Ice Race a CL72?

Hahnda · Post by **Hahnda** » Sun Feb 27, 2011 10:35 pm

This past season I ice raced a Bridgestone 175 Dual Twin. I had never ice raced or flat tracked before. I wanted to do some sort of racing and since the ice racing was local and during the winter it seemed like something I should try. I had a bunch of these old Bridgestones around and seemed like the logical choice.

More info on the build and a bunch of pictures, also a video at the bottom that you really have to check out if you like to hear the wide open whine of a 2-stroke. http://www.scramblercycle.com/racing.html

Already thinking about next year. The class I ran in this year was 125/250. Max 4-stoke size was 250 and max 2-stoke size was 230cc. As it turned out I was usually the only one in my class but I didn't let that stop me. I think I stirred up a bit of interest and expect a few more riders next year.

That brings up the CL72. Or at least parts of one I currently have. I would actually be using a 305 bottom end and frame as a starting point. The only thing 250 would actually be the top end.

I've been through a couple discussions here on using a CA77 360 degree crank and building a "Twingle". I think that might just work for the type of racing this is. We alternate between a 1/4 mile oval and a 1/2 mile oval.

Any more particulars or just some general discussion on this "Twingle" conversion? Some of the details are out there already. Any opinions on this conversion and how it might work for ice racing?

I know, I know, there are much better bikes suited for this type of thing, but as you can tell from my Bridgestone, I'm not really into to most logical choice.

Thanks,
Kevin

cyclon36 · Post by **cyclon36** » Sun Feb 27, 2011 11:24 pm

Cool! Looks fun and scary all at the same time. I hate riding on wet roads, I can't even imagine just plain ice.

Hahnda · Post by **Hahnda** » Sun Feb 27, 2011 11:27 pm

Lots of traction helps. Between the front and rear tire there are 1500 ice screws installed. Each wheel and tire combo weighs in at 40lbs. I need some torque to get those moving. The Bridgestone lacks torque but makes up for that when the revs start humming at the upper end.

flathead · Post by **flathead** » Mon Feb 28, 2011 10:42 am

Kevin,

I'm running a CL72 twingle engine in my flat track bike.
I can't really comment on the twingle vs the 180 engine for a 250, as I don't ever recall riding a stock CL72, but I can assure that it's got a ton more punch off the line and out of the turns than any stock 305 that I've ever ridden. We've only run this one on a 1/5 mile but with proper gearing I think it would do fine on the half. Just remember it's probably gonna max out at around 8500 rpm.

The biggest concern I had when I started this project, was matching a 305 bottom with a 250 top end. I was worried that it would be so out of balance that it would self destruct. That proved to be a non-issue. Balance is not a problem.

I'm running standard bore, early (higher compression) pistons, a stock 250cc head, stock CL72 cams indexed for 720 degree firing not 360 (both cyl's on compression and exhaust together), a CL72 points cam with right points only, standard timing and advance, total loss ignition with a CB750 twin lead coil, straight 1-1/2 dia pipes, 26mm CL77 carbs, 145 main jets, and an X'ed transmission. We run 93 octane pump gas.

It's been dead reliable so far. Starts and idles like a sewing machine. Comes to life like a beast.

I'm building up a 305 twingle right now to run with the 250 this season. It's gonna have TT cams, a set of the Italian racing pistons, ported head, and everthing else set up like the 250.

Mark

Hahnda · Post by **Hahnda** » Mon Feb 28, 2011 11:07 am

So your setup isn't really running like a single if I understand it correct. More like the Dream except for two carbs and the higher lift of the CL/CB cam?

What do you think it would be like if both cylinders were in unison working as a single firing at the same time. I'm sure its been done but might not be a good thing?

flathead · Post by **flathead** » Mon Feb 28, 2011 11:44 am

Kevin,
Sorry, I might have been a bit confusing with my description.

It's in effect a Big Bang single with two pistons running in parrallel. It fires both cylinders simultaniously every 720 degrees of crank rotation. Not like a dream phased 360 degrees apart.
CL points cam with 1 lobe.

It is a Good thing!!!

Mark

Hahnda · Post by **Hahnda** » Mon Feb 28, 2011 1:46 pm

Ok it is a true twingle. It sounds like something that I would like to try and build. I may just end up using a 305 top end. I'm pretty sure I can convince them to bend or change the rules a bit to allow the larger engine. I mean a 45 year old bike needs some sort of advantage doesn't it?

To re-index the cam I assume you just had to grind one of the splines and index it correctly?