I have an 87 302 with 3.55 gearing and a NP435 manual trans. It has a really low first gear which I typically don't even use it is so low. I get pretty low gas mileage as well. I was thinking if I reduced to gearing to 3.08 it might make 1st gear a little more usable as well as improve my gas mileage. Also I have 237/75-15 tires. If I go with a slightly larger diameter tire will that lower my effective gear ratio and improve gas mileage? Thaanks

 

Do you do more city or highway driving? Average mph? Whats your nomal speed limit signs and highest? My state is 70 others are 55mph.

 

How bad is your mileage? There is really not much you can do to gain a noticeable amount, unless you have a problem. All the normal mods may help, but the payoff is negligible. Taller tires will lower your cruising rpms, but it takes more power to spin a larger, heavier tire. If you have steel wheels, you could swap to lighter aluminum wheels. Headers and free flowing muffler, and a free flowing air filter. Advance ignition timing just a bit. Ethanol free gas helps. If you can lighten the load that helps. No toolbox, tailgate, bumpers, junk in the bed, etc. Seems the gassers just get 10-15 mpg and that's it. I have a 93 f350 with a 460 and it gets 9/12 city/highway, my work truck is an 05 chevy 2wd 6.0 gas and it gets 9/12 city/highway. Both of my trucks weigh right around 8000 lbs with my everyday stuff loaded in them.

 

The 302 is an engine that likes to rev a little. It doesn't make much power at lower speeds and has a relatively high torque peak. According to one website I found the torque peak is at 2400 rpm. Engines are most efficient at their torque peak, so you don't tend to get much better mileage by dropping the cruise rpm much below that.

Your 3.55 gears and 29" tires put you a little under 2500 rpm at 60 mph, so dropping the rpm some might help in your case. 3.08 gears would put you at 2100 rpm at 60 mph, probably a pretty good place. But you'd need to downshift a lot more often than you do now, especially with a load.

As far as having 1st gear be more usable, keep in mind that it's a non-synchro, heavy transmission. 1st gear is never very usable in that. If you have to use it a lot you might get pretty tired of it.

You don't say if you have a 2WD or 4WD. Figure about $1000 per axle to change gears (maybe cheaper if you find a junkyard axle with the gears you want). How long will it take for the mileage savings to pay off the investment?

Don't get me wrong, I like tall gears. A lot of people will tell you that the 302 needs at least 3.55 gears. Personally I think I might prefer 3.08s. But I don't think I'd prefer them enough to spend $1000 - $2000 to change them.

 

Chris, what does you truck get for fuel milage now and what does your driving consist of.. all in town, all highway, a mix? And where do you live? It matters if it's mostly flat or hilly where you are.

The 5.0 can get 20 mpg strictly highway and should get 15mpg average, I have consistently managed that with my supercab 4x4 so your truck could have any number of problems if it's doing significantly worse.. and we can help you sort it out.

 

That can't be possible!! I hope it is. I'm getting a 5.0 RCSB on Monday.

20 highway is a dream.

 

Thanks for the replies! Sorry for delayed response. So it looks like Ford rated truck at 13 or 14 city and a couple more hwy. Most of my driving is local and avg 45 mph I'd say. It is a 4wd and I am probably getting about 9 mpg. (I know I need to look at a few other things (cap, rotor, plugs, wires, etc) I may have access to a ttb and rear with 3.08 gears for around $200-250. Still trying to confirm the ratio. At first I was hoping it was 3.55 and I would just get the ttb and redo seals, bearings, joints, etc and eliminate my ranger style locking hubs. Its beginning to sound like the axles I'm looking at have 3.08 gears so I started considering changing out the front and rear.

 

Gears aren't your problem, pull codes. Is this a dual or single tank truck and if dual do they both work?

 

Yea 9 mpg in a half ton means you have running issues.

 

Or a heavy foot

 

Sheeeeyat is there such a thing as a heavy foot in a 5.0? I always thought the throttle pedal was on or off.

 

Conanski lives in Canada. Our gallon is about 4.54 litres and the US gallon is about 3.85 so 20 mpg up in Canada is 15 to 18 US.

 

Ah, that explains a lot.

Even so, 18 out of a 302?! That's 300-6 level territory! Does it get better if you do the MAF swap?

 

No it doesn't.. the numbers I quoted are US mpg.

That may be the only way you see it but then the SD system generally runs leaner than MAF so...

 

I was already planning on putting duals on it. Are we talking a new intake manifold, new headers, new heads? Etc