ESE's works engine tuner

[ken seeber]

It may be just my suspicious mind, but do I feel a hand on my leg again?

Frits, don't worry, you're safe

[breezy]

Wobbly/Frits , after combustion of the fuel in the two stroke cycle, the gases produced expand and force the piston back down the cylinder... this explosion causes a pressure wave . is the pressure wave a different thing to the expanding gas pressure? if the blowdown is not enough to allow the pressure in the cylinder to drop below that of the transfer ports , is it the gasses pressure or the pressure wave which causes the stalling of the transfer flow. if they are two different things, what happens to the pressure wave if some of it disappears down the transfer ports

[Flettner]

I happened to notice this addition to your original post, Neil. Normally I would have missed it. And I hate missing things, so from my point of view it would have been safer to put it in a new post instead of adding it to a post that I already thought I'd seen. Come to think of it: God knows how many valuable additions I've already missed because I usually don't go back to 'old' posts.
That Husqvarna video of yours reminds me of a Stihl patent ( http://www.google.com/patents/US6415...roke+OR+engine ) wherein scavenging is also taken care of by air only, after which the fuel-air mixture is transferred. But I don't see any similarities with the Ryger engine.

Ok, thank you.

[wobbly]

I know its only semantics but we may as well get it right.
Its not "after " combustion, its as soon as the initial kernel of ionized molecules starts to consume the trapped A/F mixture
that the pressure begins to rise due to the increase in temperature.
Remember PV=nrT, the V varies only with piston movement thus P is proportional to T ( n&r being gas constants ).
We DONT have any " explosions " at all in this process, only fuel and oxygen being converted into pressure.
There is a moving wave front within the combustion space as the burning mixture expands out from the plug gap in the center, but pressure by definition is equal in all directions
and a wave must have a vector to define its direction.
When the transfers open, and if due to the design intent, or a lack of design knowledge , we have excess pressure above the port over that
within the duct, then reverse flow into the duct occurs.
This initial reverse flow can, and if you are clever usually is ,used to affect the scavenging pattern within the rising gas column ( Frits leaning tower from Italian parts )
by delaying the bulk flow from the transfer that opens first.
This effect as a general rule works to enhance midrange power if the A port opens first, or enhances peak and overev power if the B port opens first.
So this answers the question often asked re is it possible to have too much blowdown STA - no its not in a full race setup,but its very possible in lower power scenarios
and if it occurs then we have no reverse flow having a positive affect on the scavenging.
There is 20 more pages of detail, but even this is too long.

[RAW]

Wobbly would you PM me the 20 pages. Sounds like a good read 😃

[husaberg]

It may be just my suspicious mind, but do I feel a hand on my leg again?

That's all I can say right now.

Here is some questions you can answer Frits.

I had heard of a Swissauto/Roc powered mock up. is this it?

[Frits Overmars]

I had heard of a Swissauto/Roc powered mock up. is this it?

This is a genuine Aprilia 500-V4 Grand Prix racer. That means: it was built in the Aprilia Racing Department with the intention of replacing the RSV500 twin.
But the V-4 never appeared in an actual GP. The engine was from Swissauto (very compact, but with a horrible welded-up crankshaft and a terrible vibration).
I don't recall if the frame was Italian-made or brought in from the French ROC company that built 500 cc production racers based on Yamaha V-4 engines.
A couple more pictures of the bike:

[husaberg]

This is a genuine Aprilia 500-V4 Grand Prix racer. That means: it was built in the Aprilia Racing Department with the intention of replacing the RSV500 twin.
But the V-4 never appeared in an actual GP. The engine was from Swissauto (very compact, but with a horrible welded-up crankshaft and a terrible vibration).
I don't recall if the frame was Italian-made or brought in from the French ROC company that built 500 cc production racers based on Yamaha V-4 engines.
A couple more pictures of the bike:

Thanks Frits I would say to my untrained eye the chassis it looks very ROC like.


Wobbly does it look like the same as the Pulse 500 Frame?

[Frits Overmars]

Thanks Frits I would say to my untrained eye the chassis it looks very ROC like.

I'd say you're right Husa. Here are some more pictures of the various bikes that have been built around the Swissauto engine:
http://www.google.de/imgres?imgurl=h...IVQRQsCh2L1QuF

[breezy]

I know its only semantics but we may as well get it right.
Its not "after " combustion, its as soon as the initial kernel of ionized molecules starts to consume the trapped A/F mixture
that the pressure begins to rise due to the increase in temperature.
Remember PV=nrT, the V varies only with piston movement thus P is proportional to T ( n&r being gas constants ).
We DONT have any " explosions " at all in this process, only fuel and oxygen being converted into pressure.
There is a moving wave front within the combustion space as the burning mixture expands out from the plug gap in the center, but pressure by definition is equal in all directions
and a wave must have a vector to define its direction.
When the transfers open, and if due to the design intent, or a lack of design knowledge , we have excess pressure above the port over that
within the duct, then reverse flow into the duct occurs.
This initial reverse flow can, and if you are clever usually is ,used to affect the scavenging pattern within the rising gas column ( Frits leaning tower from Italian parts )
by delaying the bulk flow from the transfer that opens first.
This effect as a general rule works to enhance midrange power if the A port opens first, or enhances peak and overev power if the B port opens first.
So this answers the question often asked re is it possible to have too much blowdown STA - no its not in a full race setup,but its very possible in lower power scenarios
and if it occurs then we have no reverse flow having a positive affect on the scavenging.
There is 20 more pages of detail, but even this is too long.

Wobbly thanks for reply... .

[breezy]

wobbly, detonation is a destructive force?... is that only because the materials used in pistons and cylinder heads spark plugs cant withstand its actions. if they could, would inducing detonation produce more heat... pressure, than combustion?

[FastFred]

Here is a Thought Experiment. re combustion vis explosion.

Given that they both give off the same amount of total energy.

On a cold evening which would you rather sit in front of:- a nice warm open fire or an exploding stick of dynamite.

Pressure is the product of the combustion heating the gases in the combustion space and the amount of heat energy is dependent on the fuel. Burn more fuel in a given time and you get more power.

So my guess is that the end result between combustion and explosion for the same amount of fuel is the same amount of heat induced pressure but the speed of the pressure rise between the two is dramatically different.

Same total energy but one gives a sliding action because its applied over a longer period of time the other is an abrupt hammering action that overloads components.

Anyway that is how I understand it and it would be interesting to hear more about this.

[husaberg]

I'd say you're right Husa. Here are some more pictures of the various bikes that have been built around the Swissauto engine:
http://www.google.de/imgres?imgurl=h...IVQRQsCh2L1QuF

Here is some other pics the Website missed.
http://www.kiwibiker.co.nz/forums/al...p?albumid=4833

When you said the crank was welded that confused me. Where was it welded
I remember Wob saying it was a bloody expensive crank.

[wobbly]

The Pulse chassis was built by the Roberts Team in England around the SA engine,I could find out easy enough if one was sent to Aprilia
either by Dave ( thieving bastard ) Stewart recouping cash or if another of the chassis was copied and sold to them by by Roberts.

Re the power potential as you approach det conditions.
As I said there is a finite energy load in each combustion event and its easy enough in a 2T to dramatically redistribute where this energy goes.
Crank up the timing or the com and more heat goes into the piston/head/water, and less remains to activate the pipe wave action.

But deto is a completely different animal.
The excessive heat in the combustion space and the resultant shock wave moving uncontrolled thru the burning mixture destroys the all important boundary layer
that protects the piston and the squish band head material.
Thus the end gases erupt,creating more heat,and this gas trapped in the squish is so violently consumed due to the spastic levels of turbulence,that free radicals begin to form.
Once this starts,huge amounts of the available energy is used to create even more free radicals - a thermonuclear reaction in reverse.
These radicals are highly chemically reactive, and it is this property that eats away the alloy piston/head giving the classic deto signs around the bore periphery.

Using up huge amounts of the combustion energy like this of course means less is used to give the pressure rise,pushing down the piston - but also less heat
escapes into the pipe.
Thus the instant deto is forming the egt drops, and NO its not lean, its about to explode - literally.
Result - power craps out big time, but as is human nature,when det counters became available the rule of thumb that gave best performance was to have 3 det
"events" per Km.
All this meant was that the tuning was being pushed right to the edge by monitoring the amount of deto happening.
Made for lazy tuners that never learned how to read a plug accurately - just read a gauge.

[swarfie]

By welded up crank he probably means that the crankpins are tig welded to the crank webs (flywheels) so that the crank doesn't go out of phase. I did that to the 90 degree crank I made for my Matchless sidecar. It stops the "push" from one cylinder from turning the web on the crankpins, as the push is phased and hence not equal or at least not at the same time or 180 degrees apart. The weld only needs to be very small (not all the way around the crankpin) to ensure the pins don't turn.