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My philosopy is to get the mechanical grip right then, and only then, add aero. Seeing the diffuser concept is in theory less potentially problematical than a venturi I will go that way. If the car still tends towards high speed understeer then it probably is the driver, it usually is :)

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Emailed McBeath about my splitter/airdam combo idea. Here is the response I got:

 

If you think can't smooth out the underside and integrate a diffuser then probably the lower the airdam is at the front the better. Combining this with your idea of (effectively) extending the lower part of the airdam forwards would offer a horizontal surface onto which the stagnation pressure in front of the car's nose could act' date=' which would probably add a bit more downforce than you'd get from a straight vertical airdam in line with the front. And yes you migth extend the area on which the low pressure beneath would act.

 

However, if you could panel at least under the engine bay so that you could benefit from a splitter as the lowest part of the airdam/splitter assembly I think in reality there'd be the potential for more downforce. I know this isn't what figure 4-11 suggests when viewing the relative magnitudes of the low pressure regions, but the model was relatively simplistic here and I don't think it necessarily reflected what would happen in the real world. A splitter would ordinarily feed into a flat panel downstream, and even into mini diffusers between the wheels and the engine, and this would extend the darker blue region you see directly under the splitter in the lower inage in fig 4-11.

 

 

The sensitivity of a splitter increases the nearer to the ground it is obviously, and if the splitter height is on the same plane as an under-car panel, I'm guessing it wouldn't be so low as to cause you problems in this respect.[/quote']

 

So he thinks my idea has some merit, but the splitter/diffuser to flat bottom to diffuser underside is a better idea for ultimate downforce production. My main beef with the undertray idea is that it seems really hard to do. His comment also seems to indicate that the splitter height can be fairly high off the ground and still function, which makes me wonder what went wrong with John's attempt.

Edited by JMortensen

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Emailed Mr. Bunch and got a long response. Here is the meat with regards to the airdam/spoiler combo:

. I had that piece of conveyor belt on the leading edge, but no more because I am convinced that it messed up my air flow under the car. That skirt might help function as a damn, but will screw up the air flow under the splitter. It was the first time I had ever done that too. Also my splitter was too flat, on hard acceleration it was up in the front. A good material for a splitter is black nylon etc that Plastic suppliers stock. It can take lots of rubbing and wears great. That is what I am changing to now. 1/2 inch thick.

 

So it looks like he thinks it's better without.

Edited by JMortensen

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Been emailing some more with Glenn, and I think what would help is a look at the rear of his car. It has a HUGE diffuser on it and apparently a full undertray as well. He was a bit confused about what I was asking, but we finally worked it out. He ended up saying: "Dont put the [airdam] on the splitter, unless you are only interested in an air dam and are willing to forget about the downforce of that tray and the splitter."

 

This makes perfect sense. You need air to the diffuser, so if you're running a diffuser, then an airdam isn't helping. Still leaves me wondering what to do since I can't run an undertray for autox but have no rules to follow for track days...

 

He also said that they changed so much stuff on the car that the driver was having a hard time getting the most out of it. He thought they had another 3 seconds per lap in there but they broke in the first session after only 3 laps and still won outright. Impressive. :eek:

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FYI - I added a splitter. Made of 1/4" plywood as a test piece. Extends 2.5-3" in front of the airdam and back to the front swaybar. Dropped 1/2 second lap time with no ill effects. It was noticeable from the drivers seat in med+ speed sweepers and seemed to help braking as well. The cheapest 1/2 sec you'll ever find and it doubled well to mow the grass. Lets just say the splitter planted to front end so well that I could apply significantly more throttle in some turns. Pushing it too hard I power on oversteered ... cracked a rear stub axle flange. Now need to find a permanent material although it's got a nice natural green patina. :)

 

Cameron

Edited by heavy85

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Did you try the airdam on it?

 

Nope. Only run two races with it and was astounded by my lap times in each so haven't touched it. Not really planning anything else for next year other than to make it out of stiff plastic or something that wont warp when it gets wet.

 

Cameron

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I am currently working to put a splitter on my car. I have sourced a plastics manufacturer locally

I spoke with a miata performance company out of Dallas that made splitters. He gave me a list of parts they used as well as design ideas. I should have something in a few weeks. Money is really tight for me right now, pregnant wife, toddler, and training for a adventure race........ So my time is limited on the z... I will post up pice when I have it done.

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I picked up a used Tegris NASCAR splitter for under $50 shipped. It will require some trimming to make it work on the narrower Z, but it should work great when done. I'm planning on using some rubber impregnated cloth connected along the trailing edge to make an under tray of sorts.

 

My main concerns were cost and ease of replacement, not weight like yours however.

 

IMG_20130405_201920_684_zpsa7253942.jpg

 

IMG_20130405_201846_179_zps3a1478bb.jpg

Edited by LanceVance

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They did a test of this airdam on splitter idea a couple months ago in RCE. Unfortunately the air dam was still pretty high off the ground, so IMO it functioned to spoil the air going under the car more than to create a low pressure area. I still think this could work, particularly at low speeds. 

Edited by JMortensen

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Strength of the splitter and whatever it mounts to is important.

 

At the mile racing events, I see between 2 to 5 cars that come back with the splitter either missing or dragging the ground.......including our twin turbo ford GT that failed downward and dragged the runway effectively reversing the intended effect.

 

Since this happened north of 200mph with the car feeling fine to the driver and watching the guys I work with make a pathetic attempt to remount it to components that would surely fail again, I simply removed the splitter and we have been running without it at speeds over 283mph with no ill effects ever since.

 

That said, a Z car is a far different beast and will surely require some sort or dam or splitter to manage the air going under and reduce lift..........just make sure it's strong because having it fail and running over it could end up like the camaro that crashed at the texas mile recently.

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I'm afraid I don't have any progress to report. The Z is currently disassembled pending body and engine work (lots of modifications in the works); won't be going back together for some time!

 

That said, I've been plotting how I'm going to mount it. The Tegris is incredibly strong, and in a low speed impact (i.e. speedbump, pothole etc) likely to destroy whatever it is mounted to before deforming itself. I've found some rods to support the leading edge that will bend and (hopefully) snap before damaging anything else. Found them at Longacreracing.com (under the misc section).

 

As far as the trailing side goes I'm planning on glassing in a thin steel band to reinforce the airdam and then attaching the splitter with some plastic/nylon bolts. This should allow for separation without excess damage to any other body panels, and should keep things fairly lightweight to boot!

Edited by LanceVance

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Give it a shock absorber. My plan is to mount the rear of mine to the crossmember with a clevis pin setup acting as a hinge. Then the front mount will be a long bolt with a rubber bushing or two on it. If the front of the splitter hits the ground or something, it will compress the bushings but it will have a little bit of give to it, instead of being totally rigid. Then I'll use cables rather than turnbuckles for supports in the front. I figure if I go off the track it's less likely to destroy the splitter. 

 

This idea comes from tube80z.

Edited by JMortensen

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Not a bad idea... A large OD bushing with a small ID used to mate the splitter with the airdam should work well with the flexible front rods. Keep with the plastic bolts and I'll have multiple break points where I want them.

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Having got my lent copy of Competition Car Aerodynamics back, finally, there is a mention of using a diffuser design in the front undertray, will have to study that more to see if its a practical design for the Z.

image_zps40f2525a.jpg

 

Like this? Its my splitter as if about an hour ago. V2.1

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