Engine Cooling - Block-Off Plates

TurboRuf · 10-03-2002, 06:58 AM

I've noticed several companies selling engine block-off plates for the 911/930. These are supposed to improve cooling since they prevent the exchanger heat from passing over the engine.

If something like this is installed, where do the heat exchanger vent tubes go? Do they just vent to air?

How much do these really help lowering engine temps?

Rot 911 · 10-03-2002, 07:15 AM

Well I don't believe "exchanger heat" passes over the engine. Air comes in thru the fan and is pushed thru the heat exchangers and then into the cabin. The blocking plates are useful in that air is blocked from going to the heat exchangers, thereby allowing more air to be pushed over the engine. Is it effective? Theoretically it should be, but I've never used them.

TurboRuf · 10-03-2002, 07:43 AM

So the left and right tubes actually suck air from the engine shroud area into the heat exchangers? If the fan blows cool air over and down through the engine for cooling, wouldn’t both tubes pull the cool air right back out? I’m trying to get a better understanding of how engine cooling actually works in a 911 so please excuse the ignorance.

Rot 911 · 10-03-2002, 07:55 AM

No you are thinking backwards. The fan pushes the air over the engine AND thru the heat heat tubes which connect directly to the heat exchangers. The heat exchangers are passive. They are just sheet metal bent around the exhaust headers creating a cavity that the air from the fan, which is pushed thru the heat tubes, is allowed to pick up heat off the headers and is then pushed forward to the heat vents in the cabin. Blocking off the heat tubes just allows more air to be pushed over the engines. Once blocked off no air is pushed thru the heat exchangers, and of course no heat to the cabin.

Steve W · Steve W's Garage

There's a article on cooling that says that keeping air flow going through the heat exchanger actually keeps the car cooler. So I would think a block off plate would be more appropriate for header equipped motors.

Cooling Boost Article

TurboRuf · 10-03-2002, 09:31 AM

Thanks guys, that cleared things up.

Roland Kunz · 10-03-2002, 12:07 PM

Hello

Those parts where used to simplify race engines ( wich used normaly headers ) plus have some space for those big dual ignition caps

Grüsse

smestas · smestas's Garage

TurboRuf,

Where did you find that photo of the block off plate. I've been looking for one of those.

Thanks in advance!

TurboRuf · 10-03-2002, 02:49 PM

http://www.billetdesign.com/index2.html

Lothar · Lothar's Garage

I am somewhat skeptical of the Cooling Boost article attached to Steve W's post above.

There was a recent thread about disconnecting the air flow into the heat exchangers. Much of the discussion was around performance and the effect of the heat exchangers running hotter as a result of air not being forced through. However, air that does not pass over the cylinders (i.e. out the exchanger ports in the shroud) won't cool anything that wasn't already designed to run hotter than snot anyway. The cylynders are finned to conduct heat from the metal to the air. Since air does not conduct heat as well as say, water, you have to move lots of air over the cylinders to pick up the heat.

I fabricated blockoffs because I had no intention of using heat in my car anyway and my engine compartment is a lote cleaner for it. I am quite happy to know that more air is flowing over the cylinders.

Of course, I will plug the holes through which the hoses passed to keep hot air from under the engine from entering the fan. The object is to have cooler air from the decklid grill.

Any of you experts care to back me? If not please correct me if I'm wrong.