240, 60, 80 Z Aerodynamics

[AK-Z]

jmortensen .... you are correct' date=' since cowl hoods pull the high pressure from the windshield and suck it down into the carb or engine bay...

 

However, this is true on some cars, and not necessarily for other cars...

 

the 240Z has that nasty firewall, which builds up tons of air...

 

YES there is HP on front of the windshield and HP inside the engine bay..

 

but which is higher?? Lets just say.. im just throwing random number out here.. but lets just say the engine bay has 25 pounds of air pressure at 100MPH .. and the front of the windshield has 18 pounds of air pressure at 100MPH..

 

The lower 18lbs of pressure on the windshield is lower than the 25lbs of pressure inside the engine bay.. High Pressure always flows to Low(er) pressure area's.. therefore ... there would be some suction going on..[/quote']

 

I see so its the difference in HP.

[JMortensen]

Well, Cary's yarn test seems to indicate that the pressure inside is not as great as the pressure at the windshield. Which means you're forcing more air under the car by popping the hood. Cary mentioned vents through the inner fender well, as did someone else (with the CPU fans). I wonder if something like the new Z06 fender vents might be done on a 240Z, maybe with a duct running from the engine compartment out to the fender. Venting it sideways doesn't produce downforce like Terry's car would, but at least it's helping to reduce the upforce.

 

Also, someone commented about reducing the opening in the front and whether that would cause the car to overheat, NO WAY. I think preith has the right idea: close half (if not more) of it off and leave a much smaller duct from the front to the rad support. He had some better pics on classiczcar.com, but I can't find them now. Here's one though:

[proxlamus©]

ahh i see Jon.. thanks for the heads up... I was just guessing/assuming..

but this is very interesting...

 

AK-Z .. when I meant HP i meant high pressure, I hope you didn't think I means horsepower... just clarifing JUST in case..

[AK-Z]

ahh i see Jon.. thanks for the heads up... I was just guessing/assuming..

but this is very interesting...

 

AK-Z .. when I meant HP i meant high pressure' date=' I hope you didn't think I means horsepower... just clarifing JUST in case..[/quote']

 

Yeah, wasn't sure it other people would get confused with horsepower, but I figured that you guys are samrt enought to figure it out.

 

Now wouldn't movin the radiator foward and angling it to match the front (with a air dam of course) help a little, even though the radiator lets air flow through it, it also restricts air and redirects a little.

[Z-TARD]

I think Terry (Blueoval Z) has the closest thing to an optimum setup for hood venting that I've seen. His is set up almost exactly the same as the Shelby Cobra Daytona Coupe (A car designed by Peter Brock of BRE fame). The radiator has beentilted forward at the top, which requires the fabrication of a new radiator support. Behind this is a large duct that leads up and over the engine, and out of the forward surface of the hood. The duct is far enough forward that the high pressure area at the base of the windshield will have little effect on it's ability to divert air from the front of the car over the top of the car. Terry's front airdam is also constructed to force most of the incoming air through the radiator. There seems to be very little room in front of the radiator for high pressure air to linger and cause inconsistant flow patterns up there.

 

I think Boodlefoof's design is also going to be pretty efficient. The rake of the windshield should reduce the pressure of the air in front of the windshield by quite a bit. Doing this will of course help the overall flow over the car, and should also let him run a hood duct further towards the back of the hood than would be practical with the stock winshield. I'm definitely looking forward to seeing more progress on that one. After looking through his pictures, I'm seriously considering buying another junk Z to try some serious surgery on.

 

Mike

[260DET]

Cary said the same thing ie vent air out of the front low pressure part of the bonnet. Some decent exit vents there could be made to look good, plus they would get rid of hot air that you really don't want flowing back over the engine and gearbox, if cooler air is available.

 

Oh, plus that hot exiting air flow would reduce/eliminate lift around that part of the bonnet.

[scott19]

Just my $.02:

 

It is my understanding that it does no good to vent the hood for aerodynamics, since there is high presssure below (in the engine bay),

and high pressure above (air flowing over the hood). It is argued that the vents installed by Nissan are for heat removal, not aerodynamic flow. What is needed is a vent to a low pressure zone, such as the fenderwells. I've joked that the S30's have "self correcting aerodynamics", since the battery box rusts out, providing holes to vent to the fenderwell. I believe TonyD had the idea to drill/cut multiple holes into the fenderwell for ventings sake.

 

A personal experience (that may contradict what I just wrote above):

My first 240 had a fiberglass cowl induction hood on it. It would pop open completely (meaning it would clear the release latch also) ever so often, usually around 50-70 mph. When it did this, it would float 6-8" above the engine bay until I slowed down below 30-40 mph. This is with about a 2x20" cowl induction hole in the rear. Take from that what you will.

[AK-Z]

I think Terry (Blueoval Z) has the closest thing to an optimum setup for hood venting that I've seen. His is set up almost exactly the same as the Shelby Cobra Daytona Coupe (A car designed by Peter Brock of BRE fame). The radiator has beentilted forward at the top' date=' which requires the fabrication of a new radiator support. Behind this is a large duct that leads up and over the engine, and out of the forward surface of the hood. The duct is far enough forward that the high pressure area at the base of the windshield will have little effect on it's ability to divert air from the front of the car over the top of the car. Terry's front airdam is also constructed to force most of the incoming air through the radiator. There seems to be very little room in front of the radiator for high pressure air to linger and cause inconsistant flow patterns up there.

 

I think Boodlefoof's design is also going to be pretty efficient. The rake of the windshield should reduce the pressure of the air in front of the windshield by quite a bit. Doing this will of course help the overall flow over the car, and should also let him run a hood duct further towards the back of the hood than would be practical with the stock winshield. I'm definitely looking forward to seeing more progress on that one. After looking through his pictures, I'm seriously considering buying another junk Z to try some serious surgery on.

 

Mike[/quote']

 

So mounting the radiator like that would help a little. How about a IC? I mean it would be alot easier to mount a IC like that instead of modifying the radiator support.

 

scott19, I stated that nissan put vents for heating, but everybody apparently ignores/forgets what I posted.

 

I stated before that I was planning on removing most of the firewall that separates the engine compartment from the compartment with the wiper assembly, is that what TonyD did? Would it help?

[JMortensen]

It is my understanding that it does no good to vent the hood for aerodynamics, since there is high presssure below (in the engine bay), and high pressure above (air flowing over the hood). It is argued that the vents installed by Nissan are for heat removal, not aerodynamic flow. What is needed is a vent to a low pressure zone, such as the fenderwells. I've joked that the S30's have "self correcting aerodynamics", since the battery box rusts out, providing holes to vent to the fenderwell. I believe TonyD had the idea to drill/cut multiple holes into the fenderwell for ventings sake.

Again, the yarn test will yield definitive results (and I think I've read peoples' yarn test results previously but can't remember for certain), but my understanding is that you have high pressure in the front of the hood, low pressure in the middle towards the back where Nissan put the vents, and high pressure at the back. Similarly you would have high pressure at the front of the roofline, but low pressure over the roof, and high pressure again if you had a spoiler. If my car were running I'd do the yarn test right now. Unfortunately it's gonna be months if not more before I can test jack at this point...

[Synlubes]

Some pix of my cowl panel mod here

 

http://24.254.252.164:9565/ZCar.htm

 

I had thought of putting a small lip at the end of the hood (close to the windshield) to help throw air over the windshield. ???

 

I don`t run wipers unless its raining.

The 280 hood vents are for removing hot air from the engine compartment at slow speeds and stopped.

I will probably reinstall the non-vented inspection lids to keep air from being sucked in at speed. It was really just a fabrication project.

[scott19]

I stated before that I was planning on removing most of the firewall that separates the engine compartment from the compartment with the wiper assembly, is that what TonyD did? Would it help?

 

What TonyD was talking about was to drill holes in the fenderwell area underneath where the battery (passenger side) and the slave cylinder (driver side) reside. To my knowledge, he never actually did it, since this was for his Bonneville car and it would have been illegal in his class.

 

I think your idea would work, to a point. But my thought is that the low pressure zone in front of the windshield would only bleed off a small amount of air from the engine bay before it equalized with the high pressure flowing above it. Also remember that wiper area is also where fresh air can get drawn into the passenger compartment. I don't think it would be a good idea to have engine air flowing into there, hence it's separation from the engine bay. But this is a layman talking. Any engineers wanna chime in?

[Z-TARD]

I think it would probably be a good idea to determine at what speed the hood duct should function. It seems to me that as the speed of the car increases, the high pressure area in front of the windshield will gradually extend forward as it becomes harder for the pressure to bleed off over the top and around the sides of the windshield at speed. At a given speed, the hood duct might become non functional as air pressure equalizes on both sides of it. At what speed is a hood duct required to maintain stability? I've read several posts on here with members taking their cars to 160+ with only airdams and spoilers for areodynamic aids. Personally, I'd like to get my car a lot closer to, if not over the 200 MPH mark. My speedo goes all the way to 200, and dammit, I want to see if it will actually do it

 

Mike

[Z-TARD]

So mounting the radiator like that would help a little. How about a IC? I mean it would be alot easier to mount a IC like that instead of modifying the radiator support.

 

I think the major reason for mounting the radiator like that is just to assist with the geometry of the ducting. Having it tilted forward makes for an easier transition into the duct going up and over the engine/out through the hood. Another good example of this is the Shelby Series One:

 

Ducting like this effectively isolates the entire engine compartment from the incoming high pressure air through the grill opening. No high pressure air in the engine compartment means it wont be venting out under the cars floorboards, causing lift. Weather it will improve the areodynamics or not I can't tell, but it certainly will improve the stability at high speed.

 

Mike

[frank280zx]

I thought it has been said that popping the hood a little on the S30 will push air into the engine bay at higher speed because the windshield dam up a lot of pressure at the base.

 

opening the hood a bit is fairly common in japan actually!

for exactly that reason, so it probably works

[AK-Z]

Every little bit helps. I'll figure something with the wiper compartment.

 

What would a firewall be like in a car with low preasure in the engine compartment?

[AK-Z]

I think the major reason for mounting the radiator like that is just to assist with the geometry of the ducting. Having it tilted forward makes for an easier transition into the duct going up and over the engine/out through the hood. Another good example of this is the Shelby Series One:

 

Ducting like this effectively isolates the entire engine compartment from the incoming high pressure air through the grill opening. No high pressure air in the engine compartment means it wont be venting out under the cars floorboards' date=' causing lift. Weather it will improve the areodynamics or not I can't tell, but it certainly will improve the stability at high speed.

 

Mike[/quote']

 

That does leave alot a room when you mount the radiator like that.

[proxlamus©]

[Chewievette]

Very cool picture! It doesn't show the windshield area which seems to be the focus of this thread. Although it does show the flow over the rear hatch "unsticking" from the car (Smoke lines are blurred) which is interesting to note. If you were to chop the top as shown earlier in the thread you could pretty much cure this phenomenon.

 

I'm not a specialist in this field but I have done a lot of research on high speed aerodynamics, mostly transonic(.7 - 1.2 mach). Your aim should be to reduce the frontal area of your car. Everything should have a path through the car. Look at any purpose built race car and you'll see what I mean. Every scoop has an outlet, and most engine bays are sealed from airflow. If I was building a high speed Z I would seal and smooth the underside, vent the radiator to the top of the hood (like the shelby series 1), vent the wheel wells through the fender(like a corvette), and slope the windshield/chop the top. A few more small tweaks and you should be able to hit 200mph no problem.

 

The latest addition to my Z collection is a 240z (sig pic), a chop top and a g nose are in the works to start the mods. Its going to be a pure street car but aerodynamics are my thing so it fits that I'd do those mods. I'm still trying to get a shop lined up to do the work in but sooner or later the work will begin!

[Z-TARD]

Good point about reducing frontal area. If any one thing is most responsible for these cars bad areodynamics, it's the abundance of frontal area. Another way of looking at frontal area is to notice how much of the sheetmetal on the front of the 1st gen Z is nearly flat faced into the wind. The hood has very little frontal area to speak of, and for areodynamic purposes is probably almost invisible. The firewall on the other hand, along with the engine and strut towers is what the air sees as it hits the car. Isolating this area is probably the single biggest improvement that can be made. The drip rails are probably another significant problem. Any air trying to displace around the side of the windshield runs right into them, most likely causing a lot of turbulent flow in the process. The underside of the car has it's share of drag inducing structure as well, but I think that adding an airdam, along with ducting the radiator through the hood will mostly isolate the undercar area too. If I remember correctly, it was determined on the 240mph Z thread that the wheel wells are actually low pressure areas. I think rather than venting them, reducing the gap between the tire and fender lip would be more beneficial. This would help prevent the air displaced around the sides of the car from entering the wheel wells. The ZG flares probably also help with this to a certain extent, but at the cost of added parasitic drag. I think the key to reaching 200+ mph is mostly just trying to keep the car controllable during the attempt. Fortunately, theres really not much you can do to a Z to make it's areodynamics any worse, other than maybe welding a Yugo to the top of it......

 

Mike

[Guest Z Draci]

I remember reading factory test data that stated that the S30 chassis had a 0.44 coefficient of drag. The G-nose brought that figure down to 0.36. Both numbers were actually very respectable during that period. Today, the standard is a sub 0.30 number for all cars. There a reason aerodynamicists are among the highest paid employees of racing teams.

 

I was doing a lot of personal research on the technology used in road going Ferraris and also digging up some technical articles on the McLaren F1. These road cars utilise a lot of active aerodynamics that change the shape of the car as it reaches certain speeds. This is, of course, banned in sanctioned racing. Cars like the McLaren F1 has vortex generators that spin air upwards to accelerate it more than with a straight flow. (This is similar to the underbody vortex generators and side panel fins on race cars.) The car also has ducts that open upon braking and air brakes to assist in stability during high speed braking. Reading up on the aerodynamics of the McLaren F1 made me appreciate the car even more. Even with a million dollars worth of engineering, the McLaren F1 is still highly unstable at 200mph. (The $4.5M Veyron is said to be stable above 200mph though.)

 

I think the S30 chassis would be just fine with a front lip, a rear spoiler, a flat underbody panel, and a method to evacuate air from the engine bay. It's a very aerodynamically primitive car for today's standard. We shouldn't expect to come close to par with what a modern car can do. Going 120mph down the straight of a world class racing circuit is probably the limit for the car.

 

An S30 will struggle to reach 140mph. I've been in cars where 140 is just another number that the speedo needle zips past on its way to 200mph.

 

I remember TonyD posting a picture of his Bonneville race car either here or on zcar.com