The article from earlier today got me thinking about diffusers. Would a properly designed one improve mpgs?
No, I am not talking about slapping a huge TT style diffuser on your family car but speaking of family cars. I have been seeing tons of new economy cars with small diffusers made into the rear bumper. Purely for looks? Or design efficiency?
Seems to me that a purpose built one could reduce the size of the low pressure dead zone behind just about any car. That would mean better fuel economy right?
Anyone know the actual physics on this?
Velox makes one for the BRZ that has shown to reduce drag and give a mileage increase, but even at highway speeds it was a small boost.
Yup, a real one can make a difference. But most of the ones you see on production cars are trying to look like supercars. They may have a nice side effect of improving rigidity of that particular piece of floppy plastic.
I think the biggest improvement would be from removing the parachute effect from the rear bumper.
If that’s a real thing. It is right?
I’ve thought about this too. I like the idea of maximizing mileage with a minor performance increase.
In reply to Daeldalus :
In theory the rear of the car operates in a slight vacuum pulling high pressure air from the front of the car to the rear and let it escape without all the turbulence would reduce drag and ever so slightly mileage would increase.
Reality would require a smooth under bottom which would cause a problem with escaping heat from the engine.
Heat could be ducted over the top effectively filling the space from the front to the windshield. But that would result in hot air on the windshield. Not a problem in the winter but a serious issue in the summer. Impossible in the event of a convertible.
Cleaning up the bottom of the car is the big part of the diffuser. You can see the effort put into new cars in terms of that- where most cars have the underside of the engine totally closed off.
So, yes, cleaning up the parachute effect is a big deal.
In reply to frenchyd :
If you didn't mind some funky looking vents you could probably let some of the air from the engine bay flow between the smooth bottom and the floorpan and then dump the air somewhere at the back (probably around the exhausts). Or use it for a blown diffuser.
