I know my factory 20s are hurting my mileage but i like em and hence they stayin. Besides takin her easy with the right foot whats the best way for us with the 5.7hemi to get a few more hp and mpgs. Im really thinking either a catback exh, or getting a venom dsp.

Also anybody got any real world numbers on say running a E3 spark plug vs a good ol champion copper plug? I just dunno if it be worth it to shell out that kind of dough.

 

https://dodgeforum.com/forum/3rd-gen...5-7l-hemi.html

General consensus is to stay with the stock copper plugs. People have actually reported WORSE performance and economy using "premium" plugs.

Tire inflation and maintenance are your two biggest factors after driving style. Other than that, get yourself an e-fan (search here for info, there's a metric ton of it in the first few pages, alone).

 

I have the same truck as you and have done all i realistically can to improve MPG's.

I have a free flow cat back exhaust, got rid of the hemi hat, run StarTron in the fuel, use proper spec Synthetics in both diffs, trans, transfer case and engine (and change them at the reccomended intervals), run ONLY 89 and recently did my plugs, new EGR valve, new PCV, Cleaned and grounded the Throttle Body. Almost all my driving is highway and i am getting around 16-17MPG. I could likley get it a bit higher if i was a little lighter on the throttle.

Use the regular copper plugs, don't waste your money on anything else. And don't bother with an aftermarket style intake with a large filter. It will NOT increase your MPG's and it will not do anything to increase HP unless you have extensive mods such as a larger Throttle body, ported heads, Cam, etc.

A programmer is the single biggest and easiest HP increase for these trucks.

 

I was hoping to see around 20mpgs. Guess that aint gonna happen with only a couple simple mods I might just get a dsp put on the 91 tune and call it a day. I cant stand how sluggish the mds is, its always cutting in and out.

I dunno what the gains are for a catback. But is there a huge difference in flow between running duals or a single? I was looking at a cherry bomb single vortex kit. I figure if the engine can breathe easier has to net some mpgs.

Anyways just picked up 16 champion coppers, for that many plugs price isnt too bad. Id hate to see the bill for that many E3s.

 

20 MPGs out of a 350'ish HP, close to 6000 lb. four wheel drive vehicle is a bit optimistic. You did hit the nail on the head in your initial post though, running 12" wide tires on those heavy a$$, 20" stock rims are hurting you at the pump, big time.

If more than 50% of your driving is non-interstate, then ditching the parasitic clutch fan for an e-fan will net you bigger gains at the pump than a tuner, although having both will help more...

 

You are not going to see 20 MPG on that truck unless you drive it like an old man and keep it under 2,000 RPM with a strong tail wind.

And adding a free flow exhaust is not going to gain much, if any MPG.

As for single vs dual? Are you adding headers too? If not, get the Magnaflow Y-Pipe (Dual 2.5" inlet, single 3" outlet) and just get a good single exhaust that of anything branches into dual exhaust. That is what i did. A true dual exhaust NEEDS a crossover pipe and that is not easy to add on these trucks. Not to mention, with a stock intake and heads and not even headers, true duals is complete overkill.

I opted for 3" into a free flow muffler with dual 2.5" outlets going out before the rear passenger side wheel. But i could have used the same setup and ran the pipes over the rear axles and had them coming out the back.

I am not sure why your truck is "sluggish" with MDS. My truck is not sluggish at all. MDS is only kicking in at cruising speed, not at idle or while accelerating. So from a stop (stop sign or traffic light, etc) you have all cylinders firing when you hit the gas. And even accelerating on the highway to pass someone, it kicks in instantly. I have a Vacuum gauge on my truck so i can tell when MDS is on or off not to mention with the exhaust, you can hear it. I recently drove a buddies 06' with MDS disabled (Predator) and there was ZERO difference performance wise driving around town. The only difference was when cruising and the truck shifts into OD, you no longer hear MDS kick in.

 

Best I ever saw on my non-MDS '05 (33x12.5/17 A/T tires, 3" BL, Flowmaster 50 series SIDO exhaust) on EXTENSIVE highway runs was a shade over 18 mpg, hand calculated, and that was actually pretty normal for road trips. Around town was/is abysmal. It is even worse now that I'm in a new location with tons of rolling hills. It seems everywhere I have to start from a dead stop I'm heading uphill...

You will not see 20 mpg, even with MDS on the highway. It's not going to help around town on short jaunts. Best I'd hope for would be 13-14 mpg in town and 18'ish on the highway. I can't comment on the MDS on the open road trips, but I have two friends with MDS trucks and they get no better than I do around town.