D
Deleted member 12676
Guest
I used to advise people to just go ahead and increase their engine compression for more power and if later on they can afford to get a Jaguar CDI then do so. Not any more. I am too convinced now that if you increase compression you stand a good chance of having catastrophic engine failure like this guy did. The overly advanced standard CDI is only good for non-modified engines with the standard low compression (~90psi).
With excessively advanced ignition the peak pressure happens too early which is not that horrible on a low compression standard engine but when you shave the head for more compression it takes the whole shebang into the danger zone. That excessive combustion pressure-
1) wears out conrod and crank bearings too soon
2) increases engine temperature which can cause detonation and engine failure if there is a lean fuel mixture
3) causes too much outward ring pressure onto the cylinder which increases possibility of the ring catching on a port and causing unrepairable damage
The following graph shows peak compression happening 40 degrees after ignition. So for peak pressure to happen between 10 and 15 degrees the ignition has to happen around 22.5 degrees before top dead center (BTDC) which is what happens with the Jaguar CDI.
Here is my page about increasing cylinder pressure: http://www.dragonfly75.com/motorbike/Compress.html
ps- the Jaguar CDI is now called the Performance CDI because of conflict of interest with the Jaguar motorcar company.
With excessively advanced ignition the peak pressure happens too early which is not that horrible on a low compression standard engine but when you shave the head for more compression it takes the whole shebang into the danger zone. That excessive combustion pressure-
1) wears out conrod and crank bearings too soon
2) increases engine temperature which can cause detonation and engine failure if there is a lean fuel mixture
3) causes too much outward ring pressure onto the cylinder which increases possibility of the ring catching on a port and causing unrepairable damage
The following graph shows peak compression happening 40 degrees after ignition. So for peak pressure to happen between 10 and 15 degrees the ignition has to happen around 22.5 degrees before top dead center (BTDC) which is what happens with the Jaguar CDI.
Here is my page about increasing cylinder pressure: http://www.dragonfly75.com/motorbike/Compress.html
ps- the Jaguar CDI is now called the Performance CDI because of conflict of interest with the Jaguar motorcar company.