A Stock racers

[LittleG]

This is getting technical! I plan on running a 20 horse engine with a vintage Ski Doo horsepower doubler between the T20 and sprockets, does that fly? If I run 6" of clearance between my helmet and top bar and have an eight point cage tied to the frame, do I have to wear pants? What if it's too hot for pants? Can I use Roman numerals for my ID number? 'Was thinking MC/X

Mike not a problem your from old family racing everything on you and Dirty uncle Don is grandfathered in. But I would definitely recommend Marc' s emporium for things still needed

[frabbit]

Dave, from what I keep hearing, get a BIG one. Movies seem to back that up.

[hydromike]

I think it was Matt O. who brought up the possibility of running pipes in A/Stock. Maybe it was down in Latrobe, but I distinctly remember several of us standing around and Matt posing the question to Dave which promulgated an absolutely perplexed look on Dave's face. Something I interpreted as "I can see where this is going...".

So with the 295R's being hogged out and people likely swapping in huge carbs, CDIs, milling down flywheels etc., I figured I needed to at least try something to see if I can be, at a minimum, intimidating if not competitive. The science behind a true tuned exhaust is relatively complex at first glance with lots and lots of tried and true references out there. The underlying math is really quite simple, and there's even free software available to help spit out a simple pipe design once you measure a few parameters on your engine. I opted to use a program called JavaPipe which is publicly available at JavaPipe: Tuned Pipe Designer.

The java application is really pretty neat, as it prompts you to enter in only 5 variables (RPM, exhaust/transfer port angles, exhaust port area and EGT) and then provides a graphic of what the pipe is going to look like for those variables, along with dimensions and (get this), it even exports patterns you can scale-up to trace on to the steel.

The intake/exhaust port angles are just determined using a degree wheel on the PTO of the engine, and is basically the number of degrees that either the transfer or exhaust port are open during one revolution of the crankshaft. The JLO 297 turned out to be about 120 and 150 degrees, respectively. After that, you can measure the exhaust port area which I accomplished by tracing the outline of the port onto a piece of rolled paper in the cylinder, and calculating that area. The exhaust gas temperature and RPM are two variables that are a bit subjective, so I erred toward the conservative edge on those two. After everything is entered in, you have your dimensions and you can start cutting.

Here we can see the complex science of a couple measuring thingies combined with a couple moderately-sized hammers. The pipe is constructed out of 18-gauge steel because I wanted something a bit more resilient. In this picture, the diffuser cone has taken its general shape and the reflector is traced out on the steel.



A plastic mallet and a steel dolly held in the vise helps to get the general shape together and once things start to get close, the last bit is clamped together with hose clamps and welded up.



It takes a bit more shaping to get the ends of the cone as round as they're going to get, and to try and massage out any big dimples/dents you've created during the process. Here's a shot of the pipe just about complete for the initial fit. I still need to get a ball/socket welded on.



And here's the pipe in the little A/stock. Once the ball joint arrives, we'll try to get it cut/bent/massaged/tweaked in a little better.



Heck, who knows if it'll even work. It might have a powerband between 3,000 and 3,500 rpm, it might burn up on the first lap. It was a fun exercise and represents a total of about $10 in steel. I encourage anybody out there with a couple hammers and a welder to give it a shot.

[Nick O.]

Mike, thanks for sharing the Java program and a great write up on the process. For anyone that's keeping costs down, it's a great way to improve the machine with a little bit of elbow grease. It looks a little intimidating but pretty simple once you start looking through it. Your pipe looks fancy

For anyone building new machines that haven't been grandfathered in, check this out so we're all legal to race and have safe fun:

F. Mufflers
1. The mufflers must be contained within the confines of the body or roll-bars. No mufflers may protrude beyond the outer limit of the body or roll-bars.
2. The muffler may be located anywhere within the confines of the body and roll-bar system for both stocks and modifieds.

[jerseybigfoot]

Mike, thanks for sharing the Java program and a great write up on the process. For anyone that's keeping costs down, it's a great way to improve the machine with a little bit of elbow grease. It looks a little intimidating but pretty simple once you start looking through it. Your pipe looks fancy

For anyone building new machines that haven't been grandfathered in, check this out so we're all legal to race and have safe fun:

nice looking tuner mike but how do you plan to fold it in half to fit within the roll bar and body????????

[Don]

nice looking tuner mike but how do you plan to fold it in half to fit within the roll bar and body????????

He could make a really long, tall roll cage.

[Andyman]

Can't wait to hear it

[countrybumpkin]

nice looking tuner mike but how do you plan to fold it in half to fit within the roll bar and body????????

Don' worry Marc, his 1st endo will stuff it nicely between the bars! ( ask me how I know!)

[ARGOJIM]

"Your gonna put your eye out" trying to grab the pull start.

Nice fab job Mike. If I ever get a 2 stroke mini bike I know where to find a muffler.

[jerseybigfoot]

He could make a really long, tall roll cage.

Maybe turn the jug around and point the stinger forward

[LittleG]

Great job mike but please put a beacon light on that so any low flying aircraft can see it.

[hydromike]

Thanks all for the thumbs-up. I knew when the program spit out the first iteration of the pipe that it was going to be a challenge to get the darn thing shoe-horned into the machine, but decided that it's easier to build to straight cones as a first step, then manipulate them in the end. The ball joint should show up in the next couple days, so I'll try and get it looking a little less conspicuous. It's about time to build something bigger so I don't have to try to fit all this stuff in such a tiny package. A test fit in the seat has my chin about resting on my knee caps, just like the D/stock and the 503....

[Model Citizen]

[hydromike]

Very, very, tasty pipe you made there, Mike.

Ha! Thanks, but I know it's a bit over the top in the those pictures. I've since been able to get it tweaked in a bit better, but it'll still need a bit more work.



I can change the overall shape of the diffuser/collector all I want but the dimensions need to stay the same, so you get what you get from a length standpoint.

I wish somebody else would post some more pictures of A/Stock builds. We all like to see what other people are working on, and the idea of keeping it all a "big secret" seems a bit ridiculous. We all like seeing what folks are building. I'm beginning to think it's just going to be Sharkey's Terrible Tiger and me going around the track.

[Don]

I can post a picture of a pile of parts. So far that's where my A stock progress lies.