ESE's works engine tuner

[Frits Overmars]

... we have a situation where at 1000 rpm below peak power, the pipe - now too long ?? for the tuned rpm, acts to create an even sooner, greater depression at the port.
Thus it makes me think that at BDC, there will be a large, unavoidable span of rpm where even with an inefficient diffuser, we will have excessive short circuiting, simply due to the pipe geometry....

Wob, I noticed that you tend to use a somewhat smaller header length percentage than what I am used to. The difference is maybe just 1 or 2 %, but it could have a noticeable effect.

Short-circuiting due to too short a pipe is somewhat self-regulating due to the much lower exhaust gas temperature resulting from the escaping cold mixture, as Neels points out.
I think this was a reason for provoking deliberate short-circuiting and/or high-speed loop-scavenging in yesterday's direct-drive kart engines.

[Storbeck]

I'm not a Viking but I am pretty sure he's using 670 Rotax cylinders that look a lot like this (pictures from ebay ads I found on the interweb).

The experts can opine if those are lift shafts, to me they are not the MOST squared off lift shaft transfers I've ever seen....but they don't look much like a teacup.

[wobbly]

The Eagle Eye of Mr FOS strikes again - of course the pipe is too short at the lower rpm - dumbarse.
And yes, I had not considered the effect of the short circuiting regime on the EGT - again an obvious error, thankyou.
The short header and short steep first diffuser section is aimed specifically to peak and overev generation, then using a steep longer last diffuser section to regain the front side.
Especially in engines with no PV, that ameliorates many evils.

[Viking]

Hi Wayne,

Currently my way of thinking on this topic is summarized in this picture.

Attachment 356519

My thinking between my simulation iterations was focused on why I don´t achieve a faster pressure drop in 'Pexport'.
Even if the Rotax 670 cylinders tiny auxilary exhaust ports are modified to enough STA,
the small auxilary exhaust ducts are very restrective and might be the problem - not the diffuser.

[Viking]

Neels, whilst working late last night it occurred to me that assuming the Rotax depression wave acts along the same lines as the R3 I am testing, then we have a
situation where at 1000 rpm below peak power, the pipe - now too long for the tuned rpm, acts to create an even sooner, greater depression at the port.
Thus it makes me think that at BDC, there will be a large, unavoidable span of rpm where even with an inefficient diffuser, we will have excessive short circuiting, simply due to the pipe geometry and
the port acting in concert, to pull the suction early and low.
I dont have any " inefficient " diffuser designs to test in a big cylinder, to see the wave front shape created in that Rotax for example at lower rpm.
I would be really interested if Viking could post the screen shot, or send me the .pack to understand what happens in this scenario.
Here is the KZ at 1000 rpm below peak to show the effect in that engine.
I assume we would only see the down side of this effect on lift shafts, using your excessive short circuit, scavenging model.

I would happily send you .pack-files, but my moving schedule is to start opening the moving-boxes in October/November, and until then I am computer-lost.

[Viking]

I'm not a Viking but I am pretty sure he's using 670 Rotax cylinders that look a lot like this (pictures from ebay ads I found on the interweb).

The experts can opine if those are lift shafts, to me they are not the MOST squared off lift shaft transfers I've ever seen....but they don't look much like a teacup.

Thank you Storbeck,
this is the kind of cylinders I will use on the engine.

Bad designed main exhaust duct, auxilary exhaust duct and transfer ducts.
Even the inlet RV duct in the crankcase is bad.
But the engine is legendary,
and dominated on the racing tracks 1992-2000 in snowcross and dragracing.

[Storbeck]

Thank you Storbeck,
this is the kind of cylinders I will use on the engine.

Bad designed main exhaust duct, auxilary exhaust duct and transfer ducts.
Even the inlet RV duct in the crankcase is bad.
But the engine is legendary,
and dominated on the racing tracks 1992-2000 in snowcross and dragracing.

Viking indeed it was!

The watercraft version was very competitive also.

[SwePatrick]

Curiosity killed the,,, butt? :O

And well worth it.
New record again, 53.6whp 13000rpm (dyno reports 59.1 crankhp)
144cc
E85

I call this engine DONE! (for now)
I might build a strange sprintchassi to mount it in.

[Frits Overmars]

The Eagle Eye of Mr FOS strikes again ....

Wob, to console you, here is proof that I also make mistakes. For example, yesterday, when I didn't get around to congratulating you on your birthday (I was rather busy in a Ferrari on a nice German racetrack, the Lausitzring). So here you go, to your health, Wob. And to mine, because traditionally my birthday is one day after yours.