'97 Jeep Cherokee XJ 4x4 overland rig

[mannydantyla]

I finished fabbing the new roof rack rails, sans crossbars.





I installed the new fuel injectors, upgraded from 1-hole to 4-hole Bosche injectors. Many people report an increased MPG or two after this upgrade.



After that doing that I reset the "adaptive memory" of the ECU/PCU/PCM/whatever. It's supposed to make it re-learn the correct settings now that it has better fuel injectors, but that may be a wive's tail for all I know. Either way I'll need to go through at least a tank of gas before I see improvements as it runs rich while it's still re-learning and it says it can take 50 warm up cycles or 500 miles before the adaptive memory tables are populated again. So far the idle feels a little smoother but I'm not noticing much else. The old injectors looked like the OEM ones but they didn't look too dirty and I've ran a few bottles of SeaFoam through the gas to keep them clean, so maybe this wasn't much of an upgrade. We'll see.

I also removed the plastic pieces behind the rear wheels. I'm still thinking about what to do with the sheet metal there, any one care to provide some insight? On one hand, it seems to me that freeing up the airflow there can help a lot - it would be like an extreme mud flap delete. But on the other hand I don't know squat and all the examples of trucks with good aero - like the Phil Knox truck - make me second guess this idea for sure.

Or maybe the air is so disrupted by the front of the vehicle that it will never have a chance to smooth out and take advantage of any aerodynamic enhancements made to the rear of your jeep.



Oh, and there's rust that would be best cured by cutting it all out. And obviously something must be done about that rear bumper...



I'm gearing up to do a light engine overhaul.

I'm going to do the mechanical fan to electric conversion. Stock for 1997 is one 15" mechanical clutch fan, and 10" (I think) auxilary electrical fan that only comes on when temp gets 220*F. I'm still deciding if I want to replace the mech fan with one 16" electric fan, or replace both stock fans with three 10" electric fans.

While I'm doing that I might as well replace the radiator since I'm having problems with it. And while I'm doing that I might as well replace the timing chain - it gets a little loose after so many miles and the valve timing can suffer. So they say.. I'm also looking into have the engine professionally cleaned via motorvac service. Maybe I can also adjust the valves/tappets and stuff.

So here would be the new serpentine belt diagram after deleting the AC compressor and mechanical fan pully:



Not only should this free up a pony or two, it's also much better for the alternator because, in the stock location, it's too close to the ground were it gets blasted with water, mud, salt, etc. and it's always one of the first things to die if doing water crossings (driving through shallow streams). So it's a win win. And maybe I can get a lower-resistance alternators - do they make such a thing?

[freebeard]

aerohead's truck looks so clean and new!

Would a Wrangler XJ bumper bolt up?

WRITE UP: Pressurized Running Water on Jeep using Stock Bumper as tank - Jeep Wrangler Forum

[mannydantyla]

I just thought of a cool name for this project: Aerokee

Originally Posted by freebeard

aerohead's truck looks so clean and new!

Would a Wrangler XJ bumper bolt up?

WRITE UP: Pressurized Running Water on Jeep using Stock Bumper as tank - Jeep Wrangler Forum

No, all Wranglers have traditional ladder frames, like a pickup's, while the Cherokee has a car like unibody. Anything that bolts to the frame won't match up, like bumpers, suspension control arms, rock sliders, etc.

The unibody is lighter but all other advantages to to the wranger: strength, simplicity, and modifyability (yes I made that word up). In fact, they sell all sorts of unibody frame stiffeners and reinforcing brackets for Cherokees to make them stronger as needed. It's a known fact that if you put 35" tires on a cherokee without strengthening the unibody frame, you'll rip the steering gearbox out where it bolts down the first take you take a sharp turn.

[mannydantyla]

Here's some interesting results I found testing with and without an air dam:

Motortrend magazine that was doing some long-term testing of the new Chevy Colorado diesel and it's 30-mpg-highway claim and they measured the mpgs with and without the air dam at city and highway speeds. Their results with the air dam off: worse fuel economy on the highway, but much better fuel economy in the city!

2016 Chevrolet Colorado Z71 Diesel Review - Long-Term Update 5

Its first test would be completely stock as delivered from the factory with the air dam affixed. Under our Real MPG cycle, our stock diesel Colorado Z71 4×4 achieved an impressive 21.5/31.9/25.2 Real MPG city/highway/combined. Compared to our truck’s 20/28/23 mpg EPA rating, the Real MPG results detail a 7.5 percent increase in the city, 13.9 percent increase on the highway, and an overall 9.5 percent increase on the combined cycle.

Not too shabby.

With the air dam and side steps removed, I handed the keys back to the Emissions Analytics team and eagerly awaited their results. Their testing shows that without the air dam, our Colorado Duramax 4×4 achieved 23.6/30.6/26.3 Real MPG city/highway/combined. Compared to the same truck with the air dam on the Real MPG cycle, that’s a 9.7 percent improvement in the city, a 4.0 percent drop on the highway, and a 4.3 percent improvement overall. Compared to the EPA, our truck—without the air dam—improves 18.0 percent in the city, 9.3 percent on the highway, and 14.3 percent on the combined cycle.

Now that's just one vehicle, doesn't speak for all. For example, here's another Chevy Colorado owner's experience, he has the gasoline engine and he experience a 18% negative difference with the air dam off: http://coloradofans.com/forums/169-2...-mpg-wise.html

[mannydantyla]

Maybe I should go crazy with it.




But the roof line would need to taper down too



Am I doing it right?

I come up with a new hairbrained idea every day I swear.....

[freebeard]

Anything that bolts to the frame won't match up .... and modifyability (yes I made that word up).

It looks like you took a few moments to think about that.

I like the Wrangler bumper because filled or emptied would change/modify/control the weight distribution. Especially if it is mounted further back (and higher?) as the basis of a boatail/difusser.

[mannydantyla]

^^^ oh that's why you like them so much. But I guess I don't follow why you would want the rear end to be extra heavy

Here's an extremely crude rendering of what a boat tail might look like.



Would this actually help? Or would the air be so disrupted by the front of the vehicle that it will never have a chance to smooth out and take advantage of any aerodynamic enhancements made to the rear?

[freebeard]

For front/rear weight distribution. Or beer.

If I interpret that correctly it's a slant chop aft of the C-pillar. Doable but a lot of work.

Here's another alternative, the VW GTI W12-650:



It preserves the existing structure and adds essentially a bubble-top coupe inside it, with an inverted airfoil section for down-force. This sacrifices some interior space, but it could be reduced in size [and effectiveness] to some NACA ducts and tubing.


https://www.miataturbo.net/race-prep...e3/#post887810

The trick is you would be working with converged jets of air and where do you want those in the wake? Maybe the upper corners?

Given the body type and use case, I'd think an open boxed cavity.

[mannydantyla]

Originally Posted by freebeard

Doable but a lot of work.

Yeah for sure. People chop up these Jeeps every which way you can image. I found a good build thread of a guy who did this (sorta, he turns it into a buggy) and all the pics weren't destroyed by photo****et. It starts at page 39 in October 2011 and he finally finishes on page 89 in August 2012. So it's a labor of love and hopefully you still love it by the time you're done.

I have a lot of free time at work in front of a computer, so I spend a lot of my day researching and dreaming about what can be done. A lot less time to actually work on the Jeep. Oh, and I'm renovating my whole house right now, doing it all myself, and we're on the kitchen now and the fiance would not be happy if I worked on the jeep instead of her cabinets lol

Originally Posted by freebeard

It preserves the existing structure and adds essentially a bubble-top coupe inside it, with an inverted airfoil section for down-force. This sacrifices some interior space, but it could be reduced in size [and effectiveness] to some NACA ducts and tubing.

Hmmm, after some reading I think I see what you're saying. That's certainly doable. Would have to be sure it would help before cutting the sheet metal.

Let's face it, doing the boat tail (or dove tail as the offroad guys call it) would ruin the jeep. It's a nice Jeep with a very nice interior. And it would take a lot of time, time that would be better spent on a belly pan, or custom bumpers, or installing a TDi turbo engine, or swapping in a manual transmission...

Actually, I already have a simple idea for the rear: get a lift gate (thats what they call the big lid that lifts up to get to the rear storage) from the junk yard and take the sheet metal around off the parameter, clean it up and screw/rivit/weld it to the existing lift gate, such that it's like a... roof spoiler? Except it would continue down the sides and tapper off to the tail lights. I don't know the name for it but it would promote a better flow separation and replace the soft round edge that there now. What do you think?



4runners used to have this rear spoiler that actually extends up and scoops the air to directing it down into the wake.. or so I image. What do you think of this?



What if I made the whole jeep a giant golfball...

[freebeard]

I don't get the first one.

Those deflectors to keep the back window clean add frontal area, and therefore drag.

Golf balls are dimpled all over to take air from any direction. A single ring at 90+ to 115° from the stagnation point would be enough for a directed flight. Eventually this reduces down to vortex generators.