Under tray

I am doing flow simulations on my first gen tacoma. I am focusing on designing two things: 1) an aerodynamic undertray 2) a custom camper shell (aeroshell)

The intention is to 1) save gas money and 2) be able to make my tacoma a sleeper and handle safely at high speeds.

I am wondering if anyone else has made anything already? I am particularly interested in the under tray since I am already modeling the camper shell.

 

I’m really curious how much you’d be able save that way. These things have the aerodynamics of a rounded off brick and a 20 year old drivetrain, there might be lower hanging fruit under the hood.


What material are you considering for it?

 

As for the low hanging fruit under the hood I already have that covered. I have a Vortex cold air intake which should improve gas mileage as long as your not constantly flooring it (it has an extra injector at intake) (see link: https://volant.com/collections/1997-2004-toyota-tacoma/products/closed-box-air-intake-18424). I got this one because I have seen guys do a 2jz engine swap with this intake and also the LCE engr. turbo kits with it.

I also have headers that shift the entire torque curve up for this truck so that when I do accelerate my engine has less resistance and more torque output to the wheels. (see link: https://www.summitracing.com/parts/...yz4Itbbx6F_A8hchCawU_z3yb9pHI4LIaAi6XEALw_wcB ) What convinced me to buy this kit for my truck was a graph of a torque curve before and after the headers were installed on a Tacoma. I can't find that right now but the area under the curve increased and the torque curve parallels the old one, it was just shifted up slightly.

I have yet to do a MPG comparison for these but before these mods I was getting 26 mpg highway at ~60 mph.

For the undertray I am going to first start with cardboard duck taped together just to get an outline and necessary cutouts. Then I am going to buy 1/2"x4'x8' insulation boards from home depot.
(See link: https://www.homedepot.com/p/R-Tech-...-Rigid-Foam-Board-Insulation-320810/202533656 ) I still do not know how I am going to mount it. I am going to make my truck able to run at 140 MPH so I am still unsure what is a good form of attachment...

I know for a fact that from my solid works flow simulations the two main contributors to drag are from under the truck and the bed of the truck. The model is a double cab with a bed that is a little longer;like the extracab.

This simulation acts as if it already has an undertray at ~60 mph. I will give updates on the flow simulation once I refine my prototype for an aero-shell (camper shell).

 

Interesting idea, looking forward to see how this project comes along. Also welcome to TW!

 

Really interesting, I imagine that a lot of the drag will be parasitic. The underside of the Tacoma is filled with crossmembers and the front IFS is in high airflow areas. One thing I have learned in the aerospace industry is that even small changes can make a massive difference in efficiency. One thing you should consider is the air coming from the wheel well area, I'm not sure how you would measure the air pressure difference but non the less it should be considered. Keep up the amazing work!

 

I have yet to make an undertray since I live in OR without a garage and its wet out there. So I have been focusing on understanding the Aero-shell. I am keeping tires out for now for simplicity. Especially since I am changing my wheels in the future anyways.

See attached for results summary. I have yet to come up with a design I like but I am learning a lot from these bad designs. Design #2 has least drag but some lift at high speeds. I can't have that!

 

An undertray has been on my mind for years. My plan is to inverse scoop around where the firewall is, bolt through the frame rails, and have a bend along the length to the meet pinch welds. If flow attachment is preferred, can strake that radius. Then basically run that back to the rear differential, with an opening for the driveshaft to move up and down. Optionally add a front lip and plates for under the LCAs.

You'll need an aftermarket ECU or frequency clamp to get over 110mph.

Also, be wary of solidworks flow calcs. When I tried, it really hated thin pieces or hollow areas in an otherwise solid block, so you may get false approximations for the bed area

Finally, don't underestimate the effect a few vortex generators can have once you design your aero shell. They keep the flow attached to the top as it tapers off to the tailgate, significantly reducing lift and drag

 

I am going for a much less robust design for the undertray with just foam, trying to keep it as flat as possible and attach via some elastic tie downs on McMaster-Carr and some Velcro in some spots.

I will have an aftermarket ECU and tune with the LCE engineering low boost kit for the first gen. Can you share a link of an example frequency clamp? I have never heard of that till now.

As for the Solidworks, just make sure flow is set to external, free surfaces with a set time domain and calculation interval from the flow simulation setup wizard. I haven't had those issues...

When you talk about vortex generators do you mean a vortex generator that makes them go in the direction depicted in the attached image? Do you have any links for buying the vortex generators or do I need to design it?

 

Let me get this straight:

You want to run140mph with a 1/2" thick piece of fiberboard attached to the underside of your truck using elastic tie downs and velcro??

Where do you plan on driving this?? Bonneville salt flats?? Not on any public roads, I assume??

NOT trying to be a smart ass, just curious

 

I want to design the truck to its limits with the goal of that upper limit being 140 MPH and I will only be driving that fast on a drag strip for testing and for fun. My goal ATM is to make the truck as efficient as possible. Most of the time the foam board will be operating in the range of 30-90 MPH. If I can make the foam board tolerate 140 MPH on a smooth strip then I know I am operating at a high enough factor of safety at lower speeds when it is bumpy. I am a mechanical engineer but do not know how to calculate stress tolerance of a foam board... I will test at lower speeds and slowly go faster, using a Go-pro or something to watch for deformation. I will reinforce as needed when the time comes. This way, the system is as light as possible, and relatively easy to take off for oil changes and stuff. I feel like I can get away with Velcro if I place the board strategically against rigid members. For example, I can place the board on the inside lip of the rear bumper where the negative pressure is sucking it down. This way the thing holding it in place is the bumper, the Velcro just holds it in position. You have a genuine reason to be concerned with the method of attachment; I am unsure how fluid flows down there since I do not have access to a wind tunnel.

After I make it as efficient as possible I want to make it as powerful as possible. The result will be a functional sleeper truck that will have mad acceleration but at the same time I can turn down the boost and drive it in a way to take advantage of the economical aspect of the 4 cylinder. I love to drift and rally my truck on the streets when nobody is around. I like being pushed back into my seat but I want the functionality of a truck. I am not going to buy a sportscar because I would rather have something custom and personal that does both. I also just like how rear wheel drive trucks feel to drive. I love to push the design limits of things because the continual improvement process is fun for me. I am a long way out from completing this project but I will have access to a garage soon!

 

I honestly thought you were a Mech Eng when I first read this - my son is also a Mech Eng and I remember this shit from his senior project - a glider.

I guess I would be concerned with the fiber board flying out from underneath while driving and causing an accident and possibly someone seriously injured or dying. That had to do with my comments about the velcro and bungee cords. Aluminum or titanium (which is what my son deals with) bolted to the underside like skid plates seems much safer.

 

You would attach to the top of the cab right before your taper starts. They induce turbulent flow which functionally help removes vacuum behind them from gradual surfaces. https://www.youtube.com/watch?v=dr_G4hbXSLQ




Here's a frequency clamp (overpriced, but PnP)
https://urdusa.com/urd-speed-unlimiter/

 

OP: Do you watch NASCAR at all???

Downforce and spoiler heights and front splitters etc. etc. etc. WAY over my head!!!!

 

I get the concern, safety is #1. Fun is #2 priority.

I do not watch NASCAR, I just like cars.

Also thx, for sharing stuff about vortex generators and how they are used.

If I am going to use something more rigid I will likely use a plastic. I honestly think insulation foam is strong enough if I run ridges of plastic or frame with the smallest size T slotted Al. If I end up using bolts I will use Nylon inserted wing locknuts with Nord lock washers. That way vehicle service is timely and I don't get charged additional labor fees.

Thank you for considering people's safety and making that a core part of the conversation.

 

140MPH ? are you talking speed over ground, or apparent wind speed that the camper/farings will be "seeing". 1st gen Tacoma's are electronically limited to 105mph, and even then you'll be hard pressed to get there with additional weight from things like under trays (aero fairings) unless you're going to be making some large carbon components. Adding a glass camper will obviously only hurt.

This sounds like fun and all, but you need some realistic assumptions in your model. 140mph is not a realistic assumption. bull shit in, bull shit out as the saying goes.

 

Not sure if you've ever seen this website OP, but you might find some inspiration for your project. https://www.aerocivic.com/

There are also some hyper-miling forums out there where people geek out on these kind of mods, can't remember any of the names though.

[EDIT] This is the forum I was thinking of: https://ecomodder.com/forum/

 

interesting
Personally I don't think foam board will hold up and I would be wary if trapping excess heat in

 

Step 1: Design and fabricate a nice set of 1st gen fender skirts. Document the process on TW.
Step 2: By the time you're done, you'll have the post count and the fan base needed to sell a few. Sell a few.
Step 3: Repeat the process for 2nd/3rd gen Tacos. Send a free set to Chloe.
Step 4: Post a speculative drawing of a 4th gen Tacoma with fender skirts.
Step 4: Announce that, due to high demand, fender skirts are being stolen at an alarming rate. Post a video of how easy it is to steal a set of your fender skirts.
Step 5: Market your fender skirt security device.

 

You make a great point about trapping excess heat in! I was thinking it would be fine since I will make cutouts around frame members/ exhaust that are large enough to allow heat dissipation. I live in OR where it is coldish but I know some people live in 120F weather so I should consider the thermodynamic side of it more. I have been thinking mostly about the aero side of it but I should consider both. Some insulation foam types are fireproof. See attached document for an external insulation board. It is fireproof and strong enough to be bolted down.

As for the fender skirts. That is one of the last things I will consider since I will be selecting my wheel size based off my transmission upgrade. Also, most people will likely not buy them since they do not have aesthetic appeal. Most car manufacturers intentionally avoid them because they make the car look less like a car. Since I would make it specifically for the Toyota Tacoma I doubt many people will buy them. In general, people who buy trucks do not care about aerodynamics. If they did, they would likely not buy a truck. For the few people that do care about the aerodynamics of their taco I can get the low hanging fruit of an under tray and aero shell which will have pretty large impacts without aesthetic losses. The underside of a the truck is pretty universal. The fender skirts are not so universal since a lot of people mod these trucks and get bigger or smaller tires. I also don't want to make it hard to rotate my tires every 5k miles...

 

Nerd shit! Love it!