[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

Howard Gifford a écrit:

My thought is that if you time it right it would add energy to the reflected wave and thus aid in supercharging. At worst it would momentarily raise the static pressure which would have an effect. My question to you is have you or anyone else tried this.

"Timing it right" would mean sending the wave, that exits from tailpipe A, upstream into tailpipe B such that it arrives at the small end of Endcone B simultaneously with the primary wave from cylinder B. I haven't tried this and I do not know of anybody else who has. I think this is one for Vannik (EngMod2T). Neels, are you there?

Frits and Howard, this is a very intriguing idea and I will investigate it over the next few days and report back. I am currently considering 3 different layouts and will make some basic sketches to make sure I understand what you have in mind.

In addition to all your posts, this post about Garelli from Frits and Jan is pure gold for some of us. Amazing power curve for engine that old.
Please continue

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Howard, is something like this what you had in mind?

Your second layout is close to what I had in mind. The length of the tube from the exit of pipe a to exit b would need to be determined. I feel it would be close to 1/2 the TL of each pipe. Maybe a bit longer to time it to when the wave actually gets to the end of the pipe. Experimentation of diameter 3 would need to be tested as well to make sure the spent gasses escape whilst preserving as much of the wave transfer as possible without adding too much heat to the system.

Okay, I will spend some time doing simulations and if it shows promise you can build it.

Since I am a newcomer here, -to my person.
I was born a long time ago, but I was interested in motorcycles from a very early age, from 61, but especially in 2-strokes, and that until today! From 50 to 750 cc, single cylinder up to four cylinder, I have ridden them all on the road, as well as on all kinds of race tracks and championships.
Of course I have rebuilt and tuned all these motorcycles and engines, once with more and once with less success. Stopped counting at 372 exhaust systems, which I made for some drivers and for me, and all exhaust systems were oxyacetylene welded by me.
In my -Leisure-!... I often made a trip to the -Endurance-World Championship-, Bol d'Or Le Castellet, Spa, Le Mans, Monza.......and this one with 750cm³ -4T-. We always arrived at the finish, but sometimes we didn't know why ourselves.
To my first question and request. I need these special piston pin plug plugs, for 16mm pins and 8 pieces of them. Mr. Frits, or other members , can you please help me?
Oh yes, they call me Carassco.

Quod et probat a écrit:

Since I am a newcomer here, -to my person.
I was born a long time ago, but I was interested in motorcycles from a very early age, from 61, but especially in 2-strokes, and that until today! From 50 to 750 cc, single cylinder up to four cylinder, I have ridden them all on the road, as well as on all kinds of race tracks and championships.
Of course I have rebuilt and tuned all these motorcycles and engines, once with more and once with less success. Stopped counting at 372 exhaust systems, which I made for some drivers and for me, and all exhaust systems were oxyacetylene welded by me.
In my -Leisure-!... I often made a trip to the -Endurance-World Championship-, Bol d'Or Le Castellet, Spa, Le Mans, Monza.......and this one with 750cm³ -4T-. We always arrived at the finish, but sometimes we didn't know why ourselves.
To my first question and request. I need these special piston pin plug plugs, for 16mm pins and 8 pieces of them.  Mr. Frits, or other members , can you please help me?
Oh yes, they call me Carassco.

Welcome, Carassco. I outsourced the manufacture of those plugs. I do not make them myself and I do not have any stock, but to enable everyone to make them, I made the drawings public; you should be able to find them here somewhere. The material used is Torlon.

Thanks for the quick response!

Whoever has current values ​​of titanium sheet material Grade 02 ASTM –B 265 with informed by Frits, or compatible in thicknesses (0.6mm) (0.7mm) and (1.0mm), I want to compare with values ​​in my locality

Howard,

After a number (fairly large number) of simulations I found the following:

1. I should have given it more thought - to time the pulse right the total tailpipe length from pipe 1 to pipe 2 must be around two times the tuned length.

2. The effect of this length, the losses passing through a 3 pipe junction and the bigger diameter to get the right resistance, is to eventually match the original pipe performance.

Maybe with a lot more experimentation it is possible to get more performance but for now I would say no.

LeonardoMRF2 a écrit:

Whoever has current values ​​of titanium sheet material Grade 02 ASTM –B 265 with informed by Frits, or compatible in thicknesses (0.6mm) (0.7mm) and (1.0mm), I want to compare with values ​​in my locality

What do you mean by "values", Leonardo?

Carlovitch1
money ($) Cash

OK Leonardo, to give you an idea, my company uses mostly Gr 1 as per ASTM B 265 (the same as Gr 2 but with a little less impurities, it is needed because we are doing explosion cladding) with thicknesses 1mm and more.
Typically from stock in 1mm thick (I suppose you don't need tons of it, so I will not talk about mill prices), in EU the cost will be around 33-35 € / kg. Depending on origin, it may vary rather sensibly (from China it may be cheaper, even if some suppliers are doing really good, from Japan and US, it may be on the expensive side).

Thanks!

Hello Frits and Jan,

First of all, thank you very much for sharing your knowledge, this is pure gold!
I would like to ask you something:
During the development process of the RSA engine it is clear that you moved the admision from the side to the front as most of the super performance kart engine do, but the mechanism for the rotary valve I guess that was much more complicated to place there. Had you ever considered to use two rotary valves, side by side, with to smaller carburators? This way the rotary valve doesnt need any extra mechanism, and the gas pumping is completely symetrical.

Thanks!

iizquierdo a écrit:

Hello Frits and Jan, First of all, thank you very much for sharing your knowledge, this is pure gold!
During the development process of the RSA engine it is clear that you moved the admision from the side to the front as most of the super performance kart engine do, but the mechanism for the rotary valve I guess that was much more complicated to place there. Had you ever considered to use two rotary valves, side by side, with to smaller carburators? This way the rotary valve doesnt need any extra mechanism, and the gas pumping is completely symetrical.

What you describe, is exactly the layout that Jan would choose if he were to design a new engine today

And maybe the carbs would be replaced by some electronic injection system?

Hello everybody on this Forum,
i got a short question about Maximum Squish Velocity.
Yes, i read all of the 5 Parts of this Topic here,but my question is still some kind of unanswered.

Max Squish Velocity is mostly pointed at 25-50m/s in Books/Internetsites and so on... but if i calculate the Engine Parameters of the Aprilia RSA/RSW in the FOS-Programm it shows a MSV around 100m/s...?
So my Question is: is that 100m/s correct in the "Aprilia-Case" or is the pure MSV "Number" not that important as i thought,respectively the 25-50m/s are some kind of failsafe numbers for the unexperienced tuners out there?

I´m asking this because i´m about to design/build a head for my 500cc Honda 1-Cylinder and the actual state of the head shows MSV Values about 60m/s even though i´m more on the safe side i.e. for Squishgap (1,4mm)/Compressionrate(12,5:1)/Squisharea(60%) and its not a real highreving engine... Its also possible that i handle the programm in a wrong way, i´m realy not sure.

Hopefully someone can give me a hint...
Greetings to all and thanks to Frits Overmars and Jan Thiel who spread their wisdom here.
Stay Healthy everybody

in my excel I only get 35.70 m/s squish velocity, are you sure your calculations are correct ?
as a way of testing : look up in Blair's book his engine data when he calculate's and use that with your calculation. if you do not get the same result as Blair, you did something wrong.

It certainly isn't a simple calculation. you can find many on the net, but very few give the same result as Blair. It certainly took me some time/work to get it correct.

JanBros a écrit:

in my excel I only get 35.70 m/s squish velocity, are you sure your calculations are correct ?
as a way of testing : look up in Blair's book his engine data when he calculate's and use that with your calculation. if you do not get the same result as Blair, you did something wrong.

It certainly isn't a simple calculation. you can find many on the net, but very few give the same result as Blair. It certainly took me some time/work to get it correct.

good idea,but:
i filled blairs data in the FOS and get way more MSV than Blair... then i recalculated without Dynamic TC Stretch(wich blair doesnt mention anywhere) and get a MSV just a little above Blairs Calculation...but still clearly higher...

Recalculated Aprilia Data without Dynamic TC Stretch and ended up with 62m/s MSV...instead of your 35m/s...

I (the FOS)Calculated with:
Bore: 54mm
Stroke: 54,5mm
Rod: 115mm
RPM: 13000 umin
TC Stretch: 0,5mm
Volume: 8,2cc
Width: 7,9mm
Squish Clearance: 0,55mm
Squish Center Gap: 0,75mm (unsure what is meant, Its the Gap at the Point where the Bowl Begins i guess?)
And Result is 112m/s at 6° BTDC

Without TC STretch and same Squish Clearance i end up at 62m/s at 11° BTDC
I have no Clue...

forgot to set the squish height correct

it's 44.65 m/s @ 8.5° BTDC

conrod is 120, combustion chamber vol is 8.61 , compression ratio is 15.50
If I use your data (gives a compression ratio of 17.45 which is too high), I get 52.52 m/s

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like I said : it's not that simple to get the numbers correct with Blair's calculation's. If you calculate is in another way, that's fine but than you will not be able to compare numbers. And than again : all pro-tuners will say the calculated number is not realy important as the effective compression in the engine changes all the time and so will the squish velocity.

here for free :

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JanBros a écrit:

forgot to set the squish height correct  

it's 44.65 m/s @ 8.5° BTDC

conrod is 120, combustion chamber vol is 8.61 , compression ratio is 15.50
If I use your data (gives a compression ratio of 17.45 which is too high), I get 52.52 m/s

like I said : it's not that simple to get the numbers correct with Blair's calculation's. If you calculate is in another way, that's fine but than you will not be able to compare numbers. And than again : all pro-tuners will say the calculated number  is not realy important as the effective compression in the engine changes all the time and so will the squish velocity.

Thank you Janbros for your excel, i like such excel things
and because of "Housearrest" i was able to go tru part5+4+3 again (2+1 are my plan for today...^^)...and look what i found
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if I reduce squish to about 0.115, the max squish velocity in my excel is about the same. only difference than (I believe) is that I use a fix squish gap, while Frits uses a dynamic gap.

JanBros a écrit:

if I reduce squish to about 0.115, the max squish velocity in my excel is about the same. only difference than (I believe) is that I use a fix squish gap, while Frits uses a dynamic gap.

And Frits FOS uses Squish Gap and the Squish Center Gap (What i guess is the inner point at the beginning of the Bowl?) to see if the Gap is Parallel or opens Conical...

So my conclusion is at the moment, the most common told 25-50m/s MSV is a static Value and at least a bit useless... because in the enginge its very dynamic...
Frits stated somewhere in here MSV should be as high as possible... just dont go beyond the limits for Squishgap and Compressionrate etc. and it should be fine...

And the easiest way to proof my head to be good or bad is to test it and look what happens...