ESE's works engine tuner

[jamathi]

A normal exhaust pipe to this form :



some exhaust pipe have this shape :



Does the shape affect the operation of the exhaust pipe ?

Yes, and quite a lot!

[Jannem]

There is one little extra tidbit that goes with this, that isn't well known. As mentioned when the pressure ratio between the upstream and downstream reaches about 2 the flow velocity reaches Mach 1 and as such the flow velocity can't go any greater by lowering the downstream pressure, and it is generally assumed from that, that the massflow can't go any higher by lowering the downstream pressure.

Seems logical of course, BUT it is only true for certain shapes such as a nice bell mouth entrance etc. When less favorable shapes are used, an orifice being one example (but certainly not the only example), the massflow can be increased by lowering the downstream pressure below the critical Mach 1 ratio. Mach 1 is never exceeded, but the unfavorable flowpath of the unfavorable shape, improves as the pressure is lowered further, causing the massflow to increase. Most flow paths in an engine are not as bad as an orifice, but not as good as a bell mouth either, so there is some wiggle room here and there regarding the massflow vs. upstream to downstream pressure ratio.

Good stuff! I really appreciate the experience based real world knowledge shared here.

[Jannem]

Keep 'm coming Jannem .
Attachment 334950

Ok.

Properly shaped, extended, undercut at port roof after the radius to allow the one-sided nozzle to acclerate blowdown flow to higher mach speed.
As the piston descends, the nozzle area ratio will become proportionally smaller with lowering pressure ratio, reducing the chance of separation. If if worked, it wouldn't need much to bump that initial flow, say .5 mach with variety of side effects, lower pressure at port entry and inertia to retain it longer being some of them.

Learning is granted, any chances of winning with this one?

[Jannem]

Yes, and quite a lot!

Curious minds want to know, if you don't mind to elaborate a little from your experience. Which, I've understood, is nothing short of massive.

[SwePatrick]

I took the opportunity to ventilate the issue to a close friend who is one of the people in charge of engine block at Volvo and he estimated that about 70% of the total development time, is flow optimising on cooling to prevent film boiling.

I think you have a lot to learn the automotive industry!

*lol*
Don´t be so easily offended.

But think again.
Quite a difference on what to develop, a race engine or a pollutioncontrolled vehicle.
Twostroke Raceengines = just run it in a happy temp where you got most power, 99.9% around 40c (about 60c marginal before boiling)
Fourstroke commercial engine = need to raise very quickly in temprature so combustion is under control, that make´s the catalysts warm up quick to let them do their work.(watertemps often around 102-105degree, about 10 degree marginal before boiling)

Do NOT mix these ones together and try to use commercial tech into a raceengine.
Keep in mind on what you are actually designing.

[Muhr]

*lol*
Don´t be so easily offended.

But think again.
Quite a difference on what to develop, a race engine or a pollutioncontrolled vehicle.
Twostroke Raceengines = just run it in a happy temp where you got most power, 99.9% around 40c (about 60c marginal before boiling)
Fourstroke commercial engine = need to raise very quickly in temprature so combustion is under control, that make´s the catalysts warm up quick to let them do their work.(watertemps often around 102-105degree, about 10 degree marginal before boiling)

Do NOT mix these ones together and try to use commercial tech into a raceengine.
Keep in mind on what you are actually designing.

I do not think there is anything constructive in this discussion.
You are talking about water tempratur and I am talking about CHF, which are different things.(Film boiling does not mean high water temp)

I think we should leave this discussion

[RomeuPT]

A normal exhaust pipe to this form :



some exhaust pipe have this shape :



Does the shape affect the operation of the exhaust pipe ?

Logic may at 1st say the more straight forward would be the best. But my experience is so confusing on this that I would need to see real testing data to show differences on more then one engine. I have felt that some pipes I tested made to fit upfront of a bike made more power then the same but under more straight exhaust.

Has it was posted earlier in this topic by woobly, if I remember the most considerably lost of power was if you let the header edges alive and not beat to round them, and if you add welding rod you should clean the interior bumps.... basicly..

Has shown sooner in the topic some aprilias RSW250 had a pipe under and other straight to the back, they probably know how much the difference was caused by this.

[shnaggs]

yes it's 360! However, my experience is very limited when I only used the program for 2 weeks. I have used other programs, so I'm not a total beginner.
I started myself with sketchup to get an understanding of the methodology. It's not as overwhelming at first and has many good exercise videos you can do. (and it free)

Thanks Muhr, keep up the good work

[shnaggs]

You are probably about where I am. If beginning and ending shapes lofted following a guide curve doesn't get you where you want to go then I guess you'd have to have some shapes in-between to loft to. And much of that will probably depend on the capabilities of your CAD software, whether you can loft with more than one guide curve etc.

Can you do a prismatic extrusion of the basic shape of the port in one direction and then use the outline of how you'd like things to look in a different axis to trim that, and then take that shape and fillet edges?

My guess is that whatever you can model is probably not exactly what you want, so you get close, cast and port it until you like it, pull a Vinamold or similar flexible casting from the port and then 3D scan the molding and then clean up the scan and work from that for the next iteration of the model.

cheers,
Michael

Thanks Michael

[shnaggs]

I'm also learning Fusion 360 to draw 2 stroke passages. What I've learned so far:

Don't use surface models (Patch) unless a solid model won't work.
If you use surfaces for passages you will need to use the split body command and then remove the piece you split off. Do that as the very last step.

Model the passages with solid lofts for both the inside and outside parts.
Use the combine feature as a cut to hollow out the part. Remember to turn off the parts you aren't working on.

Lofts like center lines. I can only suggest trial and error to see what lofts will work. Sharp bends will need more sketches to get through the curve, but the best passages I've designed only use a beginning and end sketch connected by a center line with the right curve.

Lohring Miller

Thanks lohring, I think I understand what you are saying.


Oh and sorry for the multi post, I just realized I could have done multi quotes into one post.

[JanBros]

The Aprilia pipes were not that clever, in that Jan had a devil of a time making them work.
This isnt the correct way to do things, ie make a compromised pipe, then be as clever as all hell with the porting to make that pipe work.
If you reverse the % you quoted, to something like 17/59/24% then the steepest diffuser section can become the last, and this is superior in every way for
a very high specific output engine at very high rpm.

I'd been reeding/searching a lot of stuff in this topic using "header" and "diffuser" as search words, and you talked some times about the steepest diffuser being in the middle :

The position of the start of the mid diffuser is the key to making top end and overev power.
Earlyer Aprilia and Honda designs had the steep diffuser starting right after the header, but this pulls the Ex depression down too early around BDC.

It works alot better for power production to space the main cone further along, and make the angle steeper to promote higher depression values by using a shallow last diffuser angle.
This also increases the main body volume.

I have been making the first and last diffusers around the same angle, just coz it feels right, and the sim says fill your boots.

To get a deeper depression later in the cycle this is why we have a 3 section diffuser with a relatively shallow front end, then a long steep main diffuser leading up to the mid.
A short section of shallower angle leading into the belly helps to get a steeper angle on the main diffuser - closer to the mid at around 66%.
So - as a general rule the closer we have the steep section to the mid - the later ,and lower ,in the cycle toward TPC the depression will act.
But if we have the diffuser lengths correct the deep part of the depression will always move from closer to TPO under the peak, then ideally is centred on BDC at peak power rpm, then moves toward TPC
in the over rev area.
Thus - if you feel you need to move the max point closer to TPO you need to move the steep section closer to the header.

seems to me this is what I need for my 50cc CVT MX-Moped. as shorter gearring is not available, high power at high rev's is useless to me. clutch engages at latest at +/- 4000rpm , and it is much more important to be fast out of the many slow corners, than top power and top speed. 70km/h top speed is more than enough, reached at +/- 8.500 rpm -> lot's of power at 5.000 and soem more overrev after the CVT has fully opened.

[SwePatrick]

I do not think there is anything constructive in this discussion.
You are talking about water tempratur and I am talking about CHF, which are different things.(Film boiling does not mean high water temp)

I think we should leave this discussion

Oh but there is.
I understand perfectly what you are talking about, and i say it´s nothing to worry about, that simple!
The more heat dispertion you´ve got the less heat the material will have.
Simple physics, so adding surface area will keep material cooler, and thus more far away from boundarylayer overheating.
And wanting to raise the level even more before CHF accur you can use coolingmedia with higher boilingpoint, or pressurise the water.

http://www.evanscoolants.se/powersports.html

Good luck!

[Tunisti]

Greetings from somewhat snowy Finland!



First time with decent ice spikes on real (though snowy) track. 9mm front spikes and 7,5mm rear spikes (old racing rule tyre). Skip bit before ½ way of the video for bit better riding (rebound re-adjusted and not-so-fogging helmet because iceroadracing mask).

Spikes to be installed (both 9mm, two different body models)



Btw those spikes are turned in CNC lathe one by one, 306 spikes in front wheel and 336 spikes in rear wheel.

[Muhr]

Oh but there is.
I understand perfectly what you are talking about, and i say it´s nothing to worry about, that simple!
The more heat dispertion you´ve got the less heat the material will have.
Simple physics, so adding surface area will keep material cooler, and thus more far away from boundarylayer overheating.
And wanting to raise the level even more before CHF accur you can use coolingmedia with higher boilingpoint, or pressurise the water.

http://www.evanscoolants.se/powersports.html

Good luck!

I have no interest in pie throwing!

respect your opinion

[F5 Dave]

Am I the only one suddenly pondering: I wonder if . . . 10mm ice spikes with knurled sides?