Custom Splitter on a CDC Classic Chin Spoiler

[zquez]

Worth a lot apparently. I guess those vents are further forward than I remembered, rendering lots of my questions moot.

Any piece of body work that has a convex curvature causes the air flowing over it to produce a vacuum. The apex of that curve is where the most vacuum is, hence why most louvers are placed at that point. The Tiger Racing hood louvers are placed exactly where they will be the most effective.

 

[zquez]

I agree with you 100% on this. I don't know where the "crossover point" is for air out the top vs. air out the bottom vs. enough air period. At this point I'm doing some guessing that I hope to maybe be able to test at some point.

I think the bottom line would be the least amount of air under the car that you can manage. Of course, some air flow under the car is required to create downforce but you would want most of that air passing under the nose as well since that's where most of the grip is to be had.

I think the best way to measure how much air you need under the hood may be by pressure, not temperature. IAT's are the most important factor of course, but neutral pressure in the intake tract is where the intake will be the most effective. You need to choose a speed that you want for the intake to be at the highest volumetric efficiency and duct the hood to achieve that. For you I would guess around 140-150. If you achieve the highest efficiency too soon you will create more spillage drag.

In theory the tray works better when paired with the splitter. It creates a low pressure zone under the tray that is not there stock. If you look at the OEM "splitter" you will see it has a "wicker bill" right in front of the tray. It looks like it is there to create a low pressure zone.

This is true and I thought of that after I posted. silly me.

Can you make me a couple?

ha I think Alex would do a better job.

Soooooooo sweeeeeeeet!!!!

Definitely!

Compared to doing the hood this is easy!

Maybe easier, but not cheaper! lol

We just hacked my GT500 vents/hood up to see what would happen. It reduced underhood temps about 20deg. Now at 45+mph as long as the car is moving underhood temps are only about 10-15deg above ambient (just driving around). On the track under load I'm sure it would be higher though. It doesn't seem to take as much venting as you would think to keep things reasonable under the hood. I'm going to go with even bigger louvers and more effective vents in the stock location and see what I get.

Looks great, and is in line with what I was envisioning, except with the draw vent instead of the stock ones. I need to get some more sensors in my own engine bay to see what's really going on. I plan on getting a pressure probe at the very least to measure the air pressure where the vent is and how much each modification I want to make to the vent affects that pressure. The lower I can make the pressure, the greater the vacuum will be pulling air out.

 

[Philostang]

So the $64,000 question is what is more beneficial. Exhausting the air out from under the hood or having a longer splitter? I don’t have an answer for this.

I didn’t have an answer to the question and I don’t have a Tiger Racing hood on the car yet (still deciding if I want one) so I went half way there. I used the 2010+ OEM “front diffuser” between the K-member and the radiator support. The theory being that it effectively makes the splitter longer and exhausts the engine compartment too.

That's what I suspected. Exhausting air out of the engine bay has been on my mind too, because I would really prefer a full length splitter. I also thought about going the half-solid/half-vented route. Seems that the Ford engineers were focused on the same problem, and from the reports I've heard it offers a nice solution.

My hood is from Stinger and has a decent front vent, but I may vent it further once the splitter goes in. I think we'll likely commit to a "Mark I, Mark II, etc." approach, first trying the solid bottom w/vented hood and see how things go.

Another idea I'm tossing around is using a construction technique from the NASCAR boys. They use a more permanent mount for the bulk of the splitter/under-tray and couple it to an easily removable/replaceable front "blade" for the part that actually sticks out under the chin. The way I see it you get two benefits: you can remove it for street driving to void the worry of smashing it up on curbs, and when the inevitable off-track excursion smashes it you can more readily replace it (as well as spend less on replacement expense). Don't think I'd actually use one of those NASCAR blades, but I like the design.

Not sure yet what I'd do with the splitter struts if I removed the blade for street duty. Seems like taking them on/off might be a pain. Maybe a much smaller "aesthetic" front blade could be used to tie them down and retain some of the look. Dunno, just throwing stuff out there.

Best,
-j

 

[zquez]

Another idea I'm tossing around is using a construction technique from the NASCAR boys. They use a more permanent mount for the bulk of the splitter/under-tray and couple it to an easily removable/replaceable front "blade" for the part that actually sticks out under the chin. The way I see it you get two benefits: you can remove it for street driving to void the worry of smashing it up on curbs, and when the inevitable off-track excursion smashes it you can more readily replace it (as well as spend less on replacement expense). Don't think I'd actually use one of those NASCAR blades, but I like the design.

That's a good idea. The only issue I see with it however is that the front part of the splitter gets at least some of its structural rigidity by being attached at the rear as well, at least on my design. You would need to engineer a better way to mount it, which could be hard given the location. Unless you want to put 6 supporting rods on it... lol

Not sure yet what I'd do with the splitter struts if I removed the blade for street duty. Seems like taking them on/off might be a pain. Maybe a much smaller "aesthetic" front blade could be used to tie them down and retain some of the look. Dunno, just throwing stuff out there.

It would be a pain. But so is swapping pads/rotors, wheels, alignment settings, seats, etc. It would just have to become another part of the track prep routine. My idea for a street splitter is to essentially copy the regular boss splitter, by removing all of the material jetting out in the front but retain the side parts.


You get the idea. Something tells me it would be super unstable like that though..

The other thing that could be done it to make a small street splitter that stacks with the race splitter like the 2013 Boss.

 

[SoundGuyDave]

Not sure yet what I'd do with the splitter struts if I removed the blade for street duty. Seems like taking them on/off might be a pain. Maybe a much smaller "aesthetic" front blade could be used to tie them down and retain some of the look. Dunno, just throwing stuff out there.

Less than $5.00 each... Replace the bolt or rollpin in the chassis-side splitter mount? Quick and easy that way, especially if you engineer the rear of the splitter to pull the same way. Yank four to six of these, and the splitter tray and support rods all come off as a single piece. Makes for simple replacement as well.

 

[07SGT4743]

Splitter looks great! I'm thinking of building my own when time permits. Where did you get the support rods? Are they from a racing supply, Laguna Seca part from Ford, etc.

 

[zquez]

Splitter looks great! I'm thinking of building my own when time permits. Where did you get the support rods? Are they from a racing supply, Laguna Seca part from Ford, etc.

Thanks! They're longacre spoiler support rods. You can get them from any number of dealers. $52 for two sure beats the $380 Ford Racing is asking for theirs!

http://www.longacreracing.com/catalog/item.asp?id=846&catid=21

 

[shark tales]

love this thread

 

[zquez]

love this thread

Ditto! Is that vain? lol

Less than $5.00 each... Replace the bolt or rollpin in the chassis-side splitter mount? Quick and easy that way, especially if you engineer the rear of the splitter to pull the same way. Yank four to six of these, and the splitter tray and support rods all come off as a single piece. Makes for simple replacement as well.

I really like this idea of quick disconnect pins. I see a Mk 1.5 revision in the immediate future. Sure would make it easier to get the car on the trailer if I could take off and install the splitter quickly and easily.

 

[zquez]

I got the chance to install one of my track wheels today to see how the fender flaps fared on them. The wheels have a 1mm difference in offset but the track wheels are an inch wider. Here are the results:






I also measured the height of the body work at various locations. Right now it is lowered for an AI legal 5", even though this car is years away from being an AI car...


3.5" at the rocker


Just over 4.5" at the trailing edge of the splitter


Just over 4" at the leading edge of the splitter.




The difference in height between the leading and trailing edge of the splitter is due to two things. (1) I still had my 19" wheels on the rear in relation to the 18s on the front. (2) The shape of the chin spoiler is biased towards a nose down configuration, which is also why the splitter doesn't appear completely flat from the front. I think the car could definitely benefit from a 1" spacer around the splitter, especially once I add splitters to the side skirts. I wish there was a way for me to measure suspension compression at speed from the downforce. I will be making a video soon of the car under brake dive if I can get an assistant to be my camera man/woman. I'm guessing that 450# springs are barely adequate for this set up. I am considering stepping up to 600# springs for the track, but I think I'm going to track it on these for a baseline first.

 

[Philostang]

I wish there was a way for me to measure suspension compression at speed from the downforce.

There is an old-trick I heard of for that, but to make it work you need to set things up right before you go out on a smooth track or (better) a straight where you can get up to your target speed (and then slow down w/o hitting bumps).

Short version: wrap a zip tie around your shock or strut shaft. Just before you do the test, slide it down to the top of the shock/strut body. Now drive, being careful not to hit a sharp bump that might artificially raise the zip tie.

The zip should record the maximum compression during the run, and if you know the wheel rate of your suspension then you can calculate the pounds of downforce.

Theoretically, the compression should be resulting from downforce, but you need to control for bumps, harsh take offs, hard braking, etc. Taking off slowly at a drag strip might be a decent place to do it if you don't have some smooth country road or some similar place to test.

If you try it, let us know how it goes.

Best,
-j

 

[zquez]

hmm... Probably the best place is on the interstate. It'll be tricky but I may be able to do it that way. The other thing I thought of was maybe something relatively stiff that would wear away and I could measure the amount left. That's probably harder to do than the stupid zip tie though. I suppose I could fit my gopro up in the wheel well but that'd be an expensive test if it fell.

 

[Mach2burnout]

Rubber o-rings work very well for this, but you have to put on your shock prior to install. Of course you have to leave off your dust covers from your shock/strut shaft so you can get to it. The thing I learned about the zip tie method is if you want to measure peak shock travel on track, theres a chance it may fall back down due to lack of drag on the shaft. The o-ring will 'grip' well enough that you can make a few laps and record your maximum suspension travel, or do short test for braking, etc.
And once you install it, its always there to test with any time you need to.

 

[zquez]

Rubber o-rings work very well for this, but you have to put on your shock prior to install. Of course you have to leave off your dust covers from your shock/strut shaft so you can get to it. The thing I learned about the zip tie method is if you want to measure peak shock travel on track, theres a chance it may fall back down due to lack of drag on the shaft. The o-ring will 'grip' well enough that you can make a few laps and record your maximum suspension travel, or do short test for braking, etc.
And once you install it, its always there to test with any time you need to.

I like this idea. I think I'll do this when I swap my whiteline end links.

 

[SoundGuyDave]

The only real problem with either the o-ring or the zip tie is that the final position isn't restricted to aero load, it also takes surface shock load and braking weight transfer into effect. It's a good method for determining your ideal splitter height, but for 100+mph downforce measurement, the only "real" way to tell is a linear potentiometer and a datalogger. That way you can look at the long-term suspension compression and factor out bumps and braking. Or put a strain gauge inline with the strut rods. The linear pot would be cheaper...

Also, the aero force applied will generate a pretty small net movement once you factor in the spring rates. For example, assuming 100lbs of downforce, and 400lb/in springs, you're trying to measure a net 0.250" suspension compression from that force. To measure that and eliminate the "noise" of surface irregularities and braking events, you have to look at the trend vs. time, not a net maximum compression.

Right around $250, which really isn't bad when you think about it.

 

[Mach2burnout]

I've used this method mostly for just overall travel measures. For aero yes you will need to get more sophisticated.


Sent from iPhone

 

[Department Of Boost]

There is a lot of sweetness in this thread.

Nice work Zack!

 

[zquez]

The only real problem with either the o-ring or the zip tie is that the final position isn't restricted to aero load, it also takes surface shock load and braking weight transfer into effect. It's a good method for determining your ideal splitter height, but for 100+mph downforce measurement, the only "real" way to tell is a linear potentiometer and a datalogger. That way you can look at the long-term suspension compression and factor out bumps and braking. Or put a strain gauge inline with the strut rods. The linear pot would be cheaper...

Also, the aero force applied will generate a pretty small net movement once you factor in the spring rates. For example, assuming 100lbs of downforce, and 400lb/in springs, you're trying to measure a net 0.250" suspension compression from that force. To measure that and eliminate the "noise" of surface irregularities and braking events, you have to look at the trend vs. time, not a net maximum compression.

Right around $250, which really isn't bad when you think about it.

250 for the sensor, 700-2000 for the data logger though. lol Don't worry, some sort of AIM system is on my list, but other mods are on my list before I get close to buying one of those.

I think I'm going to have to use a combination of all of the above to figure anything out on my limited budget.

There is a lot of sweetness in this thread.

Nice work Zack!

 

[Mach2burnout]

So where did you acquire the ABS plastic sheets?


Sent from iPhone

 

[Department Of Boost]

So where did you acquire the ABS plastic sheets?


Sent from iPhone

Check out Sintra. Lighter and easier to work with.