Best Roadrace Platform?

Hey Everyone:

Looking at building an AHRMA Vintage Superbike Heavyweight roadracer for next season. I've roadraced for about a dozen years, and currently race a Ducati 749R with AMA Pro (Formula Extreme), AHRMA, CCS, and WERA. I've had a "hankerin'" to try Vintage Superbike for a while, and decided to start getting serious about building one. Jeff Hinds (AHRMA 120 on this list) is a buddy and a sponsor, but he also races in the class so naturally he's going to tell me to start with a KZ1300 or some other nonsense.

For a quick recap, AHRMA's rules allow: front end swaps, as long as the forks are from the same brand of bike; wheel swaps, with a max width of 3.5" front/4.5" rear; front brakes must be 2-piston or less; bodywork must be stock and remain in place; frame can braced; must retain dual shocks; handlebars must remain mounted in stock location (ie: no clip-ons); frame and engine cases must be from the same bike; no aftermarket blocks allowed; two-valve fours are allowed up to 931cc with unrestricted intakes; four-valve fours are allowed up to 825cc with unrestricted intakes; two and four-valve fours up to 1025 are restricted to 29mm carbs (no flatslides allowed in the class.)

So, the bikes I'm considering are: Kawasaki GPz750, Kawasaki GPz1100, Honda CB750F, Honda CB900F, Suzuki GS750, Suzuki GS1100.

Right now, the Kaws and the Hondas are on my short list, and I'm leaning towards the Kaws -- if I race a Honda Jeff will never speak to me again. :whistle:

On the Kaw side, it would appear to me that starting with the 750 would be the way to go. Shorter wheelbase and better geometry (although that can be juggled with different forks/triples/swingarm/shocks) I can take the motor out to 931 and am not restricted on the intake/carbs. Starting with the GPz 1100 means a longer wheelbase, switching to a 1000 block to get to the 1025 max ccs, and I'd be restricted to 29mm carbs.

To me, it seems like the GPz 750 makes sense. However, I'd like to hear feedback from anyone else out there, particularly anyone who has roadraced any of these bikes.

Thanks!

Mark Hatten
www.woundedduc.net
AHRMA #52 (#1 for 2007)
AMA Pro #521
WERA #521
CCS #521

you could make the 750 into an 880 with the aries pistons, drop in the roadrace web cams and have quite a powerplant. Lorcan has also mentioned going to 903 with gpz1100(?) sleeves and pistons I believe
another thing to look at might be bigger valves, you should be able to go 1mm oversize on the stock seats, if you cant find 1mm over valves, get bigger ones and make(machine) them a bit smaller (to 1mm over stock)
if you want a really new set of forks, but they need clip-ons, modify the upper triple to use the old style of risers for the stock location bars. you should be able to find kits on ebay, or use the 750 twin bolt on risers(if you can find them).
Scott

The 750 works for me. With the 1100 you have to tone it down. Where is the fun in that? Sheer amount of ponies is one thing but at what point does a more compact better handling package come into play.

If you decide to go with the Honda, you should be forced to run a gauntlet of KZRiders and beaten with frayed clutch and throttle cables. Better to sell your sister to a whorehouse as the old Harley guy saying goes.

For the members here, who have tried to help my friend Hatman. He left out one of the most important specs. His body size. While I am just south of 5'7", Hatman maybe just north of 6'4". Watching him on his 749R is, well like watching him on a 749R, you can't see the bike. And I never suggested a KZ1300, but that would make interesting viewing. While most of the Heavyweight riders are tall and some big, they get around pretty good on CBX's, KZ1000's and CB900F's, and GS750 and 1000's. I personally built a Z-1 with extensive modifications. It is a little on the large size for me I feel. Hence, my belief that due to my weight and height a 750 fits me better. With the restrictions on the big bikes with AHRMA. I feel I don't need the big motor to pull me around. But the CBX is a fast bike and has gone three years of development. I think he has around 130HP if I had to guess. At DAytona and Mid-O it was like lighting an afterburner.

So I suggested the GPZ1100. But whatever it is lets help him build it and get him out there. With all the troubles AHRMA has with this lawsuit, it is one of the best out there as far as comraderie and organization. So build a bike and come on out. Plus, where else are you going to get to ride tracks like Daytona, Mid-O, Miller and Willow?

I have ridden most of the bikes on the list and the GPz1100 and GS1100 both handle like tanks. The GPz750 is shorter and has quicker steering but seemed to sit high relative to its length but then I ride 900/1000s on the street mostly. The 750 is also fairly gutless compared to the bigger blocks... I guess I would look at what the fast BIG guys in the class are riding. And CB900? Bwhahahaha slow and heavy... probably stable in cross winds? Do they have a restriction on 10 speeds? hehe Sorry, you said CB900F.. slow and heavy limited to 5 speeds!

As Jeff points out, yes, I am 6'4" tall, which is big for a roadracer. But I'm also 190 lbs. during the racing season, so I'm not exactly the Sta-Puf marshmallow man. I raced a TZ250 for several seasons, so even though I'm big, I'd rather not fight physics with my bike as well. Smaller and ligher is better.

Plus, as I explained to Jeff, when I'm racing, an 8 lap sprint race goes by so quick I don't have time to think about being uncomfortable. However, at the more, uh, "casual" pace at which Jeff races, I'm sure he has plenty of time to think about his discomfort . . . :evil:


Mark

Hi I am building up a braced z1000mk2 frame for Australian historic racing after choosing between it and the Z1000J frame I settled on the mk2 frame only because it has a 3 degree steeper head angle, if I could get the J raked in cheap enough I would probably go with it.
Our rules are a bit more relaxed than yours: 1300cc +5%
CR carbs any size, 17 inch wheels, forks under 41mm
Chris

G'day chris41,
I'm also building a bike for "Forgotten Era" historic race bike and am using a Z1000J frame, Z1000J's are 27.5 degrees, GPZ1100B1/2 are 29 degrees but by the time you put on the shorter GSXR 41mm forks most use, 17" wheels and lift up the rear end it's plenty steep enough. You going to the Island Classic? Won't have have my bike ready by then but going to spectate.
Cheers Russ

G,day Russ i am pretty sure the 1000j is only spec'd at 27.5 degrees because of shorter forks I believe the GPZ and J frames are pretty much the same I have them lined up at the moment
Regards Chris

Whoops after checking with a lazer and taking some measurments I would say that your right Russ the GPZ1100 and 1000j where jigged different, the 1000Mk2 is even steeper though and should brace up well, although some chassis straightening guys have told me the j gpz is a much stronger frame
Chris

what would be better in the end a mk2 stengthend, or a gpz deraked?

What I have always done is start with stock bike and measure wheelbase and rake and trail, swingarm length. The information on the frame from the factory I have found not to be reliable as to the bike I am looking at. Then strip the bike down to frame and motor. Start hanging the suspension pieces you are going to use. Modern front ends shorten wheel base significantly. Figure the Rake and Trail. I hang bike from engine hoist so it is just barely touching the ground. I then start to pick up the rear until I get the front to between 23.5 and 24.5. Then make rear shock struts to that length. I try to get an understanding of the cornering clearance available at that point. Then I start marking the frame for items to delete and gusseting to be added. I then dissasemble everyting and start and pray I got it right. Remember 17" wheels change a lot if you decide to use them. Ground Clearance, cornering, engine rpm and speed are also affected. My Z-1 has four inch longer shocks on the rear with a 57" wheelbase and a 22.5 degree rake,and weighs in at 440 race ready. Yes it is two steep a little. I am going to go to a set of Concour fork tubes which will allow me to get more ground clearance and up to 24 degree rake. My 650 has a 55" wheelbase and is just under 25 degrees. She is perfect. You can go anywhere in any turn at any time. I am starting on another Vintage Superbike Heavy right now, so it is fresh in my mind. When I built the Z-1 I tried to calculate the difference in rim size. Wrong,I am not an engineer. I have to see it with everything I am going to use on it. The 650 just looked right also. from fifteen feet. The Z-1 handles great but I have to fight it from tucking at full cornering lean angle. You can feel it wanting to tuck under, but the 17" Michelins stick. I only have slid the front a couple of times. Normally it is when the case starts to touch as I come in with new gring marks. Hope this helps.