3xv rear cylinder leg modification. SP 3xv-10 cylinders??

[maccas]

Hi guys,

Right over xmas I will be taking the top end off my 3xv to do a few tweaks. While the top end is off I was thinking about modifying the rear legs of the cylinder in an attempt to open the path to the transfers up a bit. So I have a few questions:

1. Do people copy the TZ layout?
2. Will piston life be significantly shortened?
3. Does anyone have any dyno evidence to prove this modification actually makes a difference?

Here is a stolen pic of a 4dp cylinder. The legs are minimal and not very chunky:



And here is one of my SP cylinders sat on the crankcase:



I see that on Paul's 3xv cylinders the inlet legs have been shortened and rounded off: (sorry for the stolen pic Paul):



I also found these SP cylinders on yahoo Japan that came with kit pistons, the rear legs have been modified on those too:



Looks like it might be the way to go? Yamaha must have designed the legs on a TZ like that for a reason.

Also using paul's photo again, has anyone tried adding material to improve the radius into the transfer tunnels where I have shown the red arrow:



Yamaha must have done this for a reason too. There is a step between the transfer tunnel and the radius on the base of the cylinder. The TZ cylinders have a lovely smooth transition from base of cylinder wall into the transfer tunnel. Looking at it I would fill that step with JB weld to get a nice smooth transition into the transfer tunnel. Would people agree that I should do that?

Also the blue arrow shows that Mr Coker has put a nice radius on both sides of the lower part of the cylinder wall, I will copy this I think. I have read elsewhere that this is the way to go now. People may argue that it is not worth doing as that part of the cylinder wall is meant to match up with cut-out in the side of the piston, but transfer flow begins well before the piston is at BDC 

All thoughts, theories, opinions welcome.

Dan

[EEKNOWS]

If you want to separate theory, specualtion , old fashioned 'what looks right'  and people who visualise things from what  just makes shitloads of HP , follow what Jan Thiel has done with the Aprilia RSA/RSW engines. These are probably the most powerful 2 stroke engines ever made. Was the result of 100 people working full time , 2 dynos and 3-4 cylinders tested per day. If it didn't make more HP it went into the recycle bin. No other criteria.
First throw away what ever you thought you knew about a 2 stroke cylinder. Then forget that Yamaha had a complete grasp of what they were doing(Bartol stories will come later)

All of transfer flow WILL BE AT BDC. That is the best time to cool the piston and form a rising column(we'll talk about the rising column later). Next is the INNER wall does all the work, the intake just follows the outer wall shape. A short transfer passages begine to flow sooner and finish sooner than long ones. Having the transfer flow peter out not long after BDC is what you wantas that helps form the rising column with little turbulence(more on that later).

Looking at the cylinders there a 3 things that stand out.
1.Altering the little legs will do SFA to promote transfer flow
2. The inner wall is far too long
3. The radius where the inner wall meets the transfer duct is to small.

Shortening the inner wall down to close to the base of the cylinder will allow you to put a decent radius an shorten the inner wall. Win win in junior manager speak.
Aprilia RSA cylinder

[maccas]

Hi lozza,

Thank you for that information, I will do some more reading 

Dan

[Paul]

(sorry for the stolen pic Paul):

quite alright dan, only i cant remember if those are my spares or the ones on the bike.
interesting observations
the entire inlet tract; rubber to piston-edge/crank was also machined out
eeknows is right (i gather from his wisdom) that there is more to it, and i believe a lot of the machining Coker did from carb inwards was an inlet volume thing.
TBH, he did very little work to the ports, just the exhaust ports were opened and raised and PV's altered to suit, most the work is in
"blueprinting" original then improving cases, bottom-of-barrel, heads and pipes.









keep in mind his instructions were to de-restrict, improve reliability and give me a nice mid range. it is not a track bike, but would love to try it on a track one day.

i just came back from a ride on the 3XV, it is hot as hell here today, and that was back to back after the TZ. the 3XV is a very pleasant and easy bike to ride, it has a mid range like you cant believe (well i think you can, your dyno graph is very similar to mine, linear) and a nice top end which i dont ride it in much (thanks to good mid range and my engine wrecking mental control, developed recently$$$$$).
are you going completely track? i would "clean it up" but not get radical, even for track, unless you got a recent sponsor!
those RSA cylinders look the bollocks

[maccas]

Thanks for the close up pics Paul that's really helpful!

It is very interesting that Graham Coker didn't raise the transfers at all. Are you running the standard thickness base gaskets?

Dan

[Paul]

pleasure
im using 0.7 base gaskets

[Neal]

Hey Dan ,
email me - nealgreyplumba@hotmail.com . I have a 50 barrel that i can send pics of . I just can't load them yet as i am a computer numpty .

cheers , Neal

[maccas]

Emailed!

Cheers Neal!

Dan

[EEKNOWS]

Dan what are the port heights from the top of the cyl? The cyl looks blowdown limited, there is free HP there demanding to be released.
I see the sub exhaust doesn't extend around to the 9/3 o'clock (or as far as it can go with a piston cut out) line on the cyl. Check the angle on the bottom of the A and B ports should be 15 deg.

Jan Thiel said he found no extra HP in the cases and the few if any people know what happens once the crank is spinning

[Neal]

My. Man Dr Neels does nothing to the cases too .
When he does porting for me . To my untrained eye it looks like not much has been done but the dyno tells the truth afterwards !

[EEKNOWS]

http://www.sylmasta.com/acatalog/Creative_Kneadatite_Putties.html This is what Jan Thiel used aparently survives replating 

My. Man Dr Neels does nothing to the cases too .
When he does porting for me . To my untrained eye it looks like not much has been done but the dyno tells the truth afterwards !

Say hello to the good Prof next time you see him Neal. 

[casal-fan]

The cyl looks blowdown limited, there is free HP there demanding to be released.

Eeknows, about blowdown limited.
Some years ago, when I spent a fair amount of time analysing TAs and the formulas (or formula) for calculations that people were using... to me it looked wrong, the old formula from the scrip "aspirin takers something " developed by 2 gentlemen when working about cylinder design for an yamaha racer.
I don´t remember the formula by heart, but it was something like it was analysing crankshaft rotation degrees generally, and not taking into account the actual speed that the piston has when traveling at at given point of the crankshaft position. (hope youguys understand what I mean).

Since then, I found a picture by Frits Overmars, of TAs analysis (wich I can´t find anymore, off course), and a writing (can´t find that either) explaining theyr point of view how TAs analysis should be conducted. And it was not just as simple as the early formulas.

Do you have fresh info on that Eeknows?

[EEKNOWS]

 The old way talked about time/area which is wrong because we never worry about time, a better term is angle/area so exhaust open 196 deg is a angle, but we are not concerned with the engine just sitting there so we add  the equation of dividing them by cc's of the cylinder and by rpm of peak torque and we get specific time/area.
You can never have enough blowdown STA.

[Neal]

So the next crazy idea is - How much would it cost me to have 2 cylinders cast by an enthusiast with all these Aprillia improvments ?

[tzr-v4]

Here is your guy !!!!
Gabriele Gnani / check his videos on youtube.

http://www.youtube.com/results?search_query=gabriele+gnani&oq=gabriele+gnani&gs_l=youtube.3...179430.180773.0.181062.4.4.0.0.0.0.144.431.3j1.4.0...0.0...1ac.1.j8PTe7JQTL4