General Chat
Q:
Hi folks,
After looking at that "Elise" post I noticed how nicely the bottom of the car was finished. Other than considerations for the exhaust, has anybody ever "finished off" the underneath of a Z? Any value in this?
John
77280Z (Spooky), 83ZXT (Garage Queen), 86ZXT (Bulldog).
Proud owner of 10/03 Z car of the month.
A:
This can be done, but you have to take a lot of aero considerations before you just go blindly into putting a belly pan on your car. If you smooth out the underside of your S30 you will have a very nice wing. At a given speed, the "wing" will create lift. Your new driving wing will then want to take off. The Lotus was designed in a wind tunnel to have a belly pan, the Datsuns were not.
1972 240Z 4-speed, header, 3.54 R200, Crane XR-3000 Ignition, 280Z tach, Tokico Blue Struts, Suspension Tech Springs, Poly Bushings. Visit me at my website for your custom EFI & restored Datsun parts
A:
The only value would be for race applications. Lowering the car & enclosing the bottom (smooth linear surface) & using a front air dam would provide the right environment for negative or lower vacuum pressure than air flowing over the top of the car. This causes the car to be pushed or sucked if like to the pavement (ground effects or down force if you like).
This whole world smells bad, I'd buy another if I had
back what I paid for another mother@#$%@# in a motorcade
A:
Unless you try for a land speed record, it's not worth the effort. The rest of the car is so draggy that a pan will only add weight and complexity.
A:
I was about to post what HybridZ just said.
I think it's a very nice touch by the Lotus engineers, and as someone else has said it was designed it a wind tunnel with careful consideration to the downforce created by the styling of the car so as to keep it firmly planted on the ground.
Post Edited (Oct 31, 19:19pm)
A:
LOL, "wind tunnel testing".
People here already have a strong case of dyno-phobia so I can't see them anywhere near a real wind tunnel (or even buying a CFD program to test things). Just pop riveting on some Home Depot sheet metal under a Z and calling it an improvement is kinda silly. Lord knows how much rust will form if you sandwich a water trap to the frame rails!
Just say no.
A:
I believe TonyD made a Belly Pan for the front of their Bonnevile Zcar to increase topend speed.
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
A:
As I stated this is only for race/high speed aplications & would only work with other body areo mods.
This whole world smells bad, I'd buy another if I had
back what I paid for another mother@#$%@# in a motorcade
A:
The PS30's did have (as an option or not I'm not sure) a belly pan that extended from the radiator back to either side of the tranny.
1973 240Z 4 screw SU's, Tokico HP's, Toyota Calipers
1946 Willys-Overland CJ-2A (restoration in progress)
2006 Ural Gear-Up
A:
With the Z snout inhaling air, it's a great idea to give the air nowhere to go by enclosing the engine bay with underbody tack-ons.
A:
Lots of people who don't know a damned thing about the S30 talking out their hind ends.
Wyowillys has it SPOT ON!
Nissan provided a BELLY PAN for the S30 as an aerodynamic aid on the PZR versions of there 432. This extended from the radiator lower support crossmember to the back end of the transmission on the right hand side, and where the exhaust header came to the side of the engine on the left. It was used in conjunction with the G-Nose and Headlight covers to drop the Cd of the vehicle from .465 to .38. This alone raised the top speed of a STOCK vehicle to over 215kph, most of it coming from the G-Nose. The belly pan was a stability item that utilized airflow management to foil lift in conjunction with the G-Nose.
People with no idea should just keep their mouths shut, and stop blathering on about things they are neither qualified, nor experienced enough to talk about.
People Are Idiots, Just look around here and you will see!
Tony D: "Knowledgeable but Caustic"... rationull
My brother from another mother calls himself "Willie D"
A:
Ah Tony I'm sure 72n03z AKA justinrhenry was just thinking of a old Z28. LOL
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
A:
Minus G-Nose and headlight covers?
I assumed the guy was talking about adding a bunch of aluminum sheeting to enclose the underside of a Z to achieve a flat surface ala the Elise in the fell-off-the-rack photos posted earlier today.
Thanks for the information.
Post Edited (Nov 14, 11:06pm)
A:
Tony - didn't Flagg take off his belly pan after having the dreaded "wing effect" occur? And do you have pic available for the pan you mentioned (unless you're talking about the stock pan)? I'm sure Brad could fab me up one for my gnose Z.
And not to make too fine of a point, when you mentioned speed and cd improvements did you mean with just a gnose or one with the added spoiler attached?
Lots of heat and sand where I'm at too. Just 10 hours ahead of you that's all.
A:
Tony, EVERYONE is saying that reserch is needed before doing such a thing. Keep your shirt on and switch to decaff.
A:
.465 to .38? That is a heck of an improvement.
1973 240Z 4 screw SU's, Tokico HP's, Toyota Calipers
1946 Willys-Overland CJ-2A (restoration in progress)
2006 Ural Gear-Up
A:
LOL, the ZX can do a 0.38 pure stock without headlight covers....
A:
Wouldn't a belly panned' Z trap heat from the exhaust?? The Elise is MR, so it doesn't have that problem.
A:
If you read through the extensive areo threads on hybridZ you will get a lot of questions answered.
Adding a belly pan works to increase air speed under the car. Without the addition of a rear diffuser it is pretty much useless. You want to have the least amount of air under the car moving as fast as possible under the car and then the diffuser with an angle of 7-11 degrees from horizontal allows the fast moving air to create a suction and help pull the car to the ground.
Having deformable (rubber) sideskirts helps to keep the fast moving air from interacting with the higher pressure air outside the vehicle. If they are deformable you don't have to worry about them breaking on a speedbump or something else. Some people use a rubber lawn edging found at most large hardware stores and it has earned the name "the home depot lip". Mostly it is used to extend the bottom of the airdam closer to the ground to keep air from going under the car.
Also another consideration to take is the high pressure under the hood of a Z at high speeds. The Z gets lift from air hitting the firewall and pushing up on the car producing lift. If you cut out holes in the battery area and master cylinder area and vent it outside the fender then a lot of the under hood pressure will be vented to the side of the car instead of down.
Just my little rant...If you go to hybridZ they are preparing ton send a Z to the wind tunel for 3 hours and do a bunch of testing with different parts to see their effect... :-)
A:
We used to use rubber conveyor belt material for air dam lips. Let it "scrape to fit" for the best possible effect.
A:
Sure the ZX has a drag coefficient of .38 from the factory, but it looks like crap compared to a first gen. Ah crap. Now I've done it. Didn't mean to upset all the ZX owners.
1973 240Z 4 screw SU's, Tokico HP's, Toyota Calipers
1946 Willys-Overland CJ-2A (restoration in progress)
2006 Ural Gear-Up
A:
I'm a ZX owner.. and you didn't upset me.... Only reason I have it is because I needed a work car and it was $400 OBO.. and it is is relatively good shape.
I would much rather be driving my '77, but it still has a bit of work to be done before that will happen.
'81 280ZX-N/A 2+2 - stolen on 11-9-2006 :-( - recovered 11-13-2006 :-D
'77 280 - now back to being my project car.
'76 280 2+2 - parts car - slowly being stripped
A:
"Also another consideration to take is the high pressure under the hood of a Z at high speeds. The Z gets lift from air hitting the firewall and pushing up on the car producing lift. If you cut out holes in the battery area and master cylinder area and vent it outside the fender then a lot of the under hood pressure will be vented to the side of the car instead of down. "
Is this true?
It goes against normal airflow logic.
1993 300zx NA
A:
There was a great post on this that showed pics taken by of all people TonyD at the 2004 ZCCA convention in NY. The pics showed the hoods of Z as they came doen the front straight at The Glen and pics of the hoods at rest. We run a cowled hood but it still lifts at speed. The holes AND a side vent would be a nice addition but the rules don't allow the sude vents, hence the exhaust out the bottom of the fender.
A:
The problem is that a cowl INDUCTION hood does not vent pressure out of the engine bay but forces more air into it. There is a very high pressure area right in front of the windshield which causes the air to be inducted into the engine bay. This has been shown by tests with yarn.
Just think about the big front mouth of the Z and where does the air go once it goes through the radiator? the 280z vents have such a small effect on underhood pressure that it does not really help.
You want to vent the high pressure engine bay outside the car. The wheelwell is a very low pressure zone but the problem if you just vent into it air can still go under the vehicle. If it is vented to the side of the vehicle it is not as low pressure but it is still lower pressure than the engine bay while at speed.
ZinSeattle: What do you think happens with the air that goes into the front of the car? The only place I can think for it to go is to compress and go under the car.
A:
Um doesn't a ZX have a drag coeffecient of .3? :-P
84 300zx AE
A:
Fluid mechanics works only when you have fluidity. The air trapped inside the engine bay of a 240z is stagnant - it produces no lifting motion from angle of attack.
The lift on the 240z is from the lack of spoliers both front and rear and the upper shape of the car producing a low pressure zone. Not from air under the hood. The amount of air flow from hood vents reduces under hood tmperatures but has no affect on the mass of air moving at 60 MPH relative to the car.
1993 300zx NA
A:
the 280zx has a drag coefficient of 0.385. first gens were 0.467. lift coefficient of a first gen is 0.41 and for the zx its 0.11. ugly or not 1979 sold more z cars than any previous years. i love my zx and Tony loves them for driveline donors, sometimes they've been neglected to the point thats all they are good for. i think nissan did a damn fine job when faced with new crash and emission regulations, but to each his own of course.
82 NA 5 spd
77 4 spd
A:
"Fluid mechanics works only when you have fluidity. The air trapped inside the engine bay of a 240z is stagnant - it produces no lifting motion from angle of attack.
The lift on the 240z is from the lack of spoliers both front and rear and the upper shape of the car producing a low pressure zone. Not from air under the hood. The amount of air flow from hood vents reduces under hood tmperatures but has no affect on the mass of air moving at 60 MPH relative to the car."
So if the air in the engine bay is stagnant and not moving at all and you are moving at 120mph in a stock bodied z car why does the front end want to lift? Sheer speed does not create lift. If only the air under the fascia goes under the car then lift would be much less noticable. A front spoiler is used to keep air from going under the car. Sometimes it is combined with a splitter to decrease the amounr going under the car even more.
Also if air in the engine bay is stagnant that means that no air is moving through an intercooler, A/C cooler, oil cooler or radiator and thus not cooling anything.
So what you are saying that in the huge scoop on the front of a first gen Z that no air goes through the radiator into the engine bay? That makes no logical sense.
If the wing effect is true on cars the rear of a Z would lift, Not the front. The front of a Z has decent downforce from the shape of the hood and the windshield. The rear has the area where airflow seperates from the body and thus causes lift.
Saying that there is no significant airflow in the engine bay is not very well informed. Why do several race Zs cut a hole in the hood and vent the air from the radiator over the hood?
If you use a belly pan you will reduce the amount of air flowing through the radiator and it needs to be vented to a low pressure area to have any cooling capacity at all.
A:
I run at the drag strip with my hood unlatched and that sucker raises up to eye level by the time I hit 100 mph. The car runs faster and quicker with it unlatched. I don't know if it is just the cold air getting in that makes it faster or if the lifting hood creates a better aero profile going down the track as well to increase top end speed.
I don't have the torsion springs connected to my hood hinges so I don't know how high it would go with the extra push that the torsion springs would provide.
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
Post Edited (Nov 16, 5:18pm)
A:
I have heard of several people having their hood pop up like that. It rises up to the point where the presure is equal on either side of the hood.
A:
norm aka santa claus needs to latch his hood before the hamsters get out.
_____________________________________________
'05 350Z Chrome Silver Touring
'73 240Z
A:
he has no hamsters...he has gnomes on pogo stocks...
No turbos... :-)
A:
"Fluid mechanics works only when you have fluidity. The air trapped inside the engine bay of a 240z is stagnant - it produces no lifting motion from angle of attack.
The lift on the 240z is from the lack of spoliers both front and rear and the upper shape of the car producing a low pressure zone. Not from air under the hood."
Er, that would follow that the belly pan Wyowillys discussed, and NISSAN installed on the car would STAGNATE the wir in the engine bay and SPOIL the front end lift.
But the FLUID FLOW of air through the radiator impinging and diffusing INTO PRESSURE from hitting the firewall before FLUIDLY FLOWING under the vehicle causes LIFT.
Do you guys even READ what you write, or do you blather on endlessly just to make yourselves seem important?
Think about what you are posting once and a while. And people wonder why I stopped posting. This is topic is a perfect example: lots of people spouting without a single thread of comprehension or thought put into what they posted...
Sad, truly sad.
Zin, try discussing this subject with some of the Nissan Engineers involved in the development of the S30. They did extensive testing on what causes lift on the front end of the Z, and it's not from lacking tacky wings and angles of attack, it's from an open maw and diffused pressure lifting the hood.
I gotta stop reading this stuff, it makes me loose faith in humanity...
People Are Idiots, Just look around here and you will see!
Tony D: "Knowledgeable but Caustic"... rationull
My brother from another mother calls himself "Willie D"
A:
"They did extensive testing on what causes lift on the front end of the Z, and ... it's from an open maw and diffused pressure lifting the hood."
Kind of supports "With the Z snout inhaling air, it's a great idea to give the air nowhere to go by enclosing the engine bay with underbody tack-ons," doesn't it?
A:
I don't really want to discuss this but since I do not like being misunderstood and condescended too I feel required. Please feel free to tell me where my logic is wrong here TonyD and Olderthanme - since you did not in the last post. But maybe I was unclear in my writing.
The air speed in the engine bay compared to the air speed flowing over and around the car is relativisticly stagnant. There are some gaps but the air speed (and the air pressure accordingly) are slowed considerably by the passage through the radiator.
Which is the greater factor on the lift or downforce (which the Z has none) for the 240z? Is it the greater amount of distance the air travels over the top of the car versus the shorter distance the air travels under the car - albeit a very turbulent one? Or the relatively small amount of air that according to TonyD creates an air flow that pushes on the air trapped between the firewall and the hood as it passes under the car?
Do I think that pressure under the hood causes the front end to be pushed up? No.
Do I think that the air flowing through and then under the car can cause the front end to be pushed up? Yes. More of a factor on overall lift than the shape of the hood, windshield, and rear deck? No.
Do I think that an under belly pan would reduce this effect? Yes.
Do I think that by unlatching the hood you can run a better eta at the track? Yes. But we are not talking about drag, we are talking about lift. Do I think the hood raises up until the under hood pressure equals the air flow pressure? Plausible but, I tend to think more that the hood raises up till the negative pressure created by the upper air flow is countered by the hood impeding into the air stream. All from above - very little from pressure below the hood.
Do I think that a front chin spoiler would help negate this "diffused air lift" by creating some front end down force? Yes, of course. So did the people who raced them on road circuits - they didn't think those "tacky wings" were useless.
So to generalize. I think that the shape of the 240z's upper profile causes it's greatest factor in overall lift. I do understand that the amount of air flowing through the engine bay and under can cause additional lift for the front end. And this may be equal to the differential between the front and rear tire weight at speed. Meaning - that if you get 300 pounds of lift at 100 MPH and you are getting 125 pounds of that lift at the rear tires and 175 pounds of lift at the front tires, that the additional 50 lbs of lift is from this underbody airflow, and thus creating a front lift bias.
An example to examine would be the g-nose conversion of course. With no underbody modifications did the elongated nose increase front end lift problem for the sake of a cleaner look and a reduction in drag or was there no change?
Oh and on a side note TonyD; I do not care for your part in the conversation here. Is it because I do not agree with what you have to say? No, it is because you are arrogant and pompous and rude. People do not have the same aversion to me based on how I state my opinion.
1993 300zx NA
A:
"
Do I think that pressure under the hood causes the front end to be pushed up? No.
Do I think that the air flowing through and then under the car can cause the front end to be pushed up? Yes. More of a factor on overall lift than the shape of the hood, windshield, and rear deck? No.
"
Zin:
You just contradicted yourself...if the car has no hood then air will not go under the car near as much. If you are running no hood at all air coming through the engine bay will come out roughly near the middle of the engine bay where there is a low(er) pressure area.
Just because you think there is no pressure pushing on the hood does not mean that there is not. Why else would a hood raise up at speed? Over the front of a Z you still get downforce but there is more lift than downforce. If you throw a rock through the air you have a few forces acting on it. Gravity, wind (which we will not consider here), downforce, and lift. Depending on the shape of the rock you could have more lift or more downforce. If you throw a rock and say it travels at 70 mph(good throw) and does not spin at all. It will go a certain distance when aerodynamics of lift and downforce will have effect and it will rise or fall at different rates depending on the shape.
If you seal the engine bay (to make the air truely stagnant) and do not have good venting then you will inhibit cooling of the engine and your engine will overheat and die quite quickly.
Zin: You need to respect people that have experience or at least knowledge about aerodynamics. Don't get mad at people just because you don't like their answer.
Things to do to help aerodynamics in no particular order:
1. Keep air from going under car as much as possible.
2. Have the air that is going under car move as fast as possible to create a vacuum and pull car to the road
3 Minimize air pressure in the engine bay (ie. venting, gnose to send air over the hood instead of into the engine bay, etc...)
4. increase downforce (front splitter, rear spoiler, flares, etc...)
5. Decrease ride height to decrease the frontal area (directly related to parisitic drag)
A:
I don't see where I contradicted myself.
My first statement you quoted sais I do not think the slight increase in air pressure from the incoming air pushes the car up.
The second statement sais I do think that the flow of air from engine to the underside can cause a upward pressure against the undercarriage.
Those are two different things.
Why would a hood raise up at speed? A fast moving fluid on one side of a surface creates a negative pressure zone. The same thing that causes a plane to fly. As far as downforce and lift go, I was assuming that we are talking about net force here - since that is what is key. The Z has lift at speed. The car has less weight on the wheels at 100 mph than it does at 0 mph. Speed goes up and the force of the tires on the ground goes down. And in automotive terms the Z has NO downforce.
As far as the rock goes. Lift and downforce are active aerodynamic terms - which a rock has neither. A random rock has no lift, it has no downforce. When thrown it has two forces that act on it after being release. Wind resistance and gravity. That is it. If the object is very round and you can put a good amount of spin on it then it is still just wind resistance and gravity. A curve ball curves because one side has more resistance to the air on one side than the other. That is my understanding.
No one here is talking about sealing the engine bay. I should not have to explain relative here.
And at no time have I ever gotten angry at somone who does not like my answer. This is my enterpretation of what I think is going on with the aerodynamics. On the other hand I do take the time to reply when I have the displeasure of reading the condescending rhetoric in the latter half of TonyD's last post and yours as well.
Please do not try to typify me as an arrogant braggart who has no respect for peoples thoughts and ideas. With a written forum it is sometimes difficult to place tone and emotion on words and having reread my initial response it sounds somewhat curt and final. For that I apologize. I should try to preface my thougths with additional wording. I.e. "From my knowledge of fluid mechanics", "What I think is happening", "I am not sure I agree that this is the main cause", ete. etc.
Which has always been my internal phrasing and would be apparant if I were talking to somone in person.
1993 300zx NA
A:
i read that air going into a radiator at 200 mph comes out at 14 mph, so i don't see air coming in at even 100 mph having an effect on lift inside the engine bay, but i really don't know. the 200mph example was used in an article about having a huge intercooler covering your radiator and not having proper cooling. the above example of course is without the aid of fans...so its subjectable once you add one or two pusher/puller fans or whatever.
82 NA 5 spd
77 4 spd
A:
None of you will ever do it anyway, so what's the big deal? lol
85' 300ZX NA
86' 300ZX Turbo
88' 300ZX Turbo
89' 300ZX Turbo
300ZX Turbo Project
A:
Okay, maybe I'm getting tired but what 300zxt will none of us do?
A:
Enclose the bottom of their Z, as the topic title says lol Yes you are very tired hehe, I was only joking anyway but this thread is getting a little unnecessarily heated.
85' 300ZX NA
86' 300ZX Turbo
88' 300ZX Turbo
89' 300ZX Turbo
300ZX Turbo Project
A:
Okay, I got it. After 30 hours and three differnt flights to get back home from overseas I was getting a little punchy.
Actually I will be trying to go this route. I already have the gnose on my street car (the 6.5 qt oil pan will make building a belly pan interesting) and the ride height is already quite low (just under 6 inches at the front rocker). A front spoiler would improve the downforce (but increase the lift at the rear) but isn't really practical as it would crack or break on anything other than a flat race track surface.
Over on Hybridz, a wind tunnel experiment will be undertaken early next year. Maybe then we can all see some real numbers.
TonyD has yet to answer my two simple questions however:
1) was the increased speed (and lower cd) gotten on a simple gnose (no additional spoiler?
2) is the belly pan discussed no more than the stock one provided by Datsun?
If anyone knows the answers to these I'd appreciatate it....
A:
>Over on Hybridz, a wind tunnel experiment will be undertaken early next year.
That's the only real way to know for certain... Will be interesting to see!
85' 300ZX NA
86' 300ZX Turbo
88' 300ZX Turbo
89' 300ZX Turbo
300ZX Turbo Project
A:
unfortunately no Gnose will be tested unless they can get one donated...It wil have to be able to be quickly mounted since wind tunnel time is VERY VERY expensive. I think there are going to have 8 hours in the tunnel and it will be a few thousand dollars...