Thumper Club Forum
Club House => Chatter => Topic started by: john g on November 27, 2006, 04:26:08 PM
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Hi, can anybody tell me what the power output of a tuned xbr engine is?
ie. basic eng (approx 44bhp)
mild tune ?
med tune ?
full tune & all the trimmings ?
& what carbs / exhaust / cdi etc.
Keeping the engine 500cc (ish) as I already have a couple of std. motors etc. & don't want to start spending on 600 barrels etc. but would like to fit a good motor in a Tigcraft race chassis ready for next year (but only if I can get some (cheap) power out of one!
All advice will be appreciated. cheers, John..........
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I think Honda were pulling everybodies Plonka when they said 44bhp for the XBR !
Having had two and worked on them for a number of years I think mid-30s is being generous.
Wait for #1 opinion he who has many........
Jethro
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Standard bike, probably mid/high 30's BHP. White bros did a nice tweek up kit. claims on other pages of measured 48bhp & 63BHP! One German guy took his GB out to 670cc with an NX650 engine & piston kit. Have a look at these.
http://www.dolecek.de/2005/cycleworld.htm
http://www.thumperpage.com/articles/gb-500faq.html
http://www.thumperpage.com/articles/GBprep.html
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When Motad made an exhaust for the XBR they had to issue a disclaimer saying that despite giving the bike a 3hp power gain it still only put out 5 less horse than Honda claimed.
As Richard Moore put it, an XBR probably once briefly made 44hp at the crank before thinking 'sod it' and going for a cup of tea.
GC
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According to the US thumpers, a reasonably high state of tune reduces the engine to bits rather quickly. It seems that this is an engine that will run forever in standard tune but break as soon as it's asked to do more. Far more logical to get one of those 450 motocross engines and detune it. Longer piston skirt, slightly lower compression, remap the advance curve, that sort of thing. It'd be pretty easy to do and you'd have maybe 55hp.
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I thought that the claimed HP for the 450's was around 55hp at the crank - by the time you detuned them enough to get longevity/reliability how much would you have left at the back wheel? Probably a lot more than a stock XBR, but I'd guess a fair bit less than a decently tuned 650/660 Yam/Honda/KTM/Rotax etc etc
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I was reading in motorcycle Sport& leisure today that KTM are going to produce a new version of the LC4 with a claimed 60BHP!! could be interesting!
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MITO 500 for ~£4000 sounds like a cheap racer! ;-)
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As Richard Moore put it, an XBR probably once briefly made 44hp at the crank before thinking 'sod it' and going for a cup of tea.
GC
I'm sure that wasn't me ;-) Anyhow, the only time I put an XBR (OK, it was a GB, same difference) on a dyno was when I had to replace a worn cam with a reprofiled one from Kent Cams. Didn;t increae the power but mved it up a bit. Peak power was 35 bhp, which is about as good as you'll get at the wheel with a standard engine. At some point I must dyno the tweaked 650 I have in it now, (a) to get the carburation right and (b) to see what it makes.
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Hi, can anybody tell me what the power output of a tuned xbr engine is?
Oh, and join the GB500 Yahoo Group, ask Randall Zempel.
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Thanks for the info so far people, but don't lose track! I only want to tweak a couple of 500 motors that I have lying around without spending too much, as they will only be used for light track practice & as a standby spare bike in case my (PROPER) XT 640 in a Tigcraft frame lets me down & I woudn't want to.............ps, if it runs ok then anyone who fancies having a go at singles racing will be welcome to run it around Mallory on a wednesday afternoon sometime next season!
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As a wise man once said theres no substitute for cubic inches (or centimetres)
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As a wise man once said theres no substitute for cubic inches (or centimetres)
An efficient, gas-flowed head, decent pipe and carbs will come close tho. And may be cheaper! :)
a
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As a wise man once said theres no substitute for cubic inches (or centimetres)
An efficient, gas-flowed head, decent pipe and carbs will come close tho. And may be cheaper! :)
a
and a damn sight more efficient than a lumbering large capacity yank tank ;-))
Having said that, I've never understood the hate hate relationship this country has with large automotive engines :-(
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and a damn sight more efficient than a lumbering large capacity yank tank ;-))
Having said that, I've never understood the hate hate relationship this country has with large automotive engines :-(
I would love to muck about in a supercharged V8, thing is the petrols too pricey :(