2 stroke comeback.

[Jimmy Jet]

Looks real good. Will you wrap them or water inject? Double skinning will take an effort!

[Jeff B]

I'll just wrap them as only temporary to see what will work. I'll squirt water into the stinger but might put some other injection points along similar to what jetski exhausts have.
Some people set up rpm based water injectors on chamber to alter the effective chamber volume based on rpm.

[Allen M]

Bit of trimming, banging and hacking and I have one pipe the right size, shape (i think) and lined up with outlet. As it is now is near identical dimensions as 3 cylinder 1200cc Polaris jetski chamber.  The belly is slightly fatter but I hope that doesn't matter too much? Can always squirt a bit of water in or smack a dent in it...

A fat belly is GOOD will give a stronger mid range. Noise could be an issue but it?ll be good to see if this makes it Howl like a good two stroke should. I suggest you keep the water to a minimum.

[Jeff B]

I can alter the length of header pipe about 50mm as that part is a bit of a guess, went to middle cylinder exhaust port but front cyl is longer header and rear is shorter so must be a compromise. This engine has slightly different port heights and compression ratios across the cylinders (from factory) so possibly this is the reason? The 3 cylinder jetskis have unequal length headers also and I thought if it was beneficial to have all 3 the same length they would be?
Much to learn.....

[Jeff B]

2x pipes in, one 30mm longer to match the cylinder bank offset. 30mm.
Bit louder than last setup (and that was not exactly quiet....

[Warwick Marflitt]

2 Stroke and Quiet in the same sentence 

[Kakapo76]

I have been following a few USA builds- one of which is powered y a 240hp sportjet- that thing is stupid loud and frankly unpleasant as its not muffled down the leg like an outboard. Good luck taming the noise in a jet tbh.

[Jeff B]

Seems more crisp with chambers.
Reminds me of the CR500 I used to own....glorious....

https://youtu.be/qJZtZ98PgmU

[Allen M]

Seems more crisp with chambers.
Reminds me of the CR500 I used to own....glorious....

https://youtu.be/qJZtZ98PgmU

Sounds a lot crisper now 
Time to get it wet again 
Hope it?s not too lean though.Be a shame to turn those pistons to ash now.

[Jeff B]

Goes hard nuts now. I have picked up about 1000rpm.
Getting over 90ks @5500rpm and then I ran out of fuel and had to paddle back to trailer.   
https://youtu.be/yxZWYQgQWM4

[Jimmy Jet]

Nice one Jeff! Going to get a long way up some skinny.

[Jeff B]

The exhaust chambers have given me about 60-80hp more than my first pathetic attempt.
I think I'm pushing close to 180-200hp currently? Was hoping to hit 6000rpm but at 5500rpm I'm a bit short. Possibly a bit too much pitch in pump to push 6000rpm as that would put speed over 100ks and I doubt I can coax that much power out of it?
It's still a little buggy off idle and I think it's my intake/carb setup.
Bit more testing required....

[powerband]

Hi Jeff, In the past experimenting with chamber I have found cutting 10.mm out of the header pipe as close to the end as possible will give up to 1,000 rpm more without losing bottom end power. If that does not work put it back in and go to the stinger.  If you increase the diameter by 5.mm you will gain top end but you will lose bottom end the bigger you go. An ETG will let you know if you are rich or lean. I have found that the unleaded fuel is not as forgiving if the motor is on the rich side. You lose a fair bit of power.

Paul.

[Jeff B]

Yeah I can trim about 20mm out of the header pipes.
As I understand it, the stinger diameter is very important as it holds the correct pressure in the whole system.
I currently have 48mm dia stingers which (on paper) is way too big but I'm injecting water into stinger as well which changes things drastically.
I might alter the water amount and see what that does as it's not a known constant like a fixed orifice.
I have an egt gauge I will mount in one chamber. Although I'm  ot sure what's a normal or save or on the edge of meltdown temp??
Also have a wideband I can fit but I'm guessing the oil will foul it quickly?

[Warwick Marflitt]

How easy to fit a pressure  gauge to the pipe and a tap to turn the exhaust water off and see how much exhaust pressure and performance change?