Jeff jet 1750

[Jeff B]

Exhaust inner all welded up.
Just need to fit water jacket to it now.

[Henry]

niiice

[Kakapo76]

How many hours in that pipe Jeff? Georgeous work mate. 

[steelo]

Didn?t something like that start the virus in China?

[tyro]

ribbed for pleasure

[Jeff B]

Exhaust looks like a lot of work, not too bad, I think about 6 hours to make inner.
Started making outer. 3mm gap for water jacket.

[Warwick Marflitt]

Jeff. Could you not measure cut and weld a flat shaped profile. Then hydroformed it making the outter chamber, then cutting and welded it over the inner? Time wise would it be quicker? It wouldn't look as fantastic.

[Keltik]

Time wise would it be quicker? It wouldn't look as fantastic.

Shhh....I wanna see nice things

[Jeff B]

I have hydro formed a couple of chambers, stainless works better, ali welds dont like it much. And it stretches the material, not as dimensionally accurate, especially if you want a jacket close to it.
Time wise probably not a lot of difference? Both pretty time consuming.
Got the jacket tacked on, just a little sleeve to fit then weld up.

[Paul]

Do you put spacers/ nuts/ washers between the skins, or is each skin able to 'float' relative to the other?

[Jeff B]

Paul this is not a back yard job, we dont use nuts and washers as packers...
Packers will just fight against befitting it up and rattle.
They are 2x seperate chambers, quite rigid not sure if I will get much flex?
Don't think I would here it rattle with the little piston jumping up and down nearly 200 times per second...

[orac12]

That's badass. Did you have the pie cuts profile cut?

[Henry]

My wee JS300 pipe just has a jacket for the first downwards 3" and baby water injection at the low point. Might be an idea when you go into production on motorbike powered jet boats

[Jeff B]

That's badass. Did you have the pie cuts profile cut?

Yes, I drew the cone sections on a basic 2 stroke exhaust development program and cut them on CNC router. Took about 12 minutes to cut one pipe (inner or outer)
Saves a lot of time and is very accurate

[Jeff B]

My wee JS300 pipe just has a jacket for the first downwards 3" and baby water injection at the low point. Might be an idea when you go into production on motorbike powered jet boats

Yes most all factory 2 stroke jetski exhausts are done that way.
The last and most powerful models had fully water jacketed chambers (dry pipe)
The water injection alters chamber volume, very complex to get it right. Some aftermarket ski pipes have needle valves sent different points along the chamber to fine tune. Some even have rpm activated window switch on water solenoid valves letting water in at low rpm then shutting it off up top.
Adding water is another variable I'm not quite ready to experiment with.....yet.....
On Mohawks 300 home made race pipe, we gained 200rpm by shutting water off to chamber.....then the exhaust rubber melted and we lost a heap of performance by sucking exhaust into carburetor (EGR) ..
.