1999 4Runner 4x4 Streamlining
 

Purchased a 1999 Toyota 4Runner, 3.4L V6, 5 Speed R151F Transmission, 4x4, 4:10s. It was selected because it has real 4WD, stick shift, 4 Doors, will fit two car seats and two adults, capable of towing and hauling, smaller than my Suburban, and has a comfortable ride. My wife has a similar one and I enjoy it (other than the missing clutch in hers). This vehicle will be for daily driving and moderate off-road use.

I am not going to mess with the powertrain on this one, mainly just some aero add-ons and a few off-road related items. I am putting this in the Aero subsection since that is the focus of this thread.

Currently planning the following:
Aero Mods:
Swap 265/70R16 Cooper AT3 to 245/75R16 Michelin LTX (in progress)
Remove roof rack, rear deflector, side steps, and fender flares.
Small boat tail attached to the rear hatch. (Fiberglass over foam)
Belly Pan/ Skid plates (1/4” Aluminum)
Tire Spats (Conveyor Belt)
Grill Ducting

Other Mods:
Change all fluids and stop oil cooler O-ring leak (in progress)
Upgraded Sway Bars
Front and Rear high clearance hitches, with winch on cradle.
255/85R16 tires on extra wheels to swap for dedicated trips.
Extra Insulation/sound deadening in interior.

Dream wishlist:
E-locker axle swap.
Dyna 5th gear swap in transmission during future rebuild.

I am open to suggestions, please give me your ideas on what all I should do/not do to this vehicle. I will post some more details below of my planned aero mods.

Aero Mod Details:

The tire swap and accessory removal is straightforward. 245/75R16 tires are more aero in addition to better rolling resistance. Wheels will be Factory 05+ TRD Off-road 16” Alloys that I have already. I will “baseline” the vehicle once this is completed.

From a rear body aero standpoint, having the rear hatch is a great blank canvas to build from, since I don’t need to hinge an add on device separately. I checked and the top isn’t going to bind. Built an upper kamm back from tail lights up. Taper at AST-II from top and 4:1 AST from sides, use existing deflector bolt holes and double sided tape for attachment. Using the bumper as the stopping point I can get about 17” on top tapering down to 8” at the sides above the tail lights. There is some existing taper to the vehicle, once I do the tire swap I will get accurate measurements to start my taper where the factory left off. I will rough it out of XPS foam, carve it to the proper shape, and fiberglass over it, same way I built the aeroshell on my 05 Tacoma.

The belly pan will be bent aluminum using ¼” aluminum material I already have. Slope down in front from bumper to crossmember, flat belly, slope back up to hitch after rear axle. Slope from frame up to body on sides. No pan under exhaust, may try to also insulate some exhaust pipes to keep down the oven effect.

Planning fore and aft tire spats to direct the airflow around the tires. Probably U shaped metal frames on bodywork with conveyor belt attached hanging down.

Grill duct is probably coroplast, ducting upper grill to radiator. Lower grill probably blocked.

4RUNNER
 

*Flush,ventilated wheel covers could help a little.
*Rear wheel skirts.
*The area immediately behind the rear wheels,from the top of the bumper,to bottom of where the mudflaps terminate right now.
*If your approach angle would allow it (off road),an airdam extension might help keep some of the air going around,rather than under.
*Your mirrors are pretty dirty,but you might need all that when towing.(safety first!)
*If you do the cooling ductwork,it may be possible to abandon all the upper grille opening.

Awaiting details on this. Is the hatch split? Horizontal or vertical? How close is the hinge line to free air?

Box cavity or cargo carrier?

Personally, I would go with a 3"-4" conveyor belt chin spoiler and rear box cavity - no belly pan.

A full 1/4" aluminum belly pan that you describe in later posts sounds heavy, really heavy.

https://ecomodder.com/forum/showthre...car-33237.html
https://ecomodder.com/forum/showthre...ded-36151.html
http://dannix.net/sites/default/file...j/IMG_2905.jpg
http://i300.photobucket.com/albums/n...ds-atticas.jpg

Everyone,
Sorry for the delay, I have been away from the internet working daylight to dark on another project. I did mange to get some of the basic things done in some spare time I had here and there. Tires have been swapped, all fluids have been changed, oil leak was fixed, front bumper replaced, side steps removed, roof rack removed, fender flares removed, mudflaps removed, etcetera. I have been driving it, but don’t have a baseline yet but I will by the end of the week.

Aerohead,
Thanks, those are good thoughts. I wrestle with the tradeoffs of lighter wheels (Factory alloys) versus more aero wheels (factory steel wheels with smooth hubcaps). I plan to rig up front and rear spats on each wheel out of conveyor belt. I want to try a belly pan on this project, versus another air dam. I would like to swap mirrors if I can find some better factory options or mirror bodies that I can adapt to my bases. I don’t want to go too custom-crazy on this project, unlike my Suburban.


Freebeard,
The hatch is all one piece, hinging on the top (with self-contained roll up/down glass). The hatch hinge line is below the bodywork, with a cavity beneath to allow it to open without binding, luckily the seam is fairly flush (1/8” down) and the slopes on the top part of the hatch are reasonable. I have some pictures that illustrate this. As long as I don’t add anything to the first two inches of the top of the hatch it won’t bind, which shouldn’t be a problem.

As for the kamm, I am planning on it just being a box cavity above the tail lights to the roof. I plan on attaching four brackets to the hatch to hold the sculpted foam fiberglass piece. I will add a third brake light to the kamm. I have started making aluminum brackets, the top two are using existing fastener locations and I plan to add two new rivet nuts or some good double-sided tape to the hatch to hold the bottom brackets securely. I want to be able to remove the kamm from the brackets relatively easily (i.e. 4-6 screws). I will block it out of foam oversized and sculpt it down to shape. I plan to go back about 23” at the top.

Kach22i,
Understood. Part of it is that I have done two project vehicles with conveyor belt air dams and I want to try something different. The 4Runner came factory with relatively thin steel skid plates, I will remove those to partially offset some of the weight gain. I do have some thinner aluminum I may use in some less demanding places. I also do not plan on lifting the vehicle (maybe 1” max) so the belly pan would serve as a skid plate for off road use, as opposed to lifting the vehicle further which would negatively affect handling. But I understand the sentiment of not increasing weight substantially and may source some additional thinner material if needed.

I drew this in 2013, I suspect you could be the first. :)

https://ecomodder.com/forum/member-f...42-mudflap.jpg

The idea is two U-shaped pieces, one metal, one conveyor material. Fastening only on the two long sides would allow the conveyor material to flex on ground strikes, allowing them to be longer. I may be wrong again.

Your post reminded me there was a good thread on this topic in 2015, unfortunately the OP changed vehicles before he got around to implementing it...

https://ecomodder.com/forum/showthre...tml#post481676

Hard to believe that was four years ago.

Trying to keep charging forward on this vehicle in my spare time. I was able to finish fabricating the two upper brackets for the kamm back and get them installed. They are nice and sturdy. My current plan is to bend two angle brackets for the lower side and install them with 3M automotive tape just below/beside the rear window. I might do that after the kamm is made to get the positioning right.

I have done lots of measuring of the surface contours of the vehicle and have been planning and doing overlays of the tail. I will block out the rough shape using extruded polystyrene foam and gorilla glue to form the blank. I will then shape it to the contours of the vehicle through rasping and sanding.

I plan to fiberglass it using epoxy resin. I hope to try the plastic film trick to get the surface smooth, my Tacoma Aeroshell taught me the difficulty of bondo work over rough fiberglass and epoxy.

That's the reason I don't like fiberglass. Instead of a rasp, use a Nichrome wire. This one (doesn't) work on D-cell batteries.

https://ecomodder.com/forum/member-f...e6263-tool.jpg

My parents used this very Lionel transformer to cut Styrofoam in a rig like a jig saw. A coping saw handle would be more portable.

https://ecomodder.com/forum/member-f...ransformer.jpg

The rasp leaves a shredded surface.

Freebeard,
Thanks for the tip. I have been sanding the shredded surface with an orbital sander as a work around, I don’t really do much foam shaping in the grand scheme of things or I would be more motivated to make/buy additional tools.

Everyone,
Speaking of foam shaping, I got a few of my pieces roughed out of foam last night. I am trying to get the foam blank closer to the final shape to reduce the amount of shaping I have to do, which is taking much longer than expected versus making a large oversized block.

Edit: I forgot to add I got two tanks in for a preliminary baseline (with tire swap and trim removal) showing 23.6 MPG for short trips and 25.6 MPG mostly highway.

Trying to keep this moving forward. Got the glueups for the sides done. I am going to add another layer to the inside of these pieces to make it thicker at the front and add some extensions on the back to get to my desired distance. I am hoping to have it shaped and start the fiberglass this weekend.

Question:
When following the AST profiles (AST-II for the top, AST for the sides), if I encounter a bump (e.g. roughly 1/8" bump from trim on the rear of the side windows) do I need to slow up the profile immediately after that (simulating that the angle of that section is less due to the obstruction) or can I press forward following curves as if the bump did not exist? Basically I am calculating the angle of the rear of the vehicle and intercepting the templates based on this angle. If I use the glass/sheet metal the angle is different than if I use the trim.

Dirt doesn't affect drag but rear-view mirrors do. There is going to be some scale, depending on the thickness of the attached flow, below which there's no difference.

It might depend on the angle of the flow to lengthwise of the trim. And it might be possible to over-reach for the optimum.

Freebeard,

For sure I don't want to over reach, but I don't want to under reach either. :) As the tail is fixed, it is limited in length due to practical reasons. Obviously like everyone I want it to be as effective as it can be in that length.

I am not quite sure I am following "angle of the flow to lengthwise of the trim," could you please reiterate?

What I think I know from Hucho's book was the necessity of window flushness decreased the further back you went, stating that a 5mm inset glass did not increase drag at the rearmost window. That led me to believe the boundary layer was built up enough to accommodate the slight bump. However I don't know if parallel glass and parallel panels with a transition translates to following a taper with a bump.

[speculation]

• A ridge parallel to flow would have negligible effect.
• A ridge athwart the flow would act like a Gurney flap; given enough height, promoting reattachment.
• A ridge at a 45° angle could trigger a vortex on the lee side.

[/speculation]

Got the rest of the foam pieces glued together to form a blank. Transferred AST-II/AST tapers to the blank via shaping to form a few contour lines. Shaped the remainder of the block freehand by eye to form the overall shape. Did lots of test fits to get the overall lines close to right. Shaped out some of the insides of the block to improve rear sight lines. Laid layers of epoxy/fiberglass on the outside and inside of the block.

Current status is that it needs a few patches of fiberglass around some corners and other tricky areas and it will be ready for sanding, prep, and paint.

bump
 

Without seeing it,it may be that it merely functions as a trip-strip,actually energizing the boundary layer as vortex generators would.
Volkswagen (Hucho/Buchheim) found that the rear hatch gap of the Rabbit reduced drag,compared to filling it in flush (taping it over) with the body contour.

foam pieces glued..............
 

Oh yeah! Nice work.I don't think you'll have any problem with attached vortices with those edge radii.:thumbup:

https://ecomodder.com/forum/attachme...p;d=1558439696

This is going along nicely. :thumbup:

So I got the shell built, I am calling this version 1.0 for now. The topside looks good from a few feet away, the underside is rough as I didn’t attempt to bondo or do major sanding to the bottom. The transition from the hatch to the shell is not as smooth as I would have liked, it has a rather large step. The overall lines are aligned back to the bodywork so it is placed where it needs to be for AST tapers as if the gap did not exist. It would have been more ideal to taper this down to nothing right at the front edge of the hatch, however the way I was building this made that very difficult. If I do not get the results I expect I will probably go back and try to fill this gap in.

I haven’t run a tank with the shell on yet, just a partial tank that was half and half. My driving throughout the week is fairly consistent and mostly highway, however the weekends are short trips, different routes, more AC use with the family, etcetera. My plan for testing MPG change is to compare my commuting tanks from pre and post changes. I will fill up at the beginning and end of each week at the same pump to enable that separation. While it is not ABA, I feel it is a reasonable method for me to estimate percentage changes. (I have no time for ABA.) The weekend tanks are far to varied to give any sort of defensible indication of changes.

My mental dyno tells me the drag coefficient of the vehicle hasn’t changed drastically, however I can tell the rear end feels much more planted in turns which I attribute to reduced rear lift. Assuming this mod shows a reasonable positive change indicating it is working as designed, I will turn my attention to the underside and tire spats.

I felt that way about the first huge air dam chin spoiler I built on my van back in 1983.

The added stability in cross winds made the effort well worth it, and it looked cool too. :)

This goes to the heart of the thing. Handling adverse winds. I can run down the road with a 53’ van behind me (full skirt & tails) and it is more the position of the tandem trailer axles that alerts me to this adversity (tandems positioned to even out weight of load with the Drive Axles) as leverage increases with length past those axles position.

In other words, most of the time I don’t notice the effect of the tail (3.5’ deep). Not until wind loads increase. It’s only judging by the Current Fuel Economy readout that the advantage is obvious in every driving situation.

I think ABBA testing not a big deal. If fill up is possible at same station pump every time to first auto-shutoff it’s more than enough. That also rules out fuel blend changes per brand.

Reading engine hours is the last. Calculation of Average MPH per tank is handy. Accounts for operator changes. Keeping it at or above 26-mph is the key to long-term engine life and FE.

Same fuel, same basic routes, same average mph covers “transparency”.

Aero aids are cake icing. Operator inputs FAR outweigh it as this is a metro-mobile, not a highway runner. The margin added is in keeping MPG high versus weather penalties per tank.

.

.

I don’t have extreme confidence in these numbers yet, but I have collected a few similar mostly highway tanks with and without the shell, same route, same pump sort of thing. Three of these tanks without the shell averaged 25.4 two tanks with the shell averaged 26.6, implying a 4.7% increase.

The reason I don’t have extreme confidence in the numbers is that I have noticed that both stop and go traffic and use of AC seem to drive fuel economy down, more so than I have experienced in other vehicles. I am not sure what to think of that fact yet. I am going to be doing plugs/wires/sensors on the engine soon. Also I plan to put heat rejecting tint on the windows and add some cab insulation to reduce the AC use.

I still feel the transition from the body to the shell is hurting me, I am planning on adding some thin aluminum strips formed to the contours to cover this gap, which would stop right at the front of the factory hatch. These would be attached to the shell mechanically. I tried to do something with fiberglass in this area when I initially created the shell but had issues…

I am still trying to form a good plan for the underbody coverage, one area of particular drama is between the front and rear tires. I am thinking running a flat bottom from the frame all the way out to the tires outside edge, turning up and forming a box shape, turning back in where the rockers pinch seam is, basically boxing in the area where the side steps usually go. This would give me a good surface to mount my tire spat flaps on.

Beware the breakover angle.

Cylinder Pressure. Is everything.

.

front clip from 2002 toyota prius

confidence
 

The old-school,SAE testing protocol was to drive at a constant highway speed,with and without,on the same route,same day,as soon as possible.This reduces variables down to one,about as much as we could hope for.In mixed driving,you'll get a composite number,but it will impossible to arrive at a delta-Cd.
At a steady highway speed,a 10% drag reduction is going to net you close to a 5% improvement in MPG.A two-to-one,shoot from the hip metric.
You ought to see around 10% better mpg.

Freebeard,
I have measured the underbody and plotted out the points to be aware of. The 4runner has a low center belly with crossmembers dropping substantially below the frame rails, so boxing in the outer area between the tires at the frame height will still be significantly higher than the center. This is quite a bit different than other vehicles I am used to (e.g. suburban) in which the frame rails are the lowest point.

Slowmover,
I hope there is no issue with the engine beyond just sensors…

Tahoe Hybrid,
Interesting, it looks as if the widths match, I would have guessed narrower. I just replaced the front bumper though and I don’t want to mess with the crumple zone, but a novel concept nonetheless.

Aerohead,
Agreed on the suggested methodology being better, however I don’t have extra time for too awful much testing, so I just compare my tanks week to week and try to compare similar tanks/conditions to get estimates. Once I get multiple projects completed I may consider ABA for a suite of things, but I can’t do that for every change I make.
I am just surprised how much lower the “bad” tanks are from the “good” ones, it is more than I had experienced in the past.
I am not getting 10% better MPG with the kamm extension. I assume I need to fix the transition from bodywork to extension.

Everyone,
Current progress on the 4Runner has been replacing both oxygen sensors (actually air to fuel ratio sensors) on the exhaust and the throttle position sensor. Also removed the rear driveshaft and replaced the rear u-joint which was going out and vibrating at higher speeds. Carefully greased the double cardan joint to extend its life, ensuring new grease made it into each cup. Rear u-joint was a pain because the rear yoke was sloped, made it a bear to press the spider out. Eventually had to weld up custom fixtures to hold it, then it was easy.

I have done some figuring on the underbody. My current plan is to lift the vehicle a small amount (about 1”) during some upcoming suspension work, which will put the lowest parts of the underbelly about the height of the rear axle tube. From there I can run a 6 degree diffuser from behind the axle tube to the rear hitch. I picked up some materials (steel tube) for my between the tires filler panel, still doing final design on that.

Put an aerodynamic bicyclist helmet upside down on the pumpkin. :)

Don't use shell Fuel it's garbage mobil or chevron do the job better

So panel gaps are far from the biggest aerodynamic problem with this 4Runner right now, but because I had to remove the front grill to access a leaky o-ring on the AC accumulator drier I decided to seize the opportunity and fill the panel gaps on the front end. I used a trim-lok edge trim with side weatherstrip profile between the bumper and the grill / filler panels and trim lock self-adhesive with the 3M adhesive around the headlight and the hood gaps. Used some thin pieces of door edge guard around the marker light to seal that up as well. Turned out pretty good I think.

Looking good! I prob need to do the same on my car, does it help much?

Haven't had a great chance to test the panel gaps, shortly after I filled them I tore all the suspension off the 4Runner to update it. Just completed that work and dropped it off for an alignment. 4Runner got new front wheel bearings, Bilstein 5100 struts, all bushings replaced, lower control arm, alignment keys, upper and lower ball joints, rebooted CV axles, upgraded sway bar, Etc. In the back it got new control arm bushings for the four link, Springs, , upgraded sway bar, Etc.

I think one of the culprits for strange MPG was one of the cylinders on the passenger side caliper locked up. I got it unstuck enough to get it in for the alignment, I've got new rotors calipers Etc on order to refresh the front brakes.

All of that work made the aerodynamics work take a backseat temporarily.

Broke out the 40 ton homemade press brake last night, started messing around with some aluminum for the underbody skid plates / belly pan.

I also started welding together some homemade Rock sliders for the side rails, they will go out to exactly the tire width and will hold the tire spats behind the front tire and in front of the rear tires.

The alignment is completed, tying a bow on the suspension work. Got a few things built, mainly the main belly pan/skid for the underside of the engine up to the front crossmember. Made with ¼” aluminum, smooth side down. It needs some more bracing for true skid plate duties but is fine enough for now. This is the first of many pieces that need built to have a smooth belly on this vehicle.

This piece of belly pan doubles as a radiator duct on the bottom thanks to some strategically placed weather-stripping, just need some buy some black coroplast to finish ducting the upper grill to the radiator.

I built a hidden receiver hitch for the front, tucked back behind the stock crumple zone. It was not easy to build this piece around all the obstructions. It uses a removable extension to allow a receiver hitch on the front end sticking out of the center of the lower grill opening, for using a receiver mounted winch or other accessories while retaining a stock front bumper and stock crumple zone. I plan to build a cover to block the lower grill off (upper grille should be sufficient with ducting), but have it openable/removable for winch use.

So I completely replaced the front brakes on the 4Runner, did the Tundra brake upgrade, so bigger calipers and pads, thicker rotors, same mounting dimensions. The best part is the Tundra calipers use the springs that push the pads away from the rotor, so the brakes should drag less. Should be much better than the partially locked up 20 year old dragging calipers that were on it.

Turned my attention to the interior, gutted the rear cargo area and removed the headboard. Added peel and stick insulation to all of the roof I had access to (sunroof is cramping access). Stuffed melamine foam (think magic eraser) into the open cavities that had a sufficiently sized access panel. Draped some thinsulate over the headboard and reinstalled. This is the beginning steps for an effort to insulate the cab to reduce AC usage.

Today after work I hope to get the cargo area sound deadened, insulated, and reinstalled. The car is noticeably louder with the thin plastic factory cargo side panels removed, so deadening that area should cut cab noise. [Edit: this wasn't entirely the case] Noted that the rubber mat and insulation in the cargo hold was melted/burned right above where the exhaust goes over the axle. Surprisingly there isn’t an exhaust heat shield there from the factory that I can tell, I will rectify that shortly.

Turns out that I was wrong about the melted/burned rubber and foam being caused by the exhaust going over the axle, it appears the vehicle was operated without a tailpipe for some distance, and the muffler was dumping directly into the front floor pan. I got suspicious when I noted the closest passing of the muffler to floor had no heat damage above it and was over a foot from the burned spot. I already knew the tailpipe behind the muffler had been replaced, and when I looked at the heat damage it was exactly where the exhaust gasses would have hit the body if the tailpipe section was removed from the muffler section.

I only had enough time last night to get the peel and stick sound deadening installed in the cargo area, having to contour it to the corrugated floor and roll the surface down took far more time than expected. It still needs insulated, then the cargo area interior can go back in.

I got the cargo area insulation and sound deadening project done and the interior back together. Made a decent difference in cab noise, which is nice.

I found an ideal aerodynamic positioning for a front mounted winch, it it called the cargo area. Using my hidden front hitch and an extension I can mount a cradle mounted winch on the front when needed, and take it back off to stow inside when not needed. It also works in the back receiver thanks to an extension cord.

MPG is definitely up after doing the work on the brakes. I have been driving without the kamm shell because I removed it to fix the leading edges that did not turn out well. I need to either find time for that or slap it back on for now.

I suggest also a wing for the rear end on the top my hybrid compared to the normal version has a slighty bigger wing on the rear of the SUV


also check the angle of it slightly more like 80 degrees instead of 90 degrees



I suggest an Air dam as well

Location is a must see the hybrid model vs non hybrid model..


the coefficient drag is 0.34 compared to 0.38(0.379)


the ride height is lower then the normal one I have not experienced any clearance issues I do pay attention to make sure i don't hit garbage on the road

I have a relatively huge "wing" I built for the rear end this spring, that is the one I referenced as a kamm shell that I need to do more work to because the leading edge transitions are not smooth enough.

I did an air dam on my last two projects, but I am trying on this one to do a belly pan system and smooth the airflow through the underside versus directing the air around the sides. This approach is used on some production cars (e.g. tesla) however it puts me in a non ideal interim situation seeing as how I don't have the belly pans done yet.

This vehicle is built around compromise between on-road use and off-road use, so I am not looking to reduce ground clearance for off-road reasons. My front end is technically stock height, but mine has the "99 tall" springs (from factory) so it is the tallest "stock" 3rd gen 4runner. (Other year third gens often order the 99 tall springs as a "lift".)

It has been a bit, but I did have a chance to work on the 4Runner this past week. I was able to build some additional belly pan/skid plates for the underside of the 4Runner out of 1/4" aluminum. I also built some "rock slider" steps out of steel 2" tube steel welded to the frame. The plan for these is to cover them top and bottom for a smooth surface, and then to mount my fore/aft wheel spats on the bottoms of them near the tires.

I also got a chance to use the 4Runner offroad this past weekend, swapping over to the 255/85R16 tires mounted on extra wheels. The trip went well, and I will swap back over to the street wheels and tires shortly but first I will put a weeks worth of driving on these offroad tires so that when I swap back I can compare the MPG between the two tire sets.

Anyway some pictures.