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2018 Mustang GT PP2 Undertray

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  • 2018 Mustang GT PP2 Undertray

    Tech Post for July 14, 2020: This post is about adding a PP2 splitter lip + undertray to a base 2018+ GT. This WILL NOT WORK on 2015-17 GTs, nor the GT350/500 cars.

    The 2015 Mustang GT came with an optional "Performance Pack 1" package that included the 15" 6 piston Brembo front brakes, wider wheels, and a better undertray.

    In 2018 the Mustang GT added the "PP2" package, which also added wider wheels, a more aggressive splitter, and MagnaRide shocks. We decided to NOT buy this package, which would have pushed the price up over $52K.

    Instead we bought the base model 6-speed 2018 GT for $34K. That left us a lot of money to make up some differences...

    We quickly installed 19x11" wheels, coilovers, camber plates, and the PP1 brakes on the car - which made a HUGE difference, and more than made up for the difference in the base vs PP2 (for far less $$). But as you can see above, there is a "shovel" nose on the base front end that curves "up" to the splitter. This feeds needless amounts of air under the car. We wanted the lower, longer extension of the "PP2 splitter", with its small addition in front downforce, but also the PP1 undertray - which had two integrated tunnels for brake cooling.

    The base 2015+ GT has wacky inverted hat front brakes (above left), and as such they can flow ZERO air from the backside through the vanes. Therefore the undertray these "non-PP" cars come with is somewhat flat-ish. No tunnels.

    In early 2019 we researched, ordered, re-ordered, and installed ALL of the parts needed to convert a base model 2018 GT to a PP2 undertray, shown above. It took multiple purchases, a lot of guess work, and a bit of trial-and-error. The "online lists" people had at the time were missing all sorts of bits and pieces, and we figured out some work-arounds to avoid a few purchases.


    We thought about selling the PP2 splitter but Ford keeps changing their prices almost weekly... we'd lose money by the time we sold one. Some of our OEM stuff has gone up 500-700% (small parts) and most has gone up 20-30% during the 'Rona. Long story short - we're just going to share what we learned here.
    • Mustang PP2 front splitter, JR3Z-17626-AA ($410.60)
    • Mustang PP1 lower lip, JR3Z-17D957-CA ($200.42)
    • Lower Cross-Member brace, FR3Z-5025-A ($30.23)
    • Lower Cross-Member Bolt, W718025-S439, qty 6 ($1.56)
    • Insulator - Undertray piece, FR3Z-6P013-B ($24.05)
    • Under Cover Retainer Nut, W717220-S300, qty 4 ($1.56)
    • Mustang PP1 undertray (belly pan), JR3Z-17626-B ($95.74)

    If you have a 2018+ PP1 car you just need the PP2 extension. But the base model cars need a LOT more parts. Don't ask us questions about this mod - this post is our "free tech" answer, right here. Take the parts list here and run with it. We can't tell you where to buy it, but the "cheapest" online places like Tasca Ford will absolutely WRECK you in shipping costs. You were warned.

    You do not have to take the front bumper cover off (above left) - just showing what the "base" lip looks like. You do have to take all of the undertray bits off, if you have a "base" GT. The PP1 cars can keep this on.

    Again, if you have a 2018+ PP1 you won't need to upgrade all of the undertray and support pieces, just the PP2 splitter extension. The base model GT folks will need a lot more parts.

    The base model lower black lip is different than the PP1 lip, which you will need. Remove the base model lip and add the "J-clips" as shown, above right.

    Add the PP1 lower lip first (above left), then the PP2 extension to that (above right). There are supposed to be a bunch of plastic clips but we shortcut the "let's order more parts from Ford" line and just used nuts and bolts - you can easily get to the backside, and we figured we might need to remove this extension later if we added "real" front aero (we never did to this car).

    You can see all of the hardware holding the PP2 extension onto the PP1 lip and front bumper cover. The PP2 extension sits a couple of inches lower than the PP1 and makes for a flatter undertray. It isn't really flat, and there is a transition down back at the subframe, but it is better than the base model's "shovel nose".

    We quickly realized we needed this U-shaped steel bracket on our base GT, which bolts to the subframe. There is also a little "hinged" plastic tray that fills that "U". This is where PP1 "undertray" attaches at the back, and connects from here forward. Lots of nuts and bolts, too.

    Next we realized the PP1 front fender liners were different - they had this "notch" for the tunnels. We just cut that portion out and used plastic clips to hold the modified liner to the PP1 undertray, around the tunnel openings.

    Two months after adding the PP1 undertray / PP2 splitter extension we got tired of smashing 4" brake cooling hoses with the 315mm Hoosiers (above left) and converted the car to our brake cooling deflectors, with guidance by engineer Marco Garcia. He designed the PP1 brake / undertray / stock cooling deflectors to combat track brake heat, and we just took his work and went much bigger. The brake deflectors work a LOT better with the PP1 undertray tunnels, of course.

    This tunnel + deflector trick makes brake cooling SO much easier, more efficient, and you don't have to worry about crushing the ducted hoses every weekend.

    Hope that helps answer some questions...
    Last edited by Fair!; 07-14-2020, 02:42 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev

  • #2
    Update - in July 2020 our tester Jon Miller bought all of the items listed above for his 2020 Mustang GT base model.

    Left: Stock 2020 Mustang GT with the base model lower lip. Right: The same car with the PP1 undertray, PP1 lip, and PP2 splitter extension

    He priced them from the online places like Tasca Ford, and it was close to $800 in shipping. Then he used a local Mustang club's "discount" to get them at a local Ford dealer:

    This includes both the PP1 under tray, PP1 lip and the PP2 splitter lip extension and totaled $942 before tax. Ford changes their prices on their parts every week, but this is here mostly to show the part numbers. Does this cost a lot for a few pieces of plastic? Probably. But the $8,500 PP2 package is pretty costly, too.

    We had Jon bring his car into our shop after an MCS install and we took a few shots of his PP! undertray + PP2 splitter extension install, which was flawless. The 19x11" Forgestar wheels and 305/30/19 Bridgestone RE-71R tires make for a BIG upgrade in grip from the base GT's 18x8 / 235mm wheel and tire combo.

    Note the modified fender liner (above right) that he trimmed to fit the "tunnels" molded into the PP1 undertray. Very cleanly done, you wouldn't know it wasn't factory if I didn't point it out. These tunnels will be utilized when he installs the 15" Brembo 6 piston brakes + master cylinder he bought from us to finish the updates to PP1 spec - making this base model GT much more track worthy!

    Last edited by Fair!; 08-01-2020, 03:24 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev