Building a track bike

[~*STEPH*~]

To chime in on the tires:  I ran a 120 (not 110) 003 on my 89 stock front rim for my last race of the year at Beaverun.  The tire fit fine and it slowed the twitchiness down just a tad.  The tire was a dream!  I am stuck with a 090 on the rear but who cares since I am not spinning the tire up every exit.  Keep us updated on what you do, especially the lightening part...

BeaveRun, as in PA?  I go to that track a lot!

[fastedmiami]

Yes, we were there racing the first weekend in October.  It's a fun little track, but I would not want to be on it on anything bigger than an sv, it's just too scary!

[~*STEPH*~]

We're done riding for the year.  It's too damn cold....and not to mention, there's no electric and we sleep in our trailer and last year in October I thought I was going to wake up w/ frostbite on my toes!!!  LOL  Maybe i'll see you around in the spring.  If you see a trailer w/ PAsportbikes.com on the side, stop by and say hi!

[andyroach]

To chime in on the tires:  I ran a 120 (not 110) 003 on my 89 stock front rim for my last race of the year at Beaverun.  The tire fit fine and it slowed the twitchiness down just a tad.  The tire was a dream!  I am stuck with a 090 on the rear but who cares since I am not spinning the tire up every exit.  Keep us updated on what you do, especially the lightening part...

What class do you race in? I assume you are using Bridgestone tyres? What suspension/ engine spec do you have? If you are allowed engine mods you may be interested in what I plan to do to the head(when I get time to actually buy a bike) I will refresh the top end(new rings, lap the valves, clean pistons and ports And possibly skim the head, if there is room )add the lunch box filter and open race exhaust. then Dyno. After that I will be flowing the head and taking pictures and writing down what I do at every step. Then redynoing and posting the results here along with all the pic's and info(I'll have to contact a moderator to help with this). I would like to find out a way of making some cheap higher lift, longer duration cams, but haven't had any ideas yet.

[fastedmiami]

I run in three classes:  Vintage Heavyweight, Vintage Lightweight and Superbike Light.  I won the championship in Superbike Lt over a highly modified fzr400 (I think the guy actually has a 600 engine in there ) and finished second in vintage lightweight by 9 points over a fzr600.  Vintage heavy weight I finished third to the same fzr600 (took second place) and a really modified ex500 (I raced this bike during one race when I crashed my gs and this bike was drafting sv650's, just to let you know how modified that ex was!)  My bike is essentially stock.  I have a slight port job done (I would consider it a stage I) with gr650 cams in it.  The gr650 cams are hotter than stock but not as hyper as full on race cams.  I have a vance & hines race pipe and that is it.  I am torn between building a motor with 79mm pistons in it or selling the bike and buying an sv.  I am also exploring other engine options in a quest to get reasonable hp for the price.  I love my gs but it is for sale so I can buy the sv to race next year.  If it doesn't sell than I will dump about a grand into the motor and have at it again.  The front end is stock with race tech internals and I have a gsxr600 rear shock internals fitted to the stock rear shock.  I missed out on buying a works shock a few weeks ago, which bums me out. I should have jumped on it and didn't.  Next year for the front end I will be installing a front end from my 93 gsxr750 since I have one laying around and will just have to pay to get the stem modded to fit my gs.  Keep us posted as what you do, I am especially interested in seeing a hp figure.  I want to build a race motor but do not want to have to rebuild it on a regular basis because it was made into a grenade.

[andyroach]

I run in three classes:  Vintage Heavyweight, Vintage Lightweight and Superbike Light.  I won the championship in Superbike Lt over a highly modified fzr400 (I think the guy actually has a 600 engine in there ) and finished second in vintage lightweight by 9 points over a fzr600.  Vintage heavy weight I finished third to the same fzr600 (took second place) and a really modified ex500 (I raced this bike during one race when I crashed my gs and this bike was drafting sv650's, just to let you know how modified that ex was!)  My bike is essentially stock.  I have a slight port job done (I would consider it a stage I) with gr650 cams in it.  The gr650 cams are hotter than stock but not as hyper as full on race cams.  I have a vance & hines race pipe and that is it.  I am torn between building a motor with 79mm pistons in it or selling the bike and buying an sv.  I am also exploring other engine options in a quest to get reasonable hp for the price.  I love my gs but it is for sale so I can buy the sv to race next year.  If it doesn't sell than I will dump about a grand into the motor and have at it again.  The front end is stock with race tech internals and I have a gsxr600 rear shock internals fitted to the stock rear shock.  I missed out on buying a works shock a few weeks ago, which bums me out. I should have jumped on it and didn't.  Next year for the front end I will be installing a front end from my 93 gsxr750 since I have one laying around and will just have to pay to get the stem modded to fit my gs.  Keep us posted as what you do, I am especially interested in seeing a hp figure.  I want to build a race motor but do not want to have to rebuild it on a regular basis because it was made into a grenade.

You may not have to have a stem made up for your gsxr front end. First off measure the gsxr stem and the gs outer cone( Outer part of the bearing that fits in to the frame) Then go to your local bearing stockist and see if there is a bearing to match your 2 sizes. If there is you may be able to get away with making up a spacer or something similar. If they are just too different you could see if you can press out your gs stem from the bottom yolk and press it in to the gsxr bottom yolk. Do a bit of measuring first to see how much difference(if any) there is. I did this on my race guzzi front end, but have also had to have stem's made up for other bikes as the difference is just too great.
Your bike sounds like a bit of a missile if it is beating FZR600's. I have been thinking about the GS head alot and I think the limiting factor is that it is a 2 valve head and you can only get so much gas in there with out trying to squeeze bigger valves in to the head(which can lead to other problems, like valves touching on over lap,loss of power at lower and mid  revs ). I was wondering if anyone has tried fitting a GSX400 head to a gs motor. You may have to machine the pistons a little, but you would get higher compresion ratio and probably a better squish from the smaller combustion chamber and the 4 valve heads give a greater valve area. I will have to keep my eyes open to see if I can pick one up cheap.
There is also a lot of stuff in the engine that could be looked at to remove weight, but until I get one I am only speculating.
One thing that I know works on these motors(I had a gs 400 in a galaxy far, far away) is to remove the starter motor and all the starter clutch etc. Then take the end off of the starter motor that fits in to the engine case and weld a large bore piece of alloy tubing to it, which you then fit a rubber tube to(I think the inside diameter was about 25-30mm) the tube then runs up the side of the bike in to a catch tank. This relieves almost all of the crank case pumping pressure and the motor spins up quicker and generally feels fitter. But the down side is that you then have to bump start all the time(the gs 400 has a kick start as well as the electric start).
Do you have any pic's of your bike? I'd like to see it.