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I just purchased a G35 and it has everything but the spoiler. The dealer is adding one for me but I just noticed that the Aero package includes something called "Rear underbody air diffusers". What exactly are they and if I order a spoiler do they usually add them as well? This is probably a dumb question but I didn't see anything explaining what they were on the Infinity site.

Rob

2003 G35C | 5AT | Diamond Graphite | Graphite Leather | Nav | Premium | Performance
 

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they are for aerodynamic purposes and add to the "zero lift" and .28 drag coefficient of the car... do a search on it, you should find more than enough info

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Discussion Starter #3
ok thanks, will do

Rob

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This helps at high speeds, really only above 100mph plus. It is great it is a factory option.

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The diffussors cost about $80 (parts only) at my dealer, and they installed in 0.5 hours. Don't have total cost, as was a freebie for buying the car a few weeks earlier than I wanted to. I like cruising at 85mph on average, and wanted the lower coef. of drag, hoping for an every so slight improvement in gas milage, and wanted a little extra high speed handling.
 

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Discussion Starter #6
Wow only $80? Thats great, I might get it for the heck of it if I can get that price. After seeing the price the dealer wanted for the spoiler ($550 I think) I figured they would try to gouge me on the diffuser as well. Might have to make a call tomorrow. Thanks!

Rob

2003 G35C | 5AT | Diamond Graphite | Graphite Leather | Nav | Premium | Performance
 

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wow i didnt relize it was only 80 dollars for the parts.. I personally do not like the spoiler on the sedan thats why i did not buy the aero package, but i deft. would buy the air diffusers if they are that cheap..

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Rlipps - you are absolutely correct - but I think that effect is for the both the spoiler and the underbody air diffusers. You're always good on that technical info.[bowdown]

Why would anyone want the underbody air diffusers and not the spoiler. The underbody air diffusers are purely a functional part; they serve no cosmetic function (unless you are looking under the car).

If you 'need' the underbody air diffusers for performance reasons - the spoiler will be more advantageous. The underbody air diffusers are not going to provide a notice a difference at 85 miles per hour and probably not even at 100.

And if you want better handling slap on a set of wider wheels or lower your suspension.

Although $80 bucks is cheap and you probably cannot compare that to the cost of new wheels or suspension, it still a waste of $$ if it provides no benefit.

But, to each their own, Just my $.02 - what you think - Ken, Semi.

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<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by jarrettblue

Rlipps - you are absolutely correct - but I think that effect is for the both the spoiler and the underbody air diffusers. You're always good on that technical info.[bowdown]<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Thank you.[:I]
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
Why would anyone want the underbody air diffusers and not the spoiler. The underbody air diffusers are purely a functional part; they serve no cosmetic function (unless you are looking under the car). <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
You are correct about the cosmetic part. But...
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
If you 'need' the underbody air diffusers for performance reasons - the spoiler will be more advantageous. The underbody air diffusers are not going to provide a notice a difference at 85 miles per hour and probably not even at 100.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I think that for $80 it would be worth it to buy them without the spoiler. Some people don't necessarily care for the stock spoiler; however; the Rear underbody air diffusers actually will help keep the back end down some. It will not add that much down force, you are correct, but it will break up the turbulent air underneath your car that tends to add "lift" to the rear end. So basically, you should see a considerable difference in rear end "lift." With the spoiler, you would feel increased down force. Hope that explains it to you a little better.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
And if you want better handling slap on a set of wider wheels or lower your suspension.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
This is a very good point. But it is still good to consider the turbulent air that will cause lift.
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">
Although $80 bucks is cheap and you probably cannot compare that to the cost of new wheels or suspension, it still a waste of $$ if it provides no benefit.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I would leave that decision up to the individual, but you did have some very good points and theories.
 

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Remember that the factory listed coefficient of drag is 0.27 stock, and 0.26 with the diffussors. I agree with the theory that they break up wind turbulance. I agree that they would only help at high speeds, but would think the benefit is linear and in-line with speed increases (i.e. it doesn't just help at only above a particular MPH). Dealer also said you might see a very small increase in fuel economy. I have some faith in this info, as they paid for the parts and labor in the car price (they didn't just say this to sell more parts after the car purchase).
 

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as a side note the most recent Nissan Skyline V Spec(R34) had 2 Carbon Fiber under body plates that cover the entire underside of the car for aerodynamics. Now that is reducinf turbulent air if you asked me!

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Drag makes a huge difference in a car speed, that is the most limiting factor.

On a Crown Vic patrol car, turning the A pillar spot light around to face forward will slow the car down. I know, I've been there and it makes a difference.

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rear diffuser sedan picture

Does anyone have pictures of the stock rear diffusers for the sedan. I see it up at everythingg35 but the picture does me no good.

As far as I have seen my car has two small black flaps in front of the tires for air flow but nothing else notable.

It does, however, have the front black diffuser cover (I thought this was standard?)

Thanks.

I realize this is old old thread, sorry.
 

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The diffusers are the two black pieces under the car at the rear wheels. The plastic pieces under the engine are standard.
 

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two small black pieces

The diffusers are the two black pieces under the car at the rear wheels. The plastic pieces under the engine are standard.
Hey, thanks for the reply. I have two very small thin black pieces in front of my rear tires put up by 2 screws (I think). These are 100+ dollars?
 

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The diffusers are not in front of the rear tires. They are inboard toward the middle of the car and are held in place by 2 nuts and a bolt or the other way around. I forget.
 

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exhaust

Ah thanks for the clarification. I have seen it on the oem parts diagram but can't make out what it really is. Would there be any clearance issues with aftermarket exhaust (thinking stillen dual exhaust for the 05/06 sedan)?

The diffusers are not in front of the rear tires. They are inboard toward the middle of the car and are held in place by 2 nuts and a bolt or the other way around. I forget.
 

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There shouldn't be any clearance issues. I would think the exhaust was designed with those in mind.
 

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center mud guard

The diffusers are not in front of the rear tires. They are inboard toward the middle of the car and are held in place by 2 nuts and a bolt or the other way around. I forget.
Finally figured out what the pieces in front of the tire are. Center mud guards.

I called a couple places that had an idea of what I was talking about (some had none) but no clue exactly.

If you have taken it to dealer or broken your own :-/ here are replacements:

Infiniti Parts USA - Your #1 Source for Factory Infiniti Parts & Accessories

btw, just received the rear diffusers for the sedan, hope to put them on soon. seems like a relatively high cost for two pieces of plastic (~100).
 
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