A while back on the "Official mpg" thread I indicated I'd do a thread for the more adventurous experimenters among us. I'll start by saying that, of all the mods. I've done to both of my Hemi vehicles (they're both modded almost identically), a good exhaust system, including tubular or SRT (for the 5.7's) headers and some sort of 3 in. straight through muffler(s), and an aftermarket cam that I advanced (against everyone's recommendations) are the mods. that made, by far, the most difference. So far, at best, I am up ~100 RWHP and ~5 mpg on each. I just got back from a 2000 mile (actually 1956 miles) with my 5.7 LX and averaged, for the whole trip, 27.01 mpg, including in town, mountain climbing (over 7000 ft. once and over 6000 ft. 3 times) and high headwinds on the last leg (only got 25.047 mpg on that leg) of the trip. A little over 4 tanks of fuel (72.4 gallons to be exact) to go that distance. IMO, not bad for a 4500+ lb. vehicle, when loaded. Best distance (but not best mpg) per tank was, 514 miles on 18.35 gallons. I did the best on the first leg (465 miles on 16.55 gallons of 87 non-ethanol fuel, with 8 oz. of acetone added. Almost all driving (~75-80%) was between ~3000-5000 elevation.
Enough of that. Now on to the mods. Aside from a good tuner (either DS or SC), a good exhaust and intake (not as important), experimenting with valve timing, i.e. cam advance, I feel makes, by far, the biggest difference against money spent on other mods. If you can do all the labor yourself, you will be way ahead of the game too, but it is not for the faint of heart, and you must have some pretty good mechanical ability. As far as the tuner goes, for folks with the 545RFE transmission, I would highly recommend the SC tuner, only because it has a complete trans. tuning application that allows you to set it up any way you want. I have mine set up for maximum MDS on time, both in town and on the highway. The DS tuner offers more flexibility in engine tuning and allows for custom tunes, if needed. It does not, however, allow for complete control of the transmission. Again, against everyone's recommendations, I am running canned tunes with my custom transmission up/down shift schedules and torque management. I get no knock retard, and I get 13:1 A/F commanded at WOT. At light throttle, the O2 Sensors dictate a 14.7:1 commanded A/F ratio, no matter what.....assuming your O2 Sensors are in good working order. For this discussion, my main objective is fuel economy (FE), more than performance.
It is possible to get considerably improved FE along with modestly increased horsepower and torque. If one goes too far, you end up with more power and less FE. Essentially, the goal is to improve the Volumetric Efficiency (VE) of the engine, which allows it to process air and fuel more efficiently. The higher the VE, the better, but it is difficult to achieve, due to many factors. Also, for Hemi owners, increasing MDS on time is a plus. On the highway, it makes a 2-3 mpg difference on either of mine.
Most stock exhaust systems are relatively inefficient. They have restrictive log type exhaust manifolds and usually triple pass (flows rear, forward, rear) mufflers. The 5.7 WK manifolds are particularly poor, especially compared to the 5.7 LX's or the SRT-8 headers. See the difference between the LX and WK's here: http://www.jeepgarage.org/showthread.php?t=19490. IMO, this should be the first order of business. On the 5.7's, a good manifold and straight through 3 inch mufflered/resonated system is a must to help bring the beast to life.
Now to the cam. Because of good deals, I chose to use the FRI Engineering Sidewinder cams in both my Hemi vehicles, They have been well proven as a "torquer cam" in the LX community, and it has been around for probably 6-7 years. When installed "straight up", dyno tests have shown about a 50 RWHP increase, with no other mods. Unfortunately, like almost all aftermarket performance cams, they develop their torque and horsepower above 3000 and 5000 RPM, respectively. How much of your driving is done in these RPM ranges? I know since I did the cam installs, it's a lot more than it should be on mine. I love it!! Most of our "normal" driving, whether it be in town or on the highway is done well below 3000 RPM.
To rectify this, advancing the cam timing, whether it be stock or aftermarket, lowers the maximum torque/horsepower RPM ranges somewhat, depending on how much you advance it. Advancing the cam will also "kill" the top end performance to some degree, again depending on how far you advance it. On my Jeep, I advanced it only 2 degrees (using a Crower kit), mainly because I wasn't sure how much difference it would make. On my Hemi Magnum I got braver and advanced it a full 6 degrees. Cutting to the chase, IMO, the 6 degree advance delivered the best results by a noticeable difference. Next time I am into the Jeep engine, I'll be advancing it to 6 degrees also. It does start to flatten out above ~5800 RPM, or so though, but down low, it torques almost like a diesel now.
For those who want to give it a try, and don't want to spend a ton of $$$, I would recommend trying the advance trick with the stock cam. The Hemi cam timing gear has 52 teeth, so advancing it one tooth would be moving it 6.923 degrees ahead...my LX, with the 4 degrees already ground in by the mfg'er. is at ~10 degrees. If you don't want to go that far, do a search for the Crower Kit. Everyone (manufacturer, seller, and some forum members) told me not to advance the aftermarket cam because the additional lift and duration may cause piston to valve clearance issues, plus adversely affect the power curve. It hasn't! It's moved it down to where it is more useable for my purposes. Advancing the stock cam should be less of a P to V concern with the lower lift and duration. I know if I hadn't gotten the aftermarket cams, I'd have for sure advanced the stock cams. Bet an advanced stock cam would even outperform the advanced aftermarket cam.....on the bottom end anyway. Any takers?? For 5.7 owners that may want to try this, I'd be glad to provide any assistance I can.....FWIW.
Enough of that. Now on to the mods. Aside from a good tuner (either DS or SC), a good exhaust and intake (not as important), experimenting with valve timing, i.e. cam advance, I feel makes, by far, the biggest difference against money spent on other mods. If you can do all the labor yourself, you will be way ahead of the game too, but it is not for the faint of heart, and you must have some pretty good mechanical ability. As far as the tuner goes, for folks with the 545RFE transmission, I would highly recommend the SC tuner, only because it has a complete trans. tuning application that allows you to set it up any way you want. I have mine set up for maximum MDS on time, both in town and on the highway. The DS tuner offers more flexibility in engine tuning and allows for custom tunes, if needed. It does not, however, allow for complete control of the transmission. Again, against everyone's recommendations, I am running canned tunes with my custom transmission up/down shift schedules and torque management. I get no knock retard, and I get 13:1 A/F commanded at WOT. At light throttle, the O2 Sensors dictate a 14.7:1 commanded A/F ratio, no matter what.....assuming your O2 Sensors are in good working order. For this discussion, my main objective is fuel economy (FE), more than performance.
It is possible to get considerably improved FE along with modestly increased horsepower and torque. If one goes too far, you end up with more power and less FE. Essentially, the goal is to improve the Volumetric Efficiency (VE) of the engine, which allows it to process air and fuel more efficiently. The higher the VE, the better, but it is difficult to achieve, due to many factors. Also, for Hemi owners, increasing MDS on time is a plus. On the highway, it makes a 2-3 mpg difference on either of mine.
Most stock exhaust systems are relatively inefficient. They have restrictive log type exhaust manifolds and usually triple pass (flows rear, forward, rear) mufflers. The 5.7 WK manifolds are particularly poor, especially compared to the 5.7 LX's or the SRT-8 headers. See the difference between the LX and WK's here: http://www.jeepgarage.org/showthread.php?t=19490. IMO, this should be the first order of business. On the 5.7's, a good manifold and straight through 3 inch mufflered/resonated system is a must to help bring the beast to life.
Now to the cam. Because of good deals, I chose to use the FRI Engineering Sidewinder cams in both my Hemi vehicles, They have been well proven as a "torquer cam" in the LX community, and it has been around for probably 6-7 years. When installed "straight up", dyno tests have shown about a 50 RWHP increase, with no other mods. Unfortunately, like almost all aftermarket performance cams, they develop their torque and horsepower above 3000 and 5000 RPM, respectively. How much of your driving is done in these RPM ranges? I know since I did the cam installs, it's a lot more than it should be on mine. I love it!! Most of our "normal" driving, whether it be in town or on the highway is done well below 3000 RPM.
To rectify this, advancing the cam timing, whether it be stock or aftermarket, lowers the maximum torque/horsepower RPM ranges somewhat, depending on how much you advance it. Advancing the cam will also "kill" the top end performance to some degree, again depending on how far you advance it. On my Jeep, I advanced it only 2 degrees (using a Crower kit), mainly because I wasn't sure how much difference it would make. On my Hemi Magnum I got braver and advanced it a full 6 degrees. Cutting to the chase, IMO, the 6 degree advance delivered the best results by a noticeable difference. Next time I am into the Jeep engine, I'll be advancing it to 6 degrees also. It does start to flatten out above ~5800 RPM, or so though, but down low, it torques almost like a diesel now.
For those who want to give it a try, and don't want to spend a ton of $$$, I would recommend trying the advance trick with the stock cam. The Hemi cam timing gear has 52 teeth, so advancing it one tooth would be moving it 6.923 degrees ahead...my LX, with the 4 degrees already ground in by the mfg'er. is at ~10 degrees. If you don't want to go that far, do a search for the Crower Kit. Everyone (manufacturer, seller, and some forum members) told me not to advance the aftermarket cam because the additional lift and duration may cause piston to valve clearance issues, plus adversely affect the power curve. It hasn't! It's moved it down to where it is more useable for my purposes. Advancing the stock cam should be less of a P to V concern with the lower lift and duration. I know if I hadn't gotten the aftermarket cams, I'd have for sure advanced the stock cams. Bet an advanced stock cam would even outperform the advanced aftermarket cam.....on the bottom end anyway. Any takers?? For 5.7 owners that may want to try this, I'd be glad to provide any assistance I can.....FWIW.