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sandman
Dodge Dakota
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10/06/2002
22:56:06
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 Subject: Hemi 5.7 Droped Cylinders
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I just read in Truck Trend magazine that the new 5.7 will drop cylinders. So you will have a 4 cylinder while cruiseing the HWY once at speed. Remember the GM 4,6,8???? Well here is what stikes me as bone headed. Dodge is planing on droping one bank of cylinders by electronicly restricting the oil flow to the lifter for that side. I am not a rocket scientist but this does not sound like a good idea. It seems like sequentialy droping cylinder by kiling injector pulse and allowing cool air to circulate through the bore could not only do the same thing but it would cool the cylinders between power pulse and add life to engine. This way it would funtion like a North Star engine in limp home mode due to coolant loss. If they added direct injection to this motor the could even vary the fuel timeing massively. I am going to weight and see on this one. GM is also working on a modern version of the old 4,6,8. The realy said thing is that alot of the New Young GM enginieers seem to think that they thought this up. They do not even have a clue that GM had an engine capable of this a long long time ago.. They were a vaccum nightmare but when they worked they worked well.
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CW
GenIII
10/07/2002
09:07:55
|  RE: Hemi 5.7 Droped Cylinders
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The only problem is if you allow air into the cylinder then you have to compress it. That will take away any adavantage of not firing that cylinder. I highly doubt they will use that on the trucks. Just the cars they are planning to put it on.
4.7 HO, CW style
2001 4.7 5sp 3.92 LSD
Ported 68mm TB, IAT adjuster, 3" flowmaster cat back, TPS @ .76V, 4" Z-tube, Roadmaster active suspention, Removed Third cat, Electric fan Convertion, HO cams, Robert shaw 180 therm, HO intake manifold.
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routesixtysixer
Dodge Dakota
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10/07/2002
10:01:29
|  RE: Hemi 5.7 Droped Cylinders
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GM is planning to use the DOD (Displacement On Demand) on ALL of their V-8 engines (especially the trucks) to increase fuel mileage (10-15% supposedly). The switched-off cylinders will not be in compression because the exhaust valves will be open to "leak" compression. The key to this new system is A) Advanced computer control of the fuel system and B) computer control of the exhaust valves (variable valve timing). According to those in the know, it is completely seamless... and reliable (unlike the old 4-6-8 Cadillac).
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nate
Dodge Dakota
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10/07/2002
12:23:48
| RE: Hemi 5.7 Droped Cylinders
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the article I read stated that all GM 8 cylinders would have the dod by 05 or 06. And, like route66er said, their's appears to have been done correctly, with the always open exhaust valve being the key to efficient operation. I hope Dodge and Ford both follow suit with a comparible system.
I am currently an Mech. Engineering student at Ga Tech, and let me tell you - there is some pretty good stuff in the works for more efficient powertrains, even in trucks. We have an explorer built by our future truck team with 210 hp that gets 40 mpg on the highway. (http://www.gatech.edu/news-room/archive/news_releases/futuretruck.html) Our 4 door tahoe had ~250hp while getting 35 mpg. Too bad the oil industry does everything it can to suppress this stuff.
-nate
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nate
Dodge Dakota
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10/07/2002
12:31:40
| RE: Hemi 5.7 Droped Cylinders
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heres a report about the suburban. looks like it was 28 mpg, not 35. And a suburban, not a tahoe. Hey, I'm not on the team, I just look at the truck on my way to class. But I do know that we didn't have the resources necassary on these vehicle to implement a DOD type system, which would give it that much more efficiency. Meisel, who heads it up, is my Energy Conversion / Mechatronics (ECE 3301) teacher, and he talks about it all the time in class.
http://www-mae.engr.ucdavis.edu/general/n_news06.htm
-nate
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Art
Dodge Dakota
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10/07/2002
13:29:38
| RE: Hemi 5.7 Droped Cylinders
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How can you drop one bank of cylinders and not have a wicked vibration,what about vacum loss for power brakes,what about if you get in a hairy situation and need some power instantly and its not there,sounds almost dangerous,like you said Sandman when it works it was great,when it didnt just another 100 headaches to fix
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sandman
Dodge Dakota
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10/07/2002
18:19:11
| RE: Hemi 5.7 Droped Cylinders
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CW the article said that DC planned on useing this system on their HD trucks with the 5.7.The article was in Truck Trend. With the addvent of lighter cleaner burning diesels and new cleaner fuels it seems silly to drop cylinders. If you need gas millage and power go diesel! Their is a reason we do not use gasoline engines in trains, tractor trailers, Farm Tractors, Fork lifts.....Especialy in a truck it is almost silly for use to hold onto gasoline engines in a pickup truck. The only places that the big three gouge people for getting a diesel is here in U.S.! If DC had a 3.5-4 liter diesel for of Dakota's I would be driven a diesel right now!! Heck a 4 cylinder version of the Cummins Turb Diesel would have been just fine with me!! You have to like the sound of a Dakota Quad Cab TD!! My son is only 3 1/2 and he can already tell the sound of various diesel engines.
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stuarth
Dodge Dakota
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10/07/2002
22:07:02
| RE: Hemi 5.7 Droped Cylinders
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All this sounds neat and should sell to the soccer mom types. BUT, if I'm paying for a V-8 HEMI, I want ALL 8 cylinders firing ALL the time. Sure better gas mileage would be nice, but I want power.
If gas mileage was very important to me, I would not of bought a Dodge V-8.
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dweishaar
GenIII
10/08/2002
00:04:50
| RE: Hemi 5.7 Droped Cylinders
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does anyone know of a link to the new dodge commercial with "the funny hemi" line?
One Eyed Fox
The Baja Dak
Have you jumped a dak..........lately?
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DaveR
GenII
10/08/2002
02:55:57
| RE: Hemi 5.7 Droped Cylinders
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I like the new comercial with the ram logo kicking the pi$$ing calvin's a$$.
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nate
Dodge Dakota
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10/08/2002
10:27:41
| RE: Hemi 5.7 Droped Cylinders
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I dont think that yall really understand the concept of having a good computer controlled DOD system. You want 8 cylinders all of the time? You have them. Like you're honestly going to notice the .00002 second hesitation.
What's your trucks 0-60 time? 10 secs, or 10 secs either way. Stomping it from a standstill results in the same accelleration as without DOD.
What's your trucks 55 - 75 time?
6 secs or 6.00002 seconds. Think about it.
So here's the trade off - 2-5mpg savings for a .00002 second hesitation in accelleration.
But you say, I want that power Damnit!
If you can shave 3 mpg off of the vehicles average fuel consumption, then the Truck manufacturer will be able to make more powerful engines that are still smog legal. Believe it or not, that is the real limiting factor here. What is the most power dodge can make and still pass federal regulations. So, you go buy your non DOD engine with 345 hp all the time @ 14 mpg. I will take the next gen DOD system with 375 hp whenever I need it that still gets the same mileage. Then we'll race, and I'm sure that you'll be like "thank god my truck doesnt hesitate 1/5000 second like his did" as I pass you 1/5000 of a second later.
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dweishaar
GenIII
10/08/2002
22:16:56
|  RE: Hemi 5.7 Droped Cylinders
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by god........the man has a point
One Eyed Fox
The Baja Dak
Have you jumped a dak..........lately?
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Brad
Dodge Dakota
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10/10/2002
14:13:18
| RE: Hemi 5.7 Droped Cylinders
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I don't believe it drops one bank. It drops every other cylinder in the firing order. Basically becomes a four cylinder under light load. GM is claiming 25% increases on their engines. I would bet there are better increases for the hemi. I think the DOD system will be introduced in the new car lineup with the hemi. The 300N I believe.
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Demon Dakota
DakotaEnthusiast
10/10/2002
14:32:25
| RE: Hemi 5.7 Droped Cylinders
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The fact that the engine is in a car will be a pretty hefty increase in fuel economy (as compared to the truck it came from). Think about the GM/GMC trucks that used the 5.7L in them, and the Z28's and Vettes that used the same basic motor, and look at the mileage differences between the trucks and the cars.
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nate
Dodge Dakota
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10/10/2002
19:04:14
| RE: Hemi 5.7 Droped Cylinders
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one of the advantages of a good comp. controlled unit is that you can turn an 8 into a 6 by cutting off every 3rd cylinder in the order. Basically, your "off" cylinders actaully rotate around the firing order so as to not make the engine run rough. The 8 -> 4 swap is actually trivial with todays technologies and engine control systems by cutting off every other cylinder for the duration. The reason that nobody has done it is because its either 4 or 8, no in between. So if your efficient 4 cylinder isnt enough, you would have to swap immediately back to an 8, even though 6 would be enough. With GM's new system, they have worked around that problem - which makes the system worth the effort to research / tool / produce.
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