Gearbox Design

[Dave DIT]

I am currently trying to redesign the gear setup on our FS car. We are using a K6 GSXR block. What i'm looking to do is move neutral to before first gear and hopefully purchase new gears to change ratios of first to fourth and remove 5th and 6th to reduce weight and reduce gear changes. does anyone know where i can purchase gears and is the best way of changing gear selection to modify the gear selector drum??

[mech5496]

You can machine a new selector drum to move neutral before first. As for the "new gears to change ratios of first to fourth", I'm quite sure you will use a chain-driven differential, right? Just use appropriate teeth number sprockets to get the final drive ratio you want....

[Jan_Dressler]

If you just want to move neutral before first:
Leave the selector drum as it is, skip the stock first gear, modify the selector mechanism (the thing that locks the position of the selector drum) so that if you want to shift down to (stock) first, it jumps back into neutral.
Then actually use 2nd to 4th or 5th gear, and use an according final drive ratio as mentioned above.

[Kirby]

Originally posted by Jan_Dressler:
If you just want to move neutral before first:
Leave the selector drum as it is, skip the stock first gear, modify the selector mechanism (the thing that locks the position of the selector drum) so that if you want to shift down to (stock) first, it jumps back into neutral.
Then actually use 2nd to 4th or 5th gear, and use an according final drive ratio as mentioned above.

Note: YMMV, and you could end up with obscenely large rear sprockets to compensate for the shift of your first gear.

[mech5496]

Actually in our previous car we used 2nd 3rd and 4th on a WR450 with a 2.57 final drive...so not that large rear sprocket here!

[Jan_Dressler]

Originally posted by Kirby:
Note: YMMV, and you could end up with obscenely large rear sprockets to compensate for the shift of your first gear.
I had to google YMMV http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
Large rear sprocket? Probably yes. Obscenely large? I wouldn't call it that... Even with a PC37 engine (and dry sump tank squeezed between engine and diff) it looked like that back when we used that system:
http://highspeed-karlsruhe.de/content/team/2011/motor/motor.jpg
The long chain was quite heavy, but the rear sprocket itself, made from aluminium, was ok.
And it was really really a simple modification compared to manufacturing a new selector drum. Saved us a lot of time.

[Mbirt]

Originally posted by mech5496:
Actually in our previous car we used 2nd 3rd and 4th on a WR450 with a 2.57 final drive...so not that large rear sprocket here! Was it difficult to drive in tight corners with such a long "1st" gear? My calculations show 15 mph at 3500 rpm for this setup.

[Dave DIT]

thanks for the advice, yeh i worked out that by blanking off 1st and using second as 1st gear, i can have similar outputput by replacing the front sprocket with a -2 sprocket.

[mech5496]

Originally posted by Mbirt:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mech5496:
Actually in our previous car we used 2nd 3rd and 4th on a WR450 with a 2.57 final drive...so not that large rear sprocket here! Was it difficult to drive in tight corners with such a long "1st" gear? My calculations show 15 mph at 3500 rpm for this setup. </div></BLOCKQUOTE>

Try to repeat your calcs with 10" tires....Actually no problem at all, both at FSG and Italy this year.

[Boffin]

Originally posted by Mbirt:
Was it difficult to drive in tight corners with such a long "1st" gear? My calculations show 15 mph at 3500 rpm for this setup. Our car (CBR600rr on 13's), is geared to be doing 20 kph (13mph) at 3500 rpm.

We compete in Australia, and even then we have no problem out of slow corners. We're running such a low diff ratio to help get out of the corners and not turn the tyres. But then again we are over-powered.

Bit different to a single, but gives you an idea.

[Mbirt]

Originally posted by mech5496:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by mech5496:
Actually in our previous car we used 2nd 3rd and 4th on a WR450 with a 2.57 final drive...so not that large rear sprocket here! Was it difficult to drive in tight corners with such a long "1st" gear? My calculations show 15 mph at 3500 rpm for this setup. </div></BLOCKQUOTE>

Try to repeat your calcs with 10" tires....Actually no problem at all, both at FSG and Italy this year. </div></BLOCKQUOTE>Assuming a 9" rolling radius, 14/36 final drive, and 2011 WR450f gear ratios: ~49.7 mph @ 11k rpm in second gear and ~65.6 mph @ 11k rpm in third. Since it's an accel event simulator, I won't put much faith in the low-speed numbers due to slip.

I might just be used to our TIGHT school parking lot courses that often need to be driven in 1st only--thus my concern.

[keegancdr]

ok guys i need help i am trying to modify our 05 yzf 450r so that we dont have a first gear and it looks something more like N-2-3-4-5. i have searched through google and fsae forums and im not quite finding the answer i was hoping for. could someone explain this to me in a very simple way. in particular how to modify the shift drum selector so that it wont shit into 1st. thanks guys

[Drew Price]

You want to remove 1st completely? You can just weld in the groove where the 1st gear selector fork pin sits. That simple.

All you have to do is block the drum from ratcheting down to the "1st" position. Could be done lots of ways.

[Boffin]

Drill + Tap + Bolt = Locked out 1st.

Just like what drew said, position it carefully so you don't go over the peak of the ratchet/star gear on the end of the barrel

[NickFavazzo]

We make our own shift drum for the 600rr, copy to stock pattern and modify the pattern to suit what ever shift pattern you want, plenty of weight to be saved on the shift drum too if you into that...

[JWard]

Originally posted by Boffin:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mbirt:
Was it difficult to drive in tight corners with such a long "1st" gear? My calculations show 15 mph at 3500 rpm for this setup. Our car (CBR600rr on 13's), is geared to be doing 20 kph (13mph) at 3500 rpm.

We compete in Australia, and even then we have no problem out of slow corners. We're running such a low diff ratio to help get out of the corners and not turn the tyres. But then again we are over-powered.

Bit different to a single, but gives you an idea. </div></BLOCKQUOTE>

But the small singles are so torquey low down, I wouldn't be surprised if the average single on an FSAE tune had equal to slightly more torque at 3500 rpm compared to the average 4cyl on an FSAE tune. Might be wrong but I'd be slightly surprised.

[keegancdr]

so if i read what drew said correctly,

essentially im just filling up the groove, that first gear would normally fall into, with a weld bead?

and that would pretty much make it so i could shift all the way down and the bottom of my shifting would be neutral?

[Kirk Feldkamp]

Yes. Get in there and physically observe how the shifter drum works. This will answer 99% of your questions. It's just a 3D cam with grooves that pins on a few selector forks run in. You're going to need to limit the movement (however you choose to do that) so that it can't move into the "1st" position. Each fork has 3 possible positions. Engaged on one side, neutral (in between), and engaged on the other side. The 1st gear position will have two of the three forks in "neutral" while one fork slides the a dog into the side of 1st gear. In case you're wondering, in that transmission 1st gear is the only gear that's physically part of the countershaft (aka the shaft the clutch mounts onto) and is located closest to the clutch.

-Kirk

[keegancdr]

do you guys have any pictures of this process that you have possibly done, id like to get an idea of an efficient way thats been tested by someone. i understand if your stuff is secret. i guess even a drawing would suffice.

[Cardriverx]

Search shifter drum on youtube and that should explain most all the questions you have.


Originally posted by keegancdr:
do you guys have any pictures of this process that you have possibly done, id like to get an idea of an efficient way thats been tested by someone. i understand if your stuff is secret. i guess even a drawing would suffice.