xbr power / torque graph

[welland99]

I just wondered if anyone has a power and torque graph to share for an XBR 500?  Or, know a link to one posted somewhere on the web?

[SteveC#222]

This perhaps?

[welland99]

Excellent.  Thanks.   

Was this for your own bike?   Was it in standard trim and tune?

What does the red, blue and green writing say in the top left corner (It is too small to read)?

[JOOLZ]

Torque curve of a steam engine

[SteveC#222]

Excellent.  Thanks.   

Was this for your own bike?   Was it in standard trim and tune?

What does the red, blue and green writing say in the top left corner (It is too small to read)?

Not my bike, but a standard XBR as I remember.  If you save the image onto your desktop you can then use something like Picasa viewer the blow the image up to a larger size. Standard back wheel BHP on the average XBR seems to be low-mid 30's the 44bhp claimed by Honda seems a bit ambitious, though early journalist tests reported being able to "lift the front wheel on the throttle in first.."....not on any standard XBR I've known.  Maybe using 'Triumph' tactics.. ( Triumph supposedly unvailed the new Tiger 110 to journalists in the morning letting them view it and potter around the factory before giving them a slap up meal prior to afternoon 'speed testing'. While they were scoffing the mechanics were frantically fitting the 'standard' test bikes with racing cams, high comp pistons etc so the bike got glowing reports on the performance in the magazines!!).

[Propellor]

Honda's claim would have been crankshaft power?

Most sources I've read reckon a 10 to 12% loss from crank to rear wheel, which sounds reasonable depending on how you view the efficiency of the final drive chain.

A rolling road dyno obviously measures rear wheel torque. To my knowledge it is then at the discretion of whoever is in charge of the dyno computer to "factor in" the losses retrospectively (so to speak) to express crankshaft power.

So, if I'm right, we should have been expecting high 30's hp rear wheel power? 39hp ish? Which we haven't got, so yes, honda's claim does look dodgy! Very dodgy!

Actual traction of tyre is something to consider and I don't know how they go on with that as a factor?

[guest564]

Somewhere I have a couple of old mags with dyno plots and they both show around 32bhp at the rear wheel so I don't think the press bikes were tweaked. This was mine with an HRC cam and exhaust:



Unfortunately it shows MPH rather than RPM. I've no idea what gearing it was on that day, I would guess its a fourth gear run.

[Propellor]

Somewhere I have a couple of old mags with dyno plots and they both show around 32bhp at the rear wheel so I don't think the press bikes were tweaked. This was mine with an HRC cam and exhaust:



Unfortunately it shows MPH rather than RPM. I've no idea what gearing it was on that day, I would guess its a fourth gear run.

Blimey. That's some hike in performance!

Mph I assume is calibrated at the circumferential speed of the drum? If so, perfectly valid as HP. We just don't know at what crank rpm and therefore what crank torque value is. Yes?

Can we plot a torque curve? Do we need to know the drum dia?

[JOOLZ]

Maybe I should get mine on a dyno, just to have some cold hard numbers I estimate around 46-48 hp with maybe an extra 5 with the methanol going
The bikes just come off the road for the winter and I will be fitting my new reworked head, doing some more lightening work and maybe a respray.

[Moto63]

Hi joolz, have you got any pics of your meth x "beast" r. I,ve just started work on my number two project xbr "brat tracker" and wud love some serious engine inspiration

[guest564]

I should still have a bunch of dyno runs but they would be on a floppy disc somewhere and I don't have a FDD anymore. I know that I did have some RPM/BHP plots but I wasn't that fussed by overall numbers I was just looking for more than I got before. The most bhp I got was with a Kent Cam but it was too peaky for the stock gearbox and lost too much power out of a corner on a twisty track.
For road use the best mod that I did was to replace the HRC exhaust with a Micron, I lost a lot of power at the top end but gained a massive amount at mid-RPM, I would say that it was much faster 99% of the time.

[Propellor]

I should still have a bunch of dyno runs but they would be on a floppy disc somewhere and I don't have a FDD anymore. I know that I did have some RPM/BHP plots but I wasn't that fussed by overall numbers I was just looking for more than I got before. The most bhp I got was with a Kent Cam but it was too peaky for the stock gearbox and lost too much power out of a corner on a twisty track.
For road use the best mod that I did was to replace the HRC exhaust with a Micron, I lost a lot of power at the top end but gained a massive amount at mid-RPM, I would say that it was much faster 99% of the time.

Interesting stuff. That's why I was interested in trying to plot a torque curve. To see how it looked mid range, compared to stock. It's the only way an innocent bystander ( can glean any such "feel" for it. I could get close based on the tyre rolling radius. In a quiet moment. Instead of picking my nose.

What do you know about 250rs tuning?



Cheers

[JOOLZ]

Hi joolz, have you got any pics of your meth x "beast" r. I,ve just started work on my number two project xbr "brat tracker" and wud love some serious engine inspiration

Have a look on the projects page, on page 2 there are photos of the bike build. Hope that helps also a youtube video

RnsIw

[Moto63]

Thanks for the info joolz, I checked out your project pages, found them very interesting and has defo given me the inspiration I was looking for

[guest564]

What do you know about 250rs tuning?
Cheers

There was a guy that used to race a Yoshi tuned 305cc RS back in the day, it did well against the FT/XL engine specials, it was primarily a big-bore kit, cam and bigger carb with a little head work. Dixon Racing used to sell the kits over here and White Bros. in the US used to sell a lot of XL tuning parts that fitted.