Street Car Aero Undertray
 

Hello all! I've got a turbo 1994 and I want to replace the factory undertray with something that covers all of my IC piping better, helps direct air into the radiator and ic (its almost summer!), and functions better aerodynamically. I'm also toying with the idea of adding ducting for the IC and rad. I daily the car so it's by no means a race car. I've seen plenty of posts about undertrays but there is a LOT of info out there that hasn't been condensed enough for me to really make a decision. As a college student that is now taking all my classes online, I have tons of time but very little money, so I'm not opposed to work as long as it's cheap. The first thing I'm stuck on is material. I've seen plastic, aluminum, even wood used and want to know whats best in terms of cost and durability for a street car. My second struggle is deciding whether to go with a "flat" undertray or creating one similar to the stock tray that protects the sides of the engine bay from the wheel wells. Lastly, what works best for you guys? Any advice to someone doing it for the first time? Thanks!

Use the LRB aluminum sides/undertray to get started. It's not terribly expensive, and I feel it's very nice quality. You will have to make cardboard templates around your IC piping, then transfer that template over to the aluminum sides for cuts.

The flat bottom piece has about 8-10 10mm screws to take off when it's time for maintenance, but it's very easy to deal with as it leaves the sides in place. I'd argue it's better than the stock tray in that regard, which has to come off in one piece.

Can't believe I've never found this before! Exactly what I was looking for, thanks!

Certainly looks like that would go a little ways toward rad ducting too, no? And be easy enough to build more ducting off of it.

LRB doesnt help you at all with ducting. If i were yall i would keep my eye on left lane designs. I hear a ducting kit is in the works.

Interesting, not even that it'd be easier to build off of?

hmm that does sound interesting...

If it was me i wouldnt waste my time with the LRB. It leave lots of open gaps and doesnt help much at all if any.

Noted, thanks. I'll keep my eyes out for a Left Lane offering.

I'm all for better... But I'm not a fabricator. I'm running the LRB stuff because I FUBAR'ed the stock undertray. For what it is worth, I can say that in two different phases of observation, LRB, then LRB + extra poly fill and taping everything up made almost no difference, but I wasn't overheating, just subjectively running hotter than I thought I should be. Frustratingly, that's still about where I'm at with the extra fill/tape removed, and going with the SM radiator. Maybe a little better off.

I guess what I'm saying is, even after reading countless posts (especially I believe it was sixshooter's) I don't know what I should be expecting given the limited miles I've put on since last year. But, I've averted disaster. But, I'm not a trackdaybro.

Funny of the timing of this post. I just picked up some plywood at HD to start a faux-splitter build. But faux, I mean that I'm not a racecar driver, and that I'm just looking to smooth out the front/bottom in the potential hopes of getting better gas mileage and a little less left up front. I currently have the GV lip on my car and am looking to remove it and replace it with this "splitter." My goal is to have it have the same frontal footprint of the GV lip but be a little higher, and then on the sides I'm going to extend it out and use some sheeting to block the air from hitting my 15x8+25's. Ducting will have to follow afterwards. My question for everyone...

Is there a particular reason the ~$50 birch plywood is used vs the CVX plywood ~$20 other than extra strength, smoothness, straightness, and rigidity? Since I'm not going to be making this thing protrude outward >2-3". If anything the leading edge is most likely going to be "built" up into the front bumper to make it flatter faced. At the current juncture with soft (7kg/mm) springs up front and an irresponsible ride height, I don't want to have a frontal/side profile lower or more forward than the current GV lip. Looking to kill a few birds with this stone.

This is the exact thing I'm trying to do! I've got the GV lip up front too and like the look but I'm more of a function over form guy so I might be parting ways with it. I will say that it seems like removing the lip frees up a whole lot of room for a splitter that won't scrape on a 2 degree incline. I would warn against the CDX because of it's lack of water resistance. It likes to warp a lot and I can't image in would survive long on a street car that is ever driven in the wet -- but then again I've never tried it so it might be worth a shot!

On the topic of the undertray, It seems like a few goals really need to be clearly separated. One is protecting the oil pan, ic piping, etc from debris. This is pretty easily achieved so i'll ignore it for the time being. The other two I see are aero and cooling. The LRB kit seems to help with the first of those problems but I agree that the cooling side of things needs a more focused approach. I'll definitely be waiting on that Left Lane Designs solution because I'm confident that it'll find a way to kill both of those birds with one stone (or at least make it easier to). In the meantime I've got some FRP lying around that needs to be trashed or used so I'm going to attempt to mock some things up with that while trying to retain the GV lip... not the best material but it's better than throwing it in the trash!

Did some initial cuts and measurements. If I go straight from the subframe to the front bumper, to keep it flat, there would be a gap that's approximately equal to the current GV lip or an OEM lip. So unfortunately, I either have to settle with an upward angle, OR revisit this if/when I raise my car's ride height. I already have issues with the part of the lip that's on the front/left scrubbing when I can't get angle on a incline/decline, so an OEM lip might be a necessary solution.

In the mean time, I'm just going to build this to fit "inside" my GV lip. There won't be any particular loads on it for adding down force. It will just be a "flat front" underneath.

That is EXACTLY what I did. It only covers the bottom and goes from the axle line forward to the GV lip and is screwed down inside the lip. It has made a major improvement in front end lift and if you cut a hole for draining oil it is only marginally a PITA to remove every oil change. Suggest 2-3 riv-nuts in the subframe so it is securely anchored.

Perfect - just found your thread. It looks like I'll just be sliding the leading edge into the lip but not fastening it to the lip...and then have some brackets made to secure it to the subframe side (somewhere near where the splash shield is mounted). Did you mean to use some rivnuts in the non-threaded holes on the side of the subframe?

If the holes can be enlarged to fit them, definitely. Otherwise I drilled a couple holes and fastened it in back there. Try cutting the leading edge to the shape of the lip, it likes to pop into the lip overlapping the area by the wheel wells and lock in. Then just pry it out a quarter to half inch and it slips back out.

Suggest you use thinned out fiberglass resin to seal the outside of the wood. I painted mine afterward with truck bed liner to add some wear resistance.

Just thinking about this again... if it's not going to act as an actual splitter... it's effectively an oversized under tray panel - does it need to be plywood - or would coroplast suffice? Needless to say, I do have plywood at the moment. Oh, and thanks for the advice on the wheel well area - noted.

Bear in mind, you can use the plywood undertray as an attachment for a shorter chunk of other material to make a splitter if you ever want to add one. That's why I chose such a heavy material. Well, that and it's general robustness against damage.

I see why people use the birch version xD Sometimes I just like to learn the hard way. Also using the "cheaper" version as a first template. The birch veneer also helps you use MUCH less paint to seal it. The plain plywood was effectively a sponge. I should've used a roll on/filled type epoxy.