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