Can the 304ci be built for fuel mileage?

[243]

Just curious, with the proper cam, carb, intake and gearing, would the 304ci make 17mpg in the Wagoneer?

[Bryan]

Good question, I posed the same question several months ago and got no reply. Generaly (but not always) smaller displacement motors get better mileage. Power probably wouldnt be a problem unless you were towing or turning huge tires, but if that were the case one probably wouldnt be looking for a smaller motor anyways smile.gif

[francis higgins]

You should be able to get that with a 360, and better (maybe) with a 304. My choked up 360 will do 16 mpg at ~70 mph loaded. I would think you would need some sort of efi, headers, free flowing exhaust, and maybe an overdrive (or high gearing) to get near 18 mpg. I'm sure it could be done though. I have actually considered this myself, but properly built, you probably would only sacrifice ~1 mpg with the 360 over a 304.

[Narnian]

You can save the money if you spend it . . .

You should be able to produce that kind of mileage with tuned port injection, a nice chip, a relaxed cam, and all the exhaust bells and whistles. My friend's two year old full sized F150 with V8 gets 22 mpg. The problem is you may spend four thousand to save $400 a year.

Looking for ways to get better mileage is great, but it is easy to miss the mark. Simply plugging in a 304 will not get you fantastic mileage. My Corvette has a 350, and my old TransAm had a 305. The TA got 25MPG, the Vette gets 30mpg. They both had TPI. Factors like aerodynamics and weight play a big factor in the game. The truth of the matter is our FSJ's have the aerodynamics of a barn, and weigh more than two buffaloes and a donkey.

[bentpushrod]

Displacement shouldn't be an issue. In cases the smaller displacement engine has to work much harder to move the vehicle resulting in worse mileage.

I have a 78 F250 weighs in at 7,000 lbs. With the original 351M, 3.54's and 35's it got about 6 mpg, Swapped in a 460 and mileage jumped to 8mpg. That 351 had to work very hard to get that truck moving, had absolutely no power either. 351M's have absolutely no power in anything though, only thing they are good for is a boat anchor.

My wag with the 360 and tfi is pulling down a hair over 14 mpg so 17 shouldn't be too hard to get. Pull all the smog crap and cat off. Put on some free flowing headers and duals, and perform a full tuneup(carb, filters, plugs, wires, timing). Depending on gear ratio 17 shouldn't be too tough to achieve

[Tom 400 CFI]

I have more input in the displacement vs milage comments.

I have an '83 Trans Am that has Crossfire fuel injection (twin TBI's on a crossram intake). I have had it powered by the original 305, then a 350, and now a SBC 400. All 3 engine have had the same induction, the CFI, and the same exhaust; Edelbrock headers and Y, SLP 3" stainless cat back, and a hollow cat. The 305 was about 230 hp, the 350 about 250 hp and the 400 I have now is pushing 310-320 hp. Oh, and the trans and rear gear have remained the same throught as well -3.45 gear and a T-5 5 speed.

All three motors have pulled down an identical 25 mpg! The engine size seems to have NOTHING to do w/fuel economy in my case. I belive it is all in friction reduction, and good TUNING.

An aside here; I think I can get even better milage from the 400 from 2 places, it has 7.8:1 compression right now, and the other two engines had 9.5:1. Also, I am putting a T-56 6 speed trans in it this winter, which has a .50:1 overdrive. This will slow down the motor and I believe increase the gas milage. Right now I feel like I'm giving the motor enough throttle in 5th gear just to make it "rev" what it needs to, to go a certain speed...like the motor is not really "working" at all. But this factor doesn't really apply to our Jeeps!

[Ralph]

I'm one to see fuel economy as another aspect of performance, just like horsepower; it's something to pursue in the way of an efficient machine.

I think if you really want to get a good blend of power and economy out of an FSJ, then your best bet would be to transplant a 258 I6 and install fuel injection. Mopar makes a kit for about $1800 and has gotten it CARB exempt for older AMC engines.

[jeepbob]

MY 360 powered auto trannied Wag with 4.10's and 33's gets 13 mpg and weighs 3893lbs (had it weighed at a certified scale). My 304 powered (3spd manual) CJ5 with 3.54's and the same 33's comes in at about 2400 to 2500 lbs and gets 15 mpg. Both engines have 600 cfm Holley carbs on Edelbrock rb4 intakes, 270/280 (adv) duration cams, the tfi upgrade, and dual exhaust. The Wag,s system being massaged stock 78 manifolds into 2.25 pipes with Dynomax super turbos with full behind the axle tail pipes. The CJ has headers into 2" pipes and some real (too)quiet turbo clones with dumps in front of the rear axle. I think I can improve the CJ by changing the exhaust system and dropping a couple sizes on the main jets, although the larger exhaust system may require the existing jets. I still do not expect to gain more than 2 mpg as this thing is a ball to drive and I have a heavy foot. My point is that threr is really not much diff between the mileage on a 304 and a 360 that can't be explained by the extra 1300 to 1400 lbs on the wag. I do feel the 304 gained more with the cam than the 360 did as far as performance gains went and I would go with a bigger cam in the 360 next time.