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So I am trying to come up with a rear diffuser design that would work on my car. The bottom of the car is super flat and so is the rear suspension box so there isn't a great way to add a kick up or angle to the diffuser. Any thoughts?

This is the only reasonable thing i could come up with but it extends 4.5" from the rear of the car.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

Is something that abrupt more likely to be a 'separator' rather than a 'diffuser' and fail to serve the intended purpose?

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

That looks typical of what I have seen on autocross cars. I am thinking about having mine continue to go up to meet the back of the car on a smooth plane almost like a rounded edge.
If you look at yours it seems to come to be inline with the rear fenders so you could tie them all together for a cleaner look.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

It is actually pretty far below my fender... wish my CFD software was working ; (

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

I have a degree in aerodynamics along with all the programs to design and see just what things do on cars . a big part of my business is designing and building aero packages for race cars .
I don't have much time right now to get to into it .
but at best one out of 1000 home build diffuser just doesn't work .
things like rolled trailing edges are more for just looks as once the angle gets to about 12 to 14 degrees the air is no longer traveling along the surface to the diffuser .
most times a straight trailing edge is best .

962porsche Care to post a photo or a good one? To point us in the right direction.

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

Yeah but all cars (models) are completely differet. It depends largely on the air flow off the back of the car and under. Yes a straight diffuser would be best for a generic application but there could be huge improvements with a slight angle change depending on the vehical.

Flow seperation is usually an issue at high angles but generally you would need at least a 10deg angle to make a diffuser effective.

I will get my cfd working and try to simulate it on my car and a locost.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

The under-body on my car is completely flat from the front to the back of the cabin which is open from there. I think that I should be able to create a good amount of down-force with a correctly shaped diffuser. I think the EMod limit is 25".

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2015 & 2016 EMod Florida State Autocross Champion
2013 & 2014 DSP Florida State Autocross Champion

Scrap Metal Build Log viewtopic.php?f=35&t=14558

me posting 100's of photos of different diffuser designs is pointless .
they have to be designed for the car it's going on . even two of the same cars may need a little different design as things like ride height come into play .
I did scam the photo that is posted and all it does is add drag .
I could get into why this is but it would be like writing a book to explain why and I suck at writing and hate writing .
you will not be able to design a proper aero package for the car on any design program unless it's one that is for designing aero . they just don't work I have tried this year ago when I 1st got into the business .
the things like laminar flow they just don't show you they simply don't have enough detail to them .
it was not until I spent lots and lots of money for a top quality program to 3D scam the hole car into a program to see just what it's doing when I found out just how bad other sim's were .

I was planning on using the solidworks flow simulation software. It is suppose to be really good

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

It looks like you could remove the rearmost bottom transverse tube. Then you would have a triangular exit for the diffuser. Not ideal but I think you should look at it as a 3 dimensional problem.

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Marcus Barrow - Car9 an open design community supported sports car for home builders!
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you mean the main rear suspension box tube! No way. Not worth it for aero.

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My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.

that system is ok but it does have it's limitations

when I ran a quick sim on it that was the problem .
it's just all flat to a sharp roll so it's diffusing any of the air in fact it's adding more surface area for the air to grab hold of .
air acts as a fluid so as the air is exiting off the rear it has surface area to run up on .
it's better with it just cut straight across air does lap over the edge some but there is nothing for it to grab hold of .
another option is to extend the diffuser out the back of the car but the down side to that is you would have to extend it but at the least 15" and that's just guessing as I don't really know the measurements of the under side of the car I'm just guessing at it from tire size .
it would also have to go much wider right up to the insides of the tires .
another problem with diffusers that stick out way past the rear of the car is departure angles .
you will be dragging that thing on the ground all the time . it's ok for track only use but forget about using it on the streets .

with the drive line in the car I would like to see the air flow over and around it . this will have a very big effect on the efficiency and design of the diffuser .

So no diffuser at all is the better choice here unless i want to extend it out way past the car?

_________________
My build: http://www.locostusa.com/forums/viewtop ... 18&t=13096


You can build the most awesome thing in the world but at some point, an 80yr old man in a crx is probably going kick your butt on the track... don't ask me how I know.