Thumper Club Forum
Club House => Chatter => Topic started by: guest1988 on June 03, 2015, 07:02:20 PM
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Hello everyone as the titles say i'm new here and joining because I have just finished my latest project and soon it will be time to finaly start on my xbr650 .yes I put he 650 engine in and had a few problem gearing it so you folks look like you know what your on about so any help(please) would be great . My interests are model engineering finished a 2 inch scale steam traction engine see picture . Now the.workshop clear Iwant to get the bike this year
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Welcome to the forum.
Have you read Dr Rod's article on the 650 convertion from one of the bike mags years ago? He used a NX650 Dominator engine and to get the gearing right he simply swapped the NX clutch basket and primary gear with the XBR ones - they are supposed to be a straight sawp - and he said the gearing was spot on.
If you want a copy of the article PM me your email off forum and I'll send it to you.
Should be an interesting project!
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Same Crank Cases and set up so shouldnt be a problem !
If you wanted to go the whole nine yards...swap various gear box parts and keep the same gear change pattern as the lever is reversed !
Jethro
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Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental cock up. The bike has been stored for about 4 years but am keen to get started .
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Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental ******* up. The bike has been stored for about 4 years but am keen to get started .
Hi
From memory looking at my brothers xbr the main problem with attempting to raise the gearing (lower the ratio!) of the final drive is that you need to either put more teeth on the front or less on the back. The front is already pretty tight with regard to the clearance to castings I think? And for memory to remove teeth on rear you risk the linksgfouling the sprocket nuts?
Give us the teeth numbers and also the teeth numbers of the primary for both versions and let's see if we can work out the problem? Are the Gearbox ratios normal xbr?
What road speed coincides with max power rpm?
Cheers.
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Thanks for the reply propeller had a look at the sprockets and the gear box sprocket has 16 teeth wont take anything bigger rear sprocket is 34 teeth .think the top speed 70 or so mph as I remember its 4 years since I last had it on the road and pops wheelys easy in 1st gear .
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Rod Gibson link. (Thanks to steve222!)
http://www.dolecek.de/xbrat/bikeclassik.htm
Just trying to find xbr gear ratios now
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Thanks for the reply propeller had a look at the sprockets and the gear box sprocket has 16 teeth wont take anything bigger rear sprocket is 34 teeth .think the top speed 70 or so mph as I remember its 4 years since I last had it on the road and pops wheelys easy in 1st gear .
If you're as far out as you're suggesting then the dommi gearbox ratios must also be different to xbr, as well as primary and secondary ratios.
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I can tell you that what you have lost in the primary you appear to have gained back in the secondary!
You are running a very high secondary gearing by what I can fathom. Probably at the limit.
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Thanks to moto 63 for e mailing me the xbr gear ratios.
Xbr top is 0.875 (top is a speed increasing ratio)
On tinternet it says dommi top gear is 0.84
Getting late so not best time to work over details, but at first glance your overall top gear gearing is about normal!
Go over again everything you know you have in there for certain and I'll check over figures tomorrow. You sure you got out of third gear? Lol.
Edit: you're not running anything weird tyre or wheel sizes?
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Thanks for the reply did read the article you mentioned in it the author suggested that maybe to avoid problems with sprocket chain pitch between the xbr and the domi it may be possible to transfer the whole of the gearbox clutch ect from the 500 to the 650 which I have done but the bike now is to low geared and red lines to the point that it has destroyed the rev counter has anyone any suggestions regarding sprocket sizes or have I .made a monumental ******* up. The bike has been stored for about 4 years but am keen to get started .
Just been re reading your posts and it looks like you have the xbr gear set and xbr primary set? So, basically, you have an xbr! As far as ratios go. But your final drive ratio is higher than stock xbr (as far as I can tell). So you appear to have an over geared xbr. This makes your opening post confusing?
Have I got that right?
Are you saying that it is too low geared because the effective engine rpm range has come down? Is it stock dommi tuning?
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Wheelies easy in first gear. WOO OO. Can I av one please. :D :D
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Stock gearing for the XBR is 15 front and 36 back.
If you know the actual gear ratios there is a calculator to estimate speed/revs
http://www.gearingcommander.com/ (http://www.gearingcommander.com/)
If it will only do 70 and wheelies easily it sounds like the gearing is way off. B&C sprockets can make almost any size to order from blanks if you need an unusual size. It should pull roughly the same speed as a standard XBR but will be quicker getting there.
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Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm
There's the problem. The difference is 1.17.
So we need to take the overall gearing found in the xbr and multiply it by 1.17.
Assuming same tyre size.
I have all ratios now for xbr and I have ratios for dommi from a tinternet site. But it would be better if anyone can provide dommi gear ratios from a manual.
Then we can work.out the best way to get Wart up to a reasonable speed!
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Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm
There's the problem. The difference is 1.17.
So we need to take the overall gearing found in the xbr and multiply it by 1.17.
Assuming same tyre size.
I have all ratios now for xbr and I have ratios for dommi from a tinternet site. But it would be better if anyone can provide dommi gear ratios from a manual.
Then we can work.out the best way to get Wart up to a reasonable speed!
Seek and ye shall find ( on page 6) ;)
http://www.eikholt.net/hpalt/download/NX650%20A%20Section%201%20Service%20manual%20.pdf
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Hmmm.... I've used a different gear calculator http://woodsware.aciwebs.com/gears/gears.asp
I put in the ratios for a stock XBR @ 7500 max revs which gives a top speed of 110mph which is about what was claimed by Honda
Using the NX650 gear ratios, with the XBR primary gearing ( clutch basket and primary gear swapped) and Wart's current final drive 16/34 this gives a theoretical top speed of 104 mph @6000rpm.
Does this sound about right?
If that is right, then it suggests the overall gearing is about right ??? but why is it only going to 70mph ( XBR's will do 70@5000rpm in top) .
(https://lh5.googleusercontent.com/ho7hkaZ_Qv2HEDbOhKxSX602FuBhm-8yoTfLIjHBj-c=w581-h567-no)
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Hmmm.... I've used a different gear calculator http://woodsware.aciwebs.com/gears/gears.asp
I put in the ratios for a stock XBR @ 7500 max revs which gives a top speed of 110mph which is about what was claimed by Honda
Using the NX650 gear ratios, with the XBR primary gearing ( clutch basket and primary gear swapped) and Wart's current final drive 16/34 this gives a theoretical top speed of 104 mph @6000rpm.
Does this sound about right?
If that is right, then it suggests the overall gearing is about right ??? but why is it only going to 70mph ( XBR's will do 70@5000rpm in top) .
(https://lh5.googleusercontent.com/ho7hkaZ_Qv2HEDbOhKxSX602FuBhm-8yoTfLIjHBj-c=w581-h567-no)
Cheers Steve.
The table above is obviously for the dommi. Trouble is that the teeth numbers given by rod Gibson don't give the ratio listed above. Who is right? Can I trust rod gibson's info for the xbr primary? Do you have any data? Mick (moto63) has e mailed me a page from his official manual showing stock xbr gear box teeth numbers, so I have those. Just need the primary ratio from a reputable database, in case the rod Gibson data has been misprinted or something.
I can do the calcs, no great shakes, but I need the data to be accurate to start with and we possibly have anomalies creeping in?
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Cant thank you guys enough taking so much time to help me out .gearing is the one thing that I just cant get my head round have no problems rebuilding the engine and on going repairs and making steam engines from scratch. The engine has had a lot (the 650) spent on it reboure piston rings cam tensioner and guides and cam little end bearing piston pin bearings as I said the bike has been unused for 4 year and is a real mess but worth doing I have both the xbr500 and the 650 Honda workshop manuals . beginning to dout my work so am going to start checking a few things am sure its ok but wont hurt to check
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Will post gearing info from Honda manual
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Cant thank you guys enough taking so much time to help me out .gearing is the one thing that I just cant get my head round have no problems rebuilding the engine and on going repairs and making steam engines from scratch. The engine has had a lot (the 650) spent on it reboure piston rings cam tensioner and guides and cam little end bearing piston pin bearings as I said the bike has been unused for 4 year and is a real mess but worth doing I have both the xbr500 and the 650 Honda workshop manuals . beginning to dout my work so am going to start checking a few things am sure its ok but wont hurt to check
No problem mate.
A) we're here to help out
B) I actually enjoy doing this stuff ;D I need a life, I know.
Nothing would please me more than to know that, between us all, we've come up against a hurdle (yours in this case) and found a solution to clear it. The alternative is to nip down your local dealer and buy a brand new bike...... Nah!
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XBR 500 PRIMARYREDUCTION 2.482 (72/29)
GEAR RATIO1 2.384 (31/13
2 1.555 (28/18
3 1.200 (24/20
4 1.000 (23/23
5 0.875 (21/24
FINAL REDUCTION 2.400 (36/15) G.11:2.7571
ANY HELP
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XBR 500 PRIMARYREDUCTION 2.482 (72/29)
GEAR RATIO1 2.384 (31/13
2 1.555 (28/18
3 1.200 (24/20
4 1.000 (23/23
5 0.875 (21/24
FINAL REDUCTION 2.400 (36/15) G.11:2.7571
ANY HELP
Yeah big help ta. Rod Gibson had 31/72 teeth, giving 2.32 ratio. To be honest that is a slight anomaly. From your description of symptoms we're looking for something huge!
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The chart is based on
1/ the use of XBR500 primary gearing ie you have swapped the clutchbasket/primary gear from the Dommi for the XBR ones.
2/ the use of Dommi gearbox ratios
3/ a final drive reduction based on 16t front and 34t rear sprocket ( I think thats what you said it was running)
4/ 6000rpm red line ( i'm not sure if this is correct)
I did a seperate chart based on bog standard XBR to check how it came out and it appears to be pretty much spot on so in theory the chart shows what you should expect your bike to do if the above information is correct.
Is it reving out fully?
I didn't bother doing a bog standard Dommi chart as it is quite a bit different.
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The chart is based on
1/ the use of XBR500 primary gearing ie you have swapped the clutchbasket/primary gear from the Dommi for the XBR ones.
2/ the use of Dommi gearbox ratios
3/ a final drive reduction based on 16t front and 34t rear sprocket ( I think thats what you said it was running)
4/ 6000rpm red line ( i'm not sure if this is correct)
I did a seperate chart based on bog standard XBR to check how it came out and it appears to be pretty much spot on so in theory the chart shows what you should expect your bike to do if the above information is correct.
Is it reving out fully?
I didn't bother doing a bog standard Dommi chart as it is quite a bit different.
Ah. Sorry. This whole thing will probably get confusing I guess. My interpretation of what he has is the xbr primary (whatever that is) and the xbr gear cluster. With a special final drive set up.
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Putting down the basics:
Std xbr setup.
Primary 2.482
Top gear 0.875
Secondary (36/15) 2.4
2.482x0.875x2.4=5.21
7000/5.21 =1343 rear wheel rpm
Wart set up.
Primary 2.482
Top gear 0.875
Secondary (34/16) 2.125
2.482x0.875x2.125=4.61
6000/4.61=1303 rear wheel rpm.
(Please feel free to correct any mistakes!)
What that rear wheel rpm equates to, we can calculate later, but it's obvious there shouldn't be much difference in top speed. This doesn't stack up against what wart tells us, but they appear to be the facts?
It looks like the dommi primary set would help raise the gearing a bit more, bringing it somewhere like a stock xbr overall ratio.
Bit of a mystery chaps. Steve has reached a similar conclusion. It's over to you wart..... :)
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Just re calculated with XBR ratios + 16/34 final drive @6000rpm which comes out with a top speed of 99mph - so something is still wrong somewhere :-\
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Just a random thought having re read your original posts - you say it revs out right into the red to the point it has bent the needle - Are you sure it's really revving out fully? The reason I ask is that when XBR tachos go wrong they read double the actual revs! ( wasted spark system so 2 sparks/impulses per rev but there is a special gremin that lives in the rev counter that only counts every other one until it gets a headache and starts counting both!)
At tickover it's not so obvious - it shows about 2000rpm but as soon as you rev it, the needle shoots around like a race bike! at 60/70mph it's bouncing off the stop!
Just wondering if you have a knackered tacho showing mega revs and a clutch slipping with the extra torque of the 650 engine? as I said just a thought - ignore me if I'm stating the bleedin' obvious - but I've found it's usually the silly little things that cause a lot of the headaches.
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stevec#222 funny you say that as I remember the taco went into the red waved about for week packed up altogether soon after clutch did slip may be it was slipping more than I realised . so I'll start pulling the bike to pieces ready for. sand blasting and powder coat frame and check engine clutch primary drive gear sure its right I'll check so should I keep gearing as is for now. Thanks everyone for the time given .
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Welcome to the group, I like XBR's and engineering :) Are you running the standard 90 section rear tire, I use an 80 and it changes the gearing quite a bit, take the height of the tire into consideration when calculating the gearing
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stevec#222 funny you say that as I remember the taco went into the red waved about for week packed up altogether soon after clutch did slip may be it was slipping more than I realised . so I'll start pulling the bike to pieces ready for. sand blasting and powder coat frame and check engine clutch primary drive gear sure its right I'll check so should I keep gearing as is for now. Thanks everyone for the time given .
Re - reading Dr Rod's article he had problems with clutch slip and had to fit HD springs and 650 clutch plates so this could well be at least part of your problem.
Also found out that the NX red lines at 7250rpm - 6000 rpm is peak torque - so re calculated gearing with your 16/34 and it gives a theoretical top speed of 119mph!!! ... I doubt the engine is going to be powerful enough to pull anything like that so you may find you eventually need to go back to something like XBR gearing of 15/36.
Keep us posted!
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stevec#222 funny you say that as I remember the taco went into the red waved about for week packed up altogether soon after clutch did slip may be it was slipping more than I realised . so I'll start pulling the bike to pieces ready for. sand blasting and powder coat frame and check engine clutch primary drive gear sure its right I'll check so should I keep gearing as is for now. Thanks everyone for the time given .
Re - reading Dr Rod's article he had problems with clutch slip and had to fit HD springs and 650 clutch plates so this could well be at least part of your problem.
I think you've nailed it Steve. Time for a beer.
I'm on my third. 6.6% as well. Hic.
Cheers chaps. :)
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Doesn't the dommi clutch run faster? Ie closer to engine speed. Because of a lower primary ratio.
This will lower the torque on it. Therefore less chance of slipping.
By eck that 6.6% beer does wonders for t'brain cells. Ok, cell.
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Talking of beer - I was given a bottle of 'Stumbro Starka' by the Lithuanian beer co for Christmas. I'm not entirely sure what it is, it looks vaugely like beer, but it's in a 200ml bottle and is 43% alcolhol! ...I think it might be some sort of Lituanian version of 'Tactical Nuclear Penguin' The ingredients don't inspire confidence - softened water, rectified grain ethyl alcohol, wine, Brady, infusion of different plants, colour & suger :o
Do I
A/ Drink it?
B/ Put it in my petrol tank and hang on?
C/ Save it for a TC rally, give it to Jethro and see what happens?
(http://manoakcija.lt/upl/items/12470-2470-trauktine-stumbro-starka-05-l.jpg)
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..........Also found out that the NX red lines at 7250rpm - 6000 rpm is peak torque.........
That differs a lot from the site I got the info from!
For nx650 6000 rpm is peak power. 5000 rpm is peak torque according to them. More anomalies!
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http://www.motorcyclespecs.co.za/model/Honda/honda_xbr500%2086.htm
http://www.motorcyclespecs.co.za/model/Honda/honda_nx650_dominator%2093.htm
No idea if this is reliable info.
Edit: bit more period info. http://www.motorcyclespecs.co.za/Gallery/Honda%20NX%20650%20Dominator%2088.jpg
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been in the shed this afternoon decided to check the bike is still a runner before stripping and restoring loads of compression and plenty of sparks drained the carb and going to have to clean it out before going any further as what came out was brown and smelled more like gloss paint than petrol . funny how you forget thing its a bugger to get the spark plug out and the bottom bolt on the card manifold a swine to get at its all coming back to me now .
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Will put up a couple pictures of the 2 xbr I'v had over the years
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This is the first xbr I got bought it new and went well longest trip taken on it was from Crewe to Isle of arran Scotland then on a small ferry to the mull of kintyer after about four days on a larger ferry to ardroson then up to fort William then to Isle of mull Mull is fantastic if you haven't been go then up to the isle of skye then home . had many more camping trip out on it .
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Bike I have now but it needs a lot of work now .
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Another one lunger I had a Bultaco tss125 liquid cooled road racer wish I still had it now seeing what they go for
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Sorry Wart, I cant get your pics to expand. can anyone help?
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Will try to make them bigger
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tried to resize
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Looking good.
Yes, we all seem to experience trouble with photos. I wonder if there's any way that could be changed? The site is a pretty popular one.
Wart, good luck with the clutch issue. If you have the dommi primary gear set, I'd give serious consideration to putting it in.
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Yes, we all seem to experience trouble with photos. I wonder if there's any way that could be changed? The site is a pretty popular one.
I'm no expert but this is how I usually do it.
If it's an online image - on google images or similar -
Left click on the thumbnail - when it bring it up right click on 'copy image location' then in the reply box on this sight select the image button ( below underscore) [img] [img] and left click between the 2 image boxes and select paste. The code should end in .jpg.
If the image is on your computer you will need to upload it onto something like Picasa, Photobox, Google + photos. Then click on the thubnail - when it brings the image up right click and select 'copy image location' then paste it into the reply box as before. You can't paste an image straight from your desktop ( at least I haven't found a way yet.)
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Nice collection of bikes you have wart, the XBR with the 650 motor looks nice. Regards Michael
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Yes, we all seem to experience trouble with photos. I wonder if there's any way that could be changed? The site is a pretty popular one.
I'm no expert but this is how I usually do it.
If it's an online image - on google images or similar -
Left click on the thumbnail - when it bring it up right click on 'copy image location' then in the reply box on this sight select the image button ( below underscore) [img] [img] and left click between the 2 image boxes and select paste. The code should end in .jpg.
If the image is on your computer you will need to upload it onto something like Picasa, Photobox, Google + photos. Then click on the thubnail - when it brings the image up right click and select 'copy image location' then paste it into the reply box as before. You can't paste an image straight from your desktop ( at least I haven't found a way yet.)
Cheers Steve.
Sorry to burst that particular bubble, but I never turn the computer on. Strictly i pad or kindle fire.
Like I say, the procedure on here is straightforward, it just won't accept anything over 250kb. I finally managed to find a way to convert a photo to less than 250kb. Only for this system to scupper me by then saying it only takes .jpg. Mine was .jpeg.
>:(
I gave up trying.
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"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm
There's the problem. The difference is 1.17. "
Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!
Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.
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"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm
There's the problem. The difference is 1.17. "
Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!
Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.
Power is a constant value from crank to rear wheel, minus mechanical losses. So the gears affect hp at rear wheel only by how many gear pairs are involved, plus of course other mechanical losses; chain, Oilseals etc.
Where gear or chain ratios reduce speed they also multiply torque by that same ratio. The ratio of the number of teeth. If gears increase speed (as the xbr top gear does) then torque is divideo by that same ratio. Some torque is lost by mechanical losses.
If you're in doubt that I speak the truth, then apply the horsepower formula and you'll see it works that way.
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"Xbr 44hp @ 7000 rpm
Dommi. 45hp @ 6000rpm
There's the problem. The difference is 1.17. "
Gear ratios are to do with the diference in turning speed, cog to cog or sprocket to sprocket, or so I thought!
Will have an influence on HP at back wheel (maybe) but can't use the above formula surely.
In the context of the thread, namely matching overall ratio to engine speed versus rear wheel speed, my comment meant that the power is the same, so is the desired rear wheel speed. The difference in engine speed is 1.17, so that is the amount we need to change the overall ratio found in the xbr, to achieve the same rear wheel speed.
Seems straightforward to me.
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I see you are still interested in the gearing problem, actual data taken from my speedo and rev counter memory is @100mph the engine was at 6128 rpm, thats a standard XBR 500 clutch and gear box with a 15 tooth sprocket but with an 80 profile rear tire
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I see you are still interested in the gearing problem, actual data taken from my speedo and rev counter memory is @100mph the engine was at 6128 rpm, thats a standard XBR 500 clutch and gear box with a 15 tooth sprocket but with an 80 profile rear tire
So it seems to be geared for 115mph? A touch more with the stock tyre?
Seems a tad overgeared for stock power?
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My bike hasnt got "stock power" :) 600cc, flowed head, special cam, big bore exhaust amongst other mods
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My bike hasnt got "stock power" ........
Ah. What power has it got? :)
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Around 40 ft lbs of torque and 50hp
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I've been reading this topic with great interest.I have no idea what revs an xbr 500 normally pulls,since mine had a knackered piston when I bought it.I have run my xbr for a few years now with an xl 600 barrel and piston,compression ratio unknown but pretty high.It is reluctant to rev over 6000,although it will do so in the lower gears if I insist.It pulls like a train in top,and if I want it will sit effortlessly at 80 - 85 for as long as I want.Top speed is about 95-98 sitting normally,just over 6000 rpms,which it reaches without too much effort.Question for the cognoscenti-has my 600 got a lower powerband/rev range due to having a 600 piston?The 600s have a power band about 1000 rpms lower than the 500,all else being equal.Should I fit a 16 tooth gearbox sprocket?
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Putting down the basics:
Std xbr setup.
Primary 2.482
Top gear 0.875
Secondary (36/15) 2.4
2.482x0.875x2.4=5.21
7000/5.21 =1343 rear wheel rpm
Wart set up.
Primary 2.482
Top gear 0.875
Secondary (34/16) 2.125
2.482x0.875x2.125=4.61
6000/4.61=1303 rear wheel rpm.
(Please feel free to correct any mistakes!)
What that rear wheel rpm equates to, we can calculate later, but it's obvious there shouldn't be much difference in top speed. This doesn't stack up against what wart tells us, but they appear to be the facts?
It looks like the dommi primary set would help raise the gearing a bit more, bringing it somewhere like a stock xbr overall ratio.
Bit of a mystery chaps. Steve has reached a similar conclusion. It's over to you wart..... :)
Blimey. This was a while ago now and we covered some ground (Ho Ho). There's a few ways to approach this, but the above post I made seems reasonably appropriate to your question. Seems that you need to be aiming for around 1300 to 1340 rpm at the rear wheel coinciding with max power engine rpm. Divide down from the engine rpm as I've done above.
How does this pan out with what you actually have?
Aiming for this rear wheel rpm is basically copying what Honda seems to have aimed for on the stock xbr500. So if we assume that they were right and that your engine power is about the same (albeit at lower revs), then aiming for the same rear wheel rpm should yield a good result for the road.
Cheers.
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Alison's XBR has a XL600 barrel and piston, gas flowed head, and bespoke exhaust. No idea of figures, but it goes like Sh1t of a Shovel, and sounds raucous ;)
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Does the standard 500 really rev to 7,800?? Mine goes off the boil over 7,000.
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Does the standard 500 really rev to 7,800?? Mine goes off the boil over 7,000.
I stand a chance of helping work out the gearing and the various torque figures. But others on here will be better able to advise on what the engines can and can't do. What I can say is that the specs for the stock 600 have it making max power at 6000rpm. That's where the data in my post above came from. So it doesn't surprise me in the slightest to hear that yours runs out of puff at 7000rpm. I wonder what the safe max operating rpm is? Before it "lets go". :o
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Knowing how Honda exaggerate horsepower figures,and the xbrs released to the Press were apparently non-standard,I simply wondered whether the bog-standard 500could actually rev as high as Honda claimed.Every road test of the xbr gives a top speed of over the magic ton-is that genuine???
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Stock mine would do 108mph, flat on the tank, which corresponded exactly with peak power in top gear on stock gearing, it had 1200 miles on the clock and the engine was in very good condition. With the Powerbronze fairing it would do 115mph with a slight crouch. It wouldn't rev higher in fifth, even with a mild cam until the cam was changed to an HRC cam and the valve springs to race springs. I think 6800rpm was about the max even with a mild tune, with the HRC cam and it would run to 8000rpm.
Years ago I created a programme that would calculate speed through the gears v engine torque, for aerodynamic drag it used a square law. Once the drag coefficient was adjusted to give the correct value derived from testing it was very accurate. If you gear too high you lose rear wheel torque and it ends up slower. The press test bikes were dynoed at 32-35bhp at the rear wheel.
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I've been reading this topic with great interest.I have no idea what revs an xbr 500 normally pulls,since mine had a knackered piston when I bought it.I have run my xbr for a few years now with an xl 600 barrel and piston,compression ratio unknown but pretty high.It is reluctant to rev over 6000,although it will do so in the lower gears if I insist.It pulls like a train in top,and if I want it will sit effortlessly at 80 - 85 for as long as I want.Top speed is about 95-98 sitting normally,just over 6000 rpms,which it reaches without too much effort.Question for the cognoscenti-has my 600 got a lower powerband/rev range due to having a 600 piston?The 600s have a power band about 1000 rpms lower than the 500,all else being equal.Should I fit a 16 tooth gearbox sprocket?
The bigger capacity moves peak power down the rev range so you lose top end. If the rest of the intake/exhaust is stock then you won't flow any more air than the 500 so peak power is not much different. I would leave the gearing as it is and enjoy the extra grunt/flexibility.
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Stock mine would do 108mph, flat on the tank, which corresponded exactly with peak power in top gear on stock gearing, it had 1200 miles on the clock and the engine was in very good condition. With the Powerbronze fairing it would do 115mph with a slight crouch. It wouldn't rev higher in fifth, even with a mild cam until the cam was changed to an HRC cam and the valve springs to race springs. I think 6800rpm was about the max even with a mild tune, with the HRC cam and it would run to 8000rpm.
Years ago I created a programme that would calculate speed through the gears v engine torque, for aerodynamic drag it used a square law. Once the drag coefficient was adjusted to give the correct value derived from testing it was very accurate. If you gear too high you lose rear wheel torque and it ends up slower. The press test bikes were dynoed at 32-35bhp at the rear wheel.
What happened on the way to the back wheel! Honda claimed 44hp at the crank and we'd expect to lose 10 to 12 percent along the way. So very high thirties. Looks like they were telling porkies. ;D
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I've been reading this topic with great interest.I have no idea what revs an xbr 500 normally pulls,since mine had a knackered piston when I bought it.I have run my xbr for a few years now with an xl 600 barrel and piston,compression ratio unknown but pretty high.It is reluctant to rev over 6000,although it will do so in the lower gears if I insist.It pulls like a train in top,and if I want it will sit effortlessly at 80 - 85 for as long as I want.Top speed is about 95-98 sitting normally,just over 6000 rpms,which it reaches without too much effort.Question for the cognoscenti-has my 600 got a lower powerband/rev range due to having a 600 piston?The 600s have a power band about 1000 rpms lower than the 500,all else being equal.Should I fit a 16 tooth gearbox sprocket?
The bigger capacity moves peak power down the rev range so you lose top end. If the rest of the intake/exhaust is stock then you won't flow any more air than the 500 so peak power is not much different. I would leave the gearing as it is and enjoy the extra grunt/flexibility.
Yes, but if the power remains the same but moves (say) from 7000 to 6000 rpm, surely you'd need to change the gearing or the bike would be undergeared? Assuming the gearing was right to start with, which it seems to be.
Edit: 108mph would become 92mph. It'd feel good getting there though. ;D
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I'm not too bothered by the mediocre performance of my xbr-I have a pair of Kawasakis to stir the blood.I bought the bike because it rekindled memories of youthful abuse of BSA singles.It has been reliable and oiltight,nothing has fallen off despite the tingles at higher revs.And it starts first or second kick,as long as you know "the routine".The kickstarter is the closest the xbr gets to a BSA single...But why go to the trouble of radial valves,complicated rocker arrangement,short stroke engine,yet producing no more power than a good British single of 30 years earlier?If Honda had given the xbr another ten horses,to equal a Goldie or a Thruxton,but with Japanese reliability,they might have produced a classic roadburner.Perhaps a standard xbr for commuting,and a sporty version for the hooligans....Imagine a GB 600 with a genuine 42 horses...
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I'm not too bothered by the mediocre performance of my xbr-I have a pair of Kawasakis to stir the blood.I bought the bike because it rekindled memories of youthful abuse of BSA singles.It has been reliable and oiltight,nothing has fallen off despite the tingles at higher revs.And it starts first or second kick,as long as you know "the routine".The kickstarter is the closest the xbr gets to a BSA single...But why go to the trouble of radial valves,complicated rocker arrangement,short stroke engine,yet producing no more power than a good British single of 30 years earlier?If Honda had given the xbr another ten horses,to equal a Goldie or a Thruxton,but with Japanese reliability,they might have produced a classic roadburner.Perhaps a standard xbr for commuting,and a sporty version for the hooligans....Imagine a GB 600 with a genuine 42 horses...
Good question. I remember reading a review by John Robinson when the xbr came out. He said it made extremely good bmep.
Kevin camerson's book classic motorcycle race engines covers a lot in this regard. Especially the two valve ducati 's contrasted with Keith duckworths four valves. Swirl versus tumble. There's more to it than meets the eye!
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Yes, but if the power remains the same but moves (say) from 7000 to 6000 rpm, surely you'd need to change the gearing or the bike would be undergeared? Assuming the gearing was right to start with, which it seems to be.
Edit: 108mph would become 92mph. It'd feel good getting there though. ;D
Once you raise the gearing the torque at the rear wheel goes down and it ends up slower.
I wrote my programme based on the original programme in John Robinson's book, which now appears to sell for a stupid price.
http://www.amazon.co.uk/Motorcycle-Tuning-Four-Stroke-Robinson/dp/0600333655
I added better graphing and torque through the gears. One day I will sit down and rewrite that programme.
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What happened on the way to the back wheel! Honda claimed 44hp at the crank and we'd expect to lose 10 to 12 percent along the way. So very high thirties. Looks like they were telling porkies. ;D
That was par for the course back then, the XL600LM was rated at 44bhp but on one magazine test dynoed it at 27bhp at the rear wheel.
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The original CB 750 was a good example of wishful thinking regarding bhp.The first 750 could manage 125 or thereabouts.The final CB750 K7 struggled to reach 110.Yet according to Honda they both produced equal power-67bhp.Honda simply could not admit that the 750 had been gradually detuned and strangled.
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Yes, but if the power remains the same but moves (say) from 7000 to 6000 rpm, surely you'd need to change the gearing or the bike would be undergeared? Assuming the gearing was right to start with, which it seems to be.
Edit: 108mph would become 92mph. It'd feel good getting there though. ;D
Once you raise the gearing the torque at the rear wheel goes down and it ends up slower.
I wrote my programme based on the original programme in John Robinson's book, which now appears to sell for a stupid price.
http://www.amazon.co.uk/Motorcycle-Tuning-Four-Stroke-Robinson/dp/0600333655
I added better graphing and torque through the gears. One day I will sit down and rewrite that programme.
You're right...... If you took a standard xbr, or any bike, and raised the gearing you'd lower the rear wheel torque. But........
We're talking here about a different bike than the standard xbr. One where the engine power and torque will have been shifted 1000 rpm down the Rev range. So, if you want to keep the rear wheel rpm matched to peak power engine rpm you'll need a different overall ratio. True, if you want to raise the rear wheel torque, then lower the gearing. But to attempt to keep the maximum power allied to the same road speed on an engine which makes that max power much lower you'll need a different overall ratio. Higher gearing.
Do the maths. Assuming the same max power (which the two examples pretty much are) and assuming the same road speed (which we can, because we already know that the power we have will get us there), then we're saying that the final rpm, the rear wheel rpm, will stay the same. Using the power formula and cross multiplying you will compute the same rear wheel torque. You have to! The only two variables are both the same value.
So, to achieve the same rear wheel rpm but with an engine which is giving that same power at a different rpm we will need a different ratio.
Would you not agree?
Edit: if we had full power and torque curves then even better. We can plot rear wheel torque curves for each gear and compare to stock xbr. We can also see how the power tails off after peak power rpm. Maybe that would influence our overall ratio choice. But the stock xbr is a known quantity and so is valuable as a datum point.
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Do the maths. Assuming the same max power (which the two examples pretty much are) and assuming the same road speed (which we can, because we already know that the power we have will get us there), then we're saying that the final rpm, the rear wheel rpm, will stay the same. Using the power formula and cross multiplying you will compute the same rear wheel torque. You have to! The only two variables are both the same value.
But now if you raise the gearing 10% then you have 10% less torque at the rear wheel. You may be able to go a little higher but, in my experience, nothing kills the top speed of an XBR faster than getting the gearing too high. If you want to go faster then you need a cam that pushes peak power back up the rev range.
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Do the maths. Assuming the same max power (which the two examples pretty much are) and assuming the same road speed (which we can, because we already know that the power we have will get us there), then we're saying that the final rpm, the rear wheel rpm, will stay the same. Using the power formula and cross multiplying you will compute the same rear wheel torque. You have to! The only two variables are both the same value.
But now if you raise the gearing 10% then you have 10% less torque at the rear wheel. You may be able to go a little higher but, in my experience, nothing kills the top speed of an XBR faster than getting the gearing too high. If you want to go faster then you need a cam that pushes peak power back up the rev range.
I would say that if you want to go faster you need more power (or less drag or both). It wouldn't matter (as a design principle) what engine rpm you got your extra power, that's the job of the transmission.
Regarding raising the gearing. Yes, I fully agree that raising the gearing of a given machine will lower the rear wheel torque. But in the context of questions asked in this thread, what we are doing is keeping the engine power the same but moving it 1000rpm lower. To put it another way we are raising the engine torque. So to raise the gearing in this instance,by the percentage difference in the engine rpm, won't lower the rear wheel torque. It will keep it the same as the std xbr.