Kymco ZX50

[Shaka]

No worries!  Don't do anything yet.  Keep in mind those are all preliminary numbers.  Just wanted to give you an update.

[zombie]

By George, I think he's got it! Those are the #'s He needed... I know you're still fine tunning (as it were) but that is exactly the info needed to repair the set-up. Now you'll be riding wheelies.

[sidthesloth]

Wheelies would be a bonus but not the intention, when I get a chance I will take it off again and try to get an idea of how far I can go. As for port duration, is that altered by the port opening size? (I didnt word that too well but I hope you know what I mean)

[Shaka]

Yes, the duration is in degrees.  It's the amount of time a particular port is open in reference to the degrees of rotation through the stroke.  I hope I worded that right!   It has everything to do with the height of the ports vertically, at what point they open and close. 

I got a response back from Step Vino and I had the deck height reversed in the program.  I had it as negative when it needs to be positive.  Anyways, the numbers all changed around!  I'll keep working them.  I think now you need a thinner base gasket, something like 0.5mm and to shave more off the cylinder top.

[Shaka]

Here's the numbers Step Vino ran.  I'm not sure exactly what it all means yet, but I'll work it out hopefully with a bit more of his help!  I'm calling it a night.  I'll try and do some more tomorrow evening, might be a little busy though.

Bore: 50.0
Stroke: 41.4
Conrod: 80.0
Deck Clearance: 0.35
Exhaust PortTop-BarrelTop: 24.35
MainTransfer PortTop-BarrelTop: 33.00
AuxTransfer PortTop-BarrelTop: 33.00
Boost PortTop-BarrelTop: 32.66
Exhaust duration: 176.8
MainTransfer duration: 123.2
AuxTransfer duration: 123.2
Boost duration: 125.6

Porting Mods
===============
Raise barrel: 0.00
Raise exhaust: 0.94
Raise main transfers: 0.40
Raise aux transfers: 0.39
Raise boost port: 0.06
Exhaust duration: 182.0
Main transfer duration: 126.0
Aux transfer duration: 126.0
Boost duration: 126.0

[sidthesloth]

Thank you Shaka, this is getting kind of interesting.

[Shaka]

Forgot to ask, do you know at what rpm your pipe makes it's power?  To really get the numbers right we need to know the intended operating range of the engine and where the pipe makes it's power.  I'm guessing you don't have this info, but it would be helpful.  Maybe you can find out?

[sidthesloth]

The engine was claimed to make 13hp @ 8,800rpm. I will ask customx22, he has one of these pipes and knows more about them.

[sidthesloth]

with regards to cutting the aluminium, being 2~3 mm thick, using a jig saw would be a bit overkill, sorta like rabbiting with a 12 gauge.
I think maybe a coping saw and a file might be a little more realistic. Hang on, 12 gauge,,,, wabbit,,, sounds a bit like Elmer Fudd.

[Shaka]

Sid, there are so many variables in this equation!  I think we are making progress though!  Here is a copy of the most recent email from Step Vino.  I guess there is a discrepancy with the deck height.

I ran the portmap through the portmap analyzer
program and came up with the BDC line too high
as well. If I change the crank size to 45mm,
then BDC moves to the right place.

The data file I sent last time has both the stock
engine durations, and the durations after raising
the ports. I wouldn't use that as a basis for porting
though, since something might be wrong with the
original specs you sent: If the crank is smaller
than 45mm, the measured deck height should have
been larger than 0.3mm.

To measure the deck height you need to have
the base gasket installed, and the cylinder
tightened down to spec torque settings.

I think it may be easier to have you do another port map as the original one is pretty rough.  I had to shop the photo to get it to work because the exhaust port was split.  The easiest way I have found to do it is to take a piece of paper and cut it so it fits the size of the circumference of the cylinder.  Put the seam between the exhaust port and the transfers.  Then line up the top of the paper with the top of the cylinder and put a couple pieces of tape to hold it in place.  To get a good transfer use a pencil and rub around the edges of the ports, then use your finger to rub it in.  This should give a nice clear transfer.  Remove the paper from the cylinder and outline the ports with nice dark lines.  Then measure from the top of the paper to the top of the ports.  That is the only measurement needed.  The only other measurement needed is the deck height.  This has to be taken with the cylinder torqued down and the base gasket in place.  Recessed cylinder = positive deck height number.  Let me know if any of this is unclear.  I think the 8,800 rpm is probably a good range to work with.  This means it is a low revving cylinder and from what we've gathered you have a low revving pipe as well.

Ps. I've been using 41.4mm as the stroke.  From my understanding this is the stock crank stroke listed in the service manual.

[sidthesloth]

Yeah, that is pretty much what I did but I will do it again it the ex port complete. the deck height is with the gasket and piston is with gasket also.

[Shaka]

I hate to ask you to do it again.  I'm not sure you really need to.  I just wanted to get a second look at the measurements to make sure they are accurate.  Unless you want to really get into porting the cylinder, I think the main goal is to determine the ideal base gasket thickness and from that how much needs to be machined from the top of the cylinder. 

[sidthesloth]

yeah, that is what I want. I think a 2mm spacer should get it close and from there adjust with different gasket thickness, being two gaskets will give more room for adjustment.

[Shaka]

I'll try and run some more numbers.  I'll figure out how much space you need to take up at the base.  Then you will most likely have to put in that amount of gasket and re-measure.  Then we can see where it sits and figure out how much needs to come off the top.  I won't get a chance to sit down again with the program until tomorrow.

[sidthesloth]

Thank you very much for spending all this time on it. have a nice weekend.