Compression Test

Tyler6357

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Pipes don't change compression, well at least not substantially any more than a reed might. Both are beneficial in aiding a denser charge, but the effect on compression is negligible. The reed will increase case pressure, and the pipe will help in reducing it through scavenging.

Case pressure and compression ratio of the chamber are two different things.Case pressure has a minimal effect on combustion chamber pressure, and chamber pressure has no effect on case pressure in normal operating conditions. Like I said the probable reason for the diff. in comp.of the two engines with same head volume and squish gap is differences it exhaust port window heights in the cylinder. If the window is higher the compression begins later in the stroke thus the volume being compressed becomes lesser. The combustion period becomes shorter, and the blowdown period becomes longer allowing more time for exhaust gasses to escape before the transfers open to introduce the new charge.
Oh, okay, that all makes sense, thank you for explaining that to me, I'm still learning. I will have to compare the two jugs the next time I have them off.
 


Tyler6357

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Sep 28, 2011
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525
don't recall the numbers, but somewhere near that level you'll need a much higher octane fuel - I doubt much of that pressure will get to the seals, but a retainer plate could be added
That's good to know. I was just using the cheap gas but I have switched to the higher octane stuff. It's hard to find gas without ethanol in it in CA, it's mostly all 10% ethanol. Also, I mix with Opti-2 at 100x1 for both of my engines. I broke them in at about 90 x 1. I know Opti-2 has less heat tolerances than most normal 2 stroke oils but the truth is, my engine never gets that hot anyway, certainly not hot enough to cause the oil to break down. I like Opti-2 because it's so clean with less carbon build up and less gunk in the exhaust and silencer. Many people at those races use racing fuel but I have never tried it.
 

Tyler6357

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Update: Okay, since I did this test neither of my engines will run correctly. I don't understand what could have happened. The GT won't start, it has no spark, I haven't dug into why yet. The Peugeot will start up but will only start with full choke on. It has been sitting for a few months because I've been riding the other bike but I had drained the tank and turned the petcock in the closed postion. I don't know what happened, I'm very bummed that I even attempted this.
 

Tyler6357

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Sep 28, 2011
Messages
525
Update: Got both bikes running again. It seems the CDI went bad on the GT bike. I put a new CDI on the GT bike and it immediately got the spark back. I'm not sure if the compression test could have shorted out the CDI but I don't know how it could have. I think my problems were just a coincidence that they happened right after I did the compression tests. The Peugeot CDI didn't short out after the test, it was just a carb problem.
 
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