I have a 1995 F-150 4x4 with a 302 and 4R70W auto transmission. The motor and trans both have a lot of miles, so I was thinking of replacing with a 351. If everything is the same, is there much of a decrease in mpg for a 351 versus the 302? Currently averaging 15-16 with the 302. If I also changed to the E4OD transmission, are the dimensions the same? I realize I would have to change the computer to make it all work.
Thanks for any input

 

I think the 302 will get a little bit better gas milage not much since its a hair smaller and the heads are angled slightly different than the 351.


The E40D Trans is a little bit longer than the 4R70W as far as I'm aware of. I had a '92 F-150 with a E40D and currently have a '95 F-150 with the 4R70W .The 4R70W hasn't let me down yet. can't say the same about E40D which i had to rebuild. My Opinion I would stick with the same setup.

 

I've read at least one guy on the internet who said he thinks 302s suck for mileage and he gets as good or better with a 351. Doesn't make a lot of sense to me, though.

IMO it's all about driving habits and what you want. If you are using the truck as a daily commuter and money is tight, the 302 would be cheaper because you don't have to change anything and it should get slightly better mileage. If you mostly only use it to tow or for fun and money isn't that important to you, the 351 is better bragging rights and has more torque/power. That's why I sold my '92 302 F150 and bought a '91 351 F250.

 

My 4R70W is currently blown for the second time, part of the reason I was considering swapping the engine also. A friend told me the E4OD always came behind the 351 from the factory, and was a little heavier-duty transmission. Maybe the heavier transmission would decrease mpg also.

 

I have the same combo as you do and have been playing with the idea of swapping in a 351 for the 302 in the interest of power but have come to the conclusion that:
1. Since Ford never put a 351 and 4R70W combo together, the flywheel (flexplate) is a real issue (if someone knows of the right one that won't kill the trans let me know). For that reason only if you do the swap, you will need to swap in the E4OD, etc to make it happen.
2. Unless purely power is the issue you are probably better off sticking with what you have. From what I have been able to find out, the 4R70W is actually a pretty good tranny and with some relatively easy add on's (LT headers, exhaust, timing, etc) the 302 can be "perked up" a bit for power (torque) without hurting MPG. Am thinking a gear change is probably the next thing that will help that 302 but haven't decided if it is worth the possible MPG loss for the effort. Mine is 3.31 now with 31's.

Just saw that your 4R70W is D.O.A. If you can get a good buy on the combo 351 and E4OD then it might be worthwhile (but still more expensive than just replacing the
4R70W especially when you consider the rest of the stuff you need to swap to make that work).
In normal driving, I suspect the MPG would end up being very close because of the additional torque of the 351 but that all depends on your use and the weight of your right foot.

 

On average there not a lot of difference in milage betwen the 2 motors, the 5.8 may do a little worst around town because it's a bigger motor. But it also tends to do a little better on the highway because it makes more TQ and doesn't require as many downshifts.. depending upon the tranny, the electronic autos are shift happy without some aftermarket tuning. My 351 only produced about 13mpg city, but managed close to 18mpg hwy. It's getting replaced with a 302 while I add some new performance parts to the 5.8, I'll be running the smaller motor for the rest of the summer at least while I collect what I need for the 5.8, so I should have some comparison numbers soon.

 

I never had a 302 in a truck, but i had a 95 150 4x4 with a 351 that got about 15 around town and 18 on the highway(in the hills, too). Its all about power to weight. of course my 302 crown vic used to get 24mpg on the highway but thats a different story.

 

Mileage as mostly about total weight of the vehicle and driving habits.

Of course you will drive it differently with a different engine it.

 

Milage depeds on area. The 351 is a good tow motor . But I live in hilly area. I run the 302s And still tow.

I currently have both and have had 19 plus Ftrucks . I get 15+ (and up to 18 ) MPG on 302 .I never broke 14 MPG Around my area with 351. So its up to you . The 351 will last/tow better . I'd avoid the e4od . After blowing 3 in a row I'm going ZF the next round.