ESE's works engine tuner

[wobbly]

The 3XV cylinder with 56 bore can be ported to match the scavenging regime of the RSA , but as it sits on a 50.7 stroke it can never match those similar cylinders for outright power
with a square bore/stroke.
I developed the 3XV in EngMod using every trick in the non existent book ,to be capable of 55 Crank Hp and that will translate to mid 90 RWHP on a DynoJet using Avgas.
The cylinders are almost done and I am waiting for confirmation that the pipe centerlines are correct , as the 3XV and the 3YL/4DP header spigot have very different exit angles.
If that does not happen soon, I can get a 4DP into my workshop in November , apart from the middle week as im going to the OZ Classic titles in Sydney.

The problem with your request for info is that ALL the good cylinders are sat on 54.5mm stroke , not 54.
The Honda 125/250 RS and TM 125MX both have good porting that can be easily modified to give great power - with the caveat that they are all T ports.
I do like the dropping gate PV on the RS and the TM twin slot system.

The KTM is also on 54.5 but has a dumb PV system the opens the Aux ports from the top down - insane, and does not work well no matter how you go about it.
The TM KZ does not have a PV ,and although some insist that isnt needed in drag racing I have seen plenty of evidence to the contrary , but for road racing the PV gives a huge
advantage and much greater options for pipe trickery.

Sadly I cannot think of a 54.5 stroke cylinder with 3 ports where all are closed by the PV like the 3XV.
I have just done a project on a TZM150 for Thailand , and that is a super good cylinder , but I have no idea about a 125 version of that sorry.

[Martin1981]

Thanks, wobbly! Yes, i know. 54,5mm stroke. Not 54. sorry. I will edit my post.

[Niels Abildgaard]

Please enjoy

https://drive.google.com/drive/folde...3NqlItJd6AGBuj

[Pagi]

I think your wording is a bit confusing , as I don't believe " volume " compared to " displacement" are the correct way to look at the elements of tuning you are examining.
The two engines that have had the most development effort put into them , and also have had the rewards gained from that work , are the RSA and the TM KZ.
In essence the only real difference between the two are the KZ's lack of a PV and its idiot straight line mandated ignition.

This gives rise to a differing approach to the scavenging regime and as well as slight differences in the port chordal widths, even though they have the same bore/stroke/displacement.
The RSA had reverse transfer stagger , as this regime favors top end and overev, as well as enabling a higher STA of those ports , due to the total width of the B/C being greater and thus gives extra area
when they are lifted to be the highest.
The KZ has normal stagger and the boost port width is slightly wider , giving a greater powerband width at the expense of peak power.
That is more natural upper mid power and a more powerful overev capability.

Both have the transfers fully occupying as much bore chordal width as is possible within the limits forced by the maximal Exhaust Port width, but both have the STA needed to support the peak power
at their desired rpm.
The RSA made 55Hp at 13,000 and was regularly reved not much past 14,000 , whereas the KZ makes just on 50 Hp at 13800 and is reved to 14800 all day.
The Aprilia regime , including a narrower boost , has been tested in the KZ, and it gained an appreciable amount of peak power , but lost so much in the useable mid ( 10,000 ) rpm
it was way too slow off all the several 2nd gear hairpins.

Thus I believe applying the correct approach to the porting regime , and matching the STA of the Transfers and Blowdown to the required power/rpm define all the ports in a very narrow window.

Thus I dont believe " volume " as such is a useful metric when both engines have the transfers taking up all the available space , and both have the required STA but utilize that area in differing ways to suit the end use.

Wobbly,

I seem to have read somewhere on this "ESE's works engine tuner" that most of the gases admitted into the cylinder during the scavenging were in the ports, hence my question, is this true or not? (without taking into account of course the STA and timing which are important), sorry for ma bad english (i use google translate) and Thank you for sharing all that knowledge.

[Niels Abildgaard]

Wobbly, Frits,

I have a question about port A, B, and C.
Is there a volume relationship between these port and the displacement? If so, what is the distribution between them?

The problem is language.
If You had asked :

Is there an optimum area relation between these independent of cylinder size?

the answer is Yes and RSA and KZ got very close thanks to a lot money for try and error .
Max power is proportional to sonic velocity times exhaust blow down area.
If You try to make that bigger by starting blowdown earlier power go down of course and waves in exhaust start misbehaving.
If you make exhaust ports wider, rings are in trouble and scavenge ports get smaller.

To design a maximum power 35ccm cylinder ,You can do Yourself a favour by scaling a Thiel 125ccm RSA cylinder.
That is multiply all RSA linear measures by Third root of 35 divided by 125 that is around 0.6542.
RSA 125 bore was 54mm and new wonderkind thus 35.3mm
The blowdown area goes down with squarerot of 35 divided by 125 that is 0.529.
When crankshaft power of Your 35ccm creation is 0.529times 55 that is 29 horsepower You know that You are in good company.
Same cleverness level as the RSA creators.
By same token a 50ccm should be able to make35 horsepower at crank

[Pagi]

The problem is language.
If You had asked :

Is there an optimum area relation between these independent of cylinder size?

the answer is Yes and RSA and KZ got very close thanks to a lot money for try and error .
Max power is proportional to sonic velocity times exhaust blow down area.
If You try to make that bigger by starting blowdown earlier power go down of course and waves in exhaust start misbehaving.
If you make exhaust ports wider, rings are in trouble and scavenge ports get smaller.

To design a maximum power 35ccm cylinder ,You can do Yourself a favour by scaling a Thiel 125ccm RSA cylinder.
That is multiply all RSA linear measures by Third root of 35 divided by 125 that is around 0.6542.
RSA 125 bore was 54mm and new wonderkind thus 35.3mm
The blowdown area goes down with squarerot of 35 divided by 125 that is 0.529.
When crankshaft power of Your 35ccm creation is 0.529times 55 that is 29 horsepower You know that You are in good company.
Same cleverness level as the RSA creators.
By same token a 50ccm should be able to make35 horsepower at crank

I totally agree with you (STA, timing,...) but my question was really to know if the volume of a port was significant (google translate is bad at translating from French to English...like me!!!!)

[lohring]

The above symposium has some great presentations on opposed piston engines. One of my favorite engines is being evaluated for military use in new advanced combat vehicles.

Lohring Miller

[wobbly]

Neils , I suggest you check your maths , a 50cc making 35 crank Hp would need a BMEP of 18.65 Bar at 17,000rpm - Im sure I could not make EngMod capable of lying that big,
let alone construct a realistic working sim..

And regarding the duct volume - yes , if you calaculate the actual volume of A/F in all the transfer ducts , it usually exceeds the swept volume of the engine.
Thus any notion of A/F being " drawn " from the case into the cylinder is based on an erroneous assumption.
I just checked the sim for the 3XV cylinders sitting on a 4DP case and those ducts that are quite short and small in entry area are damn near 125cc - so little to no flow from the case occurs when
the transfers are open, unless the VE is well above unity.

[Niels Abildgaard]

Neils , I suggest you check your maths , a 50cc making 35 crank Hp would need a BMEP of 18.65 Bar at 17,000rpm -

If a 54mm stroke thing can do 14800 rpm all day according to You, then a 40 mm stroke thing can do 19980.
And need a BMEP of 13.8 Bar

[wobbly]

You are not comparing apples with apples.

Taking the rpm at peak power ( NOT peak rpm ) the the RSA at 13,000 making 55HP had a bmep of 15.17 Bar and that is a piston speed of 24m/s with a 54.5 stroke.
I think we can all accept that as the benchmark for power and reliability , with " sufficient " overev for road race use.

Taking the 50cc engine , with a 40mm stroke and reving it to 17500 = the same piston speed of 24M/s then that requires a BMEP of 17.8 Bar to make 35 Hp.
Believe me , if I or anyone could achieve 17.8 Bar BMEP , and or achieve 35 Hp in a 50cc ,they would be more famous than Jan Thiel - and I sure as hell aint even close.
I agree, the RSA could be made to overev to 14800 like the KZ does , and the 50cc could also rev to near 20,000 rpm = 27M/s but no one would dream of making peak power at those extreme high piston speeds
as then there would be no chance of achieving any safe overev capability at all.

[JanBros]

And regarding the duct volume - yes , if you calaculate the actual volume of A/F in all the transfer ducts , it usually exceeds the swept volume of the engine.
Thus any notion of A/F being " drawn " from the case into the cylinder is based on an erroneous assumption.
I just checked the sim for the 3XV cylinders sitting on a 4DP case and those ducts that are quite short and small in entry area are damn near 125cc - so little to no flow from the case occurs when
the transfers are open, unless the VE is well above unity.

but to make 50+ BHP from a 125cc, it surely needs more than 125cc's of mixture in the cylinder, no ? after all the cylinder is filled with mixture under presure because of the pipe, just like a turbo overfill's cylinders with more mixture than it's volume ?

[Frank S.]

but to make 50+ BHP from a 125cc, it surely needs more than 125cc's of mixture in the cylinder, no ? after all the cylinder is filled with mixture under presure because of the pipe, just like a turbo overfill's cylinders with more mixture than it's volume ?

When ex closes you have less than half of the volume. And if you have 2 bar of absolut pressure, this equals to 125 cc😁
But you are right with the assumption that more volume is needed because some (or a lot?) gas is drawn into the exhaust

[wobbly]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.
The scavenging and trapping efficiency determine how much of the ingested gas in the cylinder is fresh A/F at EPC.
This is the best result I have , all the other sims hover around 1:1, or lower, which is where I got the original logic from.

[husaberg]

Well I checked to see if I was talking rubbish , and sadly it seems so. The Aprilia is the only sim I have where the Delivery Ratio is well over unity.
It peaks at around 1.4 , and that means 175 cc per stroke are passing into the cylinder.
The scavenging and trapping efficiency determine how much of the ingested gas in the cylinder is fresh A/F at EPC.
This is the best result I have , all the other sims hover around 1:1, or lower, which is where I got the original logic from.

Jan or Frits said on vol 1 or 2 of Pitlane that there was (cant remember what but something like 1.7 x the cylinder volume in the transfers. (might have been more 380?)
I could look but both would know what they said and correct what I have got wrong.....

this is not it buggar

Not really. The RSA's TDC crankcase volume is 675 cc (for a 125 cc engine!) but most of this volume is in the transfer ducts. Over the years Honda has produced cylinders with and without the lip that your picture shows, sometimes both types in the same production year. But flow through the C-port is not the most important item of a fast cylinder.
Another point to help you make up your mind: compared to a Honda RS125 or RS250 the Aprilia RSA125 produces about 20% more power per cylinder....

[Storbeck]

I'm trying to understand why the volume of the transfer ports is important.

In order for air to flow OUT of the transfer ports, doesn't an equal volume of air have to flow IN to the transfer ports?

So that the volume of the ports is not so important compared to the resistance to flowing in and out? (and through, and the angles and shapes and such).