Rear diffuser?

[Phase]

Has anyone on here made a rear diffuser for any of their vehicles?

Any tests done?

Since I’m doing a smooth under tray, I’m going to obviously fabricate a rear diffuser. Seems like it’s all benefits and no downsides

So far my inspiration is making one that’s like on the vision eqxx by Mercedes

[freebeard]

Yes.

Yes.

I haven't done one myself, the VW Beetle body doesn't lend itself.

I have squirreled away some examples:

Start big and whittle down


If the outer fences are curved, you have a start on the rear wheel spats.



That was the closest I got to that car. The fences start at the axle line and flare to the outside face of the tire.

[Phase]

Wonder why they don’t use any strakes or fins. Was going to try and make mine look like that and connect to the rear wheel skirts

[Talos Woten]

Originally Posted by Phase

Wonder why they don’t use any strakes or fins. Was going to try and make mine look like that and connect to the rear wheel skirts

Hey Phase! Strakes are only beneficial when they prevent vortices from forming because of other elements. Otherwise they deflect air that doesn't need to be deflected, i.e. they cause drag. It's easier and better to just have a well shaped smooth surface and let the air determine it's own least energy path. This is especially true if you are making mods upstream, as the optimal strake angles depend on what's happening along the entire length of the car.

If you are putting on rear wheels skirts, it might be worth having a strake on each side, as an extension of the wheel well. Then have the outside skirt and the inside strake meet, making a boat tail for the wheel. That's what all the solar car winners / serious aero cars do. (They even go a step further and make a whole fairing for each wheel.)

[freebeard]

I always like the skegs on the 1961 Oldsmobile:


https://cdn-0.barnfinds.com/wp-conte...-3-630x390.jpg

[Piotrsko]

Im a 57 chevy fan myself.

Has anybody ever run very long tufts to see exactly what is going on back there in the turbulent section?

[Blacktree]

Originally Posted by Phase

Wonder why they don’t use any strakes or fins. Was going to try and make mine look like that and connect to the rear wheel skirts

Like mentioned above, arbitrarily adding strakes can be harmful to aero. They should only be added where they're actually needed. And to add strakes without disrupting airflow, you'll need CFD and/or wind tunnel testing.

[Phase]

Originally Posted by Blacktree

Like mentioned above, arbitrarily adding strakes can be harmful to aero. They should only be added where they're actually needed. And to add strakes without disrupting airflow, you'll need CFD and/or wind tunnel testing.

i figured id just skip the strakes and go for the eqxx style diffuser

[Blacktree]

Sounds like a plan. Also, you need to be mindful of the departure angle. If it's too aggressive, the air stream can detach and create a bunch of turbulence (i.e. drag). If you could do some tuft testing, that should help.

[Phase]

Originally Posted by Blacktree

Sounds like a plan. Also, you need to be mindful of the departure angle. If it's too aggressive, the air stream can detach and create a bunch of turbulence (i.e. drag). If you could do some tuft testing, that should help.

im going to keep it fairly flat and a mild angle like the eqxx also. pretty much just extending the existing underbody shape out another foot or so