benefit you get from knowing crank numbers is bragging rights. This is what annoys me about factory power claims. An average SS600 puts down about 105-110bhp at the wheel yet some of the factories claim WAY more power... White lie's

Other thing I was reading is gearing. It makes no/very little difference from experience ive had a Dyno with low gearing then standard and I dont think it had and real effect... The only difference was down a little modifying Id done. *EDIT* Now I think about it any losses from higher gearing could have been over come by my slight modding, so it coul make a difference.

The only thing you can do to increase power reading (only on a inertial style dyno like a Dyno Jet) other than Engine tuning is to put a lighter wheel on the back. Reason this helps is because obviously there is less energy wated accelerating the mass of the wheel which means more energy transfered to the Drum on the Dyno machine which is picked up and adds to the dyno reading...

The best way to get a more accurate power output is to put the bike on an eddie current Dyno. They can hold the bike at certain revs and give real power values and more accurate fuelling as it can annalise Gasses for a longer period at a certain rev.

Hope that helps clear things up.

Originally Posted by simonDyna

Yes, your point about crank power based on rear wheel power is valid. I think we have both stated that the only way to get the correct crank output is to measure it at source.

I dont think there are many places do this... And whats the point? Its not like its more accurate or anything, it dont make the bike faster that you have the same engine with power quoted higher because you take a few of the losses out...

Basically personally id much rather hear that my bike is making ~120 at the back wheel than a guess that its making 135 at the crank.

Not having a go at you Simon. Just being overly blunt.

[yorkie_chris]

I can see what he's saying, there are times where you would need crank power, like if you were designing a gearbox or needing greater accuracy to optimise some part.

But for bike tuning, nah.

The other important fact is the DVLA state "net power output of <25kW" I interpret "net" as rwbhp.

Yeah surely the net power output = gross output - any losses

[yorkie_chris]

Indeed.

[narrator]As YC desperately tries to steer the thread back onto topical territory, and in a shocking twist, josh assists...[/narrator]

Cheeky sod. Well it's not like I've ever derailed anything before

Josh you still on 33bhp?

Originally Posted by yorkie_chris

But for bike tuning, nah.

Actually, for bike tuning, yeah. It depends on what you are using the bike for and how far you want to take its development.