75 Rear diffuser project - Page 3

elogiov6 · #31 (**permalink**) 05-10-2008, 02:08 AM

Oh no mats, I´m building my own trackdaycar but it won´t be so extreme as this one. This rac races in England. Look on ARCA - alfaracer.com - Organisers of the UK Alfa Romeo Motor Racing Championship. The place for Alfa Romeo Motorsport News for the driver.

**Craig** · #32 (**permalink**) 05-14-2008, 12:04 AM

Ok, let's try to kick a little life back in this thread.

You could try a full scale wind tunnel (so to speak).

Attach tufts of wool along one side (drivers) and the rear of your car and on a nice wind less day drive along the freeway with the passenger in another car taking pictures (or a video with the driver calling speeds).

Most of the tufts of wool would have to be attached to wire projecting below the bodywork.

So say along the side skirt you would need maybe four pairs between the wheels, evenly spaced, with one tuft say half an inch below the skirt and one halfway between it and the road. Then one pair behind the rear wheel and five sets of three across the back.

The wool should be of a nice visible colour and thick enough to be seen but not stiff.

Any takers?

BigSwede · #33 (**permalink**) 05-14-2008, 01:40 AM

That is a good idea, but it's difficult to make a video of it without disturbing the vehicle when it's got 70mm of ground clearance. Also, it's not always easy to interpret the tufts motion and what it means... :/

**Craig** · #34 (**permalink**) 05-14-2008, 02:32 AM

True, the camera vehicle can't get too close but it could be behind to the side.

As for whether it would work, it's 'suck it and see'.

scott.venables · #35 (**permalink**) 05-14-2008, 05:51 AM

This method is described in the Fred Puhn book "How to make your car handle" They just taped the tufts on with cello tape. It only really shows flow direction doesn't it? and maybe speed?

Scott

BigSwede · #36 (**permalink**) 05-14-2008, 11:35 AM

Its a way to visualize flow and check for detached flow.

jazig.k · #37 (**permalink**) 05-14-2008, 07:26 PM

its worth doing.
at least youll know a little more about your car and how the air moves around it, where the turbulance is etc.
probably worth doing for the rear bar where the air will be exiting so you can make some kind of comparison for when the diffuser is on the car. id think the air exits quite roughly at the moment, so youd just wanna 'calm the wool down' with the diffuser on. would be a starting point for a home test.