A post in the 993 section got me thinking.... On air-cooled engines, why hasn't anyone tried to pickup higher pressure air from behind the engine fan? Seems like it would be worth a few HP....

For race cars I guess it would be considered a really crappy supercharger so not worth it. Otherwise, what am I missing ??

 

How about engine cooling? Not a good idea to be losing cfms over the motor when you need it the most.

 

and blowing hot air in may be worse then not blowing any.

 

Wouldn't be any more than would be directed to the heater if it were on (heater circuit scavenges air before it goes over the motor)… But yes definitely giving up some cooling.

Between the fan and heads would be ambient temp, no?

 

Nothing under the hood is close to ambient temp, especially on an air cooled car.

Red-neck supercharger is a gas powered leaf blower. Many examples on YouTube.

 

Ambient may not have been the right word.... but the air behind the fan is at the same temp as rest of the air in the engine bay (where the stock air box draws from)

This has really got me interested.... Next time I'm at the dyno I may be bringing some dryer duct and duct tape just to see what happens.... obviously this is not staying on the car, I'm just curious if it will work and if it does.... how well???

 

Hmm....Kibort, You seek Kibort...electric supercharger he has....

 

Rememeber that you use the heater when it is cold out, and the denser air provides better cooling as well, so the cfm loss then makes no difference.

 

Well the science of it is that to "supercharge" the inlet air you have to provide positive pressure. One bar is actually a LOT of air when you are drawing it off into the intake. The air cooling is doesn't want to see pressure, that would be a wast of hp, it's designed to optimize air flow/volume. Also why newer cars use clutches on the fan belt. As dumb simple as it looks that peice of plastic is designed with the lower baffles to provide even airflow over each cyl. So if you hook a large vacuum to the air shroud you will quickly outstrip the capacity of the fan and reverse the airflow wherever you connect the tube, most likely drawing air away from one side or worse one cylinder. Run at extended period you could inadvertently overheat the cylinder and actually cause damage. I've seen this with a motor that had a rat make a nest on top of the case and starved number 3.

 

 

I did exactly this on my 993 a couple of years ago. I tried to copy the 996 GT3 Cup air intake. I turned the whole plastic air intake manifold 180 degrees, so the throttle body was facing backwards. Then i made a special air box that insulated the air intake from the rest of the engine, with direct air from the (RS) spoiler. I never dynoed this, because you need a certain speed of the car to create overpressure from the spoiler into the air intake. Also, the cooling fan draws a lot of underpressure in the engine compartment, decreasing power, actualle negative (super) charging. By insulating the air intake box from the underpressure in the engine compartment, and at the same time over charge using the downforce pressure from the spoiler, I´m sure that you can gain some "free" HP.