well if you've ever seen pictures, basically the Z tube is a straight tube, it goes from the throttlebody to the air filter box.
The G35's tube has a resonator built into it's tube. This makes for quieter intake operation, mainly by restricting air flow. So physically, it looks bulkier and is not a perfectly round tube like the Z tube is.

<font color=green>-Rambo</font color=green>
G35c 6MT DG/Willow/HyperGround/BorlaExhaust

There are two threads in here that show pictures. Do a search.

Here they are



88441-stock intake2.jpg

Another



88443-stock intake1.jpg

Z Pipe with Stillen



88445-engine.JPG

mbarrad,

I found it difficult to believe that the G stock duct
was actually designed to be this way. What a POS.
The simple 350Z duct is sooo much better. What were they
thinking? I'm so happy with my 350Z duct. Can't wait to get
my Stillen CAI.

2003 Twilight Blue Sedan 5AT, sunroof, Graphite Leather,
splashguards, GG red 8 wire Hypergrounding kit, 350Z intake duct, K&N filter.

Cato,

The design of the stock unit is quite effective in eliminating, or dampening the intake noise and vibration. I don't think your engine will be choked of power with the stock one, but you will gain better feeling of the VQ35 with the Z-Pipe. The stock unit does look ugly though.

RamboRami,

I finially got my own 350Z duct for $40 shipped from a person on the my350z.com.. Anyway, obviously I am curious also to see what's the differences. From what I can really see is that internally, if you put your hand into the duct as I can since my hand is small enough, the duct size appears to be the same, round and smooth inside. The only difference being a single hole about the size of a quarter (1 inches in diameter) that goes down to the resonator. I would image if we can block this hole, the intake duct will be internally identicle to the 350z's. Of course external appearance is different. My conclusion is that this little one inch hole cause enough disruption in the air flow that it reduces the flow to the intake, and thus less oxygen = less power.. having said that, my butt dyno seem to experience a little gain in HP especially when my engine is not too hot as in stop and go traffic.. That damn fan clutch seems to draw a lot of power on a hot day.. I really want to remove it .. but that's a nother story..

Cheers,
-PratG35
Silver 2003.5 G35 Sedan 5AT / Sports and premium package
Stillen CAI / 6 Wire grounding / Battery Quick Disconnect Switch
Eibach Pro Kit
350Z Intake Duct

Stillen dual catback exhaust (when it comes out)
Crawford Performance Plenum (considering)

I believe there are two holes in the stock duct. One connecting
to the lower compartment and one opposite to it connecting
the upper box.

2003 Twilight Blue Sedan 5AT, sunroof, Graphite Leather,
splashguards, GG red 8 wire Hypergrounding kit, 350Z intake duct, K&N filter.

Cato, you are right. The top hole is about 5/8" in diameter and the bottom is more like 1.25"...

You just want to be sure that whatever you plug it with won't come off down the road and wind up in your intake.

G35 6MT/DG/Fully Loaded

I would definitly not think about trying to modify the
stock duct by covering up those two holes to the resonators.
I think you would be asking for trouble if you did.

2003 Twilight Blue Sedan 5AT, sunroof, Graphite Leather,
splashguards, GG red 8 wire Hypergrounding kit, 350Z intake duct, K&N filter.