ESE's works engine tuner

[wobbly]

The TZ80 dyno graph shows it has a very typical and very big tuning issue.
Sure it hit 15 Hp with jetting and ignition changes, but the power is then fading seriously with every gearchange - real bad, moreso for a water cooled.
This setting would eventually kill the thing on the track.
Any engine set up correctly will repeatably hold the peak power figure thru several WOT all gear runs, even better if its on a Dynojet 168 or similar with eddy current load control

[Frits Overmars]

My thought process was that if you can help stave off deto by reducing squish to as little as possible, this is only most effective approaching peak revs. So at the bottom of the useable power there is more trapped mixture.

That makes sense Dave, I didn't think of that. But detonation at the bottom of the powerband is usually not a problem because the cylinder filling is not yet at a maximum then.

Perhaps if you could decrease deto you might be able to crank up advance at 9000.

You certainly could, but that doesn't mean you would gain any power. It would be true for foul-strokes, but two-strokes depend on exhaust gas energy and advancing the ignition reduces this energy.

[husaberg]

That makes sense Dave, I didn't think of that. .

Polini, did I think you posted a few pics of it ages ago......

[jonny quest]

You're talking about the variable compression ratio head. It didn't change squish, just chamber moved up and down

[Peter1962]

Polini, did I think you posted a few pics of it ages ago......

I think you are referring to this : http://2stroke.free.fr/culasse-polini.jpg

[husaberg]

I think you are referring to this : http://2stroke.free.fr/culasse-polini.jpg

You're talking about the variable compression ratio head. It didn't change squish, just chamber moved up and down

Yes Peter1962 .Oh I thought the squish band moved as well. but it obviously doesn't. Then again, it easily could with a few mods.........

[jonny quest]

You don't want the squish to move to the clearances you're suggesting. Way to complicated a device for such precise movements

[wax]

The big open class Jetski World Champ engines I used to build needed an absolute minimum of .15mm = 0.006" clearance
on 78 to 92 bore when running 40*C out of the case and 60*C out of the head.
On the dyno the power would fade at the end of a 30 second pull if the case went over 40* - much under that and we would certainly squeek a piston.
We used restrictor jets on the individual 6 outlet points to regulate the local temps.

Wobbly did you make an error and put the decimil place in the wrong spot there
is this supposed to read 1.5 mm

Was this a 951 seadoo with a huge piston

[wobbly]

Nope - 6 thou is the correct number and yes a 951 out to near 1200.

[wax]

wow thats tight squish.
Am i reading it wrong is that measured at a certain rpm or a static measurement
Yeah I have been around the big bore 951 a little as well not at the same level as you i never took one to the world titles
They make good power until they dont and then you throw it all in the bin

[Grumph]

wow thats tight squish.
Am i reading it wrong is that measured at a certain rpm or a static measurement
Yeah I have been around the big bore 951 a little as well not at the same level as you i never took one to the world titles
They make good power until they dont and then you throw it all in the bin

i think he's talking piston to bore....

If it is Wob, and they were forged pistons, did you have a shrinkage problem ? Or set them up tightish and run through several heat cycles ?

[wobbly]

Yes, i was referring to bore clearance needed when using the cold water from the tap - or Lake Havasu in this case.
Smitty was talking about the loose clearances they have to run when going WOT with cold water in boat racing.
The only issue was simply that the low inlet temp along with an iron sleeve meant the piston would always be growing far faster than the bore size.
In the smaller bores there were cast pistons available and after long run in cycles these would survive at 0.004".
But the big bores were forged by Mahle, and nothing I did regarding slow run in, and sanding off the high spots etc would stop them locking up
if under 0.006".
Of course this let the piston rock all over the shop, and the rings had a real hard time sealing effectively for long, but was the only way to get over 220 Hp
from the big twin for open class racing against 1200 triples that had more power but were way heavier than the SeaDoo with titanium/magnesium everything, and a carbon hull.

[wax]

OK my bad, i read it wrong. I was questioning it in my head thinking he cant be serious

[Drew]

Hang on, if the insert moves inside the head does it not fail to dissipate heat properly?

I thought everyone was saying tight as fuck is the only way to mate parts, or things would overheat very locally and the shit would hit the fan.

[wax]

Wobbly have you ever played with a triple engine with one expansion chamber.
ie as in an out board style or triple jetski engine.
Thats the one using 120 degree pulse tuning. I looking at designing another chamber for my ski to move it in a different place but i am not convinced any of the software out there will cater for what I am doing.
Its going in a stand up ski and there is not the room for triple pipes