ESE's works engine tuner

[TZ350]

I dont understand , one minute TeeZee you are running 18:1, then you go off the planet the other way with 11:1 that would be slow on petrol. 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.

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.

My 125 would have had a larger case volume than the Aprilia but you might be right about the 250's CCR, I will have to check by CC'ing it. The 250's case volume was increased with a slightly longer rod and the crank inner faces slimmed down to the thrust faces.

Thanks for the pipe temperature info, very helpful.

It was an easy swap to go back to a standard head with its 11:1. 18:1 was too much. What would you suggest as a more appropriate ratio for a 250 on meth.

[wobbly]

My take would be 15:1 as a first try for a 250 Aircooled.
This will give a good ratio of much needed cylinder /head cooling Vs increasing the power due to compression.

Be aware that the default EngMod process is you input the case CC via a hole in the piston at TDC and when you input this number into the calculator it removes the transfer ducts
and displays this ratio. This allows the code to recalculate the duct volume when a port is changed.
You can off course input your own ratio and include the transfer ducts as per normal practice.

Re doing compression CC testing.
To eliminate any variables trying to peer down a threaded hole and guess the meniscus position . I use a gauge that screws into the plug threads and bottoms such that the end is flush with the chamber.
A normal plug has 18.3mm of actual thread engagement taking the crushed washer into account , and virtually all 10 heat range race plugs displace 2.25cc in the threads - so this is the volume of
the gauges bore.
Its then real easy to fill to within 10mm of the gauge top , turn the rotor back and forth to hit TDC exactly , then fill it to the top and remove 2.25cc from the reading.
I use a digital burette , but a glass one is fine as long as you leave it to sit for 15 mins while the fluid clinging to the glass slowly runs down.
The fluid has always been ATF.

[TZ350]

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Hopefully I have got this right. To mimic Methanol in a 15:1 air cooled 250 cc engine.

I setup the temperature file by selecting the water cooled cylinder and crankcase default. And the pipe temperature varied with rpm 250 at 6000 to 350 at 9500 rpm.



Simulated two runs. One with 32 deg ignition straight line and the other starting at 34 and reducing to 7 deg. An ignition curve suggested by EngMod.

Hopefully later next week I will get a chance to do this for real on the dyno.

[wobbly]

So why would you select a watercooled option when the engine is aircooled - makes no sense.
32* straight line is insane and completely impossible , why even think about using it as no one else has done this , let alone got away with it , ever.
And the Exhaust duct temp is not going to be any thing like 250* as on petrol , I would try 180* as a start point and reduce the crank and transfer wall temps by at least 20*.
I have no idea why , but in this case EngMod is talking rubbish about the ignition , im not.

And one of the things Methanol does is to allow very rich mixtures to be used without power loss.
This translates into negating the usual effect on petrol , that when the engine is over the top of the pipe , the air flow thru the carb keeps going up , but power is going down.
Thus less fuel is needed in reality , so the carb is forcing the mixture into going rich - exactly what solenoid power jets fix so elegantly.
On petrol , going rich over the top looses power - on Meth it doesn't.

One way to help the situation on petrol is to retard the ignition over the top , thus dumping more heat into the pipe.
But Methanol basically makes the engine insensitive to fueling , and the pipe is already way shorter due to the inherent drop in wall temperature.

Thus retard over the top is not needed , as richness doesn't have the same negative effect as on petrol.
The only odd case , that proves the rule , is that when using 20:1 compression on Meth in a 125 , this needs a hugely rich mixture to live , and a solenoid power jet then heats the pipe enough to make rev on power better.
I would look at retarding as usual to 15* at peak power , then flat lining it.

[TZ350]

So why would you select a watercooled option when the engine is aircooled - makes no sense.
32* straight line is insane and completely impossible , why even think about using it as no one else has done this , let alone got away with it , ever.
And the Exhaust duct temp is not going to be any thing like 250* as on petrol , I would try 180* as a start point and reduce the crank and transfer wall temps by at least 20*.
I have no idea why , but in this case EngMod is talking rubbish about the ignition , im not.

Made good sense to me as there is not a Methanol default option. As I had no idea what the meth simulation temps should be. Water cooled was selected to mimic the engine cooling effect of Meth.

I will use the lower temperatures you suggest with the air cooled option.

32* might be insane but was starting to look possible. Top end power was increasing as I straitened up the ignition curve into a 30 deg straight line. 32 or even 34 looked like it might have been possible and EngMod agreed.

DynoJet dyno and Ignitec ignition.

But I was suspicious of the whole thing, it was quite harsh until about 9,000 rpm. A bit like a diesel model aero engine that is being over compressed.

Was it the 18:1 com ratio, the advanced ignition although it was making more power each 2 deg step of extra adv, or was the ever richer fueling at the top end masking something??? Maybe worth trying a std 11:1 head to see what changes.

[Frits Overmars]

32* straight line is insane and completely impossible , why even think about using it as no one else has done this , let alone got away with it , ever.... I would look at retarding as usual to 15* at peak power, then flat lining it.

I have tried all kinds of crazy things but I never had the guts to try 32° straight line ignition advance in the powerband of any engine with a decent BMEP.
Flat lining at 15° would be a safe way to start your ignition quest. Subsequently you can run flat lines with even less advance, en finally carefully try more advance at the rpm points that suffered from retarding.

Maybe worth trying a std 11:1 head to see what changes.

Now that is something you can safely try. You may be generating ignition and fueling numbers that are of no use whatever in a properly setup engine, as Wob says, but I would not call it a complete waste of time. It will be educational either way and you won't have to get rid of broken engine parts afterwards.

I've long been a proponent of low compression ratios. In my experience, a low-compressed engine reacts much more clearly to changes. But to take advantage, you'll need an exhaust pipe that deals extremely efficiently with the energy contained in the exhaust gases of such an engine. And the engine will need a transfer layout that can handle that amount of pipe suction.

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.

It was considered large compared to what had been done before.
The Aprilia RSW had a TDC crankcase volume of 650 cc and a Crankcase Compression Ratio of 1,238 .
The Aprilia RSA had a TDC crankcase volume of 675 cc and a CCR of 1,227, which gave a power improvement over its predecessor.
But is 1,227 the optimum? I don't know and Jan Thiel doesn't know either. You won't discover a border until you cross it, and Jan retired before it came to that.

[DoldGuy]

I’m so enjoying this learning experience that is being shared, most trials and errors are tucked away. TZ I’ve learned more about EngMod2T with your posts and others replies in regards!
Thanks again for the education…

[Condyn]

The gauges Wob is referring to are sold by L.A.D and often called L.A.D gauges. They work excellent as described above. The small bore of the gauge minimizes surface tension discrepancies. A tenth of a CC is not as critical on a 70mm bore as it is on a 54mm bore. Trying to fiddle around counting threads is foolish, especially on small bore cylinders. I feel many builders simply estimate on compression ratio, as it is tricky without the L.A.D gauge.

Just yesterday I attempted to check CCR for engmod modeling on my parallel twin piston controlled inlet engine. I plugged the inlet port with modeling clay as Wob mentioned a while ago. Next I smeared a bit of grease around the piston ring to insure nothing would seep by. Then started filling through a hole cut in a used piston. It was a learning experience. As soon as I was about 400cc into it, the adjacent cylinder case pulse line fitting started pissing. Apparently labyrinth seals do not function until the crank is spinning. (Or my labyrinth is not working) I think I will attempt to inject a wad of grease between the center bearing and labyrinth seal in order to get the measurement.

[Vannik]

Apparently labyrinth seals do not function until the crank is spinning.

Measuring crankcase volume without a labyrinth seal is both a learning and a trying experience. Can quickly turn into a very messy situation.

A labyrinth seal has a controlled but very small amount of leakage when in motion. Stationary it does not seal.

[wobbly]

Reducing the duct temp has a large effect on pipe bulk temp , so lowering it will need a shorter pipe for the same peak rpm.
As I said use the age old guide of 30 to 33% for the header and 64 to 68% for the diffuser.

Having no power valve , the front side power can be helped by a quite long and steep last diffuser section.
To gain more overev if needed , a shorter header , and a steeper/shorter 1st diffuser is the go - but this will be less of an issue on Meth due to the reduced adverse reaction to the fuel curve going rich over the top.

I completely agree with Frits's ideology , but still think 11:1 is too low even as a first try , as that would be conservative on shit pump gas.
Lastly my experiences lead to winding up the MSV with Meth , into the mid 40M/s, with a sharp corner on the bowl as this mimics having more advance by increasing flame speed due to squish turbulence
But that technique makes more power , than ignition advance does - maybe due to less compression pumping losses after the spark has fired BTDC , another reason I think anything above 30* is mental.

[diesel pig]

I completely agree with Frits's ideology , but still think 11:1 is too low even as a first try , as that would be conservative on shit pump gas.

Interesting, What compression do you think we nutter's wanting to build dirt bike engines to run on 91 petrol as one should be able get it no matter where we nutter's go?

[wobbly]

An aircooled 250 MX on 91 would go 12.5 all day , as you are not hard on the gas for long at all - and need plenty of mid snap to get off berms etc , not screaming top end.
Not that you can generate big bmep from one of those old shitters anyway, without basically starting over with welded ports and hours on the sim.

[diesel pig]

An aircooled 250 MX on 91 would go 12.5 all day , as you are not hard on the gas for long at all - and need plenty of mid snap to get off berms etc , not screaming top end.
Not that you can generate big bmep from one of those old shitters anyway, without basically starting over with welded ports and hours on the sim.

Thank you for the reply. I hate to admit it but staying on the gas of a old dirt bike does lead to 'problems'.

[diesel pig]

Also, There is no way I would start re engineering things I just wanted to know what value to look for when re building a motor. Cheers

[husaberg]

Interesting, What compression do you think we nutter's wanting to build dirt bike engines to run on 91 petrol as one should be able get it no matter where we nutter's go?

................i assume 700 octane refers to 100 octane....

pretty sure Robinson had a table as likely did jennings