I have a '74 Hiboy with a stock 360, 4spd. Can it easily be replaced with modified 300 I-6 that would have comparable performance and better mileage? Has anyone had success with this?

 

Glad to have you here.
Take a look at this link http://www.ford-trucks.com/forums/ar...-136-p-59.html

 

The FE engine and 300 straight 6 both use the same engine perches, only they need to be unbolted and moved to the forward mount holes.

You'll need the 300 engine, bellhousing and the engine side z-bar bracket. You would use your existing transmission.

The funky thing is adapting the existing exhaust or just building a new one.

The other funky thing is the radiator. The top hose is usually on the driver's side for the I-6, passenger side for FE engines. And reverse for the bottom hose. So either a new radiator will be needed or some creative use of piping to get the inlet/out to match.

Josh

 

Thanks guys for the links and info. Is the investment and time worth any potential gain in economy?

 

Tough to say in a 4X4, what gears and tires you have and how heavy is your right foot?

Also how cheap are you getting the parts? If a guy is paying full price for an engine, clutch set-up, new radiator, new exhaust etc... that would buy a lot of gas.

Josh

 

Josh- I am trying to do some of the work myself with minimal impact on full retail price, but I'm not a pro. Maybe I should just keep it simple and go back to a 360/390. What are the pros and cons of "warming over" a 360 vs. 390? By the way, the truck seems low geared, 2800 rpm @ 65 mph.

 

As for the 360: a simple rebuild, RV cam and a 390 crank and rods would be the way to go for mild manners and "decent" mileage.

In my opinion, whatever engine you already have is the one I would pursue. If I had both engines and they both needed to be freshened up or rebuilt I would go with the FE since it seems you're truck has some steep gears (running some numbers it looks like around 3.9 to 4.10 gears depending on the tire size, I guessed 31" tires) and the FE will handle 3000 RPM better than the I-6.

If I had a second truck I would want to have a 300 in it for economy no doubt, but it's hard to justify cost when all that money can be used to buy gas in the first place.

Josh

 

Why a 390 crank? You also said "handle 3000 rpm", are these trucks freeway compatible? I mean does a guy want to run it at 70 mph regularly?

 

Taking a 360 to 390 is just a matter of sourcing a 390 crank and rods, more power and better efficiency than a 360.

I have always driven mine on the highway, but back when I still drag raced I would install my 3.00 gears to keep the rpms down. I now have the 3.00 gears permanent and it wasn't unusual to go over 100 mph on I-70 to visit my family in Kansas. The only thing that slowed me down was gas stations.

For a 390, 2600-3000 RPMs is butter.

Josh

Josh

 

If I built the motor with a 390 crank , would you recommend changing from the stock intake and 2b carb? Also, if locate another 360 to build, are they all the same? I wasn't sure if some had heavier components, for example, a 4 bolt main, or better heads, etc.

 

All 360s are the same.

The only FE engines with "4 bolt" mains, but really cross-bolted mains are 427 engines and a few 406 engines.

I would actually expect slightly better economy with a 600 CFM 4 barrel and 4 barrel intake. There are a couple factory 4 barrel intakes that are decent, but heavy and some nice aluminum ones.

Josh

 

I guess if that's low, mines really low!

My '77 150 4x4 300-six does 3100 @ 60mph, with 31 x 9.50R-15LT tires, almost 3200 @ 60mph with the stock LT235R-15's (or as they said in '77, L78-15's). This is the way it's been since new.

14 mpg on regular gas all the way, though.

 

I was headed in your direction and ended up gong with a 351W and a chevy Nv4500 for the overdrive. I was lucky enough to find a 79 3/4 ton 4x4 as a donor for the frame and 4x4 stuff. My 73 had a 360 and the 79 had a 351M. The 351W fit on the 351M perches.
Bought an adapter from Advanced adapters and mounted the NV4500. Just finished the frame and rebuilding the 60 rear and 44 front. Got the brakes and back on this morning.

I have the low mileage 360 or a 300 if you need them. Also the 351M/400 with c6 and np205.

A lot of what you do should depend on how you plan to use your truck. Mine will be mostly hi-way with some towing mostly hi-way towing. I wanted 4x4 for the bad weather and some off-road. I have 354 gears and plan to keep them.

Good luck and post some pics. I will put more of mine in my garage later this weekend.

Doug