Vintage Expansion Chambers

[Darvin Jahnke]

Michael,I agree with you on several points. First,every kart owner has the right to build his kart however he sees fit. However I also like to see them as close as possible to the way they were raced. Not necessarily the way the factory built them but how they were set up by individuals and raced. There was a lot of inovation that came from the drivers and mechanics and each machine is a piece of history that should be preserved. In my time racing snowmobiles I saw changes that I made to machines appear on next years production models. I have lately been involved in racing vintage snowmobiles and have seen it deteriorate to the point where the machines running are basically new machines with vintage hoods and seats. Many times the reason given is safety. We need better brakes,better tracks etc. etc. Well we ran them with the parts that were available back in the day with very few problems. I mentioned some of these things awhile back in a different thread and someone replied that vintage kart racing isn't the same because it is just exhibition and not really racing. If this is true then why the concern about making optimum horsepower,having just the right tires,etc.? Everybody just gets in line and drives around the track.

[steveohara]

Jeff has pretty wll summed up the basic issue.... the smaller pipes create a lot more heat and tend to damage the engines. The first pipe I ever used was the spun aluminum GEM pipe and it was a little bigger than the designs that followed in the early 70s. The extra volume was a good thing but I have never seen an aluminum pipe that worked as well as the steel versions. In that same regard, the rolled or stamped steel pipes worked better than the spun steel cone pipes. Don't ask me to explain or offer any theories on why.... they just did. So, if you have a late 60s kart with a Mac and want to run a period correct pipe I recommend the GEM and if you want to make a reproduction of the GEM, make it out of rolled steel cones and use a 1" ID stinger with a whole bunch of 1/8th inch holes drilled in it and use a 2" washer on the end and a 2" outer cover over the stinger. It will offer the period correct look of a GEM, have enough volume to keep the motor happy, and be quiet enough to meet the evolving sound requirements. If your really want the period correct look, have it ceramic coated so it looks like the spun aluminum versions. How's that for a sell out compromise on all fronts
Steve O'Hara

[Michael Jackson]

This is a Gem generation 2 with a baffle insert. This is what I had to put on mine in 69 after my aluminum one got destroyed racing at Barnesville. The stinger got torn off of the aluminum one and also the track owner said that mine was to loud.The gen 2 is made out of steel.

[Tom Davis]

Guy's,
Expansion chambers in a language we can all understand........or maybe not!

http://www.kartweb.com/TechArt/2Stroke/chapter3.doc

[Gordon Duax]

Does anyone have pictures/info on what pipe was run on the old Maico kart engines?
A Monza-B by chance?
Or a box muffler like what the Parilla 13Bs came with?

My favorite for a Mac is the old GEM spun aluminum.
Don't care about max performance, if I wanted that I would be running a modern chassis with a water cooled RV Ital on it.
But the sound from the GEM is unique!
The aluminum makes a noise all it's own.
Probably why they didn't make good power, the sound wave was being absorbed by the soft material.

[Tom Davis]

Gordy,
Why don't you come to Kerrville and I'll GIVE you one!!
Tom

[Gordon Duax]

Too damn far north!
I here it gets cold up there.......

Besides, if I actually get out of San Antonio, I may not go back.