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2G Rear Diffuser Design

Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
I still haven't heard anything back from the tester. I've been busy enough with my car build I haven't put any effort into making more or finding other testers. I have made contact with a carbon fiber company that can CNC cut the main panel for me to give it much better weight and strength properties than my fiberglass layup.

That would cut down a huge amount on production times, but as it stands I don't have the time to offer this publically yet. I'll will update this thread, or the tester hopefully, if he ever is able to. He's pretty busy and his new business seems to be doing well.
 

MoarAWD

Proven Member
64
11
May 24, 2016
South Bend, Indiana
Sorry to dig up an old thread, and I'm not sure if anyone has any interest in this, or what happened to it, but....

I am an Aerospace Engineer for a university, and I have access to wind tunnels and CFD if anyone was still interested in testing some functional aerodynamics. I don't have anything to test a full-size car, but I can easily test scale models at similar Reynolds numbers, and get non-dimensional pressure, lift, and drag coefficients.
 

Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
I never heard back from the original tester.

I still have the molds and about 20 sets of strakes sitting in the garage... Honestly if it were to be picked up again, I would probably just CNC cut a flat piece of carbon fiber in the shape of the diffuser without the strake grooves, since my original fiberglass was pretty heavy. The subframe mount was great way to keep air from getting trapped, but that is a piece I would need to manufacture myself and it would be what keeps production slow; it would take me a week to make just one.

But without the ability to test it myself I could never be sure it fits like it was originally designed to. I just got unmotivated I suppose.
 

jakk220

Proven Member
1,296
288
Nov 13, 2010
Akron, Ohio
If you make one that makes it so the trunk does not have to be modified, you have my money. My rear bumper is stock with a BR exhaust, but I could take that off for fitment testing purposes if you need someone for testing. I have been dying for someone to make a good street-car friendly diffuser that still has come functionality.
 

Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
It's been a few years, but I think it just took a little banging with a hammer on the spare tire sheet metal to install the diffuser. The exhaust rerouting is what would be the tricky part for a home garage DIY install; that will be the hard part of installation, not the diffuser.

Please PM me if you are seriously interested in this (knowing this is not going to be cheap or free).

If there is more then just a few people, I will put some honest effort into picking this up this weekend. I would like to at least get the set of strakes out of my garage, so maybe I'll start with that as a goal.
 

Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
Several year graveyard super BUMP!

Anyone interested in this still? I have 9 sets of strakes to make diffusers.

If you can cut out a flat piece of fiberglass/carbon fiber/sheet metal to the shape of the underside of the rear bumper, these steel strakes are pre-bent and would allow you to not need any fancy tools to have a rear diffuser with strakes for your car.

I think the cheapest way to get this out to folks is to offer the strakes alone, so going that route for now. PM me. Looking to gauge interest.

If you would prefer carbon pre cut out for you and you don't mind the high shipping and price of carbon sheets, I own a CNC router now and it COULD be arranged, so if that would be your preference, drop a comment down below. That could be a future thing.

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Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
I had someone purchase a set of strakes from me the other day and said he would be providing installation images soon. If anyone else is interested in testing these, let me know.
 

Atuca

Supporting Member
1,129
259
Jan 6, 2007
Central Valley, California
I am down to 6 sets of strakes, so folks are picking these up but no one has bumped this thread yet with install photos. If you got some DIY time in you, I'd really appreciate some photos for others asking me for installed photos :)
 

danhans

Probationary Member
1
0
May 26, 2021
ny, Alabama
Thought about posting something like this last night. A manometer is pretty basic once you've used one but I don't think a lot of people do.

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Pressure measurement - Wikipedia, the free encyclopedia

Basically do what he said above, filling a piece of clear tubing with a little water and bending it into a U shape along a ruler (metric is best due to the small increments and easier math). Then leave one end of the tube open to the cabin air and the other end goes to the point where you want to measure the pressure. The fluid level changes based on the pressure differential between each end of the hose. Then do the math below:

Pressure = H*g*rho

where H is the difference in height between the fluid columns, g is the gravitational constant (9.8 m/s^2 in metric or 32.2 ft/s^2 in English) and rho is the density of water, which does change slightly with temperature and is shown in slugs (English unit for density) and kg/m^3 in this link.

You do have to be careful with your units. Your column measurement will likely be in 1/16 inches or mm but the rest of the stuff is all in feet or meters. Now assuming your water is pretty cold...

If you measure in mm:

Pressure (in Pascals) = H * 9.8

If you measure in sixteenths of an inch:

Pressure (in Lbs/ft^2) = H * 0.3254

It should be noted that it doesn't matter what diameter tube you use for this, though if you go to very narrow tubing capillary action will cause trouble. You should be fine with 1/8" tubing and if you add a drop or two of food dye to the water it will make it easier to see without changing the calculations enough to matter for something like this. Also, you do need to hold the tubing and ruler vertical during the test or it won't work. Just the section where the ruler is, the rest can coil around however you want. You should also avoid having water anywhere in the tube other than in the little U section.
Really nice post, I just wanted to add that if you are more interested in gensity of water you can look here: density of water converter
 
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