20.5 mpg Dodge RAM ABA testing run

[user removed]

My 92 F150 is .80 OD (5speed) and a 2.73 axle with 28 inch tall tires.
1550 at 60 MPH.

regards
Mech

[ECONORAM]

Sorry you all, it's been a busy week.

I appreciate everyone's feedback. It's been a long journey just to get here. I've learned far more than I dreamed I could dig into when I started...

@Blu3Z3rg, My truck is a 4.7L flex-fuel. Sorry, not a Hemi, so I don't have the MDS on it. When it was new I got a best of 17.6 mpg driving down to San Antonio from OKC. I honestly am not sure I have seen anything from the Ypipe because the factory muffler is so restrictive. One of my next tests is swapping in a straight pipe and comparing.

@deathtrain, sorry...I could not help myself on the cams. They are factory HO parts, worth 20 hp! I also did some research and discovered they have a closer lobe separation angle...kind of like Toyota Prius cam I learned. I hope I'll at least see no change, if not a little increase. That closer LSA is supposed to help scavenging, if I remember correctly. I can tell you it made a big improvement when I drop the hammer...

@brucepick, Thank you sir! Yep, I have slowly learned the open intake won't do anything for me. I am brewing a warm air intake idea, and I hope that will lessen the impact of my sewer pipe intake mod. You are right, I started watching the % throttle opening on my Superchips and was really surprised at how little opening there is going down the road. TX--lots of highway driving here, that's for sure. I've also driven this truck all the way to North Dakota and back, and got 20mpg the whole trip! I need to work some bracket fitting on the back half of the truck, and I can panel the whole belly... My wife will knock me silly if I hack on the topper, so I will have to hatch some sort of stealth plan...

@mcrews, I am stewing on tire sizes. My truck wears 275/60R20s. They are 33 inches tall! With my tranny's OD, it has a .67 5th, and a 3.92 rear end. The 545RFE is really a 3sp w/two overdrives (but they call it a 5sp). The gears combined with the taller tires (factory option) give me a 3.55 rear end. Unfortunately, the RAM is a heavy truck (mine is light at 5400 lbs with the topper!), so that tall gearing does not help much unless it is really flat.

ABA the cams?! OUCH. I could swap them faster the second time, but I do not want to.

@Frank Lee, you might be right about the lugging. My truck is turning about 1900rpm at 70 mph. I've read some articles about piston speed, but that seems to contradict what most folks report on the Dodge forums. Lots of them swap in 4.56 gears. But that may be because their trucks are heavy and have the Cd of a brick!

With my gearing, I am looking at some 275/45R20 tires. That would drop my truck back to a 3.94 rear end. Most trucks with the 17s from the factory (mine has [heavy] factory 20s) do better on FE and accel. I think this is gearing and wheel weight. I also thought about some 265/50R20s, or some 255/50R20s, but those are expensive. Both are a little narrower and shorter...

The supreme goal is to hit 27 mpg at 65 mph. Yes, in a truck. I figure if I can hit 25mpg on E10, I'll try straight gasoline and see what I get. That'll require some more sophisticated aero work...

[Blu3Z3rg]

Originally Posted by ECONORAM

@Blu3Z3rg, My truck is a 4.7L flex-fuel. Sorry, not a Hemi, so I don't have the MDS on it. When it was new I got a best of 17.6 mpg driving down to San Antonio from OKC. I honestly am not sure I have seen anything from the Ypipe because the factory muffler is so restrictive. One of my next tests is swapping in a straight pipe and comparing.

I just converted to a straight pipe... i'll let ya know!

Originally Posted by ECONORAM

@deathtrain, sorry...I could not help myself on the cams. They are factory HO parts, worth 20 hp! I also did some research and discovered they have a closer lobe separation angle...kind of like Toyota Prius cam I learned. I hope I'll at least see no change, if not a little increase. That closer LSA is supposed to help scavenging, if I remember correctly. I can tell you it made a big improvement when I drop the hammer...

And YOU let me know about them cams!!!!

Originally Posted by ECONORAM

@brucepick, Thank you sir! Yep, I have slowly learned the open intake won't do anything for me. I am brewing a warm air intake idea, and I hope that will lessen the impact of my sewer pipe intake mod. You are right, I started watching the % throttle opening on my Superchips and was really surprised at how little opening there is going down the road. TX--lots of highway driving here, that's for sure. I've also driven this truck all the way to North Dakota and back, and got 20mpg the whole trip! I need to work some bracket fitting on the back half of the truck, and I can panel the whole belly... My wife will knock me silly if I hack on the topper, so I will have to hatch some sort of stealth plan...

I'm looking to do underbelly pans as well, do you think this is where your most significant change is? And 3" on the intake is plenty large, 2 3/4" is what I calculated to be ideal for a 2500 power peak from flow. I won't say it has made or broke the mpgs, but I'm not going to redo it. I just have a shield I can put on or take off for the varying temps.

Originally Posted by ECONORAM

@mcrews, I am stewing on tire sizes. My truck wears 275/60R20s. They are 33 inches tall! With my tranny's OD, it has a .67 5th, and a 3.92 rear end. The 545RFE is really a 3sp w/two overdrives (but they call it a 5sp). The gears combined with the taller tires (factory option) give me a 3.55 rear end. Unfortunately, the RAM is a heavy truck (mine is light at 5400 lbs with the topper!), so that tall gearing does not help much unless it is really flat.

ABA the cams?! OUCH. I could swap them faster the second time, but I do not want to.

@Frank Lee, you might be right about the lugging. My truck is turning about 1900rpm at 70 mph. I've read some articles about piston speed, but that seems to contradict what most folks report on the Dodge forums. Lots of them swap in 4.56 gears. But that may be because their trucks are heavy and have the Cd of a brick!

With my gearing, I am looking at some 275/45R20 tires. That would drop my truck back to a 3.94 rear end. Most trucks with the 17s from the factory (mine has [heavy] factory 20s) do better on FE and accel. I think this is gearing and wheel weight. I also thought about some 265/50R20s, or some 255/50R20s, but those are expensive. Both are a little narrower and shorter...

The problem with trucks is the weight and the huge front area, which is why letting the piston speed go a bit faster is better for trucks. It allows the engine to work a little "easier" yet at higher rpms to push the truck through the wind. When I did the piston speed calculation (someone had the math posted somewhere...) I believe it was varied a few 100 rpm. I think it was 1800-2200. This is where it's common sense as well. My truck likes to sit about 2200-2400 rpm on the highway, and you can just feel it be comfortable there. This puts me about 70-75, which is plenty fast for around here since the limit is 65.
BTW, my truck is also 5400 lbs, and I have the 3.55 rear with same transmission. I believe it's actually a 6 speed, with 2 different gears for 2 or 3rd, can't remember. It will use one if your downshifting, a different one if you're upshifting. Don't quote me on that, going from memory.

Also, one more thing to try is putting the truck in tow mode while around town. When I do, it feels more like my old F150 did normally. But that thing had the 5.4 and only weighed in at 4600 lbs (std. cab, long bed, no frills work truck) and I got about 18 mpg regularly with that thing.... too bad I needed 4 doors for kids and 4wd so I could get to the plow trucks...

[Frank Lee]

GD straight pipes

[Blu3Z3rg]

Originally Posted by Frank Lee

GD straight pipes

I ain't no city boy... I feel outta place without a little rumble.
It's not as loud as you would think
Also, I went with 2.5" single, not duals. I don't wanna lost my entire bottom end.

[Frank Lee]

No, they're never very loud... in the cab.

[slowmover]

One thing that always concerns me in modding pickemups for FE is in decreasing the amount of work it can do. If I reduce trailer-towing capacity, or load-bearing capacity, then I'm going in the wrong direction. And just because I don't need it today (the future that appears like the past; magical thinking) doesn't mean that straitened circumstances may not arise tomorrow. So, gear and tire changes that make it difficult for the truck to get started under a heavy load are counterproductive . . and I may not have time or money or both to "fix" my alterations. While a grille block is easily removed, for example.

So, while it's always a pleasure to see a guy get 20-mpg in a pickemup (an impossibility in the years I was growing up, it still astounds me) and I pass along my congratulations to you, I'd be mighty careful about gearing/tire-height/load capacity changes. Burning up a trans is a nightmare, to me. As is prematurely wearing out axle gears.

I might someday need more than the book says I can do. For the time that I own a truck it is to my familys' well-being that I do so with this in mind.

One should never think ones self exempt, IMO:



.

[NHRABill]

After reading majority of the thread (skimming some) I did not see anyone mention converter lockup speed. Flubbing around with tire and gear size is one thing but ignoring the trucks cruising engine speed and converter lockup rpm is leaving a lot of fuel burned up with no benefit.

Look into a electronic lockup kit for your transmission. The typical stall converter (at least GM from years past) was 1200-1500rpm before lockup. As was already mentioned, lugging the motor with tall gears and a big tire is wasteful. When the cruising speed is below 1,800rpm you risk slippage wasting power and fuel. I installed a couple B&M trans lockup kits years ago on 700r4 and 2004r transmissions I am sure they should have something similar or better today.

I reduced my tire size because I rarely drive on the highway almost always in town heavy traffic, My trans shifts into 4th around 45 mph. full lockup happens closer to 50-55mph. better than it was and sweet spot for cruising around 1800rpm is close to 65mph.

I think I just did the long way of saying pay attention to your torque converter more so than the other items mentioned.

[ECONORAM]

@Blu3Z3rg, I think the belly panels are definitely worth the effort. The largest pain in the backside is figuring out how to get them mounted securely and so they fit together and don't flap around. I had one small glitch a month ago where I hit a big dip in the road @0230 and sent the truck airborne. That was okay in itself (except for scaring my sleeping passenger to death), but my bracket rubbed a ring on the driveshaft, because I didn't clearance it enough. My current panel kit is rudimentary, but it does show improvement over the OEM configuration (none). Once I get things smoothed out, and cover the entire belly, I figure I'll see another mpg or maybe two.
The grill block helps, I think, but I've not done some before/after. I am contemplating blocking about 90%, reinstalling the clutch fan for regular airflow through the radiator, and testing to see if FE would improve. I could probably use the e-fan in the winter, but not summer. I'm sure the e-fan has helped, although I'm not convinced it's as significant as I'd hoped. I still use it to avoid the noise of the clutch fan on start up.
Were the cams worth it? Unsure on the mileage right now. Although, I did notice on the drive to OKC this weekend, going 74 mph the whole way, the truck never downshifted from 5th on any of the hills. That was the first time I recall no downshifts. So, I think the average driver would see some FE improvement... Hope I can go testing this week.

@slowmover, I am with you. Several folks I know have pulled the overload springs, and I am really hesitant to do that. I'm still thinking about lowering it 2 inches. I am a little unsure about changing to 45 series from 60 series...'cuz I do drive it like a truck sometimes, to my wife's chagrin.

@NHRABill, I usually see the tranny lock (I think) as I watch the eng rpms drop slightly going down the road, after it shifts. However, I am curious now if it is really locking up fully... I can add a resistor to bridge a pair of wires going to the tranny that will give a lower tranny pressure signal...hence telling the computer to up the tranny pressure. I might have to get a gauge and monitor that.

@FrankLee, I hear you, as I worked on a farm for years with straight-piped John Deere tractors. I figure I'll wrap the exhaust pipe in insulation, cut the end of the pipe at about a 45* angle, and see if it is still loud in the cab. Hmm, a straight pipe should weigh less than a muffler too!

[Blu3Z3rg]

I ended up putting in a 2.5" exhaust pipe with a Jones 18" glasspack then turned it out the side right in front of the rear tire. It's actually not all that loud, BUT, I still have my cats.
Certainly a difference in power from original.
Now to see if the mpg's are better... so far it seems they are!