Hey I am looking at buying a 79 F150 with a 400 small block in it. It has a C6 transmission and a four barrel Holley carb on it. It is only a two wheel drive. I was wondering if I bought this truck, what could I expect for MPG? Thanks

 

Mmmmmm about 8-10 mpg. But really depends on what size holley it has. I'm guessing a 650cfm. But some guys often times go waaaaay over board and put on 750 or even 850cfm carbs. Then the mpg really drops and often times the car or truck runs way too rich and can't be leaned out enough.

 

Thanks a little less then I was hoping for. Might take out the engine for now and replace it with a 302 for some better gas mileage. Any suggestions on possibly a V8 motor with the best fuel mileage I can get without totally canceling the chance of having a quick, mean sounding truck?

 

A few upgrades on the 400 can wake it up and crank out a few MPG's. Headers, true dual exhaust, RV/towing cam, straight-up timing set, 4 barrel carb, 4 barrel intake, etc.

 

But how much do you think these upgrades would cost and how much mpg could this thing get. I know the 400 is a good building block motor that you can pull tons of power out of I'm just not looking at spending too much money at the moment. Would probably keep it if I replaced it and build on it when I have a little extra cash

 

You can always check the size of the jets inside the carb. And replace with a smaller size. Just don't go to small or you will have a lean issue. Also a good tune up and proper adjustment of the carb can help as well.

 

Probably in the neighborhood of $1000 if you're thrifty. If you swap in a 302, your going to need new perches, a new transmission with the small block bolt pattern, and the matching driveshaft. A 302 won't do much better on gas and will disappoint you when it comes to power.

 

Thanks! I'm hoping to get this pig up to 14-15 if possible without spending too much. Anything else I can do? Or do you think that'll do it?

 

How much more mpg would this upgrade get me? I'm sorry if I keep asking I'm just really trying to get this to be my dream truck without having to run to the gas station everyday haha

 

Try removing the lead from your right foot. Honestly I think 10-12 is do able. Anything more will be pushing it.

 

My understanding, that a 302 in a vehicle this size, the mpg wont change much because you need more gas to get and keep the vehicle moving.

 

That's going to be pretty unlikely. 12 would be on the high side of what you can expect to get. I'd get an aluminum intake and 4bbl carb for starts (that will set you back about $500) and then headers (another $170 for cheap ones) then you should really look into advancing the timing. These motors were retarded 2* from the factory for emissions reasons. advancing it really helps a lot. The 400 honestly had the potential to be a good engine, but it was hindered by the emissions standards of the time. I'm getting ready to rebuild mine actually. I'm addressing all the major issues. On of the big things you can do to get some more power is to replace the pistons. These later 400s had terrible compression ratios (again for emissions) by replacing the stock pistons and bumping up the CR you can really start to see some decent power. I'm speaking with Tim Myer (the 335 series guru) and we are estimating my rebuild to make about 340hp and 440 ft.lbs with his rebuild parts and some other add-ons. But just intake and exhaust should yield noticeable improvements. If you ever consider doing a total rebuild talk to Tim. He is seriously the best in the industry when it comes to 335 series Fords

Note: The 400 is not an "M" block engine. Ford goes by series and the 400 is a 335 series. It is also not a small or a big block (those are chevy terms).

 

Im lucky to get 15 in my 07. These are bricks, if you want mpg by a smart car, or put a desiel in it.

 

A friend had a 79 with a 460. Went to a 351W for better gas mileage. No improvement. Went to a 302. No improvement. Still 10-12 mpg.
I had a 75 SCab 3/4ton 360 C-6. Seemed it would get 11mpg no mater what- loaded or empty. Dropped a cylinder. Still 11mpg on 7 cylinders.

 

I was under the perception that the 400 was more of a Torque oriented engine, rather than a HP monster. With that said you want better MPG's might as well just fork out the cash for a 5.0 Cyote engine and a O/U Drive slapped in there. These trucks are 5000 to 6000lbs of pure steel bricks running down the road. Cause if you an effiecient running enigine the drag coefficent, weight and Drive train loss will drag your MPGs' down.