Thanks Aim.

 

With large tires, 3.92s may actually help with mileage, but in your current setup, I'd have to agree with aim (for highway mileage at least).

 

Yeah I would think around town it would not effect it all, and would probably actually help it. I know I am not driving an economy car here, but quick question for you guys, which mod would effect highway mileage the least?

 

Explain to me how reducing friction and letting the engine breathe easier will hurt mileage.

I saw a gain in mileage (0.5-1MPG) with 1.7RRs.

 

Interesting

 

The higher valve lets in more air, which in turn uses more fuel to keep the a/f ratio at the specified fuel values within the pcm fuel curve tables.

I saw no such gain in mileage on my 5.2l.

 

Yes, but if more air and fuel is coming in, then more power is being made, and you will accelerate. To stop accelerating and cruise, you use less throttle, therefore using the same amount of fuel and air as before, with slightly less throttle. So at any given amount of throttle, in theory, you will use more air and fuel compared to stock, but by simply using less throttle, you will not consume anymore fuel while also reaping the benefits of reduced friction from the roller rockers. As you said, the PCM will keep the closed loop cruise AFR the same, so really no fuel is being saved from the increased lift, it's the reduced friction in the valve train.

I'm not guaranteeing there will be a gain but there certainly won't be a loss.

 

gears dude.. not only will it better your 'around town' mileage, it will give you better performance, AND make life easier on your transmission..

on the highway you won't see a serious drop in mileage.. w/ 3.92:1 (which were stock on my rig) I ran slightly under 2kRPM@70ish.. w/ 4.56:1, I run about 2200~2250RPM@70ish.. when I head west and into hill country, rarely do I drop out of o/d.. that actually helps mileage, where it was often searching for gears w/ 3.92.. my rig is heavier than yours though..

I'm really really happy w/ mileage in my rig right now- and I've bumped gears and 1.7rr's.. I run efans, airgap, genIII spitters, HF SCT tuned @91 and 93fuel, headers/ true dual w/high flow cats, ram air.. the only thing I've done to hurt mileage is the gears and bigger tires..

w/ the heft of an '02 quad cab 4x4 5.9L magnum, I'm getting 13.5 overall MPG's (math NOT drive computer, and GPS'd miles/speed).. I haven't ran it on the highway any sustainable time to gauge hwy miles yet, but I'm confident it would be all over the magic 15mpg..

I've two more mechanical tricks to pull to attempt better yet- all while improving performance as well. I honestly think 15mpg overall is achievable, and that's my aim.. while I'm doing these mods, I'll hook up the vacuum gauge I bought some time ago, and put it in the pillar- where I can keep an eye on driving habits, and possibly squeeze a few more tenths of a mpg even still, by letting the road and conditions choose my speed instead of a street sign..

I see you live in FLA.. flat like 'round here.. the 3.92's will get you to speed easier and help you stay there easier.. If you can control your driving habits, it's my opinion you can easily maintain your current economy..

that said: I still rec the RR's dude.. they're definitely worth it too..

 

Thanks hahns and drew for your input. It's still a difficult decision. I just don't want my wallet to be hurting every week because of the gears. I like the idea of the Roller Rockers better if it will effect my mileage the least. If I were just staying around town I wouldn't have even posted this thread, but since I will be doing mainly highway driving for a couple years, its hard to pick.

I know fuel economy and performance don't go hand in hand, but I am basically trying to squeeze as much performance as I can out of my Ram before mileage starts to decrease. Maybe I have already reached that brink and shouldn't do either like Zman suggested?

It seems like the majority here feel that the gears won't decrease the mileage too drastically? If so, might just have them installed then.

Thanks guys

 

I think this is a misconception.. I think they DO go hand in hand.. If you're improving your engine/drivetrain, you are doing both.. the question is, can you keep your foot out of it..

the rr's eliminate a stress point and lessen parasitic power loss on an engine.. the engine has to work less to move those rascals.. it's my opinion (and that isn't worth much) that getting rid of that slight parasitic loss of energy 'pushes' the slight consumption of fuel.. they cancel out..

the gears (assuming you have 3.55:1) aren't going that much lower (to 3.92:1).. it's not even the difference in o/d on/off in what you have now imo.. the truck will, however, use less energy to get going.. and it will hold the gear a lot easier.. Honestly, that is almost a 'push' as well imo.. the overall 'gear to the ground' drive ratio isn't altered all that much. it's 1st, and 2nd you will feel it most.