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Old 11-04-2011, 02:48 PM   #1
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Default Front Splitter Mounting - With or without front lip?

Well I'm currently building a custom tubular section for the miata's front end crash bar and rad support... and this tubular section I want to be setup for a splitter to pull down on the frame properly from.

Would it be better to have no front lip and splitter meeting the NA bumper directly, or would bringing it down a few inches closer to the ground, and have it mounted up against an R or GV lip, be the better way to go?

With the front lip on, it seems a front splitter would need to immediately angle up toward the oil pan,, in order to continue with a flat underbody/belly pan.

Front splitters. With lip, or without? Opinions.
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Old 11-04-2011, 03:28 PM   #2
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With. Get the splitter as low as possible.
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Old 11-04-2011, 03:48 PM   #3
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So what about the transition into the oil pan area, especially if you want to follow a flat underbody profile...

The lip hangs a lot lower, so there has to be a transition, or a step, to bring it up closer to the subframe.
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Old 11-04-2011, 05:45 PM   #4
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Quote:
Originally Posted by GT42R View Post
So what about the transition into the oil pan area, especially if you want to follow a flat underbody profile...

The lip hangs a lot lower, so there has to be a transition, or a step, to bring it up closer to the subframe.
That transition can be called a "front diffusor", and be designed as such.
How much energy you spend on design and testing is up to you.

If I ever get the energy (2020 or even later I guess) hinging a bent splitter plane in the subframe and hanging it from the bumper frame (wires or thin stuts) would be the choice (of today). The front aero plastic just needs to seal softly to the splitter plane. Flexibility to move up helps when surfing the curbs or digging gravel.

Last edited by NiklasFalk; 11-04-2011 at 06:05 PM.
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Old 11-04-2011, 07:00 PM   #5
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If you have a TR/GV lip, with a splitter up against it, the splitter will be parallel with the ground, to meet with the steering rack. On my car, the front subframe jacking point is 0.25" lower than the pinch weld, and the lip is 1/8" lower than the front subframe jack point.
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Old 11-04-2011, 07:43 PM   #6
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You want it as low as possible, but I don't think you really want to use a GV or OEM lip with the 'brake duct' holes. A splitter is going to be significantly more effective with a fairly well sealed bumper area above it.

Also, try to integrate deflectors on the sides to keep air from hitting the tires directly as they spin. See ThePass's various build threads for what I mean.
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Old 11-04-2011, 09:20 PM   #7
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Quote:
Originally Posted by greeenteeee View Post
If you have a TR/GV lip, with a splitter up against it, the splitter will be parallel with the ground, to meet with the steering rack. On my car, the front subframe jacking point is 0.25" lower than the pinch weld, and the lip is 1/8" lower than the front subframe jack point.
Hmm... I had always thought the GV lip would be hanging at least 1-2" lower than bottom fo the steering rack/cross member, but if its in fact as you say, with the splitter parallel with the ground, bolted up to the lip and rack... than i know what im doing...
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Old 11-04-2011, 09:59 PM   #8
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My real GV lip definitely did not point at the steering rack. Also, this guy's GV lip plus splitter, doesn't look parallel to the ground, either:

https://www.miataturbo.net/cars-sale-trade-6/1994-mazda-miata-%247000-56575/
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Old 11-04-2011, 10:08 PM   #9
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With TG lip on mine the splitter was parallel to the ground with the back bolted to the K member. If it isn't parallel it'll err towards being leaned forward, so you can shim the back part lower to come parallel.
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Old 11-04-2011, 10:34 PM   #10
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Quote:
Originally Posted by kotomile View Post
With TG lip on mine the splitter was parallel to the ground with the back bolted to the K member. If it isn't parallel it'll err towards being leaned forward, so you can shim the back part lower to come parallel.

Well... if that 'shim' is in the form of a 1-3" block/stand off... ... ...


I'm going to see and measure for myself this weekend when I put the car up and see exactly what type of profile this ought to have...
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Old 11-05-2011, 09:30 PM   #11
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Quote:
Originally Posted by GT42R View Post
Hmm... I had always thought the GV lip would be hanging at least 1-2" lower than bottom fo the steering rack/cross member, but if its in fact as you say, with the splitter parallel with the ground, bolted up to the lip and rack... than i know what im doing...
Mine is based on a TR lip, and I find the lowest point of the lip is heavily dependent on how meticulously it is mounted. Some examples show horrible fitment. When I had the TR lip on, the fitment was not flush with the splitter on the pax side as it was on the driver side:

I could have redrilled/refitted a mounting hole further back to make it 100% flat, but ended up getting rid of the lip altogether.



Also I made my claim specific to MY car. Also, look at how much tire is showing. =/
I've since widened the lower corners of the front bumper by about 1.5~2"... which required I remove the TR lip.

Quote:
Originally Posted by kotomile View Post
With TG lip on mine the splitter was parallel to the ground with the back bolted to the K member. If it isn't parallel it'll err towards being leaned forward, so you can shim the back part lower to come parallel.
I did not have to shim mine:





If you see the 2x bolt heads at the back, those are bolted onto the 2x M6 holes right in front of the steering rack.

Quote:
Originally Posted by GT42R View Post
Well... if that 'shim' is in the form of a 1-3" block/stand off... ... ...


I'm going to see and measure for myself this weekend when I put the car up and see exactly what type of profile this ought to have...
Always best to measure your own car anyway. My exact measurements were:
4.75" front pinch,
4.50" at front subframe
4 3/8" below TR lip.

It can very well vary between cars. From what I know, to make efficient use of an airdam, you want to block off as low as you can while not exceeding the lowest point of your car's undercarriage so as not to add excessive drag.
Attached Thumbnails
Front Splitter Mounting - With or without front lip?-dsc01620.jpg   Front Splitter Mounting - With or without front lip?-dsc01605.jpg   Front Splitter Mounting - With or without front lip?-dsc01601.jpg  
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Old 11-05-2011, 09:42 PM   #12
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Like said before, getting the splitter closer to the ground makes it much more effective. Lips to bridge the gap between the top side of the splitter and the bottom lip of the nose can be made cheaply and easily with plastic flower bed trimming from Lowe's or wherever. It works great. I am looking for pictures to post up of mine.
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Old 11-05-2011, 09:48 PM   #13
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Like said before, getting the splitter closer to the ground makes it much more effective. Lips to bridge the gap between the top side of the splitter and the bottom lip of the nose can be made cheaply and easily with plastic flower bed trimming from Lowe's or wherever. It works great.
Is there a point when it is too low?



The previous pix were from a while back.

I am now at 3.5" pinch, bottom-most point is at 65mm from the ground. I have articles in mind suggesting I should cut an opening at the middle of the air dam to let air in, similar to how the RB Type II nose is? The article in mind is in regard to what was done on the Opel Calibra where the middle is higher to get a 0.26 Cd.

Note how much more of the tire is covered. Not to mention the previous pictures are with a 205 on x6.5" while this newer picture is on 205 on x9 et36.

The compromises I see in mine is the vagueness of the stagnation point a pocket of pressure right below the splitter. The car feels as stable as ever at speed though.
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Front Splitter Mounting - With or without front lip?-tumblr_ltbuxjf5rb1r31zr5o1_500.jpg  
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Old 11-06-2011, 04:48 PM   #14
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Quote:
Originally Posted by greeenteeee View Post
Is there a point when it is too low?
It depends on how often you want to replace it... The one on my previous car would touch the ground on a fairly regular basis(depends on the track conditions), but I settled on a height of about 1.5-2" at rest.
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Old 11-06-2011, 06:13 PM   #15
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What he said. If you watch some of the pro classes that run splitters, like German Touring Cars, you will see them practically dragging the ground in some corners. The lower it is though, the more likely you are to damage it.
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Old 11-06-2011, 07:14 PM   #16
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Also, most of them have wear strips (usually a thin block of wood) on the underside that can be replaced easily. This is usually on the higher end sandwich/honeycomb composite pieces though.

I used 1/2" birch with a layer of glass top and bottom. If it got scraped up, just added a bit of glass.

I'll probably go a bit higher on the next one I make...I am long past the point of finding any enjoyment in the process of building splitters.
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Old 11-07-2011, 09:46 AM   #17
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What he said. If you watch some of the pro classes that run splitters, like German Touring Cars, you will see them practically dragging the ground in some corners. The lower it is though, the more likely you are to damage it.
The lower you go the bigger effect, until you flap the thing to the ground and get a pumping effect and loose all control over the airflow.
Adding wear-strips fore-aft will reduce the normal wear and will ensure that the airflow never will be zero. Unless you have a minimum ground clearance rule.
A splitter surface is a wear item, not something that will last year after year.
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Old 11-07-2011, 12:54 PM   #18
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You can buy teflon and HDPE rub strips from McMaster. I will repeat my previous statement that the 'brake duct' holes in the GV lip will significantly reduce the effect of a splitter mounted underneath it. Sealing them up (even with duct tape) will make the whole assembly much more effective.
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Old 11-07-2011, 04:35 PM   #19
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Originally Posted by rlogan View Post
It depends on how often you want to replace it... The one on my previous car would touch the ground on a fairly regular basis(depends on the track conditions), but I settled on a height of about 1.5-2" at rest.
So no theoretical reasoning?
Quote:
Originally Posted by rlogan View Post
I'll probably go a bit higher on the next one I make...I am long past the point of finding any enjoyment in the process of building splitters.
Do you guys factor in your ride height? Mine is approx 65mm from the ground. Going too low could also add frontal area, who knows the effects on drag, which is what I am mainly concerned with.

For the tracks closest to me, there are corners where the TR lip would contact the ground at a 3.625" ground clearance so adding the splitter decreased my minimum height, not to mention since it would protrude further past the TR lip.
Quote:
Originally Posted by NiklasFalk View Post
The lower you go the bigger effect, until you flap the thing to the ground and get a pumping effect and loose all control over the airflow.
Adding wear-strips fore-aft will reduce the normal wear and will ensure that the airflow never will be zero. Unless you have a minimum ground clearance rule.
A splitter surface is a wear item, not something that will last year after year.
Which is why I do not want to have to build these too often.

I've read an article about the Opel Calibra where they blocked off too much with their airdam and it actually hurt the Cd. Aero is heavily application-specific so if you have any Miata-specific info/data, that is what I'd like to hear.
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Originally Posted by vehicular View Post
You can buy teflon and HDPE rub strips from McMaster. I will repeat my previous statement that the 'brake duct' holes in the GV lip will significantly reduce the effect of a splitter mounted underneath it. Sealing them up (even with duct tape) will make the whole assembly much more effective.
This is why I got rid of the TR/GV style lip, it also allowed me to lengthen the width of the bumper.

If you have suggestions for improving my front aero, feel free. I am aware of my compromises considered for clearance. Mainly adding the extra airdam reduced the clearance, but I am okay with scraping the added piece. I upped the spring rate to 12k up front for any decrease in lift. The main compromise was an uncertainty of where the stagnation point would be.

My priority is to reduce drag. Any resulting decrease in lift (which will happen regardless) is an added benefit.
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Old 11-07-2011, 05:08 PM   #20
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If you want reduced drag, then don't run a splitter. Well, I guess I should say, don't run a splitter that protrudes past the lip/bumper.

The height of the splitter will affect downforce far more than drag.

I hate making these generalizatiosn, but...air passing under the car does not add drag (other than the fact that the bottom of the car is not completely smooth)

By adding the splitter you divert more air over the top of the car which increases the speed/pressure differential from air going under vs over the car. This creates the downforce...but adds drag.

If you simply smooth out the bottom of the car...you will reduce drag, but actually decrease downforce(add lift). Great for a straight line/salt flats car, not so much for track car.

There are a couple of interestng books you should read if you are really interested. One in particular talks about the primitive nascar/oval track bodies and how the front downforce is generated in a very unorthodox way. The air coming uder the car is so turbulent (because they have no splitter) that it creates a low pressure area resulting in downforce. Below is a link to one of the better ones.

Amazon Amazon

Last edited by rlogan; 11-07-2011 at 05:30 PM.
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