KDXRIDER.NET

Has anyone ever measured the port " mostly exhaust " height of a 200 vs. a 220.

Just curious as I'd like to lower the port height of our 200.
Debating about having the cylinder turned down.

One day I'm going to get around to finishing all the measurements on this thing. I keep telling myself anyway.

Works out to approx 178 deg exhaust duration, 117 transfer duration, and 30.5 deg blowdown. I spoke with Eric Gorr at a trade show last fall and he mentioned that the transfer port height on the 220's is too high. I'm not sure I understand, as it's already quite low, transfers tuned for ~6,000 rpm peak.

I don't understand that myself as the 220 porting is focused on bottom to mid throttle.
Some just don't like the 220 in general , not sure why ?

Unless they like that the 175 / 200 was basically born as an over bored 125 and has plenty of
power if you ride it 1/2 to wide open.

Forgot to get back in here.

http://www.vespalabs.org/User:Internets ... _Port_Maps has an image of a scanned port map for a KDX200. Pic is way too big to post up, 6208 x 5120.

On another page he said to have found reference that the exhaust port opens at 86 deg ATDC, and the transfers at 117 deg ATDC.


That would give
KDX200
Exhaust duration - 188 deg
Transfer duration - 126 deg
Blowdown - 32 deg

KDX220
Exhaust duration - 178 deg
Transfer duration - 117 deg
Blowdown - 30.5 deg

Assuming all was measured correctly by both parties. If it is correct then it's easy to see why the 200 is the rev bike (aside from carburetor size as well).

I had the cylinder in my KDX200 custom sleeved with the exhaust port lower. Man oh man did I love the change in the powerband. Made it faster even though the powerband was lowered. Less clutching out of turns, etc. I rode it on MX tracks for fun.
Here is my page where I recommend lowering the cylinder 1.7mm: http://www.dragonfly75.com/moto/KDXpowerband.html
(No I haven't made the special KDX pipe yet. patience Grasshopper)

See, so the 220 is already perfect.


I see on there you talk about improving the pipe. Did you have dimensions for the original or an aftermarket KDX pipe? I know on some boards for other bikes people often suggest modifying the pipe here there or else where, but have no idea how the pipe on the bike actually dimensions out.

adam728 wrote:See, so the 220 is already perfect.


I see on there you talk about improving the pipe. Did you have dimensions for the original or an aftermarket KDX pipe? I know on some boards for other bikes people often suggest modifying the pipe here there or else where, but have no idea how the pipe on the bike actually dimensions out.

Not to sway this thread to a pipe debate but I've tried several and the PC platinum 2 has the best all around power on both engines.

Great to hear about the 200 lowered port as the 220 is SO much better in the woods.

Mod the 220 some and you have a great bike.

Very useful comparison of ports here.

Here's the specific link to the port map files, I didn't see it at first just searching that page for the search term "KDX."

http://vespalabs.internetscooter.com/la ... -port-maps

Thanks for documenting this

Update - the vespalabs site is down, and I can't seem to find an archived version of the KDX 200 port mapping, but the shell of the page is still archived:

https://web.archive.org/web/20230323232 ... -port-maps

This thread below has some good additional information on port timing, and on boring out a 200 to 69mm/216.8cc or 70mm "225" (223.2cc):

viewtopic.php?f=77&t=17911&p=163178

Just saved these from a recent 69mm overbore 200 thread on ThumperTalk:


200H port timings:

220R port timings:
https://www.thumpertalk.com/forums/topi ... swap-dyno/

(thanks to James Zichelle)