Dyno fun with an 8V G.

[luhbo]

My reply was too short to give correct readings, I'm afraid What I wanted to adress with "false readings" were false readings as a result of where the probe is located and also false readings as a result of valve overlap in combination with low revs and wide throttle.

These ARF readings furthermore are a result of two different probes. The one built in, a cheap switching probe working in closed loop and located somewhere far behind the combustion chambers, and the one connected to the dyno, located somewhere in the open muffler, obviously wide band and a lot quicker in response. Add the small time you need for one sweep going from 2000 min-1 to redline and ARF numbers from a dyno are loosing a lot of their charm/importance. At least that's how it works for me.

 

At second sight the ARF curve doesn't look too weird. I think I can recognise some sort of pump emulation when you open the throttle, then the internal O2 probe kicks in and brings ARF back over 14, waves a bit around this official target, then finaly quits its service above 140, letting fall the ARF into a very rich condition.

It seems that at low revs leaner gives more power (of course, same fuel but more air).

 

Hubert

[pete roper]

I think I can recognise some sort of pump emulation when you open the throttle,

 

Hubert

 

Now this 'Pump Emulation' is something I have read about several times. Can you explain to me why on earth you would need to have such a thing on a fuel injected engine? The reason you need accelerator pumps on carburetors is that there is always a lag between the point when the manifold depression drops when the throttle is cracked open and the time when the fuel delivery increases to compensate as the atmospheric pressure pressing on the top of the fuel in the float bowl has to overcome the inertia of the fuel and push it up through the jet and atomiser into the venturi. With an FI system you simply don't have to do this. Butterfly opens, more air goes through, tps detects opening and delivers fuel accordingly. Why would you need to copy something designed to work within the limitations of a carburetor???

 

Pete

[luhbo]

At least two reasons come to my mind and I think I'm not too far off with them. My model is that as soon as you open the throttle the pressure inside the manifold rises and a lot of the former vaporised fuel recondensates and falls out of the air stream (you can watch this effect nicely on open carbs btw). Second reason, or maybe the same, these droplets are remarkably heavier as the air around them. So the accelerated, sober air just leaves them behind.

Countermeasure against the resulting hickups is a decent pump emulation. I tried it out with the MyEcu, running a firmware with the emulation set to zero. It works, but the engine behaves critical when cold especially, and even warmed up it looses a lot of crispness.

Cliff helped me with such a version after I "complained" about similar "fat" spots when I opened the throttle.

 

Hubert

[pete roper]

At least two reasons come to my mind and I think I'm not too far off with them. My model is that as soon as you open the throttle the pressure inside the manifold rises and a lot of the former vaporised fuel recondensates and falls out of the air stream (you can watch this effect nicely on open carbs btw). Second reason, or maybe the same, these droplets are remarkably heavier as the air around them. So the accelerated, sober air just leaves them behind.

Countermeasure against the resulting hickups is a decent pump emulation. I tried it out with the MyEcu, running a firmware with the emulation set to zero. It works, but the engine behaves critical when cold especially, and even warmed up it looses a lot of crispness.

Cliff helped me with such a version after I "complained" about similar "fat" spots when I opened the throttle.

 

Hubert

 

Ok, that makes sense. Thanks.

 

Pete

[Chris Wilson]

On 2/24/2010 at 10:20 PM, pete roper said:

 

 

It's the baffling in the muffler itself that is important. Pipe length and diameter, (And any taper in the overall design.) that will control the accoustic tuning of the pipe. What I'm convinced is neccesary is actually nothing more than a glorified 'Blockage' to slow down the egress of the spent gasses. "But surely," people will say "You want the gasses out?" and yes, you do but also remember that as they exit the system they are cooling rapidly and conracting so a longer time within the pipe means less volume of gas to flow. Running substantial overlap on the cams with a very narrow included valve angle means that there is a LOT of opportunity for new mixture to exit the exhaust valves on overlap and that is exactly what it will do if it is encouraged to do so. Because the speed of sound is a constant you can only rely on the percussive wave moving back from the end of the exhaust to work to this end over a quite narrow rev range. So trying to use what many describe as 'Back Pressure' but I preffer to think of as a restriction, within the entirety of the exhaust system from valve head to the end of the muffler will have a far greater ability to discourage the expulsion of fresh charge than relying on accoustics alone. Because of the amounts of gas being expelled at different RPM and loadings the restriction within the pipe will also vary due to the density of the gasses being expelled varied by heat.While I'm not certain I would think that this would mean that you could expect a more usefull result over a wider range than you would get relying on percussive tuning alone.

 

I may be completely wrong. But working on those principles the results I'm seeing make sense, to me at least. It is my belief that the engine is timed and it's ability to breathe is designed to work with a restrictive exhaust because that is what is demanded by modern emissions legislation covering both noise and pollutants. While I'm sure you can build a map to make the engine produce bulk power up top I'm convinced that to completely release its full 'Potential' it would need not only a new map but completely new valve timing to make it behave like an 'Old School' hot-rod. I'm sure that someone will, eventually, go down that path and hopefully the results will be spectacular and please them.

 

My aim in everything I do is to maximise the, if you like, 'Base' potential of the machine by exploiting its strengths and minimising its weaknesses WITHOUT embarking on a remanufacturing programme that could cost tens of thousands of dollars. I also think that in this day and age there is no reason for loud, open, antisocial pipes. Especially if we live, as most of us do, in fairly urbanized environments where our actions impact on our neigbors. You can have a bike that sounds GREAT to you, the rider, without having to deafen everybody in the next suburb and if, as in the case with this engine as it is timed now, making more noise also makes it LESS efficient?? Well, if you *have* to go down that path you're a wanker. Don't get me wrong, I love the sound of a well tuned 'Old School' motor but if I had to live with it every time I rode or, worse still, if I had some numb-nuts over the road who several times a day pulled his incredibly noisy and poorly-performing shitheap out and blasted off up the street making enough noise to wake the dead I too, like Mr & Mrs Average, would get the shits. While I'd just go over the road at 4.00AM and do the 'Dog Turd in a Burning Paper Bag' trick to the idiot in question Mr. & Mrs Average will simply vote for politicians who will enact ever more draconian legislation targeting internal combustion vehicles. None of us need that!

 

Also there is more of a challenge in getting the best out of something that has been deliberately engineered in a counter-intuitive way. Every time you have a win it's like you can give yourself an elephant stamp because you've 'Beaten the System'. I know it's puerile but I still enjoy doing that

 

Pete

Long time since the above quote was posted but since the author is definitely around I have to ask why the you say that the speed of sound is a constant when it is heavily dependant on temperature and the medium it flows through.

That and reflective acoustics, return waves tend recognise the first reflective wall they come to which may or may not be the intended baffling.

The pretzel is such a chicane that it wouldn't surprise me that it acts as a tuned length and keeping more heat trapped into the header system and less at the muffler end.

Having tight and varied curves as a reflector instead of the classic perpendicular wall broadens the range at which the signal reflects and in turn broadens the rpm band in which it works.

To me the header/pretzel is a sacred combined system designed for broad power and the muffler keeps that system pressurised and heated to adjust the speed of sound for the reflected wave.

Take away the standard muffler with its restrictions and you lessen heat in the header/pretzel system and slow the speed of sound.

Just my thoughts and look forward to others.

Chris.

[Lucky Phil]

47 minutes ago, Chris Wilson said:

Long time since the above quote was posted but since the author is definitely around I have to ask why the you say that the speed of sound is a constant when it is heavily dependant on temperature and the medium it flows through.

That and reflective acoustics, return waves tend recognise the first reflective wall they come to which may or may not be the intended baffling.

The pretzel is such a chicane that it wouldn't surprise me that it acts as a tuned length and keeping more heat trapped into the header system and less at the muffler end.

Having tight and varied curves as a reflector instead of the classic perpendicular wall broadens the range at which the signal reflects and in turn broadens the rpm band in which it works.

To me the header/pretzel is a sacred combined system designed for broad power and the muffler keeps that system pressurised and heated to adjust the speed of sound for the reflected wave.

Take away the standard muffler with its restrictions and you lessen heat in the header/pretzel system and slow the speed of sound.

Just my thoughts and forward to others.

Chris.

Hence the use of exhaust valves in MotoGP bike exhaust systems today. You can control the exhaust back pressure/density therefore the speed and timing to some extent of the reflective wave. Just another piece in the complex puzzle of exhaust tuning.  

Ciao

[pete roper]

I've also thought about this since that message was posted. I think the pressure drop and condensing of the fuel is an irrelevance, the fuel is delivered way beyond the butterfly and anyway there is little or no Venturi effect in the choke of a throttlebody.

No, the speed of sound isn't a constant but at the speed gas is moving in the exhaust and the rapidity with which pulses are occurring means that in a simple system like a Guzzi exhaust it might as well be. How the pressure waves within the gas, (I detest the term 'Back Pressure') move will be governed far more by their frequency of occurrence than the density of the gas through which they move.

YOMV.