In a message dated 5/25/2006 10:28:27 A.M. Eastern Daylight Time, atlasyts@bellsouth.net writes:
Lynn, where do we stand with John? Our engines have the high
compression rotors and they are turbo charged. Should we use different
plugs than the stock ones that everyone uses?
Thanks
Buly
http://tinyurl.com/dcy36
The correct technical answer is that I have no clue. The very coldest plug possible would be my best guess. The "stock turbo" plugs should do well. The turbo engines run lower static compression because the turbo and supercharged engine keep changing displacement as the boost goes up and down. The head space is always the same, so the dynamic compression ratio can go way up very fast in operation.

So, if the boost is way up, and you are force feeding 160 cubic inches of mixture to your 60 cubic inch engine, have you raised the compression ratio?

Controllers designed for turbo use have a retard feature the is actuated by the Lambda knock sensor. At the first hint of knock
(detonation) the lambda pulses the controller and the controller pulls out, say, 2 degrees of advance and waits for another revolution to be completed. If it gets another Lambda hit it will pull out another 2 degrees, and so on.

This saves the engine by reducing combustion chamber heat. (Detonation is charge temperature dependant). It also reduces engine power over the short run. Other inputs can reduce charge heat, for example a temp sensor might light a warning light, as well as the Lambda hit through the controller. A temp sensor might also switch on a water spray to the water and or oil coolers. Or the inter-cooler.

The object of ignition timing is to develop the highest cylinder pressure at the correct crankshaft angle for maximum efficiency. Note that retarding the timing is therefore reducing efficiency. This would involve many items such as burn rate, compression ratio, chamber temp and soon.

Note also that higher cylinder pressures increase ignition voltage requirements. So turbo, and supercharged engines have very exotic ignition systems. Lower boost numbers less trouble.
Higher boost numbers more trouble.


Lynn E. Hanover