ESE's works engine tuner

[husaberg]

No force = no acceleration; right. But as the piston is approaching BDC there is as lot of force, not from the non-existent gas pressure, but from all the reciprocating parts that try to keep moving towards the centre of the earth.
Before BDC that force is accelerating the crankshaft rpm; after BDC it is slowing down the crankshaft rpm. So what is the nett gain in transfer time.area?


Are you referring to your first or your second picture Husa? Your first picture does not show an Aprilia V-twin (or W-twin if you like) crank; your second picture does.
The inserts give the twin-cranks a distinct asymmetrical appearance because the resultant of the inserts' forces must be at a 45° angle to the crankpin position.
Attachment 336470Attachment 336471


Correct.Yes, after Jan retired, some geniuses in the racing department seized the opportunity to 'correct Jan's mistakes'. They packed the insides and then wondered why a 2008-RSA was slower than a 2006-RSA...


The original left-side balance mass was a full aluminium disk with mallory inserts. The geniuses changed it into a triangle, saving a tiny bit of weight and increasing its air windage losses (luckily the left-side balance mass did not run in oil).
Attachment 336472 Attachment 336473

Yes I was referring to the first pic of the crankshaft with the original balancer next to it.
I identified that as being RSW125 by the balancer when I went back through my album
I have add some brackets to my original post to clarify it up a bit. Thanks for your response.
So all the pics I posted (below)with the non clean inside of the crankshaft are post Jan RSA modifications.

This I think is one of them (RSA125). I think it came from the frits file? Maybe Frits or Jan would like to comment seeing as they know the answers.
Attachment 336467

I do know this is a RSA125 crankshaft. and if you look closely its porkchoped.
Attachment 336462Attachment 336463

[Frits Overmars]

So all the pics I posted (below)with the non clean inside of the crankshaft are post Jan RSA modifications.

Yep .

[Muhr]

two-wheeled vehicles tend to handle horizontal forces better then vertical. where off the cylinder position is crucial for seting up a balance factor.

Somthing else that may be worth considering is Critical Speed that you want to avoid in your rpm range.(Critical speed occurs when the crankshaft begins to flex)

[lodgernz]

Thanks Wobbly, Frits, Neels and others for your comments regarding exhaust duct length.
The general feeling seems to be that, for oversquare engines, a duct volume about equal to the cylinder capacity would be a good starting point.

The established rule for nice triple port or T-port engines is "CSA reducing from port window to 75% of window CSA over 1.5 * bore, then transitioning out to 100% for another 0.5 * bore".

It seems clear from the discussion that the measurements based on the bore probably aren't valid for oversquare cylinders. So the questions are, for my POS oversquare engine:

A. Should I still aim for a 3:1 split for the lengths of the two sections of the duct?
and
B. Should I still aim for the 75% & 100% end CSA for those sections?

I realise nobody knows the answer to these, but I'd appreciate any intuitive opinions.

One of the problems with oversquare engines is that the exhaust window area is significantly less than that of a square engine, since vertical real estate is far more valuable than circumferential, and is even worse if the port is a single or T port. With a small port window area, a duct with the cylinder capacity as suggested, may result in an impossibly long duct.

For example, my 53 x 44 97cc T-port cylinder has a total window area of only 600mm2, allowing for radial and axial duct angles, and I can't make it much bigger without breaking through the water jacket.
If I follow the accepted rule of thumb, but not relating the duct lengths to the bore, the suggested duct for this engine would start with a CSA of 600mm2 and reduce to 75% of this (450mm2) over a length of 3x, then have a transition piece of length x, ending with a round outlet with a diameter of 27.6mm (CSA back to 100% or 600mm2). A total length of 4x.

For this construct to have a volume of 97cc, the total duct length of 4x would have to be around 183mm. Completely impractical of course, hence my questions.

[tdc211]

Thanks Wobbly, Frits, Neels and others for your comments regarding exhaust duct length.
The general feeling seems to be that, for oversquare engines, a duct volume about equal to the cylinder capacity would be a good starting point.

The established rule for nice triple port or T-port engines is "CSA reducing from port window to 75% of window CSA over 1.5 * bore, then transitioning out to 100% for another 0.5 * bore".

It seems clear from the discussion that the measurements based on the bore probably aren't valid for oversquare cylinders. So the questions are, for my POS oversquare engine:

A. Should I still aim for a 3:1 split for the lengths of the two sections of the duct?
and
B. Should I still aim for the 75% & 100% end CSA for those sections?

I realise nobody knows the answer to these, but I'd appreciate any intuitive opinions.

One of the problems with oversquare engines is that the exhaust window area is significantly less than that of a square engine, since vertical real estate is far more valuable than circumferential, and is even worse if the port is a single or T port. With a small port window area, a duct with the cylinder capacity as suggested, may result in an impossibly long duct.

For example, my 53 x 44 97cc T-port cylinder has a total window area of only 600mm2, allowing for radial and axial duct angles, and I can't make it much bigger without breaking through the water jacket.
If I follow the accepted rule of thumb, but not relating the duct lengths to the bore, the suggested duct for this engine would start with a CSA of 600mm2 and reduce to 75% of this (450mm2) over a length of 3x, then have a transition piece of length x, ending with a round outlet with a diameter of 27.6mm (CSA back to 100% or 600mm2). A total length of 4x.

For this construct to have a volume of 97cc, the total duct length of 4x would have to be around 183mm. Completely impractical of course, hence my questions.

If i where you. I would just put length at 50-60mm long
And 75%. At exit
Build a pipe and get delivery,traping,charging decent in sim and put it on the dyno and see.

[wobbly]

I would for sure use the 75% and 100% area guidelines.
But try this as a thought process.
The guideline lengths relied on 125cc square engines with really high bmep.
So modify the duct length total of 2X Bore by your actual numbers.
First the bmep.Say yours is 12Bar and the Aprlia is 15Bar,so we have 53X12/15 = 42.4.
Then we have the bore to stroke ratio 42.4 X45/53 = 36
So now assume your effective bore is 36
Times 1.5 = the 75% area position = 54 and the 100% position = 2X36 = 72
So this gives a slip on transition length of only 72-54= 18
Make this 22 long with the smallest CSA at say 50.
Seems reasonable to me,but the real proof is in the mach number at peak power of the 75% CSA = 0.8
Do the lengths come close to achievable ?

[SwePatrick]

Duct volume as a measiring tool must be very inexact?

To put it in extreme, if duct is 200mm long, do you still use the term?
I would say it is far more important to use area, and area at certain distances away from piston.

[Vannik]

I would say it is far more important to use area, and area at certain distances away from piston.

And area times distance is volume? I think the issue is to get the required length of small cross sectional area. Too much is maybe less damaging than too little?
Port volume is a very important parameter in the 4T world.

[SwePatrick]

And area times distance is volume? I think the issue is to get the required length of small cross sectional area. Too much is maybe less damaging than too little?
Port volume is a very important parameter in the 4T world.

Same problem there, if port in head is so long that it is the complete runner, still important?

If focusing on the 'correct' volume without having the areas correct one can end up with a really oddshaped runner if not knowing better.
One need to know where to put the smallest area in the runner, and one need to know how hard one can taper the runner.
One need to know how hard the runners turns in an another direction, and know how tho shape the runner to maintain the airspeed/flow.
Just giving a value of volume is leaving a lot of room for misunderstanding.

[Muhr]

images from the caster!

For once, I have a little luck, the casting was successful.

[tdc211]

I think a pic of header and flange is worth more than words,
I should say the end of the extunel, which is what you are looking at ,on ktms un boltable face

[wobbly]

But I have never seen a duct in a competition type engine that is too long.
Plenty that are way too short - especially those that have a female header plug in as part of the cylinder.
Having the really good guide of 75% smallest and 100% again at the header makes choosing the areas simple, and they work.
I would be interested to see the result of using both bmep and bore/stroke shortening multipliers in a severely oversquare project.
In the example I did ,the lengths seem quite usable , if the actual cylinder is a bit longer then I doubt it would have much negative effect.

[SwePatrick]

For once, I have a little luck, the casting was successful.

Nice!
Never had a doubt.

That company you chose to cast is one of the best.

[teriks]

For once, I have a little luck, the casting was successful.

Im impressed, would for sure love to see that in action once finished!

[Muhr]

Nice!
Never had a doubt.

That company you chose to cast is one of the best.

The problem was that they did!

Im impressed, would for sure love to see that in action once finished!

Much of what I've done with the cylinder has been inspired from this page, not least the huge number of pictures and drawings Frits has uploaded, and discussions about both exhaust port bottom hight and water channels inside transfers, which I applied both. So I feel it would be my duty to upload results if there is interest.

Right now I am working on the intake and crank so it's a bit left until I can test.