One off two stroke exhaust

pumpguy · Post by **pumpguy** » 07:38 pm Aug 25 2015

Can anyone suggest someone here in the US that can provide dimensions for an expansion chamber for a very old two stroke engine? I've looked at published data from Gordon Jennings and Alexander G. Bell, and, well..., I'm afraid my eyes just glaze over.

Case in point is a cast iron cylinder from a 1959 250 Maico. I chose this because of it's good low speed torque and tractability. I've ridden it with a straight pipe and Bultaco muffler on it and while the performance suits me OK, I would like to get even better low to mid range performance.

I'm thinking a properly designed expansion chamber would be a worthwhile addition. I can provide most of the engine data needed; port timing & etc.

Any suggestions would be appreciated.

Post by **Julien D** » 10:14 pm Aug 25 2015

You might reach out to Dynoport. I think they still do custom jobs. I know there are others out there as well, google will probably bring up a ton of results for you. At any rate, a custom pipe is going to definitely cost you. I'm sure that '59 Maico powerplant is worth the cost! Just a note, an expansion chamber as opposed to your straight pipe is probably going to add more mid-top, and you might lose a bit of that low end torque you have.

jjavaman · Post by **jjavaman** » 10:44 pm Aug 25 2015

Maybe you can use this?
http://www.mh-aerotools.de/airfoils/jav ... ain_en.htm

Jim B · Post by **Jim B** » 12:23 am Aug 26 2015

Maybe you could adapt something from a different brand, but similar displacement? I'm sure it would be easier if it was a similar configuration to your bike (right side exhaust, left side exhaust, etc.) I'd think you'd be fairly close to the correct size pipe.

Post by **KDXGarage** » 12:39 am Aug 26 2015

I like Jim B's idea. Try a KDX200 pipe. I think a modern 250 pipe would be too much.

Jim B · Post by **Jim B** » 12:42 am Aug 26 2015

I was thinking along the lines of an old Yamaha DT250 or something like that. (I'm assuming they made a DT250, BTW.) For a 1959 (!!) Maico I think something skinny would be a good idea.

Jaguar · Post by **Jaguar** » 09:46 am Aug 26 2015

for a custom setup you need a custom pipe. DIY after getting fully informed by reading http://www.dragonfly75.com/motorbike/ECtheory.html

pumpguy · Post by **pumpguy** » 10:34 am Aug 26 2015

Thank you all for your replies.

I am very familiar with the expansion chamber principle and what it can do for performance. Making the pipe is just metal work; it's the dimensions that mater.

Waaay back in the day, made one for a Harley Hummer using dimensions provided by BSA Bantam guru George Todd in England. It was a real goer but too fragile; trying to fix a slipping clutch ended up with broken cases. Moved on to Maicos from there.

Spent quite a bit of time on Google on this, but no real answers found so far.

I had thought about adapting a chamber from another bike, but rather than going the cut-and-try, seat of the pants route, I would like to start with some numbers based on this particular engine and performance target. It's just a simple piston port, 2 transfer ports engine; bored .080" over giving 69 X 70 mm bore & stroke dimensions.

I'd like to see what a pipe would look like tuned for around 3500 RPM. This engine is listed peak at around 5000 RPM in stock trim. From what I have read and seen offered for other bikes, I would assume this would be a short fatty pipe, but plugging in numbers from a proven formula would provide a good starting point.

The quest goes on.......

Jaguar · Post by **Jaguar** » 05:25 pm Aug 26 2015

your "no real answers" reveals you have not read my info nor tried to use the Excel pipe calculator I made.
How is it that you think a 250cc peaks at 5000 rpm when the later Maico 400s and 440 peaked at 6900 ?
the pipe is made longer, not shorter, to tune for a lower rpm peak.

pumpguy · Post by **pumpguy** » 12:21 pm Aug 27 2015

You are correct, I have not studied the Excel pipe calculator, nor did I realize it was something you put together. I'll read through it again and see if I can navigate through it. Maths are not my best skill.

The top end I am using is from a '59 Maico Blizzard cast iron cylinder road bike. Maico's spec sheet for this engine is around 15 HP @ 5200 RPM. These use a 26 or 27mm carb. Maico used this basic cast iron cylinder 250 engine in many applications, most notably the M250B for the German army which placed an order for 10,000 units in the early 1950's. The port timing and cross section area are mild and small when compared to more modern 2T engines.

I also have a '65 250 Maico light alloy oval barrel top end which uses the same piston as the '59, and will fit straight on the 59 cases and lower end. Maico's specs for this are 24 hp @ 5800 RPM. It used a 30mm carb, has greater transfer and exhaust port duration, wider ports, and a bridged exhaust.

This performance is still mild compared to Maico's later square barrel (28 hp @ 6000 RPM) and radial barrel (36 HP @ 7500 RPM 250s.

After posting here, I discussed my project with others that know about this stuff, and was advised that what I was really looking for was Trials bike performance, and no exhaust pipe changes would improve what I now have.

Well, I still think it would be a worthwhile project to look into, so I'll study that Excel calculator and see what it shows. Not sure if a very long pipe can be made to fit the bike and still be practical.

Thanks again, We'll see.........

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