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Custom Skid Plate (Flat Floor Pan?)

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Henderson
#1
So I jacked up my Lil' Red Turkey the other day to swap back to my rally wheels and mock up a skid plate. Sliding around in the rocks and sand has taken its toll on the underside of my FiST, especially the fuel line protections on the sides.

(Sorry, my potato of a cell phone camera sucks...)



I've looked around the web and I cant seem to find a full body skid plate, which is what I need/want. So out came the cardboard, markers, razors and measuring tape. I took out some screws on the bumpers and drilled through the cardboard and used some push pins to hold up the back to get an idea where it would sit on the front.



Cut out where the wheels will go and where the control arms would rub. Then moved to the middle, bolting up a sheet where those protectors secure too. Measured the holes and had to get a little creative to get the angels and side holes. Finally dropped the cardboard down and cleaned it up a little bit and remeasured.



I want the front to stick out a little bit and fold up, then carry to the rear. I have a plan for the back axle as well, just ran out of daylight to get it mocked up. Once I get the middle figured out, I'll R&D the back end. I have a hinge system in mind that might work.... maybe... only a trial by fire will tell.

Today, I started mocking it up in AutoCAD to try and get a more.... polished version of design. That way I don't have to carry around a huge cardboard cut out of what I want. Plus now I can make sure all the math adds up.







Still need to work on the front shield, but its a good base to get an idea of how it will be. I emailed a shop near me to see if they can help me out, so we'll see what they say.

Preliminary Specifications:
- Aluminium
- 3-5mm thick
- Front bumper to rear bumper
- No openings for oil changes

Not only will it be good for me on the dirt, but more aerodynamic at the track and autocross. I am a little worried about heat and have a few ideas on how to combat that, but I need to see what the shop can do for me first.
 


jeffreylyon

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#4
End goal is for it to be a one piece aluminium, 3-5mm thick, skid plate from front to rear. Not only will it be good for me on the dirt, but more aerodynamic at the track and autocross.
Cool project. A flat bottom FiST will get pushed out of the Street classes and into full Prepared or even Modified. You're legal in SP and SM until you get past the forward opening for the wheels, so the first of the three panels will probably be legal, so maybe you'll be better off cutting the plate in 2 or 3 panels.
 


OP
Phoenix104
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Henderson
Thread Starter #6
Cool project. A flat bottom FiST will get pushed out of the Street classes and into full Prepared or even Modified. You're legal in SP and SM until you get past the forward opening for the wheels, so the first of the three panels will probably be legal, so maybe you'll be better off cutting the plate in 2 or 3 panels.
It's good to know and clear that up for anyone interested in competing at autocross. If people are interested in the final product, I can make adjustments in CAD pending on the rules and regulations, then see about making it. But that's for a little later. =D

Personally for me, autocross is a side task. I've been in SMF every time I've gone since I put a Blow-off valve on first day I bought it. Been running again fully built, caged and tuned Civics and Miatas all while doing quite well considering that a blow-off valve was my only modification, but alas. I go there to have fun and not to compete. I just like racing and being around other cool cars, stock or modded.
 


jeffreylyon

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#7
Personally for me, autocross is a side task. I've been in SMF every time I've gone since I put a Blow-off valve on first day I bought it. Been running again fully built, caged and tuned Civics and Miatas all while doing quite well considering that a blow-off valve was my only modification, but alas. I go there to have fun and not to compete. I just like racing and being around other cool cars, stock or modded.
Yeah, SCCA rules seem a little arbitrary - BOVs put you in SM but BPVs are open in SP. Slap on a carbon fiber hood on your otherwise stock car and you're in SM. Turbo charged cars are limited more than N/A cars in ST. I think that I'd prefer NASA's point-based system, but we don't have an active chapter in Western PA.
 


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#8
Interested. This is something I've looked at/contemplated as well.
 


Siestarider

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Stuart
#11
Not only will it be good for me on the dirt, but more aerodynamic at the track and autocross. I am a little worried about heat and have a few ideas on how to combat that, but I need to see what the shop can do for me first.[/QUOTE]

Several of us traded info back and forth on Aero Mods and Cooling thread on this forum. I found cooling problems with just front pan, similar to what you show. Had to cut wheel wells further toward center. Also found aero was not improved to the extent I expected as measured in Coast Down, even detrimental.

RMAudio used a clever vent system on his front pan and did not report cooling problems, but he also has the first (reported here) big radiator plus oil cooler.

All the engine heat has to leave via front wheel wells or beneath belly and exhaust "tunnel". Don't get too far from home if you try the full belly shroud, case you have to limp.

I was planning to revisit this idea when I can look at what Ford did with Focus RS. Probably some good clues in their belly pan.
 


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#12
^ I can tell you for fact that there's not nearly the shrouding you'd think. Less than a C6Z06 Vette. I've seen the bottom of both first hand. We just PDI'd another RS the other day, I didn't take any pics of the bottom, but I think a coworker did. I'll ask him if he can send me the pics. Just texted him...

I think your best bet will be small panels in strategic places to help ease airflow across the bottom of the car, rather than one simple flat sheet. I tend to put my car up in the air every week or two, I'm going to start brainstorming some stuff with it and will report back as I have
time to experiment. I usually have it up on Saturdays while I'm working, so my time is limited to sit and ponder life under my car, and I'm not sure that I'll be implementing anything until spring when I can actually test it.



Edit to add, I have this pic I took from the first one we got. You can see its kinda just filler panels to get rid of pockets on the bottom.
 


Siestarider

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#13
^ I can tell you for fact that there's not nearly the shrouding you'd think. Less than a C6Z06 Vette. I've seen the bottom of both first hand. We just PDI'd another RS the other day, I didn't take any pics of the bottom, but I think a coworker did. I'll ask him if he can send me the pics. Just texted him...

I think your best bet will be small panels in strategic places to help ease airflow across the bottom of the car, rather than one simple flat sheet. I tend to put my car up in the air every week or two, I'm going to start brainstorming some stuff with it and will report back as I have
time to experiment. I usually have it up on Saturdays while I'm working, so my time is limited to sit and ponder life under my car, and I'm not sure that I'll be implementing anything until spring when I can actually test it.



Edit to add, I have this pic I took from the first one we got. You can see its kinda just filler panels to get rid of pockets on the bottom.
The interesting stuff is in front where Fost has an elaborate pan vs Fist. Thanks for this rear shot, Ford keeps the exhaust tunnel open. Maybe for heat diffusion via rear wheels and tail. Hard to tell from this shot where front pan stops and how it lets hot air out at front wheel wells.

Theory says the heat is best exhausted as far to rear of car as possible. Theory also says ducted heat outlets should be of greater cross-section than inlets for best heat extraction. Our car sort of has this latter feature with relatively open air paths along both sides of engine behind coolers.

I added experimental hood vents along sides where WRC cars (and my pressure tests) indicate lowest exterior hood pressures could serve to evacuate heat via hood. I can stick my hand out window at 80 mph and feel the hot air from drivers side hood vent, but I have not figured out a way to measure hood heat transfer vs wheel wells and underbody heat transfer.

The vents do not make a noticeable difference on track in terms of water and oil temps, but I have not installed "lips" along upper side of vents to increase low pressure area yet.

Also, I have not reinstalled my modified belly pan to see what that does for hood venting.

All this stuff still fascinates me, but I decided to get a ride height on the coilovers set before more experiments, have not finished that yet.
 


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#14
Reference, had a new viper on the hoist this morning.





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Siestarider

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Stuart
#15
Reference, had a new viper on the hoist this morning.





Sent from my SM-G870W using Tapatalk
Wheel wells opened further than my last undertray experiment. Seems like the small entrance (grill) big exhaust diffusers (wheel wells) suits Viper. Also reflects your "use panels" approach. Viper is very fast straight line, my bet is they put some wind tunnel time into this. Thanks for posting.
 


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#16
Yep, should've taken more pics of the back, it has a functional diffuser, no strakes, but imagine you just closed off our entire rear from the swing axle to the bumper skin and made the rear mesh functional. The gt350 uses a much smaller diffuser, that narrows to the pumpkin. The viper will be back on the hoist in a few days one of the apprentices fucked the rear tire on the tire machine. $1000 tire, ruined.

I'm sure another gt350 will go on the hoist at some point. But we've only sold 2 RS's from our dealer, so I don't know the next time one will be in.

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#17
Merry Christmas.

Focus RS undertray








Engine side (top side) of undertray, you can see the additional air redirection flaps they have in there. Most of the ducting is to get air onto the PTU (center "diff") and up across the transmission.





This is back by the gas tank, you can see again, it's just panels to help reduce pockets for dead air to collect in. Yes, the hoist pad is contacting it, no it's not going to damage anything, and I'm not the one that lifted it, the owner of the car did.


Focus ST for reference.


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#18
It's also worth mentioning that this tray must have been expected to do something at least, since it's the only one I've ever seen on a Ford that has a clip to support the middle of the tray. It's barely visible in the 3rd picture up, right behind the large vent to put air onto the PTU. Presumably that will keep it from sagging as under-vehicle pressures drop.
 


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