I'm not sure how possible this is without the software or anything, but is it possible to run the 4.0 as a 3-cylinder on the highway? Id think it would be possible depending on if the say 1-6 cylinders are at the same height as with 2-5 and 3-4 (i think thats how the firing order is/works). If there was some way to have a switch on the dash to cut (or give) power to the injectors for say the 1,2,3 cylinder (dunno if thats going to cause too much torsion/stress at the center of the crank maybe? by having half with lots of force and the other half just hanging in there. I'm not sure exactly what the MDS on say the hemi does, but im pretty sure it could be possible on an XJ. Any ideas, im sick of crappy mileage and dont have the money to get something else as fun/better mileage than my XJ.
MDS For 4.0
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5-90
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Interesting thought - I wonder how badly torque output would suffer as a result?
Anyhow, you aren't going to want to just "cut out" one bank - that makes torsion a greater problem. More like fire "front bank - rear bank - front bank" - can't give you cylinder numbers offhand, but that would allow you to distribute torsional stresses through the crankshaft more evenly.
Sounds like work, tho. How bad is your fuel economy, and what have you (or haven't you) done for your engine management lately? Also, what gearing and tyres are you running, and is your aero profile "dirtier" than it would normally be? (Roof rack and the like.)
Anyhow, you aren't going to want to just "cut out" one bank - that makes torsion a greater problem. More like fire "front bank - rear bank - front bank" - can't give you cylinder numbers offhand, but that would allow you to distribute torsional stresses through the crankshaft more evenly.
Sounds like work, tho. How bad is your fuel economy, and what have you (or haven't you) done for your engine management lately? Also, what gearing and tyres are you running, and is your aero profile "dirtier" than it would normally be? (Roof rack and the like.)
Torque would be less than half, because you still have to do work on compressing air and then pushing it out on the 3 unused cylinders as well as general wear. My fuel economy isn't too bad, usually 15-16mpg and its usually my right foot at work but it was more for an interesting project. If my highway mpg goes from 20 to 30 i'd be happy. This isn't something id do to my jeep unless it was somewhat simple and not compromise my DD, but just hypothetically.
It would probably shake and spudder and run like ass IMO. I don't know for sure but I am sure the newer vehicles have something to release compresion on the cylinders that are not running. Otherwise you just have that much more resistance to work against.
5-90
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BBeach said:
Somewhat simple? Hardly.
Also, you'd realise more fuel economy if you had a way to "lock open" valving for the three cylinders not in use, so you don't have to pump and compress air (eliminate the compression, and pumping becomes far easier!)
I do find the idea interesting as a thought experiment and as an engineering challenge (retrofitting multi-displacement to an existing engine and control system. Hmm...) but it's going to be an awful lot of work to do, and to do properly. I'd also debate the overall savings in fuel against the cost of doing this as a "one-off" mod - even if it can be done with mostly OTS parts.
It's likely going to remain a thought experiment, and not much past that.
Well thats where itd be nice to have something to keep the intake/exhaust valves closed (not easy at all especially with our engines, maybe something with OHC). I know this isn't "simple" by any means, its not like im going outside and unplugging me injectors. party1:5-90 said:
It's just a thought, must be much easier with something with OHC and such. I think that V8's are simpler to design this around due to their firing order and having it as an I-4 of a sort.
5-90
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BBeach said:
"Open" - not "closed." Keep the valves open and the cylinder will be at or near ambient pressure, which will eliminate compression. Closing the valves will still result in pressure swings in the cylinder - the amount of gas will be constant, but the pressure and volume will be constantly changing.
j99xj
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BBeach said:
I don't think you can get 30 mpg and still be able to travel highway speeds. You MIGHT be able to get 30 mpg if you lug along in overdrive with the cruise control on at the lowest allowable speed. (I think its around 35-40 mph.)
But that isn't practical and is very dangerous for anything but country roads in the middle of nowhere.
I have found that 22-24 is not out of the question with a light foot and being "fuel economy" minded. (When 60s VW beetles and 80s Ford Festivas out accelerate you/go faster than you.)
After adjusting your right foot a little you should condsider the following:
Is your air filter good?
Are your spark plugs gapped properly?
Is your cat running ok?
Are your tires running at 35 psi cold?
jeepnuts311
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pull off three spark plug wires, and the injector wires.
you wont get anywhere.
not only will the engine not run well (if at all) but it definitely wont keep you going highway speed.
these jeeps dont get terrible mileage if they are maintained. i get about 16 out of my XJ on 35s with 250,000 on the clock on the renix 4.0... simple, regular maintenance, simple power upgrades, and gearing to match the tires is all it takes to keep stockish mpgs on big tires.
i bought a DD which is an 07 tacoma reg cab. 2.7l 4 cyl with VVTi and a 5 speed, i get 21 mpgs in it...not much better considering it was designed 2 decades after my jeep was, has 2 less cylinders and tons more technology built in. Hell, its even OBD III
quit complainin.
-Tim
you wont get anywhere.
not only will the engine not run well (if at all) but it definitely wont keep you going highway speed.
these jeeps dont get terrible mileage if they are maintained. i get about 16 out of my XJ on 35s with 250,000 on the clock on the renix 4.0... simple, regular maintenance, simple power upgrades, and gearing to match the tires is all it takes to keep stockish mpgs on big tires.
i bought a DD which is an 07 tacoma reg cab. 2.7l 4 cyl with VVTi and a 5 speed, i get 21 mpgs in it...not much better considering it was designed 2 decades after my jeep was, has 2 less cylinders and tons more technology built in. Hell, its even OBD III
quit complainin.
-Tim
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I think at 55 in O/D locked (basically 100% you're at that speed this is the case) you'd be fine, maybe with 4.10's or putting it in 3rd locked you'd still be saving gas. Where have you ever seen an xj gettin 24mpg other than downhill? It might be possible if you just go on a flat road at 55mph.j99xj said:
Im not complaing about fuel mileage, it was more of a thought that i was wondering was feasible, im obviously not doing this to my DD....
My air filter is fine, i just cleaned/oiled it within 1000miles ago, i just did the plugs/wires within the past 5000miles and they are fine.
My cat is in question but affording a new one installed it out of the question as of right now.
Tire pressure is fine too, i do all that i can do keep it in good running order within reason and again, im not whining about mpg's...i just was wondering of this as an engineering project.
And jeepnuts, as ive already discussed before it might not be the best idea to do that as far as torsional stresses in the crankshaft. MDS prolly isnt the best idea for I-6's, mostly more for V8's.
http://en.wikipedia.org/wiki/Variable_Cylinder_Management5-90 said:
"It uses a solenoid to unlock the cam followers on one bank from their respective rockers, so the cam follower floats freely while the valve springs keep the valves closed."
I shouldn't quote wikipedia but oh well.
Plus wouldnt leaving the valves open give you the chance to suck in exhaust through the exhaust valve which could eventually make its way back into the intake manifold? I guess its a poor mans EGR haha.
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5-90
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BBeach said:
The "poor man's EGR" idea would apply if you still had combustion in those cylinders - but you don't. Also, since the exhaust ports are all individual, and there are longish runners on the exhaust manifold, I'm inclined to think the effect would be negligible.
I'd be more worried about the turbulence caused by intake reversion, meself. However, the losses due to compression "for no good reason" (you're not firing the cylinder, so why make it do work that won't help you?) would be rather more significant than any losses due to exhaust reversion, I'd think (as far as the EGR idea itself goes, I've found it to be of specious utility at best. There are better ways to do the job that EGR does, and RENIX engines actually run cleaner without it! I'm fairly sure I still have that smog report somewhereabouts...)
OK - reading the linked Wiki on "variable displacement" (the one that references the Caddy V8-6-4, not the Honda J30,) the "air spring" idea has some merit, and I hadn't thought of that. It still seems to me there will be significant pumping losses - but that's just me. As far as quoting Wiki - as long as you're not doing a serious scholarly work, no worries. In comparison on various subjects, I've found Wiki to be mercifully free of apocrypha and "bad data," so no trouble there, either.
There's still going to have to be a good deal of thought applied to this sort of idea, tho. Especially since we're working with a six - deactivating cylinders may take more "adaptive thinking" than we first thought...
j99xj
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BBeach said:
That's how its done.
We in the XJ community often forget that the XJ was designed specifically for decent fuel economy.
Before the XJ, people who wanted a Jeep wagon had nothing but the very large and heavy SJs to choose from, and getting 10-12 mpg out of these beasts was the norm.
When the state of the art XJ came along getting over 20 mpg on the highway it was one of the most efficient 4x4s around, and as we all know, the XJ sold like water in the desert in a time when the future of the oil industry was unknown.
Unfortunately, 20 mpg is terrible by todays standards. Although I still think its decent.
Well there are still small things here and there that i'd love to work on to get it up there, granted something like MDS wouldn't be as easy with our application i still think it'd be fun to do projects in that area.
And 5-90, what happens if the say 5th cylinder is "open" all the time and the 6th cylinder behind it is in the exhaust stroke pushing it out, but also past the 5th cylinder exhaust tube (or in the case another "intake" runner). Its still as possibilty but idk if its a large problem.
And 5-90, what happens if the say 5th cylinder is "open" all the time and the 6th cylinder behind it is in the exhaust stroke pushing it out, but also past the 5th cylinder exhaust tube (or in the case another "intake" runner). Its still as possibilty but idk if its a large problem.
5-90
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BBeach said:
If we had a "log" manifold, or one of those short-runner cast iron types that are popular on V8s, I could see it being a rather larger problem. However, we've got rather longer individual runners (not a true "header," but closer to it...) so reversion would have to be drawing the exhaust pule from one longish runner back through another. Doesn't eliminate the problem, but it does make it a bit less likely. Installing anti-reversion cones in the exhaust runner enries would also help this - but I don't know if it would be actually necessary.
5-90
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BBeach said:
I'd have to check - but I seem to recall them working that way. Pairs as 1/6, 2/5, and 3/4, with each cylinder 360* out of phase with the other in its pair (i.e. - with #1 at TDC Compression, #6 would be at TDC Exhaust.)
I got 24 in mine with a built stroker, 37" tires, 4.88 gears, traveling from salt lake city to price Utah, anything but flat roads, doing anywhere from 55 to 65 following a friend in a ramcharger, it can be done, I've never gotten that good before this and probably won't again due to my heavy foot.BBeach said:
I believe all the MDS vehicles have a fly by wire throttle as well. So throttle position might change when its in fuel saver mode as well.
My Dad just bought an 07 Magnum RT with MDS. I rode in it today and its totally seamless you never feel when it goes in and out of it...it does have an indicator though.
My Dad just bought an 07 Magnum RT with MDS. I rode in it today and its totally seamless you never feel when it goes in and out of it...it does have an indicator though.
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