KTy

Can anyone kind enough to explain me in what case you need a spacer for the HP4 ? I will be driving an ET3 stator on primavera (VMA2M) engine with a PK HP4... Spacer needed for me ?

Do you think the grey ring on the outside of the center tip is suspicious ? :plemplem: I suspect it could be the cause of some *small* *occasional* troubles at high-rpm... And yes, I'm running too rich. BUt what matters to me is this "grey" ring.... It's a B8HS NGK running on a stock PX125E. Thanks KTy

Thank you So you're piston is very unbalanced ? :plemplem:

@100 spezial: Can I ask you a drawing ? :wasntme: Ok people, I'm going to try anyway... :haeh: Do you think I should keep the skirt on the other side of the boost port ?

:plemplem: ... bolt the split off piece direcly into the engine block... Errr... Isn't this even more risky rather than not putting anything... ??!! :heul: I just measure, at BTDC the piston is guide for 4cm where the piece split off, while it is guide for 5.4cm on the other side of the boost port. The question for me now is whereas I should keep it like this or cut the other side... I think I'm gonna try like on the picture...

HUm... you're probably right. :wasntme:

I guess that you cut the remaining cylinder wall... Did you reduce the piston skirt accordingly ? Your piston skirt is totally asymmetric ? Like 1 or 2 cm longer on the exhaust side ?!

It was "bonsoir", so you were more than half right I'm pissed off... it is freshly rebored ! 0 km :puke: ( I don't know... I'm not looking for a daily rider... I had only two events planned for this year with this scooter... I may do something "silly"... :grr: Shit ! :uargh:

What could be the maximum length of the piston skirt to tolerate no guidance ? 1cm could be ok ?

Give me your feelings.... With GS piston... I was planing to massively cut the skirt of the piston, but I'm affraid it could be too much..... ( KTy - :heul:

@Vespaflow: Did you have to rejet or, at least, to play with the air/mixture screw with a bigger timing advance ? I'm asking because on my PX125, used, old, crap, but still working, I had to unscrew about 1 turn (richer) the mixture screw of my SI20/20 so that the engine doesn't "bog" or chock when accelerating from very low rpm with a big load (for example, accelerating in 4th). Timing advance was about 25° @ 2000rpm and 23° @ 4000rpm. Does it make sense for you to adjust the carb settings or do I have another pb ? Thanks

I suspect much better results could be obtained with non-linear curves... One can clearly see that at low/mid-rpm, the 28°-21° curve have 0,5-1bhp more, but at high-rpm, advance is too much and torque decreases... If a programmable ignition :wasntme: was to be used, one could map all these advance values in order to obtain a better overall achievement... The red curve is really strange... (edit: well, actually, no it is not ! I suspect advance to be already below 16° at 5000rpm... That's my understanding !) Anyway, I really find these curves encouraging

Would be nice to try with my similar setup ... Polini133 133/199/35, 70%, GS piston, Malossi-GS head, vForce3 RD350, Koso32.... and zirri silent I'm looking forward for a comparaison with a HZ !!

Alloha, I'm looking for an HP4 flywheel for PK (and PX). Interesting price... Cheers, KTy

Mine Seriously, these data are pure speculation So, does anyone have an idea on TA target ? :) With the previous version of this engine, I already had *no problem* to pull all the gears with a 2.34 + zirri 4th + zirri silent. I will rebuild it with a 2.56 primary with short 4th in order to have a really fun scooter...

First point is, I didn't correct the boost port area . Reading MacDizzy I was planning to do it, then I forget ! But, my understanding of this problem of steep angle is that it shouldn't change the timing nor the heigth of the boost port. A corrected factor should only affect the area, as few mixture can flow through this port... But that's my understanding ! I have also milled a lot this port even though it's still not much... That's where I'm stuck right now... I don't really know what to target in term of T.A values and BMEP... And anyway, my timing are already "extreme" (199/133/35), so the only thing I can try to optimize is the transfer width and of course, the exhaust width. As for the Blowdown Area, ... what is the question ? :plemplem: Maybe I don't calculate well the mean line . I thought it was only a function of the transfer opening timing... As both primary and secondary transfer have the same height (there is a drawing mistake but I correct it), I thought they would have the same mean line... :wasntme: ? I have the old DOS based version... I have to investigate more how to use it... Hum.... I haven't made this sheet, so I assumed all formulas were ok ! Maybe you're right even though doing =N42/1,36/D30/D8*600000 gives strange results... According to MacDizzy http://www.macdizzy.com/formulas.htm it is the correct formula...

@100 spezial : Very nice :love: For those of you interested in some numbers and pictures, PortMap HighRes: http://ktylife.free.fr/vespa/KTy133/200507...133.PortMap.JPG Excel sheet fed with some number more or less exact: http://ktylife.free.fr/vespa/KTy133/KTy134.xls

Danke :grins:

Ok, thanks Any advices and experiences on different shapes for the exhaust port ? I read that a rectangular port is more noisy but delivery very sharp wave pulse that could make the exhaust works better. Oval shape is common, but could reduces exhaust efficiency. Finally, V shape or trapezoid is often found on modern cylinder... I was thinking that because I have to enlarge of 6mm (!!) the width, I could enlarge the exhaust port width to 70% just for the blowdown area... Just an idea.... :wasntme:

Alloha , I'm back again on my Polini 133 project , well it's more a KTy 134 now... I have a 58mm GS piston and I'm doing a port map of my actual cylinder (already modified)... I didn't work too much on my exhaust port width, and now what I measure is odd too me. On *the paper* of my port map, I measured a maximum exhaust port width of 37mm. So, the actual width of the port is: 58*sinus(37/58) = 34.5mm , that is 59.5% of the diameter of the piston. Could this be correct ? I'm planning on increasing the exhaust port to 69-70%, that would be a 40.5mm port width (44.9mm width on the plannar port map), 6mm more compare to my existing port ! :plemplem: So if I haven't made any calculation mistakes, here goes my question: On a Polini 133, can you enlarge that much the exhaust port without making a "hole" in the exhaust transfer ? I don't want to see the studs through my exhaust port !! :plemplem: Thanks for your help ;) KTy -

Err... Because... I don't have the tool to precisly measure... ?! I should go buy a syringe... :wasntme: Hum, speaking of this Malossi head, is anyone riding with a long sparkplug (BxES) ? The hole is soooo long, I don't understand why one would use a small sparkplug (bxHS) :plemplem:

Sorry Claus :wasntme: And I have the Malossi GS head in front of me, the squish is 0.6mm on the outside... But you told me that, as it makes a positive angle with the piston, the average squish height is 0.75mm ... Did I misunderstand ? :plemplem:

Yup... With 1mm of squish and 1:12 of uncorrected compression ratio, it gives something like 11,09cc... It shouldn't be that far from the truth... As Clauss told me the *average* squish height is 0.75mm and the squish surface was 50% ...

Hi guys :) I'm looking for a quick information on the Malossi head adapted to the GS piston by GrandSport itself... :) Does anyone know its volume ? Should be something like 10-12cc... Thanks ;)

If I have understand correctly, you're probably right. BUT there are other interesting points that make me continue to develop this thing: * it's fun and entertaining :) * I'm pretty sure it can definitely bring low end achievement and probably some overrev facility * it can measure EGT and CHT for instance, reduce advance in some cases and prevent damaging the engine * it can drive a powervalve according to RPM, I will need this... * ... This only for the variable unit ! I can also imagine designing a whole new complete vCDI system with a new stator, combining waste spark, enhanced spark energy, to improve overall performance and reduce emission... The point is, maybe it won't give you +2HP everywhere, but it may help you to fine tune your engine... To be continued :wasntme: KTy