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Diffusers and belly pans


rustrocket

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After reading a recent post on the extremely limited top speed of the Z car, (i have a 260) I did a search on diffusers and belly pans, but i was unable to find anything recent, or with working pictures. Can you guys share some of your experiences with making or using front/rear air diffusers and belly pans? Any pictures would be extremely helpful. Thanks

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I considered adding a belly pan, but then realized how difficult it would be to make. The bottom on a Z isn't that flat, with all the fuel & hydraulic lines, the suspension& driceline, and other frame pieces sticking out, would make fabrication difficult and the resulting bellypan would not be as 'smooth' as it should be.

 

The next best thing would be to add a few deflectors underneath.

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There is a fair amount on this topic. One of them I started where I've been working on a rear diffuser.

 

Search "belly pan" or "rear diffuser"

 

Some of the topics have not been updated for a while. I will add more to it as my car has come out to play for the summer again, and work will resume where i left off.

 

normal_bellypan.JPG

 

This is my front belly pan.

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Do you mean the black strip?

Its about 4 inches... about the same as lawn edging...as a matter of fact, exactly the same as lawn edging found a home depot!

 

hehe Its a very old trick of mine. I don't care if it scrapes the ground. I get the air dam effect with out the worries of damaging my expensive air dam!.

 

Nice and low..

 

When damged..replace!

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Well I only have a couple of high speed runs under my belt since I had that pan installed.

 

I've seen the high side of 140mph with the car feeling solid. Heck I even did something very stupid and gave the dude I was racing a thumbs up out the window at 135mph. I didn't feel like I needed both hands on the wheel to keep it straight.

 

Stupidity aside, the car has felt very stable at speed. I have driven my car when it was flat stock, and I know the feeling most Z owners describe at 90mph+

The car doesn't wander at speed either (road surfaces not withstanding) even when passing trucks on windy days.

 

I have no numbers to tell ya though.. only seat of the pants. (BTW the belly pan was my last mod... except for last year.) so I know the effects of the rest of the suspension on the handling.

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  • 5 weeks later...

the 76 280Z 2+2 Andy Flagg races at Bonneville has seen 173+mph, and was running a full belly pan.

The front radiator grille was completely blocked off, so the comparison isn't really apples to apples, but without the front blocked and the belly pan in place the same car is around 10mph slower.

And that's a considerable change, seeing as the engine looses HP by running the exhaust full out the back of the vehicle and not in the shortie dumps that it was dyno tuend with!

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  • 1 month later...
Guest z1 performance

we are about to do one similar to the R34 style (front and rear) on my 280ZX...the car sees the better part of 160 now, but it gets quite twitchy

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Guest BigWhyteDude

thats kind of the idea. Except your trying to make an upside down wing. So you get down force instead of lift. At least that how i see it... then again i did ride the short bus. :ugg:

 

Andrew

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The problem with stock Z's is that the air kinda "piles" up under the body while smoothly going over the top, creating a high pressure area underneath and eventually lifting the front off the ground if you have the nads to keep pushing it.

 

The belly pan helps the air smoothly exit the rear of the car and keeps the pressure from building up. There is still a pressure differential between the top and bottom of the car, it just requires much higher speeds to achieve lift. (or lift-off, if you prefer).

 

I still think the idea that the high-end ferraris use is the best. They use a full front-to-back belly pan with an hourglass shaped depression that tightens near the center, creating a venturi effect under the car, effectively "sucking" it down to the road. Very slick engineering.

 

Bill

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actually, the air hits the FIREWALL, and piles up under the HOOD, lifting the front end.

This is why both the G-Nose and the S130 have a below-the-bumper-line air inlet for the radiator, and most later vehicles are total bottom-breathers!

 

The lift on the back end is aerodynamic from the shape of the decklid.

But the lift up front is from that open maw ramming air against the firewall, where it acts similar to a diffuser turning velocity into pressure. The air speeding under the vehicle acts similar to an "air door" preventing easy exit, adding to the diffuser action of the firewall.

By adding a Factory-Style Z432R bellypan, along with the G-Nose, the air admitted through the raidator is at the bare minimum to cool the vehicle (when I partially obstructed my G-Nose inlet, the car ran 15 degrees hotter, removed some of the offending items---teeth if you must know--the temperature went back down. Airflow therough the G-Nose inlet is only what it needs to be, and nothing more!) and this allows the FRP bellypan used on those models to smooth the airflow under the vehicle to almost the rear of the tranmission....where it acts like and ejector due to it's relatively highspeed, "sucking" air out of the tunnel and evacuating the engine bay of it's diffused airload.

 

Clever, those Japanese :D

 

One of the popular (though styling wise probably would not catch on here in the USA) is the addition of vents through the front wings relieving the pressure along the sides of the body. Holes are cut along the inner fenderwell to allow the pressure to relieve to the inner fender well, or through a duct to the outer fender surface. This is very effective, and if you look at the interiors of may high speed performance cars, you will see louvres near the rear of the engine bay venting to the wheel wells. Most hink it's for keeping underhood heat down---whit IS a function, but that can be accomplished through a simple 4" louvre. But having one square foot of louvres on each inner fender near the firewall (wichi is about the equivalent area of the radiator opening....) there is more to it than simply "heat evacuation". Remember, heat radiates UP... Not sideways. Overheating at speed is rarely a concern, it's in stop and go that underhood temperatures soar. So maybe a bit of "misdirection" is involved in the stated purpose of the vents. But then again, an automobile company would NEVER obscure a speed secret from the general public, would they? :lol:

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