ESE's works engine tuner

[Storbeck]

Great info but I'm a little unclear on some things:

Jetski's give you the opportunity to really do some great things with the cooling circuits.
In the 1100cc SeaDoo world champ engines , they had water jacketed pipes. This meant I could double the
cold length of the Exhaust duct,

What length is being doubled? The "Wobbly on exhaust port design" doc says 1.5*bore for length of exhaust port, so double that? OR do you mean like double whatever i was before you modified it?

with hot water on the other side -

Hot water on the other side of what? You mean the exhaust port portion was kept very cold then the rest of the manifold/exhaust was much hotter?

this gave way less deto level from hot A/F being shoved back past the piston.
The head was a completely different circuit, with hot water taken from the pipe to reduce the temp delta between the combustion chamber wall and the expanding hot gasses.

How hot did you run the head? So you did this by blocking off coolant flow from cylinder to head and running water from the exhaust water jacket to get the head hotter than the cylinder?

On the dyno it was found that what I thought was a good cylinder exit temp, was way too cold.
We ran big clearances , but there was more power to be had with the exit temp up at 70*C due to bore friction I think, than down at 50*C to over cool the incoming transfer charge.

Super interesting. I have a couple of engines currently running around 120 degrees F (~50 C) on a heat tape stuck on the head (so I assume water temp is about that). Sounds like I should be trying to get that a little warmer, and the head even warmer yet. My thinking was cooler = better, or at least I didn't think 120F was too cool.

The cylinders with close bore centers like all the RD/LC/TZ/YPVS/Banshee's respond real well to the cold transfer tops, that in stock form had a completely random " water everywhere " approach.

So one approach might be to isolate head from cylinder, run water in the top of the cylinder water jacket from the intake side, let it flow past transfers and down around the exhaust port and into the first part of the exhaust manifold and out, so the intake side of the cylinder and top of the transfer ports is coolest. Then run hot water from the exhaust into then out of the head.

[wobbly]

JetSki's typically have super short Exhaust ducts , the big oversquare ones would be lucky if its length equals the bore.
In the case of the Seadoo I doubled the duct length as part of the pipe header, and there was a separator plate between that and the hot pipe water jacket.
The duct plus the bolt on manifold extension had cold water supplied thru the flange face as is normal in those engines.
There was no flow at all from the cylinder to the head, it had a plain copper gasket with no holes, O rings on both sides.
Thus the cylinder exit temp was controlled by jets, as was the head exit flow , with completely separated supplies and exit jets.

The cylinder made best power at 70*C - honestly, cant remember how hot the head was - but it was well over 100 though.
But I did drill a radial series of holes just outside the bore O ring to allow the colder cylinder water to cool the alloy head insert right next to the squish band.
Those engines were very deto resistant in the config with squish band and extended duct cooling - enabling much higher com than we had previously maxed out at.
The thing was a raped ape to the first buoy.
Keeping the back of the combustion chamber hot, has no effect on deto , but helps prevent combustion energy simply being dumped into the coolant for no reason.