Exhaust Expansion

hey I would just like to know if anyone has tried this and would like to know the good and bad sides to it and how much power it will add thanks

 

it didn't quite go anywhere, but we have discussed it...a new member, wavygravy, lives closeby me & he is very into pocketbikes...he insists we'll be able to get a reed-valve and expansion chamber on one of these "super happy time" engines. guess i have to wait for him to get one before we start playing.

http://www.motoredbikes.com/viewtopic.php?t=674

 

augi I was looking at some tecnigas made ones. They are for 50-whatever cc engine. I did see some 70cc engine tecnigas I am curious how well they work? I saw somebody had part of it I cannot remember who but did not have the total expansion chamber for it.

 

my problem is i don't know, & until i get some "hands on" time with the techie stuff, i won't know :???:

anybody else? there is some more techie info about chambers on the board somewhere...if i find it in my travels, i'll toss it in here for ya.

 

Unless you can tune your "tuned pipe" for peak power at less than 6000 rpm, you are wasting your time and money.

If you set it up properly to "come on the pipe" at say, 4000 and peak at 6000, you'll get a power boost there, and a decrease at anything lower. You will also increase fuel consumption quite a bit.

 

i know (well, i don't know, but you know what i mean)

...it's improbable we'll ever come up with a full-range or generic chamber, because there's no such thing, i'm told again & again.

but i think it's general consensus that something better could be developed, yaknow, proper shape of exhaust to match port, technically correct specs on muffler size and flow capacity, etc?

see, joe, i look at this issue not from a tweak standpoint but with the optimization frame of mind. there has to be a "best" configuration, eh?

 

Yes, a larger volume "can" would be a lot better, say double the present volume.

You could cut the muffler off, fit an aftermarket two stroke muffler and it would have a better sound and a bit more power overall. Same effect as removing the baffle, but a bit quieter.

Heck, you could make a decent can if you can work aluminum and a pop riveter, or know someone with a TIG welder. The hardest part would be the ends, especially the one the exhaust "header" goes into.

Problem is, the more free flowing a two stroke exhaust is, the louder it gets and that's not a good thing as far as our bikes go. Our exhausts are not however, "optimal".

Our engines are low performance two strokes....so there is not a lot you can do to them without sacrificing reliability.

I would say that the carbs are the weakest point in good performance. These one jet jobbies are really horrible as far as a good mixture throughout the rpm range.

 

flowing it!

i agree with bike guy joe the weakest part is probly the carb! it needs a adjustable main jet not just the slide neddle! maybe correctly flow the intake & exaust ports & polish a bit, then go for the tuned exaust! how about the old racers trick of crankcase stuffing?

 

Re: flowing it!

Whats crankcase stuffing???

jon

 

it seems that a pipe tuned for a wide power band with 6000rpm max and a 24mm equivilant cylinder port would be 1400mm long and 51mm dia{thats over 4ft long and about 2in dia}not very practical.{didnt know the ex timing so i just averaged it at 87degrees}70 to 105 was the options.for a narrow power band it,s 81mm dia and 1400mm long.these are proximit number,s.that,s for a 2 stage chamber 3 stages are also avalable.you can find the program here.

http://www.bevenyoung.com.au/mota.htm

 

Crancase stuffing

A good description of crankcase stuffing at:
http://macdizzy.com/cranks.htm
(near the bottom of the post)

 

thanks, bit i still dont understand it, the loss of compression changed my mind on the whole thing...

thanks fo the link, ill look more into it later :grin:

jon

 

I ran an expansion chamber on my Grube 49cc. on the Stingray that I rode to Galeburg. Going "on the pipe" occured at about 38 mph. and felt like a pulsing thrumming that would push me up to 44 mph. But vibrations are crazy at that speed.

 

Did somebody say tuned expansion chamber? Heh heh....I will work on a nicer header pipe but still experimenting a little....works great tho!
Andrew

 

You a plumber by any chance?

 

HA!...No not a plumber but it was the only thing I could use to get the lengths right and still not interfere with anything..I tried muffler shops etc...to make the custom pipe but the couldn't bend something that small...I am going to experiment a little more (vary the header lengths)....Once I get something that is as close to right as possible I will send the hole pipe setup to a shop in CA to have a nice header pipe made....Actually the galvanzed fittings might outlast the rest of the bike....they are heavy walled!
Andrew