Ultralight news has all the specs. for the 377 compression ratios included, it will tell the 2 ratios I was referring too.
Ultralight news has all the specs. for the 377 compression ratios included, it will tell the 2 ratios I was referring too.
The 11.6:1 is probably a calculated or theoretical compression ratio. The actual or effective compression ratio is probably in the neighborhood of 7:1.
That is the website I was refering to. It has a number of mistakes - easy one to spot is the sparkplug is listed as 12mm when they are 14mm.Originally Posted by cliffo
Another one is that they list is the 447 as having CDI ignition - then give the contact points gap - CDI doesn't have points.
That is why I am trying to find two Rotax sources saying 11.6. from different time periods, just in case they made changes over the years. Manuals I have cover the last years of the 377 (90's) I need the early 80's stuff to see what was going on then.
If I can find another official Rotax manual that says 11.6 I will know the site is wrong.
If another ROTAX manual says 9.6 theoretical then there must be two different style heads - regular and High compression
If there are two Theoretical ratios - then I will need to widen my parts search for different heads
Last edited by sightation; 10-16-2017 at 06:47 AM.
447"s have been fitted with both CDI and points, I have an 80's model with points, don't know when they became available with
CDI. As far as the heads go I know the older (70's) Cuyunas had a wedge type combustion chamber on the 430 that was a higher compression, but I'm not privy to any thing like that with the 377. You might try referencing old sled motors. Good luck on your quest
Two cycle compression ratios can be "calculated" as in a four stroke using bore and stroke or "effective" based on the exhaust port closing position. This may be the difference in compression ratios you are seeing. Also the start versus run compression ratio accounts for the compression release if installed.
My comment only. The facts may differ and others may have conflicting opinions.
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