Manifold Plenum Heater – Deicer

Straight 6 cylinder engines with performance manifolds can sometimes test ones patience on cold winters mornings. Thanks to AussieSpeed they have helped to alleviate the frustration with this weld on plenum heater box, also referred to as a Deicer [de–ice–r].

The Problem; The typical in line six has it’s manifold out to one side and away from the engines radiant heat, which is great for performance because it easily allows us to have cooler intake temperatures for denser air to pass through the carb for better volume of fuel atomisation and allows us to make good horsepower. However the trade off is that it can take some considerable time on cold mornings for the engine to get warm enough for us to drive off at normal street speeds with out over revving the engine or slipping the clutch.

You may have noticed when you tossed away the OEM inlet manifold and exhaust manifold that in some way they were connected or passed very close next each other in their basic design. The reason for this is the same reason that OEM V8 manifolds have the exhaust gas cross over duct right below the plenum under the carb. Now most people think it is a good idea to block this cross over off to make more power, this is true however, the extra power made will be when the engine is revving harder, like on hard acceleration in the lower gears and the air speed is high in the ports. Great I hear you say this is just what I want, so what is the problem?

First a little bit about gases; what happens when you heat a gas up? The answer is that it’s particles accelerate and collide and bounce off each other. Once the fuel is atomised into the air as it gets sucked out of the venturi of the carburettor you have an air & fuel gas. One of the main issues in inlet manifold design is to keep air speed high enough in the plenum and ports so that the fuel droplets that are suspended in the air do not fall out of suspension and dribble along the bottom of your intake runners. Ideally we want the coldest air possible passing through the venturi of the carbie then once it is in the manifold heat it up just enough to accelerate the gas particles so the fuel stays suspended in the moving air all the way and into the cylinder. If we can also get this air/fuel gas closer to ignition point as it enters the cylinder so it will burn/ignite easier then even better.

In winter we compound our drivability issues on a cold morning because our performance engine now usually has a bigger carb, bigger plenum and bigger ports, low vacuum at idle and our cold morning air is really dense so it all is working against us until the engine heats up a bit, ………..when it heats up, the gas particles accelerate, it is hotter and closer to ignition point so it ignites easier too….. all most of us really notice is that it just starts to run better after a while.

So all the manifold plenum heater does is allow you to route hot water from the engine’s cooling system through this box so that where ever the box is attached it will heat up quicker and hey presto, your daily driver will heat up quicker on that cold morning and hence it will run nice again in the winter. Be sure to route water straight from the block and not from the thermostat controlled side.

For summer and performance driving just have an inline stop tap to stop the hot water circulating to the plenum. So just weld it on to the bottom of the intake manifold and route some hot water hoses to it and you are away. Too easy.