Crude Belly Pan Idea *pic*

[74_5.0L_Z]

John,

 

I am building a front belly pan that (so far) looks very similar to yours. I have a few questions.

 

Was your pan level with the ground?

 

Was the pan even with the lowest point of the front crossmember?

 

What would you do differently to prevent it from producing lift?

 

 

I do know that the latest vettes redesigned their front pan with holes in front of the tires. In the initial design, the high pressure in front of the tires was causing lift. In the redesign, they put the inlets for the front brake cooling ducts in the pan in front of the tires and killed two birds with one stone: they ducted the brakes from a high pressure area, and relieved the pressure from below the pan (reducing lift).

 

I was thinking of starting with a pan similar to yours and adding vents ala C6 vette.

 

Any opinions or suggestions will be appreciated.

 

Thanks,

 

Dan

[zero]

I think that some venting either in the hood or near the firewall portion of the pan would be helpful in releasing the high pressure (and hot) air from the engine compartment. Hell, if you got the air under the car moving fast enough it might effectively suck the hot high pressure air out of the compartment. Maybe a step as in the firewall forward portion is 1-2 inches lower than the rest of the pan rearward, leaving a gap.

[johnc]

Was your pan level with the ground?

 

Yes and no. One of the more subtle aspects of a splitter is that the front edge (about 3 or 4 inches) needs to actually tilt up a few degrees to pack more air under the car. I didn't do that and relied on tilting the whole part up just a little bit.

 

Was the pan even with the lowest point of the front crossmember?

 

Yes.

 

What would you do differently to prevent it from producing lift?

 

Lower the car significantly. One of the problems with making a splitter work is that it has to be close enough to the ground to actually accelerate the air under the car. If its too high (as in my case) the air doesn't really accelerate, it just packs up. This, because of the slight upward tilt, causes lift. I was told that my splitter needed to be at most 3" off the ground.

 

"If you can get all of the toe of your shoe under it, its too high off the ground." - Charlie Cook, ALMS Tech Chief.

[rudypoochris]

Huh intresting john about the foot under it thing. But isn't a belly pan a plus even if you can get your shoe under it because it w ill still be smoother then the bottom of the chassis?

 

Maybe the belly pan section in front of the firewall can get that slight angle before the x-member then behind the x-member a set of louvers to let out pented up air.

 

Also is vr8ed bellypan/diffuser at a good enough height?

 

 

VR8ED do you have clearence troubles on the street (if you drive on the street)? Thanks

[v8dats]

i was just checking out darius's progress and found a pic of a rear difusser on the car. looks like its coming along pretty good.

check it out!

http://servinitup.com/gallery.php

[rudypoochris]

 

Thats the picture the psot above refers to, and oh my that is manly looking

[johnc]

There's a big difference between reducing underbody drag and generating downforce. Reducing underbody drag helps by requiring less horsepower to move the car through the air. That's most effectively done by reducing the amount of air flowing under the car with a big air dam which will also increase top speed and reduce fuel consumption.

 

Splitters, belly pans, and diffusers are deisgned to work buy actually puting MORE air under car and make the air accelerate. Properly designed splitters, diffusers, and belly pans actually increase the drag on the car, slow the car's top speed, and increase its fuel consumption. That's not a big issue because what we are concerned about is faster corner speeds which lead to faster laps.

 

Darius' diffuser will work better if he puts flat plates on the bottom of the rear LCAs and puts a plate under the diff extending forward.

[rudypoochris]

Okay john you seem very knowledgable this is what im going to propose as the final idea could you please critique it.

 

For the front: Air damn with belly pan connecting to bottom of the air dam angling down until it goes flat at the front x-member from there it will extend back to the firewall and stop. (suggest how to vent engine compartment air, louvers?)

 

Middle: Nothing just floor boards

 

Rear: Under differential pan, Pans sticking to rear control arms, and a diffuser like darius's angled at 7 degrees (is the 7 degree the mark i want?)

 

[johnc]

Air damn with belly pan connecting to bottom of the air dam angling down until it goes flat at the front x-member

 

That will create front end lift and is similar to what I ddi with my splitter. Its got to be flat or, at most, have the first few inches angled up slightly.

 

Back to the basic question: Why are you doing this?

 

1. Drag reduction?

2. Downforce generation?

3. Looks cool?

4. Where will you drive this car the most?

[ZR8ED]

 

Yes my car is a street car.

 

My front belly pan pictured above (before new paint) is level with my front cross member and mounts to the bottom edge of the fibreglass airdam, (not the plastic black strip.)

I have verfied NO lift issues with the front end and I have seen the high side of 140mph.

 

The rear is not fully tested, as I have not had the car above 120mph since. No negative effects have been noticed.

 

My rear diffuser when the car is parked. starts parallel with and the same height as my rear control arms. It then angles up at 7 degrees to the back of the car.

[ZR8ED]

Oh and its ZR8ED. I didn't buy "Z rated" rubber for nothing! hehehe jk

[Guest Z Draci]

Has anybody played with the idea of having a front diffuser?

 

Preferably, you would want the air entering through the front grill and radiator to escape UP through the bonnet and NOT DOWN through the bottom of the car. If aligned properly, vents in a front belly pan would direct air upwards through the engine compartment and up through the bonnet to create some front end downforce. Many mid-engined cars have front diffusers that are aided by fans.

 

Something like this seems extremely difficult to implement on a front engined car. I've never seen anybody make a bonnet for the Z that has vents that would work in this application.

 

Here's an front engined car that tries to do what I'm talking about.

(no, I am not talking about hitting your car repeatedly with an ax)

 

[rudypoochris]

That will create front end lift and is similar to what I ddi with my splitter. Its got to be flat or' date=' at most, have the first few inches angled up slightly.

 

Back to the basic question: Why are you doing this?

 

1. Drag reduction?

2. Downforce generation?

3. Looks cool?

4. Where will you drive this car the most?[/quote']

 

I am not thinking about doing it anytime soon and if i did it i would do it for a minimal gain in traction and stability, mainly for the experience and the furtherment of my knowledge on the subject. Kinda just to do it. Right now it definatley isn't a priority was just thinking about aerodynamics

[Dave88SS]

This would be the perfect article if someone is a subscriber:

http://autospeed.drive.com.au/cms/article.html?&A=2455

 

http://www.datsuns.com/Tech/aerodynamics_and_cooling.htm

 

http://www.gmecca.com/byorc/dtipsaerodynamics.html

[rudypoochris]

OO that first link looks like it will be a good one if we can find someone with a membership :S

[johnc]

Here's a link to pictures of the front splitter/diffuser used on the 2000 Audi A8s.

 

http://www.mulsannescorner.com/audir8nose.htm

 

Notice how shallow the diffuser section is and how a lot of the diffuser is directed to the front wheel wells. The air exiting the diffuser is directed to the belly pan and accelertated again before reaching the rear diffuser.

 

If you look at these sketches of the Dallara LMP car you can see how the diffuser air has nothing to do with radiator cooling.

 

http://www.mulsannescorner.com/dallaralmp10.html

[rudypoochris]

Ya i know in those applications hot air from the engine already has its own ducting and what not. But in the case of the datsun i was worrying that if i put a belly pan all the way under the engine compartment that i might end up restricting airflow and creative too much heat. I guess louvering the belly pan would defeat it's purpose though (by slowing down the underbody air flow)? or would the air be sucked out of the engine compartment aiding in cooling (killing two birds with one stone)?

[rudypoochris]

Just found another picture of the 01-04 r8 and it's front diffuser:

 

http://www.mulsannescorner.com/audir8-01-3.html

 

I see that the front diffuser is angled up towards the back. On a 240z where would the diffuser angle up? Right after the x-member? If it were angled up i think the angle would be too steep making it impossible to route air out of the engine compartment just creating build up. But maybe thats okay?

[Guest Z Draci]

Ya i know in those applications hot air from the engine already has its own ducting and what not. But in the case of the datsun i was worrying that if i put a belly pan all the way under the engine compartment that i might end up restricting airflow and creative too much heat. I guess louvering the belly pan would defeat it's purpose though (by slowing down the underbody air flow)? or would the air be sucked out of the engine compartment aiding in cooling (killing two birds with one stone)?

 

Read my post above. You need vents in the bonnet to route the air UP, NOT DOWN. If you want to decrease front end lift, you need to minimize the airflow below the car and/or streamline it to increase velocity.

 

Just found another picture of the 01-04 r8 and it's front diffuser:

 

http://www.mulsannescorner.com/audir8-01-3.html

 

I see that the front diffuser is angled up towards the back. On a 240z where would the diffuser angle up? Right after the x-member? If it were angled up i think the angle would be too steep making it impossible to route air out of the engine compartment just creating build up. But maybe thats okay?)

 

I would angle the diffuser up right behind the radiator bracket. Then have vents placed on the hood so that the airflow from that diffuser plus that from the radiator can both be routed out through the bonnet.

 

[Chewievette]

I recently obtained a front belly pan from some sort of audi street car, its completely flat with three NACA ducts built into it. I dont know if its any use since its quite a bit beat up but if you want I'll take and post some pics tomorrow. I just got it earlier today and havn't really had a chance to look at it yet.