engmod, real life, detonation, MK?

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ief
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engmod, real life, detonation, MK?

#1 Post by ief » Fri May 19, 2017 6:32 pm

Back to the rd after some years.

Engmod developed over time...

Anyway, I ran into detonation issues, not at peak but at 5 to 7 K.

Wonder if that is a real life problem or will be jetted out? Is this the splutter? (though that seems rich, not lean)

Tried a bunch of things with the exhaust but I wonder, espesialy after reading the pv bit, why I get deto there? (and if it's real)

Obviously a consurn none the less.

What's your take?
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ief
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Re: engmod, real life, detonation, MK?

#2 Post by ief » Sat May 20, 2017 5:22 pm

ps: your question at the end, (pv open vs open and more power) Not really looked into it but has to be temperature related I guess?
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waltmil
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Re: engmod, real life, detonation, MK?

#3 Post by waltmil » Sat May 20, 2017 5:58 pm

Are you running a programmable ignition?
Red/White US '84, Spec II pipes, Y-boot w/K&N, Fox Shock, Mikuni carbs?

ief
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Re: engmod, real life, detonation, MK?

#4 Post by ief » Sat May 20, 2017 6:49 pm

This is theoretical :)

Sort off.
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Bare
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Re: engmod, real life, detonation, MK?

#5 Post by Bare » Sat May 20, 2017 11:30 pm

Detonation? And you assume it IS detonation How?
Often these things (LC's Much more so than YVPS engines)
Do have a sputter event at those rpms when things get slightly messed from an as new setup.

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Re: engmod, real life, detonation, MK?

#6 Post by ief » Sun May 21, 2017 9:02 am

Because engmod 'shouts', warning, detonation at me ;)

Simming on euro 95 btw, to be on the save side. There is a peak in temperature around 5 to 7 k depending on exhaust and pv setting. Since MK made a pdf about changing the pv to open even later than stock and he tunes his bikes as well I was wondering what he thought of this. (and he has engmod as well)

If I input a more capable exhaust the problem gets worse.

It can be alleviated by putting a better reed (vforce for example) in but loads of bikes run stock and are tuned none the less.

Just wanted to pick his brain some...
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sispeed
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Re: engmod, real life, detonation, MK?

#7 Post by sispeed » Mon May 22, 2017 11:11 am

What is the end diameter of your pipe before muffler?
Try going a mm bigger
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kenny
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Re: engmod, real life, detonation, MK?

#8 Post by kenny » Mon May 22, 2017 12:33 pm

I opened the PV at 4800 and fully open at 8400 this lowers the compression ratio at that point. You could also take out some advance on the ignition to the point it doesnt detonate at that point.

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Re: engmod, real life, detonation, MK?

#9 Post by ief » Mon May 22, 2017 3:27 pm

Cheers guys, it's not that I don't know how to resolve the issue but the relationship to MK's proposed modding of the powervalve to open up later since engmod suggest problems then (on tuned bike anyway) and I was wondering how he feels about that or that it is a none issue in real life due to just jet bigger or something. (and liked his question on the difference in power with open, none working valve and working one :))

I'll have to dive in it some more...

https://www.google.nl/url?sa=t&rct=j&q= ... zuyCNbmQDA" onclick="window.open(this.href);return false;
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Re: engmod, real life, detonation, MK?

#10 Post by slinger » Mon May 22, 2017 11:05 pm

If your seeing deto at that rpm I'd look at you static comp ratio the delivery ratio of the pipe. Like Kenny pointed out pv will change the dynamic comp ratio, your right on the point of max torque. I spent a huge amount of time testing before the PV opens and the shape of the exhaust port floor to gain Blowdown Flow.

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Re: engmod, real life, detonation, MK?

#11 Post by ief » Fri May 26, 2017 6:52 am

I'm sure optimising that would be of great benefit as well , the PV itself isn't helping in this regard but for most users that is not an option, they just slam on a pipe, in best case have some dyno sessions and that's that. To me it seems that one can get into dangerous territory pretty quick. (be it it will be countered by jetting)

Anyway, this is totally related but it's doing me head in for months now. what happens when you get a pipe that is working 'better' (fatter, stepper angles) on an engine that doesn't support it and how to make that visible in engmod, i.e, look at this or that and you see what goes 'wrong'.

Trying to understand 2strokes has become, trying to understand engmod, lol.

I've seen major (200 degrees C) diferences in tubmax temp, for not such much improvement in output, swapping the angled header to a straight one solved it without to much powerloss.

(yasuni scooter exhaust on slightly tuned tomos engine for example)

Pipes, fassenating things :)
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Re: engmod, real life, detonation, MK?

#12 Post by Bare » Fri May 26, 2017 6:23 pm

What could be more directly related than a Cheap Ass Yasuni Scooter engine Pipe?
on a Tomo moped engine..?
My prosaic Shindaiwas have seriously more sophisticated designs,
as they are designed for beating the daylights out of Lawns.. albeit 8 hours a day.. for 3 years at least (warranty period).

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Re: engmod, real life, detonation, MK?

#13 Post by ief » Sat May 27, 2017 8:11 am

Although you seem to TOTALLY miss the point (again) calling yasuni a cheap ass exhaust goes a bit far don't you think?

Happen to have a couple of them and I thin they are pretty well build, besides that, I wouldn't call them cheap exactly and for purpouse intended they seem to perform pretty good as well so... what you'r on about?

https://www.tuningmatters.com/reviews/e ... aust-test/" onclick="window.open(this.href);return false;

Don't forget these are production pipes and NOT custum made.
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ief
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Re: engmod, real life, detonation, MK?

#14 Post by ief » Tue May 30, 2017 10:40 am

Thought a bit more about Slingers statement and I just can't get it to make sense.

If optimizing BD flow helps then why is an exhaust with steeper angles (header and/ or diffuser) make the problem worse while in essence it's doing the same thing, optimizing flow due to less restriction and more sucking... or is it (?)

Dilution of unburnt and burned gases, overscavenging, more short circuiting (but then why does it make more power) ????

Like I said, it's doing me head in :)
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Re: engmod, real life, detonation, MK?

#15 Post by sispeed » Fri Jun 02, 2017 6:53 am

I allways have to scratch my head if thinking to long about that.
My understanding is steeper angles suck more so more fresh mixture get's out of the Ex. So less cooling and the returning gasses are hotter during the time spend in the Ex Duct and Header.
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