expansion chambers

[lyonsy]

hey
wanting to know has anyone done anything with expansion shambers on 4 strokes.
now dont laugh ive seen the results of it but cant get any info on it and as i will be needing one soon to help the old 250 along (anything i can get to get extra out the setup i get i will take with both hands)
drift

 

[wallaka]

You mean on the exhaust like on a 2-stroke or the intake like I see for those 1000 hp Supras?

 

[lyonsy]

hey
on the exhaust like a 2 stroke
drift

 

[Anonymous]

Those pipes would be very long, the assembled exhaust system would be very heavy (when it wasn't falling apart), the engine would be very peaky, you'd need a six-speed box, and you would be up and down that shift pattern so much that you'd think you were rowing the car down the road.

 

[XFlow_Fairlane]

I was looking into putting a chamber on my MT250 that has a big turd looking pipe on it right now. I was told not to. being a dual sport it would make it peaky so it would be a bear on pavement and on trails it would be a big handle to ride also. granted I picked up a spare pipe for it and a buddy has an old 250 chamber from a later model bike laying around so we might make up a chamber for it to see how it is.

 

[jamyers]

Check out David Vizard's article on exhaust. Sounds like a long header collector leading into a resonator or chamber-type muffler is the way to go.

 

[aussie7mains]

Just to correct a few misconceptions, two stroke engines are VERY differnt to 4 stroke and shouldnt be directly compared. Two strokes have extremly rapid opening and closing ports and make lots of sharp sonic pulses in the exhaust which can be harnessed to add suction to the transfer ports, and add restriction to trap any fresh gasses that may otherwise be sucked right out of the cylinder.
Expansion chambers can be made for two stroke engines to operate over a reasonably wide range of speeds, they dont have to make the engine peaky, but they can if that is your desire.
I dont see how the 4 stroke could benefit fron that type of exhaust, a reverse cone mega perhaps! four strokes just need a low pressure pulse to arrive back at the cylinder before tha inlet valve opens, a reverse cone may help at certian speeds to prevent over scavenge of the cylinder, this will only work over a small range of speeds, and wont be any use on a silenced street engine.
A7M

 

[lyonsy]

hey
the expansion chambers arnt very helpful in standerd engine's and wont suit most cams.
how ever in big overlap cams they are very helpful especialy in restricted heads in the amount of port work they have etc.
iam not to woried about over scavanging the cylinder as id rather a fresh charge every time rather then guessing if its scavanging all the charge.
plus if i can have it over 1000rpm its perfect for what i want as thats where the engine will mainly operate.
drift

 

[lyonsy]

also when you see a 10rwkw gain from one on the dyno its cheap horsepower.