Rear Diffuser

Chai

New member
RE-Amemiyadiffuser.jpg


I have a question wouldn't air get stuck in the area where the diffuser starts right before the suspension parts and around the area where it outlines the muffler?
 

Roundy

New member
The effect is called Venturi. you might remember it from high school physics or college physics. Venturi Effect states (from wiki)The Venturi effect is an example of Bernoulli's principle, in the case of incompressible fluid flow (in our case, let's just use air flow under the car) through a tube or pipe with a constriction in it. (think the road to the underside of the diffuser) The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to conservation of energy: the gain in kinetic energy is supplied by a drop in pressure or a pressure gradient force. (read: same amount of air flows faster in a smaller channel than through a bigger channel.)

As the diffuser sweeps upward, it creates a lower pressure. think like the top side of a wing. it'll suck upward. well the diffuser is 'upside down' when its installed on the underside of our car, so this sucking motion will in a sense suck the car down toward the ground, thus theoretically giving the car higher downforce. starting the diffuser closest to the rear axle and having it gradually sweep upward to the end of the car is most beneficial. but with all the junk underneath our car, its a little bit harder, so we have to work from rear subframe back...

Oddly enough i think that is backward...

The diffuser in isolation does not generate low pressure, so doesn't generate downforce.

Imagine a very simplistic model, you go from under the car of a certain cross sectional area, then the diffuser is a gradually increasing area.

The air has to LOSE velocity through the diffuser and hence GAIN pressure, creating LIFT

However to gain pressure the air needs to be more dense...so where does that extra air come from?

It comes from IN FRONT of the diffuser, which accelerates the air flow before the diffuser, thus generating a low pressure under the car, and subsequently more downforce.
 

Simba

New member
Chai":2uqm8rub said:
I have a question wouldn't air get stuck in the area where the diffuser starts right before the suspension parts and around the area where it outlines the muffler?

Simply put, yes, which is why that "diffuser" is for show and is functionally useless.

A few things to note about diffuser development on the AT:

- You don't really need it unless the car is extensively modified with higher gearing. It's perfectly stable at ~150 mph, which is about as fast as the majority of cars can go. If you gear it higher, run a higher rev limit or tire setup that allows you to get into the 180 range, it's not a terrible idea to add some downforce on both ends.

- A rear diffuser is entirely useless without a reasonably flat bottom to the car. No diffuser design is going to perform to a reasonable degree unless the area between the front suspension crossmember and diff housing are enclosed to a significant degree.

- Most of the diffuser photos posted have been largely cosmetic. For a functional low-speed diffuser, you need considerably more side spill prevention, which means: Longer strakes.

- Use of a diffuser should be met with a flat front closeout panel, and a fairly aggressive front splitter.

- Both a diffuser and splitter will create more than a few clearance issues on the street if executed in a functional manner (most are not).
 

nbx33

New member
Buy an SRT Charger Diffuser. you shouldnt have much issues installing it with the Bumper off. Just get a dremel and take ur time.
000_2911.jpg


IMG_1503.jpg
 

soarer.jzz30

New member
using a stock bumper to cut up and a 2014 lancer gt rear difffuser panel you could easily make this happen. yes tha penal is essentially useless, but I like simplicity.
 
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