Functional Rear Diffuser

SPOHN

I have started making a custom one myself. The S2K guys have a lot of neat stuff where I have been getting my ideas. Another week my final drawing will be complete that will work for my car and Amuse rear.

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Masterbeatty

Nice. once it stops raining i am going to jack up the car and make a template. Look into mounting points and where/ if needed some heat shielding near the muffler and midpipe.

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2011 MB 6MT
Masterbeatty journal

ResIpsa

The angle of my diffuser follows the natural slope of the rear bumper. According to my cheap a$$ Harbor Freight angle gauge it is somewhere between 8 and 10 degree slope. My research suggests that 9 degrees is a theoretical limit for a diffuser. However, the addition of strakes should prevent my diffuser from stalling.

Yes. I run a fairly aggressive front splitter. I have not fabricated a flat bottom yet.

I have been working on this diffuser for nearly 2 years. Here is what the initial design looked like. My initial testing (as described below) showed that it was very effective but I was always concerned about the huge vortexes I was creating at the diffuser turn downs behind the wheels.




After some more research, an article in GrassRoots Motorsports, and an article in Race Car Engineering I modified the diffuser to its current form. I realized that a diffuser should be as wide as possible between the inside of the tires. As you can see, my original design had the turbulence from the rear tires impacting my airflow. That is when I created the second set of strakes to act as the outside walls of the diffuser.

My preliminary testing shows that my design is fairly effective. I also was reaching speeds on the front stretch of Summit Point (determined by how fast you take turn 9) that I had never reached before. However, this could be purely coincidental or related to other factors.

One trick to test the functionality of a rear diffuser is to wait for a day with heavy rain and have a friend drive your car and you follow in another vehicle. As you follow, take a look at other cars on the road and notice how rain is being dispersed behind them (better yet, have another 370Z without a diffuser drive along side of the 370Z with a diffuser). You will see most cars on the road have sprays emitting from the front and rear wheel wells (not very efficient). Also take a look at how rain flows from the rear of the cars. If you get lucky and spy an Evo or Lotus with a functional diffuser the rooster tail of spray will be noticeable.

When I tested my first design of my diffuser (with front splitter) I was quite pleased. I drove behind my 370Z and noticed that there was absolutely no water spraying from the front or rear wheel wells. Also, it was kicking up such a rooster tail that driving behind was almost blinding. My only concern was the large water vortexes emanating from the points where my diffuser turned down. My research suggested that vortexes may not be beneficial.

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The Reed Law Firm; Michael Fasano VA Attorney and Counselor at Law: A Virginia Traffic, Criminal, and Family Lawyer.https://reedlawva.com/

ResIpsa

Research and experience has shown me that the majority of the force acting on the diffuser is at the diffuser throat.

The bolts that hold the little piece of bodywork (splash guard?) behind the tires are perfectly located to anchor the diffuser. In fact, the first thing I did was take a long piece of aluminum carpet molding, drill two holes in it, and mount it under the car. This formed the back bone.

The front of my diffuser is anchored with aprox 8 trim screws directly into the edge of the bumper.

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The Reed Law Firm; Michael Fasano VA Attorney and Counselor at Law: A Virginia Traffic, Criminal, and Family Lawyer.https://reedlawva.com/

SPOHN

First don't be talking about Harbor Freight. Love that place.

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kenchan

i was wondering when you would chime in, SPOHN!

ResIpsa

I apologize. You are correct.

Where else can you get a 4 x 8 moving blanket and a 6 piece screwdriver set for $3.98?

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The Reed Law Firm; Michael Fasano VA Attorney and Counselor at Law: A Virginia Traffic, Criminal, and Family Lawyer.https://reedlawva.com/

Masterbeatty

Damn that's dollar store status right there. What ever works right. Too bad there isn't one near me.

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2011 MB 6MT
Masterbeatty journal

SPOHN

They have some cheap things I wouldn't touch like drill bits. But most of the things are damn good.

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