ESE's works engine tuner

[skako]

.
All the other details of the 1971 Kawasaki F81M 250.

Hallo,
While I'm studying what I forgot or don't know, I tried to design an exhaust pipe for simulation during my pause.
I was not able to find all the necessary technical data for the Kawasaki F81M 250, so I partially evaluated them.
I'd love to see a graph of how it looks in EngMod2T with this exhaust pipe and symmetrical intake. Duration 180°, opening 90° btdc, closing 90° atdc, full opening 45° btdc, intake length 120mm, carb. dia 38mm.
Everything else unchanged.
Thank you,

[TZ350]

If meth works at ~450* EGT as stated before,wouldnt this mean that you need an exhaust TL of about 950mm for 9500rpm and 200* exhaust port instead of 1000+?

Yes, I would have thought so too. Not sure what is happening here, just looking to EngMod for guidance. I suspect I may have messed up the data input when designing the pipe.

[Francisco Erjavec]

https://www.youtube.com/watch?v=nkBabPAMIsc

Hi Frits!
Whats your opinion about the belly butterfly valve shown in the video?

[TZ350]

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Standard 250 head. 11:1 com ratio swept. Will get a chance to run this up maybe mid next week. A tropical cyclone is coming, and I need to get ready for that, we got pretty wet in the last storm.

[F5 Dave]

Um why are you showing a picture of a pressure gauge? What has that got to do with compression ratio?
Please tell me you used a burette. Two threads up from the bottom works well.

[TZ350]

Um why are you showing a picture of a pressure gauge? What has that got to do with compression ratio?

There had been a bit of talk about dynamic compression pressure so I was curious to see what the cold cranking pressure for 11:1 looked like.
If I had of had more time I would have popped the other higher compression head back on for comparison.
Also EngMod-2T gives a cranking pressure for your chosen com ratio. A handy check. If you'er not seeing something close to the expected pressure its time to ask yourself some questions.

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

No Burette, although I have two glass laboratory one's. We find it much more convenient and safer to use plastic syringe's.
They are cheap, readily available, quick and easy to use with good accuracy. They come in a variety of suitable sizes. Team ESE achieve results with them that we are confident in.

[F5 Dave]

Ok so at least you measured it static. Pressure gauge, one way valve or not, tells you limited information, often disinformation.

Burette is cheap enough from online suppliers. Easy to use. I favour 5w fork oil.

Measure thrice. Cut once.

[DoldGuy]

Attachment 352312


TZ, I’ll go ahead and confirm my idiotic thinking by asking the question, in the EngMod2T Head file shows 300 mm dome radius???

[TZ350]

Attachment 352312 TZ, I’ll go ahead and confirm my idiotic thinking by asking the question, in the EngMod2T Head file shows 300 mm dome radius???

300mm dome radius refers to the curve of the piston crown. In the lower right box you can also see the calculated compression pressure for the chosen com ratio.

[Orengo98]

Hi Orengo, my first reaction was: if you want to learn a lot, go ahead and do what I did. If you want to ride, don't.
My engine came with one central spark plug. I fitted a head with two plug holes after the original head had cracked, because that was all I could find. But I could only fit the forward plug; my monocoque frame got in the way of the rear plug.
It taught me the difference a plug position can make. Maximum power was not affected but with the forward plug the engine idled much nicer than with the central plug.

Hi Frits,

Thanks for your answer! really interesting!

Part of the idea is to try to make parts for the engine, experiment and learn so it is fine.
Thanks for sharing your experience with the plug placement, the ignition was another place where I had doubts. This engine is extremely over square, and reading a paper about the bore/stroke ratio, they found that as the ratio increased, the combustion efficiency dropped. The dual plug design maybe has some part on solving this problem, as Bultaco stated a slight power increase with the dual plugs. Do you believe this design is advantageous?

In my experience, low compression ratios make it easier to extract power from an engine. But for an air cooled big single with a shrunk-in cast-iron sleeve I would not go too low; relatively cool exhaust gases are more important than power. About 12:1 should be a good value.
The transfer design on my engine was rather different from the original MX-engine. I had enlarged the A-transfers and added a big third port where the piston-controlled inlet port used to be.
The pipe belly was considered huge at the time, but rather modest with 51 years of hindsight: 112 mm if I remember correctly.
I think nowadays that would be a good belly diameter for your more-or-less standard engine.
Attachment 352306

Thanks for the tip, I'll try a 12:1 head with a concentric toroidal chamber design to start with, seems like an easy mod to try.

Your engine must have been quite powerful, the gears on that engine are tractor like, really wide!
The problem of the primary gears seems to be usual, once the factory power is surpassed, the axial force of the helical gears is greater than the press fit of the clutch basket bearing. The TSS had and advantage there as well as the 5 speeds. I have the port map of the factory racer, really similar, wider transfers, taller exhaust port, and two extra transfers carved behind the sleeve. Maybe I can post it here if it is of some use for someone building a similar engine?

The pipe is kinda strange. It was wide for the era as you say, and also has a huge stinger, looks like a canon hahaha. It also has two big "dents" to clear the frame and rear wheel, that I'm sure they produce a noticeable pressure trace.

Thank you a lot for the details and insight in your learnings and engine!

Bert Flood prepped an el bandito for road racing in the late 60's or ealy 70's it was pretty successful
On two wheels detailed it.
i have a copy somewhere.

Hi Husaberg!

If I remember right, it was a bike for speed records? Is the one in the pictures I attach?

[Flettner]

What to take heed of when running two separate pipes off a single cylinder?
Fit a joining tube from the two mid sections?
Make the reverse cones adjustable so as to be sure the tuned length is the same in both pipes. Adjust them on a dyno to get them in sync?

[husaberg]

Hi Husaberg!

If I remember right, it was a bike for speed records? Is the one in the pictures I attach?

Started with a road racer thats the one i most remember.
It was very mildly tuned.
i started to look on Friday.

[ken seeber]

What to take heed of when running two separate pipes off a single cylinder?
Fit a joining tube from the two mid sections?
Make the reverse cones adjustable so as to be sure the tuned length is the same in both pipes. Adjust them on a dyno to get them in sync?

Fletto, it's a modern Jawa....go 2 pipes..

[Frits Overmars]

Hi Frits.... Thanks for sharing your experience with the plug placement, the ignition was another place where I had doubts. This engine is extremely over square, and reading a paper about the bore/stroke ratio, they found that as the ratio increased, the combustion efficiency dropped. The dual plug design maybe has some part on solving this problem, as Bultaco stated a slight power increase with the dual plugs. Do you believe this design is advantageous?

The dual plug setup may have been advantageous in that Bultaco combustion chamber (now there's a real bathtub chamber for all you guys who keep calling a bowler head chamber a bathtub). But as I wrote, I had only room for one plug, so I cannot answer from experience. But never mind, stick to a single-plug toroidal chamber like you planned.

What to take heed of when running two separate pipes off a single cylinder? Fit a joining tube from the two mid sections? Make the reverse cones adjustable so as to be sure the tuned length is the same in both pipes. Adjust them on a dyno to get them in sync?

KISS and KISS again Neil. No joining tube. And you can use adjustable reflector cones if you wish, but I don't think you'll need anything that fancy to synchronize the pipes.
Sticking to the design dimensions should be accurate enough.

[wobbly]

I dont understand , one minute TeeZee you are running 18:1 that would be considered a good spot for a 125 water cooled race engine - and completely mental in a 250 aircooled , then you go off the planet the other way
with 11:1 that would be slow on petrol.
Whats the point of testing that at all - except wasting a pile of time generating ignition and fueling numbers that are of no use whatever in a properly setup engine.
Either way is not even close for a 250 aircooled engine on Meth.

Meth pipe design has been done and dusted. A normal petrol pipe wall temp that works is 325 at the bottom of the power band and 425 at peak power - where egt would be in the 600's.
The Methanol numbers are 250/350.

And a header length way past a normal max of 33% at 37% is also not even close to optimal, and is always going to give weird arse anomalies in the powerband shape.

A CCR of 1.2 without the transfer duct volumes included also simply cant be right , shit the Aprilia was at 1.24 WITH the transfer ducts - and that was considered large.