ESE's works engine tuner

[husaberg]

Don't tell me it's as simple as a hose clip clamped around the con rod holding a rubber boot that is also anchored to the alloy plate in the crank case? There we have it

A zip tie would be simpler.

[Flettner]

A zip tie would be simpler.

That's ten years development right there.
Hose clips are more manly, zippie ties are for pussy's.

[husaberg]

That's ten years development right there.
Hose clips are more manly, zippie ties are for pussy's.

That pussy comment pieced me.
Harry Ryger actually mentioned bellows.

[PVO]

Wobbly, I appreciate the following info you have supplied regarding exhaust duct sizing.

"Next issue that is my favorite hobby horse for today is Ex duct exit area.
You will find a heap of free power, when using a T port or a Tripple port configuration, by limiting the duct exit area to around 75% of the Total Ex Port Effective.
Then make the header start at the area = to the Total Effective.
Join these with an oval to round adapter in the spigot or flange, where the width = the header dia all the way thru, to enhance the flow from the blowdown area,and
the height at the flange face forms an oval to give the correct 75% area.

Simple answer re the odd shape and reduced area of the Ex duct exit is that with a 3 port cylinder, the area of the main port is plenty big enough to support the gas flow
created by the power being made.
The big Aux additional area allows better Blowdown STA, but this area is only needed above TRO.
Thus having a huge duct simply drops the velocity, reducing the wave amplitude into the header.
The Aprilia shape promotes the flow from the Aux ports by keeping the extra horizontal area all the way into the pipe - thus helping blowdown flow and overev power..
Reducing the duct vol by having area reducing steps, keeps the velocity high and again promotes the flow regime in the side ports.
There may be a case to say that the steps reduce backflow from the pipe at low rpm when it is too short,but for sure there is no outflow disruption,and in any case tests showed that power went up as the duct became smaller.
I have exhaustively ( pun ) tested the vol/shape effects on a T port ( as has Mr H ) and an oval to round transition with no steps works better."

Is it beneficial also to raise the exhaust port floor up to reduce duct volume? If this were done the total effective exhaust area would be reduced and subsequently the duct exit area and starting diameter for the manifold (if your rule of thumb sizing recommendations were followed). Blowdown and transfer STA are what primarily influence power so raising the exhaust port floor up may not hurt power until the port radii start to have an effect on the blowdown STA? I'm assuming the raised port floor would also help to prevent short circuiting of the A transfers? If I did this would I find that the duct volume can be made too small? I'd be very appreciative of any further insights you are willing to share on the sizing and design of the exhaust ducts.

[wobbly]

Jan raised the Aprilia port floor at the duct entry 2mm ( on a 54.5 stroke ) above BDC I believe, and the bottom corner rads were
made progressively bigger and bigger to reduce the duct volume.
This is dyno proven ( his and mine ) to make better power, so go there straight away, but as you say dont reduce the blowdown width
of the main port above TRO.
Testing the reduced duct area at the port, and reducing/varying the area at the duct exit is easily optimized in EngMod, except of course as its not a 3D FEA flow code
like Fluent etc it cant verify the effect on power of reducing short circuiting.

[PVO]

Jan raised the Aprilia port floor at the duct entry 2mm ( on a 54.5 stroke ) above BDC I believe, and the bottom corner rads were
made progressively bigger and bigger to reduce the duct volume.
This is dyno proven ( his and mine ) to make better power, so go there straight away, but as you say dont reduce the blowdown width
of the main port above TRO.
Testing the reduced duct area at the port, and reducing/varying the area at the duct exit is easily optimized in EngMod, except of course as its not a 3D FEA flow code
like Fluent etc it cant verify the effect on power of reducing short circuiting.

Thanks for the info Wobbly, that will get me going in the right direction.

Do you have any recommendations on the port exit angle? I'm aware the RSA was 30 degrees from horizontal. If I recall this angle was partly chosen for packaging reasons. Obviously as duct angle decreases port effective area increases, but there is a trade-off with gas flow. Do you know if 30 degrees was also the best flow angle or has another angle between 0 and 30 been proven to work best?

[wobbly]

Jan tested everything and 25* was best.

[peewee]

does anyone know how high the exh floor can be raised before power drops ? seems like jan mentioned he was working on figuring this out but never got time to finish. would the window need to be any lower than the blowdown phase, thats the question i guess

[husaberg]

does anyone know how high the exh floor can be raised before power drops ? seems like jan mentioned he was working on figuring this out but never got time to finish. would the window need to be any lower than the blowdown phase, thats the question i guess

If you look at some of Frits posts when Rob was doing the dam in the ex port.

Quote Originally Posted by Jan Thiel

So that you might be able to raise the exhaust's 'floor'.This helps improve blowdown flow, as seen on a flowbench.In 2007 we started to raise the underside of the exhaust port.The first results were very promising!But at the end of 2007 I retired, so I could not finish what I started.The idea was to raise the exhaust underside as much as possible until power dropped.
And then, with a smaller exhaust port underside it might have been possible to widen the A-ports more
without losing the fresh charge into the exhaust.

Attachment 284480

The piston skirt was exposing the bottom of the exhaust port at TDC so as an experiment I am screwing and gluing a piece of alloy into the exhaust port floor. With any luck this will let the piston seal the crankcase and I have made the wall a little higher than the piston at BDC.

I remember (hopefully correctly) Frits talking about Jan experimenting with this and that it made more power by reducing short circuiting.

But they had not found the upper limits of how high the wall could be. If I can make the wall high enough it might not be to far fetched to add another transfer port there, after all once exhaust blow down is complete there is little point to the lower 1/3 or so of the exhaust port.

Attachment 284547Attachment 284546


The stuffer plate is held down by screws through the exhaust port floor, the glue is only there to seal it.

Here's an example, something on raised exhaust port floors from Jan Thiel on that same page too.
It seems that one have to click the link (arrow thingy to the right of "Frits Overmars") to see the picture..

Now, piston rings might not like that export witdth.

To make the raised floor work as part of an overall plan that was seen all the way thru by Jan at Aprilia, the area reduction at the port should be extended all the
way to the flange.
Making this oval, and reducing the duct volume all the way to the exit then works with the 75% area guideline for T or tripple port duct exit geometry.

When I first tried the Triple Exhaust I got 29.5 rwhp (I had previously done better with a single port at 31 rwhp)

Tried to improve the Triple Exhaust and it fell to 18.6

Raised the exhaust port floor and went from 18.6 to 24.8

Thrown the cylinder in the bin and started again.

[Frits Overmars]

does anyone know how high the exh floor can be raised before power drops ? seems like jan mentioned he was working on figuring this out but never got time to finish. would the window need to be any lower than the blowdown phase, thats the question i guess

Here are some pictures to help you on your way Peewee.

[wobbly]

The only kicker in the idea of lifting the Ex floor is as I stated before - Jan only actually dyno tested the small 2mm
step, and then the corner rads were changed by CNC machining the duct to get better power again ( as per Frits left hand drawing )..
I also have only gone 2.5mm on a 54.5 stroke and actually proven it on the dyno ( so as to not make the added material so obviously against the regs ) - so going there immediately is a no brainer.
Going higher without the dyno work is just a guess.

[Martin1981]

jan once told that (one of the) last cylinders he has made had their ex floor as high as the transfer roof. but then he realised that he would retire and see no test results anymore...so he had machined the floor down to standard....

[husaberg]

jan once told that (one of the) last cylinders he has made had their ex floor as high as the transfer roof. but then he realised that he would retire and see no test results anymore...so he had machined the floor down to standard....

Quote Originally Posted by Jan Thiel

So that you might be able to raise the exhaust's 'floor'.This helps improve blowdown flow, as seen on a flowbench.In 2007 we started to raise the underside of the exhaust port.The first results were very promising!But at the end of 2007 I retired, so I could not finish what I started.The idea was to raise the exhaust underside as much as possible until power dropped.
And then, with a smaller exhaust port underside it might have been possible to widen the A-ports more
without losing the fresh charge into the exhaust.

Helmholtz frequency, my dear Watson. The smaller crank will give the pipe more crankcase volume to breathe from. This larger volume will also lower the resonance frequency of the inlet system, hence the drop at high rpm. It can be compensated with a shorter inlet tract, a bigger carb diameter and a later inlet closure. To put it real simple: if you have more volume, you need more time to fill it. But more time, i.e. later closure, has adverse effects at low revs. So my preference is a shorter tract (unless you go the 24/7-way and employ a reed for the low revs, and swing it out of the way at high revs).

To put it real simple: if you have more volume, you need more time to fill it.

Most of the volume is concentrated in the transfer ducts. Then there is the volume inside the piston of course, and the 1 mm shear-avoiding clearance at all surfaces of the crank.
But that is not nearly enough volume. If you take another look at the Aprilia crank below left, you will notice that the space between the crank webs is the same as the space needed for the big end bearing. In other words: the crank webs have flat insides, good for another 60 cc or so, if I remember correctly.

Summary: you need a large crankcase volume. Ideally all of this volume should be situated in the transfer ducts. In real life you will also need to lodge part of this volume between crankshaft and piston, i.e: use a long con rod. Avoid nooks and crannies. Crankshafts should be small and smooth. Big end bearings must never be shrouded by recesses in the crank webs or by stuffers.

Frits on the Ryger?

[TZ350]

This exhaust port floor dam gave a very positive result on the dyno but the cylinder was written off before I could finish the experiment. An exhaust port floor dam is something I am defiantly going to include in my next motor.

[twotempi]

I am defiantly going to include in my next motor.

The word " Definitely" may be a better choice to use in this phrase ??