ESE's works engine tuner

[TZ350]

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Attachment 352376

Ok thanks Husa, so from Bells book 15.7:1 pretty close to Wob's suggestion of 15:1 for Methanol. I will aim for 15:1.

Please tell me you used a burette. Two threads up from the bottom works well.

Here we go, a 10cc burette and 10cc syringe.

The burette can easily be read to 0,1cc and the syringe 0,2cc. Probably 0,2cc is good enough for a 250 or even a 125 but I agree being able to easily read 0,1cc or with care 0,05cc is much better for a 50.



At 15:1 for the 250 I will be looking for 17.75cc for the combustion chamber including the 0,8 squish.

With CNC machining someone could probably get that sort of accuracy. But with my hand carving in "mister rattly", our old faithful lathe, I will be very lucky if I can get close to 0.2cc of the target either way.

[wobbly]

Getting the cc correct has nothing to do with the equipment , just your patience.
Spinning the chamber in a battery drill would do , as using 80 grit emery cloth under your finger ( form tool No1 ) you can easily remove 0.05cc at a time by polishing alone.

And as an aside to all this talk of compression , and the looming threat of detonation - fuel quality is , in racing , of utmost importance.
As I tell every customer I have in karting or track racebikes , if you leave 98 pump fuel in a 1/2 empty drum , or in a vented tank overnight - its fucked the next day.
Its now 91 if you are lucky , as every time the lid is removed all the light front ends evaporate to atmosphere.
The Reid Vapor Pressure has dropped thru the floor , and this results in huge un atomized raw fuel droplets entering the engine.
These do not burn during combustion , and the tune appears rich on the piston and the egt, so you naturally lean it down and bang - siezure or deto.

Thus all race fuel should be bought or immediately decanted into 5L containers , with no airspace , and only one mixed and used at a time.
Absolutely vital if you are reading a weather gauge ( your phone App and the local airport ) and have jetting records based on RAD or Density Altitude.

So yes a 250MX will be happy with 12:1 but not on 91 fuel thats been in the tank for 3 weeks.

[porttiming124]

Hello everyone . I have a question about the shape of the slight hook of my b port.
If I measure before the little hook it gives me 20 mm . If I measure at the liner at the bore it gives me 23 mm.
IF i look on the aprilia rsw(pic CC) the tunnel seems more regular until the end.
Am I correct in thinking that the port should shrink gradually to the edge of the bore?
because in my case it opens before arriving at the edge of the bore.
I would love to hear your opinion on what you would do.

[wobbly]

This is the age old problem , you want to use Aprilia like technology , but your Transfer Ducts are nothing like one at all.
Your hook has virtually no radius on it and in the Aprilia both front and rear wall are perpendicular to the bore center line.

[porttiming124]

Ok perfect then I will forget to try to compare with the aprilia.
To come back to my old B duct what do you see to improve?
Should I modify the front and rear wall more perpendicular to the center of the bore or am I still wrong?
thanks.

[wobbly]

The best B port configuration for max power and overev is both walls perpendicular and a full radius in the hook corner , but for example a TM Kart , where front side
is important due to no PV , the walls are approx 15* but both parallel , plus the corner radius.
And the hooks should point to near 1/3 from the boost to bore center.

EDIT - and the A port front wall does not look angled back enough , where does its radial intersect.

[porttiming124]

It's an acceleration snowmobile engine with a cvt clutch so the front side doesn't really matter.

The front walls of the A ports intersect in the center of the bore.

[porttiming124]

I just came across a recommendation from tsr software that dates back to 1999.
What do you think of it 24 years later?

[Frits Overmars]

It's an acceleration snowmobile engine with a cvt clutch so the front side doesn't really matter.
The front walls of the A ports intersect well in the center of the bore.

It seems you've already made up your mind, so posting the image below won't be any use. But I'll do it anyway.
The radial angles of the A-port front walls are more important than any other radials, in any two-stroke. And look where they intersect the center line.

[porttiming124]

Hello Frits.
No I haven't made a decision.
I removed the word well in my sentence. (conflict between me and google translation).
Thanks for posting the image anyway.
Indeed from what I see on your image the intersection of the front wall of duct A must be done about more towards the back.
Thank you.

[Condyn]

PT, I do think a Very small amount of focus is to be put towards front side power with a cvt. After all, clutch engagment is lower than maximum power rpm. From data logs, I can see this area is used for 4-6 tenths of a second on my 440cc. Not much… but enough to be important to critical 60 foot times. And much more important than over-rev the way I see it.

[porttiming124]

Hello Condyn.
Actually, I totally agree with what you are saying.
This engine will drag on (soft) snow.
For this discipline (215+hp) we are constantly looking for traction.
I notice that the stronger the engine is at 6000rpm the bigger the traction problem.
Example a 600cc of 120 hp does not experience this problem.

This is why I feel like the front end of the power curve doesn't matter as much.

[lohring]

Below are a series of posts by Wayne I copied years ago. They may be helpful.

Lohring Miller

[porttiming124]

Thanks Lohring. Much appreciated.

[wobbly]

My take would be that in this case ( very unusual ) where the initial acceleration phase is traction limited , then the " front side " is important once the thing is hooked up and the clutches are locking.
This area may only last for a few tenths of a second , but is all important for the 60ft times.
A port front wall intersection points have been gradually moving back toward the boost port over many years , this being a function of the initial realization that fat pipes can easily
overcome the A port exit stream coherency , and second , we have had visual wave simulators for long enough now to have got a handle on what area of each diffuser section affects the power
band shape.
Having the intersection point well back near the boost , means steeper angles can be employed , and this is just as easy to bias toward peak power for a CVT as it is to generate front side.