Footwell Blower Question

hoss4659 · 05-09-2015, 06:19 AM

What is the CFM rating for the footwell blowers?

wwest · wwest's Garage

The CFM of the cabin heat blower in the engine compartment with the inlet open to atmosphere is ~115 CFM. So the likely CFM of the footwell blowers is 50-60 CFM each, MAX.

hoss4659 · 06-12-2015, 05:45 AM

Thanks West. I am without the cabin heat blower in order to install the SSI header/heat exchangers on a 3.2 car. Was wondering about using marine axial bilge blowers (with 100+ cfm) to insure a good defrost function.

wwest · wwest's Garage

Quote:

Originally Posted by hoss4659

Thanks West. I am without the cabin heat blower in order to install the SSI header/heat exchangers on a 3.2 car. Was wondering about using marine axial bilge blowers (with 100+ cfm) to insure a good defrost function.

There is a good design, safety reason why the footwell blowers are interlocked against operation absent the engine compartment cabin heat blower being simultaneously operational.

Footwell blowers alone would create a vacuum in the heat flow duct possibly drawing in exhaust gasses.

Jack Stands · Jack Stands's Garage

If you convert to the SSIs, they can receive air flow from the engine fan like in the early cars. I'd imagine that the footwell blowers would still be safe as long as the engine is running.

However, I always keep a carbon monoxide detector in my old Porsches as it is odorless and can easily kill you. Best of all, leave the top off if you can and enjoy the drive!

wwest · wwest's Garage

Quote:

Originally Posted by Jack Stands

If you convert to the SSIs, they can receive air flow from the engine fan like in the early cars. I'd imagine that the footwell blowers would still be safe as long as the engine is running.(***)

However, I always keep a carbon monoxide detector in my old Porsches as it is odorless and can easily kill you. Best of all, leave the top off if you can and enjoy the drive!

*** Only as long as the MINOR portion of the engine fan airflow diverted to the cabin is equal to, or greater than, the footwell fans "pull".

3000 RPM?

Actually I don't have any idea.

Tremelune · 06-12-2015, 08:20 AM

If there is a leak in the exchangers, I would expect the exhaust pressure to be higher than the engine fan pressure, such that it will get into the cabin regardless of how it is being moved forward.

More details on your setup will help. Why can't you attach the fan(s) in the engine with the SSIs?

Why not just install stock footwell blowers? Marine blowers will do about the same thing if they can withstand the heat, but you'll still have to cobble together the weird hose ducting up front.