I really do love my 300 straight six, but it's got 350K on it and it's getting 10-12 miles per gallon right now and I'm ready to make some big changes.

I pulled the computer and all the EFI stuff out, put a one barrel non-feedback carb on it with a manual choke and switched to an HEI distributor. It runs a lot better now, but the mileage is still lousy and with my 16gal tank I end up having to fill it up constantly.

I'm ready to save up some money and put a new motor and transmission in it. I love the reliability and simplicity of the 300 and was thinking of putting a new one in and switching out from my C6 to a five speed transmission. I'm looking for something simple and reliable and to improvement mileage.

Anyone have a better suggestion?

My only conditions are it's got to be a ford motor (Anything else in an F150 is sacrilege! Hahah) and something I can get either crate or rebuilt for under 5K.

 

If you like the six, I would stick with it. The 5 speed would be a good option for a mileage improvement. I swapped in a 5 speed in place of the c6 in my truck and gained 3mpg. Your six should be like my old diesel, it likes to lug along in overdrive turning very low rpms.

Have you thought about the option of having your six rebuilt? Do you have any good shops locally that do it?

 

I would say if you like the 300 I would go back with it.


Now you also did not tell us what rear gear you are running as that has a lot to do with MPG out come.
Also what carb did you go with?
There is a post of a member doing the MPG game and what he has done but don't remember who it was?
Dave -----

 

I'm open to having my old straight six rebuilt, but I don't know any good shops in Baton Rouge. Not to say that here aren't any, I just don't know of any.

My rear end is the 3.55 non non-limited slip.

Carb is a UREMCO 1bl remanufactured 1976-78 model carb from Summit Racing (model 7-7533). I replaced the hot air choke with a manual choke lever.

I know David- 1986F150six, has a mpg thread, but he's using the duraspark conversion, I stripped all my EGR stuff out.

 

When I asked the questions because you were talking of a 5sp and did a carb change.
My thinking was if some big old after market carb it needed some "tuning" to get the MPG back, not that that also might be needed with that carb?


On the rear gear and 5sp you could be below the "sweet spot" of the motor and why I asked. I think with the 3.55 gear you would be ok, wished I had that gear if/when I go with a Gear Vender unit I would still be in the "sweet spot".


As for a shop to rebuild your motor or say a junk yard one if you have any speed shops, remember them?, close by stop in and ask them who they would use.
I am in the same boat if I was to get a motor rebuilt as I don't know anyone down here so I would ask the only speed shop here, think they do machine work?, and other car/truck guys.
Dave ----

 

The c6 is known as a very strong transmission, but is also known as a power hog. You will certainly have some sort of gains getting rid of it and going with a 5 speed overdrive trans. Your new engine will last much longer turning less rpms, and it's so much quieter on the interstate. True if you just putt putt around town alot you may never get to use 5th gear much. It would be mostly a gear to stretch it out on the interstate at about 70mph.

 

351 4-V, and ZF 5 Speed

 

460 and ZF5 are the best drop in combo for 80-97 trucks. If you don't tow and don't intend to run very large tires a 351w and ZF5 would do just fine and offer a couple more MPG, since it sounds like MPG is a concern. For MPG you'll want high compression with a cam that has little overlap but aggressive ramp rates, port the exhaust side of iron heads or just run aftermarket aluminum since small block heads are cheap.

Another consideration these days is price of 91+ octane vs 87 and the ROI on the MPG increase of building a high dynamic compression engine that is more efficient but requires high octane. It was always a no brainer to run on the ragged edge for available octane as cost per mile was cheaper. Now with a $.50+ spread from 87 to 91+ it may or may not make sense if low cost per mile is your goal. You'd have to crunch the numbers. However is you are concerned about MPG for max range, then definitely go with a more efficient high compression build.

 

I do not believe a 351w would win a mpg contest over a 300 six. Power yes, mpg, no.

 

300 vs 351w MPG... Is going to be very small, if any depending on vehicle configuration. 50 cubic inches is a fairly small difference. OP hasn't stated if he has any MPG or $/mi goal. If cost savings is the goal then determining TCO is more important. For all we know he wants range, which could be remedied with his 10-12 MPG six-banger with a 38 gal rear tank.

As for MPG improvements, a 460 will get better than 10-12 MPG. My 460 truck came with 351w HO engine and I saw a best of 17 MPG highway, averaged around 15. That's in a nearly 6000 lbs F-250 Supercab 4x4. OP hasn't stated what vehicle he is working with.

I think OP needs to give more vehicle info and let us know what his goals are with the truck so far as power, economy, and intended use.

 

Thanks for all the input guys. Truck is an 86 F150 4 x 4 single cab. Here's a little more info on what I was hoping for in a motor/ auto trans combo. [edit to add: I don't normally pull or haul anything]

15 mpg or better in town/17 MPG or better Hwy. ( but yes, cost savings is the goal so cost to operate per mile is what I'm trying to get as low as I can).

Reliable. I'm tired of spending all my time wrenching, I just want to just be able to drive my truck. I have a 73 Harley Davison that lets me do all the wrenching I ever want to do.

More power would be fun, but not as high a priority as reliability and better mileage. All three would be nice.

Finally… I'm trying to stay at 5K or less for the project.

Does that help?

 

I would do it in baby steps. I would get a new long block or get yours rebuilt, and re-use your carb and distributor. You know what you have, you have been using the dist and carb.

The overdrive trans is going to get you close to your mileage goals. That along with a fresh engine should get you there. If you have a lift and or oversize tires, then there will be a upper limit on the mileage you can get.

 

Yup agree with Dave on this one. Rebuild your 300 and swap out the C6.
I would swap out the C6 for an AOD, the AOD will bolt right in place of the C6 (short of a flywheel change) and you may not have even have to change the drive shaft. I have done C6 to AOD swaps and was able to keep the existing drive shaft on a few occasions.

A rebuilt AOD with the 2" OD band and "A" servo (not sure you would need the wide ratio gear set with the 300 but it may help a bit with city fuel mileage) will give you an AOD as reliable as the C6 behind the 300.

This swap can be done with off the shelf/wrecker bits and easily within your $5K budget for both the motor and tranny.

Going to a 5 speed will be a fair bit more work, and in the end won't be far off the cost of the AOD swap.