ESE's works engine tuner

[dinamik2t]

Here, I turned them into Gif:


I remember that your starters' pipe calculator also creates big baffle angles, especially in large cc engines (with fat bellies), Frits. So far, I thought it was a "calculation compromise" of the simple form of your equations.
I am curious -if you can explain within little lines- as to why this happens. (the non-problematic operation with 155D-32* I mean)

The above pipes are originally built under the 'modern' design function of EngMod. I think its based on Blair's equations and Neels' own experience.
Ah, by the way.. A forumer has turned your equations to an online calculator a few months back. It's here: http://www.underdogsracing.com/fospipe.html

[Frits Overmars]

...I am curious -if you can explain within little lines- as to why this happens. (the non-problematic operation with 155D-32* I mean).

The large cone angles come with high piston speeds and short exhaust timings. I can only guess at the exhaust timing you used, but aiming for max. power above 10,000 rpm in a twofifty is definitely provocative. I don't think the time.areas will be up to it. But like I wrote: try it and you'll find out.

Cone angles in themselves have little meaning, especially when reflector cones are dealt with. Short pipes tend to have steep cones and there is nothing wrong with that. The longer a pipe, the more the reflected wave is developing a steep front on its way back to the cylinder and the greater the risk of it developing into a shock wave that is very inefficient in shoving back washed-through fresh mixture.

One last word of advice: I would not build the second pipe in the above drawing. You succeeded in making it look like an Aprilia pipe, but those many cones just require too much cutting and welding. My overall rule of thumb: keep it simple.

[dinamik2t]

I have a friend cutrollwelding my pipes, so who cares? (only keep quiet about it)

My excuses TZ for being so specific here.
The engine is 72by61, 200deg exhaust and STA's sufficient upto 60kW -according to EngMod that is. The sim runs are with a 48 lectron!
But, please, don't let me down like that. It took at least 15+5min to design and test this pipe!

[ief]

Sorry,yes i forgot the 50mm in the cylinder with the diffuser end calc, its 678/1083 = 62%, a very old fashioned number..
For a street setup the longer header and longer diffuser expand the powerband width, but as it has a powervalve this changes everything,due
to the very low blowdown area when the valve is down.
Normal range for header = 30 to 33%, and for the diffuser = 64 to 68%, so I would be shooting for the longer on both for a stock add on pipe.
The longer diffuser gives better max case depression around BDC,later in the cycle, thus boosting mid scavenging efficiency.
Very long - 36% headers only work on piston port engines - like say TZ350,as this then allows a steeper initial diffuser angle, boosting power in the limited band the piston port can operate within.
There is no case for a header angle under 3* incl and dual angle rear cones are best with shallow then steep angles.
The main effect here is to increase the belly volume, thus smearing the wave amplitude over a lower, wider band.
Its always a combination of compromises, but helps you if the basic geometry suits the application,and the physical limitations presented.

Tnx and tnx and tnx again wob!

But, please, don't let me down like that. It took at least 15+5min to design and test this pipe!

Hmmm, The need for engmod grows, takes me about 3 hours messing around with excel and another program and then still i can't see the angles

Lovin it anywayz and I get a smiling and cooking exhaust to boot!

[dinamik2t]

You can always calculate the angles by hand or even add some extra cells/formulas in your excel sheet!
It's handwritten but I think will do :d




Or you can just post here and some EngMod user can turn your dimensions to a pic like above. I can do it too, if you send me those through a pm..
Here's your 1st design, assuming a 50mm ex duct.

[ief]

Got to get it into excel but well, i'm not a star at the stuff but i will get it, don't want to bother other people all the time but tnx for the offer and tnx for the pic!

One thing i noticed tho... i presumed the ratio you where talkin about was simply dividing exhaust volume by cylinder volume but that makes 25.2 and not 35.51 ?


edit: quick guess, could be volume above ehm... lemmy try this

edit2: Pfffffffff, gotta love being a math nitwit with this stuff but... Taking the volume above the transfers gave me the right figure so i can only presume.....

[Frits Overmars]

... i presumed the ratio you where talkin about was simply dividing exhaust volume by cylinder volume but that makes 25.2 and not 35.51 ?edit: quick guess, could be volume above ehm... lemmy try this.
edit2: ... Taking the volume above the transfers gave me the right figure so i can only presume.....

Keep it simple, Ief. That ratio should be exhaust volume divided by cylinder volume. 30 is a good value, but it's not critical (and you probably won't be able to achieve it on an RD350; not if you want to keep some cornering clearance).

[ief]

Ok, then I was right the first time, got thrown of by the pic of dinamik2t where it said 35.51...

Shoot for 30, non critical, got it.

[wobbly]

I could babble on forever about pipe specifics but here are a few pointers.
Rear cone ( single ) max out at around 28*,the multi angle setup used by Aprilia can be equalled simply by a single cone set at around this angle.
In a 250 it is counter-productive shooting for the same swept/pipe vol ratio as a 125, you need to be aware that there is a finite amount of energy in the wave
running down the pipe, and huge diffuser angles dumping into a huge mid section will loose more of this energy than will create a bigger depression around BDC,or a bigger
plugging pulse heading toward EC from a very steep rear cone..
I have found the best compromise is at around 135 dia.
The very over square engine will theoretically rev harder, but you will by default a have a very heavy piston,plus needing big timings to create the STA necessary for power over 10,000
means any perceived advantage is lost in reality.

[dinamik2t]

Just to report it, tfr timings were 130-132, ex 200. I don't know whether the whole result is realistic or not; I guess it has to be found out the hard way.
And thank you for the advices!

Ok, then I was right the first time, got thrown of by the pic of dinamik2t where it said 35.51...

Shoot for 30, non critical, got it.

Ah, sorry for that. I input the exhaust data under an 125cc engine file.

[ief]

You can always calculate the angles by hand or even add some extra cells/formulas in your excel sheet!
It's handwritten but I think will do :d

Ok, that was just the push needed to figure out how to get it in excel and it worked! So tnx again

[dinamik2t]

I 'm glad then.
One thing I did not write: the opening angle is 2*φ; you should use that to compare apples to apples, as in most references you'll find the full opening angle.

[ief]

Yep, figured that out allllll by myself

[ief]

One more and then I'll try to give it a rest for a while

Perhaps I'm getting a little ahead of myself (wouldn't be the first time) but something came to mind and well... just to see if i'm on the right track here...

Presume we have an engine/ exhaust combo that works the way it should which relies on low cv for scavenging for a great deal (I think/ presume that's the case with stock rd 350 ypvs ), now we enlarge the crankcase for some reason by a fair amount and there is no possibility to make the exhaust diameter bigger.

Would it then make sense to try to get the stronger part of the pulse sooner (for instance; make the first part of the diff. shorter and more shallow so the second part starts earlier and can be as steep or steeper) and/or make the diff shorter so it will be steeper once again?

Even wilder, would that be the case when using a way bigger carburator/ membrane combo as well? (to a lesser extend I presume)

[wobbly]

Many combinations will "work " just as well as a myriad of others, when you are offsetting the negative effect of one element by overriding it with the positive effect of another.
That isnt clever, its just using knowledge to mitigate the necessary down side of some one else's arbitrary decision, that was wrong.
Simply put the best way forward, is to limit the down sides,and implement as many truly clever elements as you can, to synergistically work together.
For example , the proven need for huge case vol in a full house race rotary valve engine, isnt even close to being a positive element in a stocker reed valve engine with
seriously crap transfer ducts.
Quite the opposite will produce better power in that scenario.
The smaller case vol gets the flow going sooner and more effeciently when the duct geometry is compromised , but then of course peak power
cant be the object of the end game, with that upsetting mechanical limitation.
Its been proven a hundred times in Jetsjkis etc that have won world titles with ease, due to combining the best effects to limit the inherent issues preventing a better result.