94 ktm 550 porting question

[travism]

this will be the first one that ive done. this will only be used as a snow bike with a timersled setup on it. the way you ride a snowbike is pinned most of the time. you really want max power on top would be nice to have some low end grunt aswell

my question is witch ports should i bore out. and how much any info will help with this build ill post some pics after i get done with the port job.

 

[wake_rider]

Porting rarely gives any more power without precise machining and a wealth of knowledge. I would look into other options for trying to find more power, but if you do decide that this is the direction to go, I'd send it off to someone who really knows what they're doing. Eric Gorr comes to mind...

 

[Rich Rohrich]

my question is witch ports should i bore out. and how much any info will help with this build

This statement alone is a testament to the fact that you would be well served to do some research before you start hacking away at those unsuspecting ports. Knowledge is the real power here.

This book would be a good place to start:

http://www.amazon.com/Two-Stroke-Performance-Tuning-Bell/dp/1859606199

 

[helio lucas]

since i own this book i only want to add one thing:
from my experience with ktm cylinders they have very poor matched transfer ports. actually both of my ktm360 cylinders have at least a mismatch of 1mm between right and left on some ports. i would begin there :cool:

 

[plynn41]

I've got a bad feeling about this... This is the poster's first post I see.

That's an awfully special engine you're about to start grinding on friend. I'd leave it alone.

 

[travism]

spare bike
i was just looking for info if you dont have any to give then dont post

 

[plynn41]

Now you've got 2 posts! :nod: Welcome to the forum!

 

[julien_d]

You did get info. Just not the info you wanted.

Send it off to be ported, or leave it alone.

 

[_JOE_]

I think what these kind fellas are trying to say is that someone with the ability to properly port this type of engine would most likely not be asking for directions on a forum......especially in thier first few posts. They are trying to save you time and money by advising you to send it out to someone with the proper tooling and knowledge. Best of luck to you!

 

[Rich Rohrich]

spare bike
i was just looking for info if you dont have any to give then dont post

From your post it's obvious to even the most casual observer you don't understand much about porting or even how two-strokes work. People have been impressively kind in their responses to your post.

It's fair to assume based on your attitude that people's willingness to guide you in the right direction is likely exhausted. I'm sure that approach will take you far in life. :coocoo:

 

[Pete Payne]

First thing to do is degree the engine to se where the timing of each port window is . Also cc the head as well as the trapped volume of the assembled engine.

Then you may be able to see a flaw or 2.

remember -- measure twice (at least) and cut once !!!

 

[OriginalRider]

Porting SOME people say is equal to a big bore kit but in your case you already have a big bore and trying to port it is just insane to me but i would probably be doing the same thing.I ported and polished my CR250 cylinder the other day.Remember one thing porting is not about making the ports bigger its about making them smoother!!.If porting is not done right it could be critical!!.Take your time following each port.I did all the ports on mine.i didn't go insane i just did very mild porting and polishing.Do very lightly see how its coming out then go from there i spent about 1 hours porting mine making sure everything was the one i wanted it.I was thinking about posting pics but of course my camera wasn't working.BTW i also did my crank case,and head.I haven't start it but for some reason it feels as if i have more compression.Or maybe im just very tried hoped this helped you!

 

[_JOE_]

Porting SOME people say is equal to a big bore kit but in your case you already have a big bore and trying to port it is just insane to me but i would probably be doing the same thing.I ported and polished my CR250 cylinder the other day.Remember one thing porting is not about making the ports bigger its about making them smoother!!.If porting is not done right it could be critical!!.Take your time following each port.I did all the ports on mine.i didn't go insane i just did very mild porting and polishing.Do very lightly see how its coming out then go from there i spent about 1 hours porting mine making sure everything was the one i wanted it.I was thinking about posting pics but of course my camera wasn't working.BTW i also did my crank case,and head.I haven't start it but for some reason it feels as if i have more compression.Or maybe im just very tried hoped this helped you!

There's a reason the cylinder had texture to the ports walls. Smoothing things out doesn't make it better.

 

[_JOE_]

And "porting' is actually changing the height/shape of the ports to shift power around.

 

[OriginalRider]

Yea so just make the ports 3inchs big and ruin the cylinder

 

[whenfoxforks-ruled]

Properly finished, the port walls appear as ruff as the original casting. Well, closer than a mirror anyways! I am pretty sure they get multi textured. But, there goes the terrible hit off bottom, from brap, to buwharap. And the case mod, that just got REAL expensive to replace! Increasing the size of the intake, transfers and exhaust, just a lost cause, scrap metal. The nicest I have heard this referred to is bar-room mechanics, no proven science. And yet there is a proven method and science to back it up. Vintage Bob

 

[Rich Rohrich]

Yea so just make the ports 3inchs big and ruin the cylinder

Joe and foxforks are correct. On a two-stroke bulk flow through a port is rarely the issue, while Time-Area relationships are always critical.

Here's and older thread that goes into much greater detail on the subject : http://www.dirtrider.net/forums3/showthread.php?t=67001&highlight=time-area

 

[whenfoxforks-ruled]

That is an awesome thread. Has there been a change, or did I read it wrong about the base of cylinder transfer area, to case transition:There is a reason for the step? Aside from the:If you remove metal, you have to put it back some where issue, I would swear I got yelled at for making it smooth.