My Dynotronics experience; Thank you Specialty Z

jrb55gh

As a Dynotronics customer with a stock 370 etune and about to install hfc and cbe I am concerned with the detonation issue in this thread. A couple of tuners and probably more on this forum have found the way to make additional power without detonation on 93 octane fuel. I have been thinking about what they may have done differently than Dynotronics to achieve their results. I have done some research on preventing detonation with a given fuel. Charge temperature, pressure and burn time seem to be the big hitters. There are several adjustments that can be made to intake and exhaust valve timing to address these conditions.

Since the exhaust cam is not adjustable on the 370, the exhaust valve opening and closing times are locked in. The compressed charge temperature and pressure must be controlled by the intake cam timing and duration. Charge temperature can be reduced by increasing intake valve overlap with the exhaust valve when the exhaust system is free flowing. The idea here is reduce the compressed charge temperature by purging the hot spent combustion gases from the combustion chamber at the end of the exhaust stroke and beginning of the intake stroke with cool fresh charge. The other way to limit compressed charge temperature is by late closing of the intake valve for a given rpm. This lets some of the charge drawn into the cylinder during the intake stroke to flow back into the intake manifold before the intake valve closes. This also lowers the compressed charge pressure.

The late closed intake valve reduces the amount of charge inducted into the combustion chamber and limits the amount of power that cylinder can make. But that smaller charge with ideal timing and 93 octane could possibly make more power than a fully charged cylinder with limited timing and 93 octane fuel. That is the trade off.

The concept is straightforward but implementation requires much dyno time to determine how much valve overlap, intake closing after bottom center, ignition advance and air fuel ratio is required at each rpm to get maximum 93 octane power. That is a large number of variables to juggle, but it has been done by auto manufacturers such as Mazda in their Skyactiv (14:1 cr) vehicles and even NASCAR engine builders in 16:1 cr engines that are required to run a restrictor plate. Probably some of the 370 tuners have done it too.

For those that want to learn more about this technique research: Atkinson thermodynamic cycle.