Going to the track

[jkotsi]

Looking to turn this 82 CBX into a track bike for vintage racing.



Starting with the basics getting the suspension upgraded, will be looking for possible frame bracing, and a diet, cutting off all the extra bits.

What is there:

CBR F2 rims on another roller, swapping out Dymags
F2 forks installed in 900 triples with Race Tech springs, emulators are on bench to be installed
Twin shock will be relocated and replaced, using Pro link swingarm for basic set up


What I would like to do:

Install F2 triples, less offset, more trail.
increase the swingarm drop to 13 degrees with adjustment to go plus or minus
Adjustable shocks, on a budget so they likely won't be fully adjustable
Swap the swingarm for a GSXR, boring frame to fit pivot rather bushing swingarm.

[EMS]

The CBR600 front end will lower this bike significantly. You may have a clearance problem on the track. Don't know what the swingarm situation is. Obviously not a Prolink anymore. What GSXR swingarm are you going to use? Do you want to use dual shocks?
Make sure you look into the rules first and determine what changes are allowed for the type of vintage racing you are going to do.

[jkotsi]

The swinger in the pic is a Pro link with mounts for the shocks. The shock length is 14.25" but they are POS for track use. There is a forward lower mount that would raise the rear but does not reach 13 degrees.

The F2 forks are about 1/2" shorter than CB900 forks. How much shorter than stock CBX forks?

Once the rear is set I will check the rake, trail, wheel base and height of engine. Longer forks will reduce the rake, I was thinking less than 25 degrees would be a good start. Adding to the top of the fork or a drop triple would be the fix if required

The GSXR swinger is from an 89 un-braced.

Jim

[jkotsi]

I haven't seen many posted pics of frame bracing. Is there much that can be done?

Top of the shock mount, tying the two together, possibly some gussets.


Jim

[EMS]

. Longer forks will reduce the rake, I was thinking less than 25 degrees would be a good start.
Jim

Longer forks will increase the rake. Increasing the length of the fork will pivot your frame around the rear swingarm pivot or rear axle and thus increasing the rake.

[NobleHops]

Looking at your photo your wheelbase looks way long, although that could be my imagination. I'd investigate that, as it will obviously make the bike slow to turn if so.

[EMS]

Looking at your photo your wheelbase looks way long, although that could be my imagination. I'd investigate that, as it will obviously make the bike slow to turn if so.

Good point, Nils! The Prolink has a longer wheelbase to begin with. Modern swingarms can worsen that. Not something you really want in a track bike.

[jkotsi]

. Longer forks will reduce the rake, I was thinking less than 25 degrees would be a good start.
Jim

Longer forks will increase the rake. Increasing the length of the fork will pivot your frame around the rear swingarm pivot or rear axle and thus increasing the rake.

Your right, said that backwards, still looking for 24-25 degrees rake.

Haven't measured the length but it should be shorter than stock 82's. The Gixxer swinger can be modified to allow a shorter wheel base. The problem with shorter swingarms is that the centre of gravity moves back. To balance the bike, looking for better that 50/50, I will need to move the engine forward.

Initially moving the engine looks straight forward but the chain alignment is affected. Need to set the basic suspension then see what can be accommodated.

[EMS]

Stock rake is 27.5°. A combination of lowering the front and raising the rear should get you where you want to be.
Corner clearance will be the major issue. The CBX motor is rather wide on the bottom. Even with stock running gear you run out of room at moderate lean angles.

[jkotsi]

I won't be doing a lot to the motor but will be re building the carbs and will need velocity stacks.

Z1parts.net has them listed, are there any other options? Looking for different lengths. Z1 lists theirs at 75mm overall length.

http://www.z1parts.net/product/carb-vel ... -52mm-54mm

[EMS]

I take it, you know what to do to the carbs to make that engine run with velocity stacks.

[jkotsi]

No, I haven't looked into the carbs. I was assuming CBX are the same as CB carbs and was thinking that the RSC carb mod would work.

I will be ordering the Mike Nixon carb manual before I start, does it detail setting up stacks?

[EMS]

Mike Nixon's book does not go into changes required to run stacks, although Mike would certainly know how to address this. You probably going to run into a little "trial and error" before you find the right set-up.
The CBX's CV carbs with the vacuum operated sliders rely on the airbox to an extend, to work properly. The Honda engineers put a little effort into the design of the air intake. In order to compensate for the unequal length of the intake runners between carb and head, they designed the intake between airbox and carb accordingly. People who want to toss the airbox and run pods for the ease of service, face the need of rejetting the carbs and shimming the needles.

[Larry Zimmer]

You mentioned 'diet'; although, nothing specific. Definitely would eliminate the alternator, battery and starter. Use a small LiPh for a total-loss ignition. Get a rear-wheel spinner for starting. As always, how much you do is significantly related to the depth of your pockets. From there, weight-saving becomes a bit more sophisticated: titanium exhaust bits, carbon-fiber seat pan, etc. As mentioned above, check what the rules allow. (And, your budget.) Above all, remember reliability.

[jkotsi]

Mike Nixon's book does not go into changes required to run stacks, although Mike would certainly know how to address this. You probably going to run into a little "trial and error" before you find the right set-up.
The CBX's CV carbs with the vacuum operated sliders rely on the airbox to an extend, to work properly. The Honda engineers put a little effort into the design of the air intake. In order to compensate for the unequal length of the intake runners between carb and head, they designed the intake between airbox and carb accordingly. People who want to toss the airbox and run pods for the ease of service, face the need of rejetting the carbs and shimming the needles.

Found this site, http://www.velocity-of-sound.com
Do the velocity stacks vary in length on a CBX? Looks like they should.

My interest was in improving the mid/upper rpm performance. I will try their velocity stack calculator when I am back on the computer.

You mentioned 'diet'; although, nothing specific. Definitely would eliminate the alternator, battery and starter. Use a small LiPh for a total-loss ignition. Get a rear-wheel spinner for starting. As always, how much you do is significantly related to the depth of your pockets. From there, weight-saving becomes a bit more sophisticated: titanium exhaust bits, carbon-fiber seat pan, etc. As mentioned above, check what the rules allow. (And, your budget.) Above all, remember reliability.

The alt will be pulled, starter once everything is in tune. I have tried the Ballistic Lithium battery, not impressed, charging was an issue. THere are newer lithium available, any recommendations?

A copy of an a 1100R seat and a Harris 1100R tank are in the garage, both need work but fine for the track.