So everyone knows that the stock muffler has a little diffuser on it to help direct flow under the Z.

So when you change to a custom exhaust, especially the true duals, you lose this diffuser. (The borla comes close).

Does anyone make anything to fit in this new open space?? Some sort of "skid plate" looking piece of plastic to perhaps help the flow of air under the car?

I swapped my exhaust and I was looking at how the bumper looks like a giant air anchor now without the stock muffler there.

It would be great if someone started making some sort of custom piece to fit in there....slightly different for different exhausts. I.E. Greddy EVO2 which I'm swapping for my injen ses.

Thoughts???

 

If you haven't already bought the Injen, you might get the APS exhaust which retains that underbody air diffuser. They're the only ones I know of that do that.

 

the drag that is created by not running that diffuser is not much at all to slow you down on the top end. it's there, but you have to be going very fast, i the triple digits to really notice anything....

 

Lets say I'm in triple digits daily...any solution?



Seriously tho, even a sloped plate might look pretty cool. As it is, I could fit my tool box and Jimmy Hoffa up there and still have room left over.

 

There are the track model rear diffusers that will close up the rear bumper area and help out a litlle, but they are not exactly what you are talking about.

 

Are you saying the Borla True Dual forces you to lose this diffuser? because I currently have a Borla and the diffuser is still there..

--mike

 

odds are the affect of the diffuse really won't be noticed unless at extremely high speeds

 

How do you have the diffuser on? We are talking about that flat plastic piece that is bolted onto the oem muffler. If it is on your car please tell me how, I would love to do it myself.

 

Do you have a pic of what you are talking about?

 

The stock muffler has a piece of plastic tacked onto the front edge of it to help with aerodynamics.

The Borla is similiar in shape to the stock muffler, so you get some flow with that.

I'm just wondering if someone would come up with a plate that could go from the differential to the rear bumper to close up that huge hole.

Once you remove the stock exhaust and go to a twin muffler design, you end up with a big empty space where the old muffler was, and the bumper just hangs down. I just wanted to smooth things out mainly for aesthetics but also for some function. A lot of cars use this space for the gas tank.

I guess I'll just try and fab something myself.

 

I'm almost positive I've seen pics where the 350evo guys cut their rear bumper on early versions of their race car to remove the "parachute" effect that results from removing the stock exhaust and running a true dual (Injen).

I think more recently they started stuffing an oil cooler in the gap. Not sure if they're still running the cut bumper.
--
Jeff

 

yes I need a pic because the piece I'm talking about is the "V" shaped metal thing under the exhaust which I assume is some sort of diffuser..

--mike

 

I am pretty sure the defuser on my back box was metal when I took it off. I'll have to look again.

My next mod will be a plate to go between the two Injen mufflers I just installed last night. I have been thinking about this for a while. I want it to look as OEM as possible but not block the rear view of the mufflers. I'll post what I come up with, but give me a few weeks, I am going out of town soon and wont have time before then to mess with it.

Chris

 

You're on the same page as me. Let me know how it turns out and what material you end up using. I'll be doing the same thing for my greddy evo2

 

I was thinking that that stock diffuser is actually creating some very much needed downforce on the rear of the car. I dont have one anymore, with the Greddy evo2 exhuast.

I would be VERY interested in a bolt on rear diffusser, ala Viper, that could help generate some downforce in the rear, without using a wing.

 

Might want to see if Altered Atmosphere can come up with something.

 

i have thought about that big space there too cause i have an injen. I might try and make something outta sheet metal and see what it looks like and if it works try and get some aluminum sheets and make one. my dad has an air conditioning business and i know how to make some stuff so i might mess around with it one day

 

well, i think they used that diffusor because the OEM muffler is a single piece, which would block the air and actually cause more of a drag if they did not put the diffusor there. with a dual like the injen the space where the OEM muffler use to sit is opened up, IMO allowing more air to escape out the rear.

 

Without the diffuser, the rear bumper would create drag/turbulence for any airflow that got ABOVE the rear muffler, and trapped under the rear bumper......changing the underbody ground effects.

I had similar concerns when I saw the HKS Dual Exhaust configuration....good discussion.

 

it is not very clear from this image

but with the injen exhaust, I think there is definitely some areodynamic problems

the rear bumpers litteraly becomes a parachute: