hi i am changing my wet clutch for a dry one and i have rk5 sp gearbox and a mc28 sp one which has the closest ratios or is the better box thanks

Saying which one has the better ratio is hard as what one person likes another might hate.

The MC18 has the better gear selector mechanism though (I think).
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If I have to take the carbs off once more...

That's a useless answer Steve . Paul , if you look on Jamie's nsr site under the specs section you will see the gearbox ratio's . You can see for your self that the ratio's are closer on the 18 than on the 28 box .

Yes they are closer on the '18 but are they better? That's for the individual to decide. Personally I think the MC18 has the better selector mechanism compared to the '21 and '28.
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If I have to take the carbs off once more...

I think a good combination would be the mc18 transmission along with the mc28 primary gears.
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The '28 primary's are lower, that's only "good" if you don't go higher on the final drive.

If you do they achieve nothing.
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Surely the 28's will be geared to get the most out of bugger all horse power?
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it wouldn't be fun if it was easy!

Effectively it is;

All NSR gearbox 1st, 2nd and 3rds are the same.
The mc18 is geared lowest (and thus closest) on 4th,5th and 6th.
Then the mc21, then the '28 is geared highest.

But the '28 has a lower final drive (it's only geared for 115mph flat out in 6th) so the '28 as a whole bike has the lowest gears. Add that to what is in the real world a far more flexable motor in stock form than any mc21 or mc18 and you have a bike which gives overall very similar on road performance at legal speeds.
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fontyyy wrote:The '28 primary's are lower, that's only "good" if you don't go higher on the final drive.

If you do they achieve nothing.

Yes, ofcourse you are right and giving it a second thought the 60 teeth primary will apply more & unnecessary torque on the the tranny. That might cause some issues on gear changes with a non undercut transmission unit, well, in a well modified engine that is.
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I agree with Steve on the subject of the MC18 gear selector. Better than 21/28. More positive and less missed gears in my experience.

Also, gear ratio's that suit some people/engines may not suit others. Fitting the closest box you can find all sounds very good until you realise that if you're after top speed you can't get away from the lights without frying the clutch, or if you want a quick easy getaway then the thing hits the red zone in top way too early. My 300 street bike has an F3 box. It's geared for about 60mph in first and will thankfully pull it without too much grief. I wouldn't want this gearbox on a stock 250.

Yes, the 28 primary (2.5:1) puts more torque on the gearbox than the 21 primary (2.36:1). I know of at least three (HRC supported) race teams back in '95 & '96 that were using the 21 primary gears on their 28's.

I have a spare gearbox . How do i determine what gearbox i have ? What teeth do i count etc. ?

Thanks

Neal wrote:I have a spare gearbox . How do i determine what gearbox i have ? What teeth do i count etc. ?

Thanks for giving me the opportunity to represent my skills on graphic designing...
Check the gear ratios and compare them with the numbers in the "Specification" page.

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