View Full Version : Lets get technical: Piston covering up a transfer port at TDC

Billy Golightly
06-22-2006, 08:56 PM

I was playing around with an extra topend I had when I discovered this. Ok, so here both transfer ports are open on this side of the cylinder (The piston is hanging out of the top the cylinder way past TDC, dont worry about that right now.)


Now in this picture, the piston is near TDC (The piston is just held at the top of the cylinder to keep it from falling out so its not exact) and look how much of the transfer closest to the exhaust is open, and the back one is closed almost half way off. This is off of my 500R. Whats going on here? Is it just because its a Wiseco? Are the stock and Pro-X pistons any better? That has to be hindering a substantial amount of mixture flow. I dont really know the answer to this, I'm looking for suggestions and theories. This isn't a "I know the answer and you guys have to figure it out" thread :cool:

Original large pictures:

http://img59.imageshack.us/img59/523/p62200026lf.jpg (Transfers Open)
http://img460.imageshack.us/img460/4083/p62200037mv.jpg (Transfer Covered)

06-22-2006, 08:57 PM
pics arnt showing up try the """" tags

Billy Golightly
06-22-2006, 09:00 PM
Fixed. I should have known that shouldnt I? :lol: oh well

06-22-2006, 09:23 PM
At tdc the transfers are not moving any mix, the intake ports should be filling the crankcase (primary compression area). When the piston makes it way back down the cyl the transfers are going to open allowing the a/f mix to move to the combustion chamber (secondary compression area). If anything check to make sure the transfers are fully open at bdc.

Billy Golightly
06-22-2006, 09:37 PM

Heres what happens at BDC! :eek:

Billy Golightly
06-22-2006, 10:14 PM
http://img157.imageshack.us/img157/2873/bdccorrect11nw.th.jpg (http://img157.imageshack.us/my.php?image=bdccorrect11nw.jpg)
http://img235.imageshack.us/img235/2416/bdccorrect26nh.th.jpg (http://img235.imageshack.us/my.php?image=bdccorrect26nh.jpg)

Thats alot closer to BDC then the first ones I had posted. I know it looks like its down to far but according to how the cross hatching is worn around the cut out in the pisto n on the intake side thats where it should be.

06-22-2006, 10:17 PM
Now we're talk'in. I tried to take pics, but they came out blurry. I pulled out my old FTZ 250 motor and piston. Same thing. At TDC the intake side port is almost 1/2 covered. At BDC, the psiton closes approximately 10-15% of the base ports (for lack of better explanation). I would ask the piston manufacrurers if that is intended or opportunity for more power. Oh, the piston is a Wiseco also.

Billy Golightly
06-22-2006, 10:28 PM
SO! Your 250R is the same way too...I'm wondering now if this is a Wiseco only trait. Anyone got a Pro-X or stock piston laying around??

06-22-2006, 10:30 PM
I used to run Nik's pistons, but they kept cracking. After the 2nd piston cracked, I gave up on cast pistons. I looked, but I didn't keep any.

06-22-2006, 10:33 PM
I had a MAX (Dont ask i dont know) .50 over piston in my 250R when i got it, it did the same thing... Thats odd that they do that now that you bring it up... Maybe the tecate does it too...

06-22-2006, 11:09 PM
You sure that piston ain't in backwards Bill? (lol). If anything Wiseco's designs will either correct or better stock piston performance. I'm wondering if you have the wrong year piston in there or something like that. If not, then it may be covering it up on purpose, to rectify some sort of timing issue Wiseco believed was hindering engine performance. JFSnG, What does the intake side look like?.