Vintage Dirt Bike Q & A

Are those diagrams generated by a pipe design program? That's great! I've wanted to try pipe design myself, but since I don't have a metalworking shop - and it seems the pipe makers I've found online all design in-house, and aren't taking new work - I figured, what's the point? But, hey, you're in a different position - go for it.

I have Hooker and Jemco MR175 pipes, and I've checked out photos of the Al Baker, Bassani, and Torque Engineering pipes when they've come up on eBay. I've also recently finished modifying my stock pipe, with excellent results; it goes back on the bike today after painting.

Honestly, I think I would trust your own design - created with technology the 70's guys could only dream of - more than any of these old aftermarket creations. With the exception of the Bassani, all of them use very long head pipes, which results in a flattening-out of top end power. The Hooker and Jemco pipes have good low end and excellent midrange, but then just sort of rev out without any kind of top-end hit at all. To me it's a poor trade-off for the big increase in noise level (and in the case of the Jemco, a burn on my right thigh). On the other hand, if either of these pipes were fitted with a tapered header and a decent silencer, and the Jemco tucked in better, I believe they would make truly excellent pipes.

Let me make a few suggestions, based on the results of my hybrid MT125/MR175 pipe (which is now my #1 pipe by far).

1) use a tapered (flared) header, starting as close to the inlet flange as possible (I know, these are a bitch to fabricate - that's why I stole mine from the MT125 pipe)
2) design for delayed (i.e., ineffective) convergent-cone reflections above 5,000 rpm (long center section)
3) keep the max diameter as small as possible (see #4 below)
4) tuck the pipe in as well as possible in the area from 4" behind to 8" ahead of the seat/tank junction
5) use a 1.125" outlet pipe or similar, to accomodate modern silencers
6) use a 39mm inlet tube (matches '76 - '78 CR125M manifold, which is really the best one for this motor; stock is 36mm, can be bored to 37mm)

That's about all I can think of for now - hope it was helpful. I'd definitely be interested in in an MR175 pipe that pulled welll to redline, and didn't fry me.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Here's the dimensions of the Jemco MR175 pipe:



The Hooker pipe is kind of like a sardine can with tubes, it doesn't really translate to cylindrical/conical shapes.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric