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I've decided to paint the roof top white. It won't help my MPG or anything but it will help it be a few degrees cooler inside the jeep in summer. And, best part yet, I can call it the "XJ Cruiser" !
Originally Posted by Joshua White
Please don't weld galvanized pipe...you could die
Originally Posted by Bugout4x4
^^^^^^^^^^^^^^^ This cannot be STRESSED ENOUGH. Don't do it...
That's actually not true. The zinc burns off and immidiatly mixes and reacts with the oxygen in the air to become zinc oxide. Zinc oxide fumes will give you a headache and can make you feel sick for a day or two if you inhale enough, but there's no long term health effects and I really don't think it can kill you. (I'm not an expert or a doctor, this is just my understanding from reading things on the internet).
I've finished most of the welding, tried not to inhale to much zinc fumes but of course I did a little, but I never got a headache or any adverse effects at all.
However it was not the easiest **** to weld.
Last edited by mannydantyla; 01-18-2018 at 04:40 PM.
You must be mistaken because you can die, it takes a lot to make it happen (no ventilation, lots of welding, no concern for the onset of symptoms) but it can happen.
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.
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.
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...
Maybe I should go crazy with it. Boat tail! Like the pic of the T100 truck above. By far the best (but not easiest) way to get the largest improvement in aerodynamics. It could be like this pic but the roof line would need to tapper down too:
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?
Last edited by mannydantyla; 01-29-2018 at 02:59 PM.
If you are overheating at speeds over 65 MPH, then you need to check the head gasket. Use a combustion leak tester to check if exhaust gas is leaking by the head gasket into the coolant passages. Common enough, pumps hot exhaust gas into the coolant. Over powers the capabilities of the cooling system. Tester like this:
As far as your pursuit of better MPG, I'm watching. My 90 4 door (4.0l, AW4, 4.10 gears) is sitting on 33s w/ 5" of lift. I average 13 MPG combined driving. Highway driving (fuel up, get on highway, get off to get gas) I get 18 MPG.
If you are overheating at speeds over 65 MPH, then you need to check the head gasket. Use a combustion leak tester to check if exhaust gas is leaking by the head gasket into the coolant passages. Common enough, pumps hot exhaust gas into the coolant. Over powers the capabilities of the cooling system. Tester like this: https://www.amazon.com/UVIEW-560000-.../dp/B000NPDL76.
BTW, the coefficient of drag for the Jeep Cherokee XJ is 0.52. For comparison, the ZJ Grand Cherokee is 0.42, a Jeep Liberty is 0.39, a Toyota Corolla is 0.33, and a Honda Insight hybrid is 0.25 (about as good as it gets). So the 0.52 is pretty dang bad but it's slightly better then a Wranger TJ's which is 0.58.
Here's the design of the roof spoiler that I came up with:
Here's how that might look:
So is it a roof spoiler? partial kammback? boxed cavity? partial boxed cavity?
Sorry but if it's going to be permanent then aesthetics are at least somewhat pertinent for me.
Even at that small of a size, a guarantee you that I'll get sticky notes stuck to my windshield at least once a week saying "Sweet spoiler, broh!!" I live in a college down (Lawrence, KS) and park near the football stadium to go to work every day, and yesterday someone stuck a sticky note to the windshield saying "broh! nice roof rack bro!" and I'm still scratching my head wondering if they were laughing at my expense or genuinely complementing my welding skills or somewhere in between.
If it was the size of this kammback then people would be shouting out their windows at me daily:
^^^ That's a good thread, btw. Although he never says how long it is, but it looks like 18" to 24" to me. So maybe twice the length of the one I designed, but it goes all the way to the bumper.
However, the bottom is not closed off. Which flies in the face of this quote from aerohead:
Originally Posted by aerohead
Your cardboard mockup is more like a box-cavity,and for it to work,it needs to be as low as the bottom of your bumpers bottom,and it needs a 'floor'.It cannot be open on the bottom unless there is a back on it,and the back is airtight.
(I really hate photobucket, btw)
That quote is from this thread - http://ecomodder.com/forum/showthrea...k-29583-4.html - in which a fellow SUV ecomodder tries a cardboard kammback/boxed cavity, and sees only a 1% increase in MPG over stock and after several days worth of testing.
So, given all these things, can I realistically expect maybe 1/3 the results that MetroMPG got with that minivan? Which would be a little over 1% so I would go from 15 mpg to 15.15 mpg which is insignificant IMO.
Still though I will try and test it. Today the scan tool is supposed to arrive in the mail, but conveniently I broke my iphone last night! Which it needs to connect to. I could use my fiance's maybe, idk.
(don't mind me, I'm just going to continue dumping my brain out into this post)
You see these roof spoilers on every new hatchback and SUV being made today and they seem to be getting longer and some are even going over the sides too.
So I guess that's what I'm going for.
BTW, that last one is the 2017 Lexus RX. I found this:
A team of researchers has used the principles of fluid dynamics and numerical simulation to design a new rear spoiler for bluff-backed vehicles (such as minivans and SUVs) that can reduce drag and lift [...] by 5% and more than 100%, respectively, when the new spoiler is attached to it.
Are there any vehicle in production using a spoiler like this?
Is 5% a lot?
If I take this data...
...and ignore the "1.9d" part and follow Mair's assumption that it's a function of the width not the length, then I get this:
And that shows that I can get the same 5% reduction in bluff body drag with only 5 inches of "partial boxed cavity" as I call it.
Yeah I know I'm speculating big time. Mainly that a partial boat tail has the same aero benifit as the "partial boxed cavity" that I'm talking about.
I completely agree that the huge drag pocket in the back needs to be eliminated, It would be one of the most efficient changes you could make to that if you want to reduce drag on these bricks. But what you are sharing here will not do much to ELIMINATE that drag pocket. Reduce it maybe but not eliminate it. The cure has been around for many many years and has been used on station wagons (IE Cherokees) for a long time and IT WORKS.
Here is an Buick "Safari" with the cure as an example. Now to do this with an XJ would be a little tricky because of how the hatch and hinges work. But two of these, one mounted on each side of the hatch would absolutely accomplish the exact same advantage. The reduction in overall drag far far outweighs the very little resistance the scoops would add with this concept.
This is what I am going to do to mine to both reduce that drag pocket in the rear, and to keep dust from sucking up and landing on everything back there. But I am going to make mine out of plastic mounted on rubber so that bushes don't break them off the hatch when out in the sticks.
Keep it simple, because sometimes simple is the best answer.
Update: I picked up a set of pull-off mono shocks from a 2017 JKU Rubicon, they should be perfect for an XJ with 2" lift. It may not sound like an "ecomod" but they should allow me to more comfortably run with the tires at a higher PSI. We all know how much the road comfort is in these jeeps.
Originally Posted by Bugout4x4
I completely agree that the huge drag pocket in the back needs to be eliminated, It would be one of the most efficient changes you could make to that if you want to reduce drag on these bricks. But what you are sharing here will not do much to ELIMINATE that drag pocket. Reduce it maybe but not eliminate it. The cure has been around for many many years and has been used on station wagons (IE Cherokees) for a long time and IT WORKS.
Here is an Buick "Safari" with the cure as an example. Now to do this with an XJ would be a little tricky because of how the hatch and hinges work. But two of these, one mounted on each side of the hatch would absolutely accomplish the exact same advantage. The reduction in overall drag far far outweighs the very little resistance the scoops would add with this concept.
This is what I am going to do to mine to both reduce that drag pocket in the rear, and to keep dust from sucking up and landing on everything back there. But I am going to make mine out of plastic mounted on rubber so that bushes don't break them off the hatch when out in the sticks.
Keep it simple, because sometimes simple is the best answer.
I'm not pretending like I know diddly squat about aerodynamics.
I really don't know **** and that is why everything I do, I will test to see if makes a positive difference or not. I bought a $20 OBDII wifi dongle that lets me connect to it with an iOS or Android app, and it tells me instant MPG as well as all the sensor data (coolant temp, intake air temp, fuel air mix ratio, etc). I'll use that to do my testing.
Maybe I'll test this spoiler design too. There's certainly a place for spoilers, if applied right they usually help, but they can also hurt. Aerodynamics is a bit of a dark art, it seems to me.
But I also suspect that the spoiler like the one in your picture is to prevent dirt buildup on the back window, like this:
Just a guess.
Like you said, simple is, more often than not, the best. And there has always been one design shape in vehicle aerodynamics that always works, every time: the "tear drop" aka "boat tail" aka "dove tail". Here it is, superimposed over the XJ:
As you can see it would have to go back very very far. Here's someone who tried, until another driver took it off in a parking lot:
He gained 1.4 MPG, or 9.3% of the EPA combined MPG of 15. That is quite a lot.
Look at that ****ing thing! You ain't going offroading with it, that's for sure. And that's just a "partial boat tail", not even the full length! But it doesn't have to be, it can just stop abruptly like that - they call it a "chopped teardrop" shape - also known as a "kammback" named after 1960s car designer Wunibald Kamm who came up with stuff like this:
The shape follows the teardrop shape, then abruptly ends. Similar to (d) in the below figure:
Compared to the standard blunt end (a), adding what they call attikas (fascias or parapets; flat, parallel panels) (b) delays separation and moves the tail vortices back (reduces Cd by up to 10%); these can be set inward (c), further reducing the size of the „dead zone“ (reduces Cd by 0.06, which is about half as good as the ideal tapered tail); the open-ended Kammback made of flat panels (d); and „Fluid Tail" (e).
D or E is what I'm going after, I'm not quire sure the difference. "Open-ended Kammback"
Last edited by mannydantyla; 02-02-2018 at 02:07 PM.
Update: I picked up a set of pull-off mono shocks from a 2017 JKU Rubicon, they should be perfect for an XJ with 2" lift. It may not sound like an "ecomod" but they should allow me to more comfortably run with the tires at a higher PSI. We all know how much the road comfort is in these jeeps.
I'm not pretending like I know diddly squat about aerodynamics.
I really don't know **** and that is why everything I do, I will test to see if makes a positive difference or not. I bought a $20 OBDII wifi dongle that lets me connect to it with an iOS or Android app, and it tells me instant MPG as well as all the sensor data (coolant temp, intake air temp, fuel air mix ratio, etc). I'll use that to do my testing.
Maybe I'll test this spoiler design too.
But I also suspect that the spoiler like the one in your picture is to prevent dirt buildup on the back window, like this:
Just a guess.
Like you said, simple is, more often than not, the best. And there has always been one design shape in vehicle aerodynamics that always works, every time: the "tear drop" aka "boat tail" aka "dove tail". Here it is, superimposed over the XJ:
As you can see it would have to go back very very far. Here's someone who tried, until another driver took it off in a parking lot:
He gained 1.4 MPG, or 9.3% of the EPA combined MPG of 15. That is quite a lot.
Look at that ****ing thing! You ain't going offroading with it, that's for sure. And that's just a "partial boat tail", not even the full length! But it doesn't have to be, it can just stop abruptly like that - they call it a "chopped teardrop" shape - also known as a "kammback" named after 1960s car designer Wunibald Kamm who came up with stuff like this:
The shape follows the teardrop shape, then abruptly ends. Similar to (d) in the below figure:
D or E is what I'm going after, I'm not quire sure the difference. "Open-ended Kammback"
01-18-2018, 04:37 PM
