'04 hemi 1500. Any chance I can reasonably upgrade to the MDS hemi engine without replacing the engine? like i said, im doubtfull but it wont hurt to ask.

-kevin

 

About anything is possible if willing to throw enough money at it. However, I suspect you could buy a lot of gas with the bucks it would cost, unless done exclusively with electronics. Even then, at a maximum of about 20% better mileage, it would still probably take considerable timeand miles to just break even.

All the best.

 

I've been looking at trucks and the stickers only rate the '06 with MDS as getting 1 mpg better than the '05 without it.

Either way you will be pushing a heavy square truck down the road, I don't think there is anyway to get good mileage in of our trucks.

 

In their official press release, Dodge more or less admitted that the MDS system on the Ram pickups only worked in the 45-65 mph range.

I suspect that the 20% increase number they loved to bandy about in their advertising occurs at 50 mph on a level highway.

The MDS works on the principle that having the throttle near full open gives better fuel economy.

Basically what happens is that when you are running on all 8 cylinders at 50 mph the throttle is closed so much that the Manifold Absolute Pressure (MAP) is only about 35% of full atmospheric pressure. When the MDS cuts in, this drops out 4 cylinders and the throttle then opens to about twice the MAP and runs on 4 cylinders at 70% power.

But what happens when you at travelling at 75 mph in your Ram?

Well, at 75 mph with 8 cylinders you may be about 60% MAP. The MDS system cannot cut in, because if you doubled the load on the 4 cylinders it would be 120% load and that is impossible (without a turbo).

Bottom line: in the smaller Jeep Cherokee Hemi and Durango Hemi the MDS can cut in at speeds up to about 80 mph and so MDS is a practical fuel economy improver. In the much heavier 2006 Ram with its big frontal area and "brick-like" aerodynamic Cd, the MDS can only work in the slower speeds.

MDS is mostly an advertising gimmick that the marketing dept at DC is using to try to get technically ignorant people to upgrade to a 2006 model Ram. I don't blame them for this, because Ram sales are always hostage to high gas prices, and many DC employees jobs depend on sales.

In the older Rams you can always get better MPG by slowing down to 60 mph.

In the new 2006 model year Rams with MDS you can also get even better MPG by slowing down to 60 mph, perhaps as much as 3 MPG more.

But how many Ram owners drive 60 mph on US interstate highways?

The better technical fix is to have a 7 speed transmission and an engine with variable valve timing. With this combo you can match the best fuel economy of the engine to truck speed over a wide range. Even better would be a continuously variable transmission.

 

Hank- Very well put. Another suggestion (especially in light of the fuel problems these days) would be variable mixture control. During highway speed, rather than maintaining the 14.7:1 (or whatever it is) the ECU could reduce it unless the rpms suddenly increase (going uphill) then would adjust for best power. I have been experimenting with different techniques and have found MPG best in the 1500-1700 RPM range without sacraficing too much power. Rather than watching my speedo, I concentrate on the tach thesedays. I aslo built a homemade HAI (hot air intake) and it was working great The best economy I got was 16MPG (2002 1500 4x4 5.9l 4.56 gears). Shortly thereafter, I realized that I had a belly pan gasket leak and after it was fixed my MGP dropped to 13 with or without the HAI. I'm not sure why. I guess for some reason the ECU was not compensating for the belly pan leak and I was running lean. The lesson I learned is next time my belly pan gasket leaks, I guess I'll leave it for better economy!

 

Thanks for the information. I was feeling a bit cheated about the MDS in the '06 but now I feel much better.

 

Aviator:

I'll take a little less mileage over an uncontrolled lean condition every day, especially for any length of time. If in doubt, I've got a great collection of broken and otherwise destroyed Arias and Ross pistons I can send pix of.

If you are even remotely serious, I'd suggest you forget the tach and install exhaust temp sensors in the manifolds and they may change your mind--when the mix leans out and exhaust gases reach 1600 degrees or more!

And sorry, in over 5 decades of vehicles of all stripes, I've no idea what a "belly pan gasket" is or where it is located. My ignorance.

All the best.

 

It pays to keep in mind the difference between leaning out at 'part throttle' and leaning out at full throttle.

Leaning out from 14.7 air to fuel, to say 16.7 at part throttle operation where the MAP is around 60-70% of full power actually DECREASES the tendency to detonate. Detonation is worst at 14.7 air to fuel. Moving richer or leaner is better than staying near 'stoichiometric'.

Things are completely different at full throttle.
The stock Ram PCM computer is trying to keep the air to fuel ratio in the very rich 10.5 to 11 air to fuel ratio at FULL THROTTLE so that it can live with octane as low as 85 in a bad tank of gasoline. If you decide to start leaning out at full throttle from these very rich air to fuel ratio - the first effects are gains in peak horsepower as the mixture leans toward the 'window' of 12.5 to 13.5 where peak BMEP occurs. This is what the Mopar Performance PCM does. The MP PCM depends on having 92 octane or better, so it both advances max ignition timing and LEANS the air /fuel toward 12.5

Superchips and Hypertech are doing similar.

But if the octane isn't there in the fuel
(or the air temp is high, or air humidity is very low, or engine coolant temp is way high)
then the worst of the eight cylinders will begin to detonate as the previously way rich air to fuel ratio begins to get closer to the worst situation of 14.7 at Full Throttle.

You can also get detonation from a miss. After a miss the cylinder doesn't have the 20% left over exhaust gas. It now has 20% unburned air and fuel as 'left overs' instead. On the next cycle you have nearly 100% air and fuel instead on the 'normal' 80%. When the sparkplug fires this 'super fill' the burning is so much more than normal that the end gas usually detonates once, and the extra heat of the detonation overheats the sparkplug electrodes makes subsequent cycles keep detonating.

Since Dodge's factory accept/reject standard on combustion chamber size on the older 5.2/5.9 Magnum cylinder heads was a pretty loose 57cc to 63 cc range there is plenty of room for the eight cylinders to vary.

 

WOW!! Thanks for the automotive lesson HANKL! I needed that! Man, we have some pretty sharp individuals here. You have cleared up a lot of things for me too. They almost had me with the MDS like they got me with The New "HEMI" engine which is not the true hemispherical engine that most people think of. Which makes me wonder.....................

 

Well I just got my best mileage per tank of gas in my 05

391. I probably could have pushed to 400 but the little overhead said I had 0 miles for about 3 miles. LOL.

26 Gallon Tank (with 2.5 extra gallons???? according to the build sheet)

So it looks like 15 MPG if yo go 26 gallons and almost 14 if you go with 28.5.

This is all my wifes fault, I would have been well over 400 however she made me take her shopping over the weekend and wanted to take the truck.

So I spent saturday morning bouncing around between stores.