2 stroke comeback.

[Jeff B]

https://youtu.be/0SWU0Ympd-k

[Jeff B]

Surveying a spare block for forced induction prototype. This is same basic block but the putt bomb 150/175hp version. The block is the same casting but sleeves are different, lower/smaller  exhaust ports. I'm thinking this might be better for turbo use as will get a bit more power stroke and the boost will make up for it....
Likely will just blow more unburnt fuel straight out the exhaust? But I guess a suitably sized turbine at the end of expansion chamber will increase back pressure as boost pressure rises?

[Allen M]

Surveying a spare block for forced induction prototype. This is same basic block but the putt bomb 150/175hp version. The block is the same casting but sleeves are different, lower/smaller  exhaust ports. I'm thinking this might be better for turbo use as will get a bit more power stroke and the boost will make up for it....
Likely will just blow more unburnt fuel straight out the exhaust? But I guess a suitably sized turbine at the end of expansion chamber will increase back pressure as boost pressure rises?

I agree with the thinking re the lower exhaust port timing in a turbo application.

[powerband]

Hi Jeff.  With the testing that you have done so far how does it compare to a Yamaha 3cyl 1200cc 2 stroke?

Paul.

[Jeff B]

Hi Jeff.  With the testing that you have done so far how does it compare to a Yamaha 3cyl 1200cc 2 stroke?

Paul.

Well I guess at this stage it's not a lot different to a well set up  big 3 cylinder 2 stroke? 
I'm getting about 90ks @5500rpm.
The hull and pump are excellent, I feel I'm pretty good there.
The engine ideally I want another 500rpm to really be singing over 100ks
I would be stoked if it went as well as 2x 3 cylinder ski engines but not sure if that's possible from this configuration?
I have other more "sensible" boats to keep me on the water while this one develops further.....

[Jakedale]

I'm building a jet boat with a 1200cc Yamaha here in Sweden. There are a lot of lakes here but No jetboats so i thought i should be the first one to introduce this here 😁 I ran across a Suzuki 200hp outboard and i thought that it would work in a jet boat but never heard anyone doing it and here you are. Thank you for a great thread!

[Jeff B]

Some more 2 stroke development in progress.
Anyone know the optimum firing order for inline 4 cylinder 2 stroke?
Think I'll do a cross plane crank rather than big bang.

[Ross Goldsack - JBNZ Immediate Past President]

In the second photo, are you about to straighten it by driving the forklift over it?

[LBD]

Neat progects going on here....

In the late 70s a guy up in Picton inboarded a 135 Chrysler in a small racing hydroplane, it went well but was just a little too noisy for the driver with a huge exhaust opening next to his head.

But this thread has got me thinking now... I have a 150hp outboard jet pump... I could inboard that with a 150 power head... maybe even leave the exhaust out through the jet.... hmmmmmm I wonder?

[Allen M]

In the second photo, are you about to straighten it by driving the forklift over it?

He may well need to after the crank has twisted with all that torque going through such a long press together crank.

[Jeff B]

Some weekend bbq action

[Jeff B]

The seperate cylinders are pretty handy, does make the engine pretty long though but easier to work on and modify.
Can go 1600cc-1800cc depending on what top end, power valve or non power valve.

[Jeff B]

Clamped a solid chunk of 80mm chrome bar in it. Should keep it straight.....

[Jeff B]

I now have a nice inline 4 crankcase.
Next job is to use these 3x bung 3 cylinder cranks and make one good 4 cylinder crank.....
Still not sure what's the best firing order??
1342??
1324??
1234??

[Paul]

Have you split any the crank parts you have? Are they able to be 'clocked' in any position, or are they splined/indexed/etc (giving only certain options available)?

A 4-stroke 4-pot is normally 1342 for vibration and smoothness (piston masses equal& opposite and bending-moment on crank minimised).

Chev V6's run down the crank from flywheel end (654321).

I seem to remember Ford V6's (Essex etc) run down the crank starting at front pulley end, (which due to strange cylinder numbering, is 142536). I think Honda had the same cyl numbering - not sure about firing order though.