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Windtunnel Testing the Datsun S-30 Z


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#1 Mikelly

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Posted 10 May 2007 - 03:43 PM

I really didn't want to take this down, but until the other issue is resolved, we'll have to...

Mike

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#2 Mikelly

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Posted 13 May 2007 - 08:45 AM

OK Gang, The initial post and pics are done. I'll edit and add links to video over the coming weeks, but feel free to discuss the findings. I'd like to thank the following people for making this happen:

John Hines for finding the folks at Aerodyn2 and making the initial investment in time for making this happen! Also for his hard work and time away from the family in making the Pantera hatch. The effort put forth was a real eye opener!

John Tedder for pulling the group together and coming up with a plan, and for putting up with a huge amount of ribbing from yours truly... Johns is one of the best guys to hang out with and chew the fat!

Mark Ulrich and Roddy Sugg, for working on a plan, along with JohnT. and Tom Barnett, and for their hard work, thoughtful designs of pieces used, and work towards getting companies to donate parts.

Tom Barnett, One of the sharpest knives in the drawer. Tom worked doggedly during this whole process and came up with the ulimate test plan, along with John T., and worked hard to keep us on track during the tests. Tom's attention to detail was simply amazing. His efforts towards getting vendors to step up forged a relationship with MSA, APR and SDI that made this event much more successful.

Austin Hoke, for showing up and busting his butt all day. He pretty much did as asked and gave a lot of ideas along the way. It does my heart good knowing that there are sharp, mature, and talented young guys like Austin within the HybridZ community!

Tom Harris, For being my co-pilot, pal, and friend during this epic adventure. Tom, alot like Austin, is the kinda guy who'll jump in head first, get dirty, and give thoughtful insite along the way. These youg guns are truly the future of HybridZ!

Mark Icard, for showing up late and making up for lost time. Mark is a dentist by trade, but doesn't mind using his, rather large hands to dig in deep and get dirty. He's also one heck of a generous guy, and offered up significant donation funds during the donation drive!

David Spillman, for not only donating a fair chunk of change during the donation drive, but also PAYING an employee of his to drive his car trailer up to Mooresville, with a very special 240Z inside. David recognized the chance to make history and wasn't affraid to let us use the car for the testing.

HybridZ as a community. You folks are a cut above. I've never seen an internet car club come together in times such as this. We made history, and you folks were all a part of making it happen. This test data, the images, and the video is yours. I just hope you appreciate and use it for the true treasure that it is. It was hard work collecting the funds, defending the slips in schedules, dealing with the many barbs from other bulletin boards, and making this happen. The support given by the folks on this site made it all worth the hard work and long hours producing this product!

Thanks you all for your support and enjoy the data!

Mike Kelly
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#3 JMortensen

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Posted 13 May 2007 - 11:54 AM

I have so many questions and things to say that I'm not going to spew it all out in one post. First though, thanks to all who participated and donated. I wish I could have given more to the cause, next time I will. OK, so here's my first round of questions, and a few suggestions for next time:

1. I know you guys were keen on blocking the open space between the air dam and the rad core support. Was there any attempt on any of the cars to seal the top of the core support to the underside of the hood?

2. Along the same lines, did any of the tests have an enclosed air box which took air from the front of the car to the radiator and didn't allow it into the other holes in the core support, or over the core support?

3. Looks like the last test, #28, was done with the 5.25" spoiler on the back. Is that correct?

Suggestions for next time:

1. Test a front end where the flares and airdam COMPLETELY cover the front of the wheels.

2. Test a rear flare where the front of the rear flare COMPLETELY covers front of the rear tires.

3. Take the front lip off of Roddy's airdam and test the effect that just the lip has on downforce.

Roddy-- That's some pretty innovative stuff you have going on there. Very impressive!

Jon Mortensen, owner/operator www.petdoorstore.com


#4 Mikelly

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Posted 13 May 2007 - 12:03 PM

Jon M., We didn't test any advanced airboxed. We tried to stick mostly with basic stuff.

As to the comments about the spoilers covering the wheel/tire competely, Bob Smith had had some interesting comments in regards to this issue as well... The MSA Type3 with the ZG flares did an excellent job covering the face of the tire.

Roddy's car had his stock small MSA 2.5 inch rear spoiler. We made no changes to the rear of his car.

Mike

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I will not be a spectator in the sport of life!
mjk 1994


#5 JMortensen

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Posted 13 May 2007 - 12:34 PM

As to the comments about the spoilers covering the wheel/tire competely, Bob Smith had had some interesting comments in regards to this issue as well... The MSA Type3 with the ZG flares did an excellent job covering the face of the tire.

What were his comments?

Jon Mortensen, owner/operator www.petdoorstore.com


#6 Mikelly

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Posted 13 May 2007 - 01:26 PM

Well lets backtrack to the other comment you made for a second... You're worried about an extravigant sheetmetal box for the radiator, but you missed the whole section on how the radiator only needs 2X4 inches of space to stay cool... That sheetmetal "box" is probably effective at doing that, but probably isn't as big of an aerodynamic aid as you might think, so you have to think in different terms there.

Now, Bob Smith commented that the winglets Roddy has on the sides of the fender flares are not effective because they don't cover a section of the tire, effectively running the length of the fender flare down to the chin spliter. Covering the whole face of the tire does help aid in assistance. My guess is if we'd had the money to do the other tunnel with the rollers on the tires, we'd have been able to see that in the tests with tests 20-25!

I'd recommend going back and re-reading the article and the data a few times. I've studied it for two weeks, and my notes I took from conversations with Bob. It was highly informative and totally frustrating trying to keep up with his intellect! :laugh:

Mike

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#7 JMortensen

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Posted 13 May 2007 - 02:08 PM

Well lets backtrack to the other comment you made for a second... You're worried about an extravigant sheetmetal box for the radiator, but you missed the whole section on how the radiator only needs 2X4 inches of space to stay cool... That sheetmetal "box" is probably effective at doing that, but probably isn't as big of an aerodynamic aid as you might think, so you have to think in different terms there.

I'm not sure you're getting the point of the box. It isn't only there to limit the amount of air coming into the radiator. That is it's less important purpose. It's more important purpose is to eliminate the pressure from the underside of the hood. And this ties in with the other question as well, about sealing the core support to the hood.

If you have positive pressure inside the nose of the car and have not sealed the core support to the hood, then presumably just as the air can go down underneath the airdam under the car, the air can also go OVER the rad core support and through the holes in the core support as well. This will increase the amount of pressure under the hood.

If one were to seal the core support to the hood, then air would have to go through the radiator or holes in the core support to get into the engine compartment where it would be either evacuated by the vents or by traveling underneath the car. But in the area between the hood front and the core support, there would be a large pressurized area exerting force in all directions.

If one were to do the box structure and seal the hood to the grill area so that all the air that went into the box went through the radiator, then you'd get a couple of benefits. You guys already showed that cutting down the amount of air is beneficial. In addition though, you'd cut down the size of the pressurized area in the front of the car. In fact, you could probably get negative pressure in the front hood area above the box. Negative pressure under the hood, coupled with the pressure of the air being diverted over the hood = more downforce, and that's why you see so many race cars using that type of radiator duct. If memory serves I think preith has this type of setup on his car, with a sealed box and a much smaller inlet hole for the radiator.

Here is a link that describes what I'm talking about from a circle track magazine: http://www.circletra...ch_definitions/

The magazine article has some flaws, but the article estimates a 180 lb downforce gain from this type of box. It also talks about using a wide airdam to suck air out of the fenderwells.

Jon Mortensen, owner/operator www.petdoorstore.com


#8 Mikelly

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Posted 13 May 2007 - 02:25 PM

Jon, No. Not according to Bob Smith. His comments were that you're going to get air packed in under the hood... There's no getting around it. Sealing off the nose of the car in general, like Roddy Sugg's car does, is an effective way to deal with the area at the mouth of the car. Look at the test data for #28, along with the other data for closing off the grill in other tests...


Also, remember, air is exiting the radiator/fan assembly at 15mph. You're travelling a lot faster than that (we hope) and what does that create? An area for air to pack up and create lift. Forego the whole "Aerodynamic downforce" theory of yours for a moment and think about just closing off that gaping hole in the front of the Zcar, known affectionately as the "grill". Do that, provide minimal feeding for air, and then funnel that air to your radiator however you wish, via ducts, tuning, sheetmetal/plastic radiator box, or whatever. Just remember that the air isn't travelling any faster than that, which means the larger that opening, the more air is getting caught there... and remember the first lesson we passed on from our friend Bob Smith. What happens at the very front of the car will impact everything else along the way... Total package, JM. Total Package!
Mike

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mjk 1994


#9 JMortensen

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Posted 13 May 2007 - 02:34 PM

I think I'll have to disagree with Bob on that point then. I don't think you'd see so many race cars from so many different classes doing the same thing if there were no point. The opening to the box I'm suggesting could be whatever size you want to get a very small frontal opening.

This is very similar to the point you guys proved about sealing the air dam to the core support. That prevents air from spilling out UNDER the radiator. The box prevents air from spilling out OVER the radiator and through the holes in the core support. And if you have a LOT less air in the engine compartment you might just make a low(er) pressure area under the hood, which translates to more downforce.

Jon Mortensen, owner/operator www.petdoorstore.com


#10 jt1

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Posted 13 May 2007 - 02:44 PM

Jon, we didn't have time for any pressure data, but the yarn indicates we never did get a negative underhood pressure, even with Roddy's car with the grill almost completely blocked. There was air flowing out the vents in all tests.

If we could get to the point of negative underhood pressure, then the radiator box makes a lot of sense, but there's a good bit of work to do on the frontend to get there. We're not even close at this point.

John
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#11 Mikelly

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Posted 13 May 2007 - 02:46 PM

I won't debate "IF" a box would have worked, since it wasn't tried. But Bob Smith has tested hundreds of cars, and his insite was amazing. All these boxes on these cars could very well be tested, or could very well be something people "Think" is a good idea. Until we test them, I'm listening to the man that does this stuff for a living. he wasn't wrong pretty much every recommendation he made... choice is yours to trust a pro. I am.

Mike

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#12 JMortensen

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Posted 13 May 2007 - 03:01 PM

Jon, we didn't have time for any pressure data, but the yarn indicates we never did get a negative underhood pressure, even with Roddy's car with the grill almost completely blocked. There was air flowing out the vents in all tests.

If we could get to the point of negative underhood pressure, then the radiator box makes a lot of sense, but there's a good bit of work to do on the frontend to get there. We're not even close at this point.

At this point I think THE KEY to getting underhood negative pressure is the box. Everything that you've done to limit air from going where you don't want it to go has been successful, but there seems to be a resistance to the box idea which I don't understand.

The circle track article states:

This team built the airbox in front of the radiator with the top angled down as it runs from the radiator to the front grille opening. The old box ran straight from the top of the radiator to the top of the nosepiece and did not allow enough air space for a low-pressure area to exist. The gain in downforce from this design is estimated at over 180 pounds.


So they're saying that BOTH of the boxes that they used sealed the nosepiece to the radiator, but this version of the box allows for negative pressure directly above it. Just that small increase in available space for the neg pressure to act upon change the downforce by 180 lbs. That's not counting the rest of the hood!

By the way, the yarn only shows where the air is going, not what the pressure difference above and below the hood is. I know that doesn't sound like it makes a lot of sense, but to put it in other terms, Bernoulli's Principle will allow you to evacuate the crankcase and create a strong vacuum by attaching it via a hose to the pressurized exhaust. You would think on the face of it that the pressure under the hood HAS to be higher for the yarn to show air coming OUT of the hood. In fact this is not the case. Just like the crankcase example, air flowing past the hood vent, especially one that is properly designed, will suck air out from under the hood even if there is negative pressure under the hood and positive pressure over it.

I am not going to press this particular point any further after this post unless a new angle is brought into the discussion. I don't want to wear you guys out right off the bat, and there are a lot more things to talk about than just this.

Jon Mortensen, owner/operator www.petdoorstore.com


#13 Bob_H

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Posted 13 May 2007 - 03:42 PM

The circle track article states:

This team built the airbox in front of the radiator with the top angled down as it runs from the radiator to the front grille opening. The old box ran straight from the top of the radiator to the top of the nosepiece and did not allow enough air space for a low-pressure area to exist. The gain in downforce from this design is estimated at over 180 pounds.


So they're saying that BOTH of the boxes that they used sealed the nosepiece to the radiator, but this version of the box allows for negative pressure directly above it. Just that small increase in available space for the neg pressure to act upon change the downforce by 180 lbs. That's not counting the rest of the hood!

Jon,
That's not the way I read it. My G-nose has the exact same issue, and I'm glad you posted that article because I was originally going to find a way to run it straight forward, but that didn't allow the hood to open/close w/o pinning all 4 corners,(not very track friendly).
But back to your assertion - if the change in angle of the top of the enclosure increased downforce - I don't think it was from allowing "more space for the neg pressure to act upon", but rather it changed the nature of the flow around the car, meaning less air was let in that opening, possibly pushing more air above the car, contributing to downforce.
I don't see how a change in the design affecting the area behind the bumper/air dam would allow more neg downforce. I am fairly sure it comes from the change in overall flow around the car. I imagine that the "straight top", if you will, allows more pressure to build up in front of the radiator, which "robs" some of the pressure in front of the car which can go over or under the car. For all we know,(it isn't specificed in the article), it could be the opposite -that the "curved top" design allows a greater pressure in that space, changing the flow in front of the car.
Let me try another tact to explain what I'm having a hard time conveying.
Take the 240's opening. If you sealed everything up front so the only "hole" is the radiator itself you have a ~1ftx4ft opening,(rough guess). The airflow at the front of the car has to deal with this big "box" in front of the car. If we close that down to a 6"x2ft opening,(the size of the one pictured in the article), the "box" creating drag is smaller allowing more of the airflow at the front of the car to flow elsewhere - where? we can't really say.
Now, the opening didn't change in the design in question - so that to an extent becomes moot. However, the opening behind the 6"x2ft opening is larger,(in the "straight top" design) and changes the flow path to the radiator, meaning there could be more or less flow - again, we don't know. But if there were less flow,(with the "curved top" design) it means more of the airflow around the car is going over and around the car, not through the radiator - which is my assumption for the reason the downforce is higher,(less flow through the radiator = less under the car, and more over/around the car).
On edit to clarify from the words in the article - it states:
"The old box ......did not allow enough air space for a low-pressure area to exist"
So in essence, the "straight top" box had a high pressure in front of the radiator, where the "curved top" had a low pressure,(or lower, it didn't specify the datum). This should contribute to my thought that less air was flowing through the radiator, and more was flowing elsewhere.
That was my take on the article.
Either way, it finally justified me installing a "curved" top to the airbox for the intercooler and radiator allowing me to keep the hood installed with hinges instead of 4 corner pins. I have pictures somewhere - just not where I can find them - I think they are in my Super Datsun thread... I'll take a look later.
-Bob

#14 jt1

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Posted 13 May 2007 - 03:57 PM

The box doesn't create negative pressure. It separates the high pressure air headed for the radiator from the (hopefully) low pressure air under the hood. Then the low pressure air can work on the additional underside area of the hood & nosepiece, which was previously exposed to high pressure, and create additional downforce.

By the way, the yarn only shows where the air is going, not what the pressure difference above and below the hood is. I know that doesn't sound like it makes a lot of sense, but to put it in other terms, Bernoulli's Principle will allow you to evacuate the crankcase and create a strong vacuum by attaching it via a hose to the pressurized exhaust. You would think on the face of it that the pressure under the hood HAS to be higher for the yarn to show air coming OUT of the hood. In fact this is not the case. Just like the crankcase example, air flowing past the hood vent, especially one that is properly designed, will suck air out from under the hood even if there is negative pressure under the hood and positive pressure over it.


Note the tests where we taped up the vents on Roddy's car. There was less front downforce with the vents taped.

I think the box is a great idea, and my track car will have one on it. I just don't think it helps much until you get the underhood pressure to go negative.

John
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"Good plan."

#15 rags

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Posted 13 May 2007 - 03:58 PM

think about just closing off that gaping hole in the front of the Zcar, known affectionately as the "grill". Do that, provide minimal feeding for air, and then funnel that air to your radiator however you wish, via ducts, tuning, sheetmetal/plastic radiator box, or whatever. Mike


Mike/Jon,

Aren't you guys saying the same thing? As quoted above, if you block off the entire grill area and duct that opening to the radiator, aren't you in fact sealing off the rad support to hood? How would air otherwise get to the area on the outside of the duct that is feeding the radiator if the airdam is also sealed to the bottom of the rad support? I know the airdam to rad support has not been discussed in this thread but I know it was mentioned previously.

Joe

#16 gnosez

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Posted 13 May 2007 - 04:56 PM

I need a lot more time looking over and digesting this data.

What I am interested in up front is where all that air (with the windows rolled down) goes? I doubt it exits in enough volume through the side vents and must build up in the back of the hatch air causing drag and lift. Since we run the race car with the windows down (rules) other than the window deflectors is there some concept/benefit to dumping this trapped air out of the Z and if so how?
"you're only young once, but you can stay immature indefinitely"

#17 Tombarace14

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Posted 13 May 2007 - 05:17 PM

What I took from the whole thing is this. Reducing the frontal opening is key to reducing drag. But the major point in making air flow over and under the car. Is to stall the air in front of the car, this is done with the radiator. Any and all air that comes thru the front of the car has go thru a radiator. This stalls the air in front and actually splits the air, before reaching the forward most point of the car. The air going thru the rad. slows down to 10-15 mph, after that it dosent really affect anything. Everytime we talked about getting the air in the engine bay out. Bob Smith told us that it couldnt be avoided, basicly time could be better spent elsewhere on the S30. Hope this helps clear things up a bit.

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#18 JMortensen

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Posted 13 May 2007 - 05:21 PM

The box doesn't create negative pressure. It separates the high pressure air headed for the radiator from the (hopefully) low pressure air under the hood. Then the low pressure air can work on the additional underside area of the hood & nosepiece, which was previously exposed to high pressure, and create additional downforce.

Exactly. The book Tune to Win has some more detailed info on flow and radiators, how to shape them so that you get good flow across the entire radiator, etc. if you're interested Bob.

Note the tests where we taped up the vents on Roddy's car. There was less front downforce with the vents taped.

That's exactly what I would expect. More air trapped under the hood, not getting sucked out by the Bernoulli Principle. So are you agreeing with me there, or did I miss something?

I think the box is a great idea, and my track car will have one on it. I just don't think it helps much until you get the underhood pressure to go negative.

Might be fodder for the next testing session. I'd be REALLY interested to see the results of that particular item.

Jon Mortensen, owner/operator www.petdoorstore.com


#19 Tombarace14

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Posted 13 May 2007 - 05:22 PM

Gnosez, Bob had made comment that making the A-piller an 1/2 in wider would help out alot. Making the air flow out past the B and C piller.

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#20 jt1

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Posted 13 May 2007 - 05:34 PM

So are you agreeing with me there, or did I miss something?


I think our test cars had positive underhood pressure, and that air is flowing out the vents because of the pressure differential. The Bernoulli effect is helping, but it's effect is secondary.

If I am understanding you correctly, you think the underhood pressure is negative, and air flows out the vents solely because of Bernoulli.

What happens when the hood latch of a Z at speed unlatches?

And why?

John
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"Good plan."




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