ESE's works engine tuner

[Javier Ruda]

There are people in this world that uses an Excel spreadsheet and acoustic theory to create what they claim is a simulator that calculates what your exhaust pipe should look like. They publish this mostly on Farcebook so I thought it would be a good idea to add another installment on gasdynamics. Please give comments so I can improve this.

Attachment 350438

Thank you Neels for sharing this knowledge, so far my understanding was “sound waves type” .

Now I am modifying a Rotax 122 cylinder, and I need to increase blowdown sta. For not increasing exhaust timing, my intention was to make the auxiliary ducts taller, but after reading the gas dynamics article now I think there is possibility of contributing to a shock wave that looses energy as heat.

For increasing peak power, Is there a rule of thumb for auxiliary vs. main exhaust port timing?

[andreas]

If it's a rule of thumb, I think 3-5* delay ie. double total, for the aux goes.

[Javier Ruda]

If it's a rule of thumb, I think 3-5* delay ie. double total, for the aux goes.

Thank you andreas. That is around 2 mm, then I still have a bit of margin.

[lohring]

That's no where as bad a mistake as filling the tank with gasoline only, no oil mix. That's really hard on an engine at 15,000 rpm or so when the piston seizes.

Lohring Miller

Living the dream........ quitting regular work for a life of following his passion. I take my hat off to everyone who has done that.

Attachment 350460

[philou]

expand boosters to increase blowdown

quick superimposition with photoshop of the pvp cylinder (Aprilia copy) portmap with that of the 122 cylinder the setting of the port heights is not respected.

It gives you an idea for the shape of the ports.

[Javier Ruda]

expand boosters to increase blowdown

quick superimposition with photoshop of the pvp cylinder (Aprilia copy) portmap with that of the 122 cylinder the setting of the port heights is not respected.

Merci philou!

That will be a good inspiration. I am limited by a piston pin without plugs, but there is plenty of mm2 there.

[philou]

I did not raise the engine myself or create the engmod2t file. so to check on a cylinder in real life.

data on transfers and TA values of the stock cylinder.

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B

[Javier Ruda]

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B

Merci philou!

My plan is to raise transfers 0.6 mm and I will try to do the angle upwards too. With the tools I have, I can widen the B transfer only a bit. Do you know if there is a benefit on widen C transfer too?

[philou]

the C is already too wide

the B deserves to be widened to a close to the C

on the file the B (12°) has an upward angle greater than the A (5°).
it has to be the other way around.

why do you say you don't have enough blowdown?

[Javier Ruda]

the C is already too wide

the B deserves to be widened to a close to the C

on the file the B (12°) has an upward angle greater than the A (5°).
it has to be the other way around.

why do you say you don't have enough blowdown?

Merci philou, I will not touch C then, and will work on B as much as I can. I need the blowdown for matching the transfer sta increase. I did some calculations with Janbros spreadsheet and that was output.

[andreas]

Merci philou!

My plan is to raise transfers 0.6 mm and I will try to do the angle upwards too. With the tools I have, I can widen the B transfer only a bit. Do you know if there is a benefit on widen C transfer too?

You want to have as much area as possible. If the rings are to stay in the same location, naturally there is a potential benefit from widening the c an b port respectively.

[philou]

to choose in my opinion, it is better to work on the efficiency of scavening even if it means losing a bit of surface.

enlarge the C even more, will decrease its effectiveness

[JanBros]

the greater the angle of a port, the smaller it's effective flow area.
so widening the C-port (for example 4mm) by the same amount as widening the sum of the B-ports (for example eacht B-port 2mm) generates less extra TA than widening the B's,
and keep an eye an the angle of the scavenging column while changing the ports so that you do not end up with a crzay angle.
and don't mkae the angle of the A's to big, as the higher if flow's , the easier it can flow straight out the exhaust.

[andreas]

Obviously this is the case, but it didnt seem like he was about to change the ring-pegs locations.

[HenkS]

I did not raise the engine myself or create the engmod2t file. so to check on a cylinder in real life.

data on transfers and TA values of the stock cylinder.

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B

I believe some numbers in your calculation are not right.

Total Port Transfer area sum = 834.91 (not 940.14).
Eff. dia area 852.13 = 32.94 (not 34.85).
Eff. dia area 1019 = 36.02 (not 37.78).
Eff. dia area 132.62 = 12.99 (not 17.16).


In that case results as 10.500 rpm also can't be right, or am I wrong?