After spending a day under my Z installing an aftermarket cat back I had noticed that the underbody is quite flat to reduce drag. I had also noticed how well the stock muffler tucked in by the bumper. One thing that had me wondering was the wedge shaped piece bolted to the bumper, I had come to several conclusions.
1 Heat dissipation
2 Guard to prevent leaves, plastic bags or whatever getting trapped between muffler and underbody and possibly causing a fire.
3 air flow, reduce drag

I am leaning more towards 2,3

Now this got me thinking, the Nismo exhaust does not provide mounting for this piece from the pictures I have seen, so could it really be that important?

For us single and twin canister guys we now have quite the pocket left open from where the stock muffler used to sit. Anyone think that this pocket causes allot of turbulence and traps allot of air? Anyone thought of making rear underbody panel or diffuser to smooth the rear out. I am not talking about those fake diffusers that are mostly show pieces.

Just my thoughts.

 

You have been doing a lot of thinking.

The underside of the 350Z is a compromise: drag, performance, safety and cost. A aftermarket cat-back exhaust is a performance mod. Will it, like all other performance mods, compromise drag and safety? Maybe.

 

this is defanitely a good question....

 

I don't know about all that. All I know is after I installed my Nismo exhaust I measured a 2.6 MPG increase in fuel economy over the stock exhaust. If it creates more drag, that is overcome by it weighing less and being more open I guess.

 

Without the diffuser there is a little more drag and a little more rear lift.

As far as I know the only aftermarket system that keeps the rear diffuser is the APS 2.5 system.

At some point when I get some time I plan to remedy my Nismo situation on my car with some well placed fiberglass fabrication but it's still a few projects away.

Chris

 

Further good news for the performance enthusiast is that the APS High Output Exhaust has provision for the stock wind deflector on the leading side of the muffler assembly. The stock wind deflector is an aerodynamic aid that slices through the turbulent under body air flow and channels air under the muffler.

So according to APS I was right, nice system, 4 bolt flanges are a plus. I am surprised that they did not bother with an H or X pipe.

I am thinking of making a pannel similar to this, probably starting from the rear diff all the way to the bumper.

 

A while back I remember someone was gauging some intrest in a carbon fiber diffusor similiar to the one that you just pasted. If I am not mistaken they took one off a Ferrari and photochopped it onto the Z. Looked really good and like it would work really well also!

 

More back pressure,More heat (stock has more back pressure) Mainly though --Nissan coverin their ***. If ur building and selling 100s of 1000s of cars u have to go by the rule ---If it mite happen it will happen