I am thinking of rebuilding a 1978 I6 4.9 liter to replace my 1984 I6. Are there any major differences between the two?

 

Not really any difference that I know of. There might be a difference in the horsepower and compression ratio but it is physically the same engine.

 

Thanks Mantta

 

my dad has a 85 truck with 4.11 gears a bulldog 4 speed tranny and original 300 l6 motor and i have a 83 with 3.55 gears a bulldog 4 speed tranny and a 73 model 300 l6 motor and my truck has more tourqe horse power and compression hope that helps even knowing there are a few years between the motor i have and your motor

 

There are a few.
Up till '79 2x4 trucks had a mid sump pan & 4x4s had a rear sump. After 1980, all trucks I've seen (2x4 or 4x4) with a 300 have a rear sump pan.
I have a '79 300 (same block that you're rebuilding) in my '84. The main difference you'll find is that the '78 block does not have a second dipstick hole for the rear sump application. The '84 block has an additional dipstick hole right behind the oil filter. If you get the chance to look carefully at each block you'll see what I mean. (If not, send me an e-mail as I have some pictures of bare blocks that show what I'm talking about.) You'll need to get a rear sump pan that has the dipstick through the pan for this block. With that, you'll need the oil pick-up tube & the #5, right-side main brearing cap bolt as it has a built-in stud to support the oil pick-up tube. Of course, if the '78 engine all ready has a rear-sump pan with the correct dipstick, then you're good to go. You could probably get the tube & bearing cap bolt off of the '84 block.
I'd recomend keeping the distributor off of the '78 as it should be the duraspark II set-up, a bit better than the TFI that would be on your '84. If you do that, I'd recomend swapping the truck over to the duraspark, you'll only need the module & harness. Again, if you're all ready done this swap, you can disregard.
The '78 engine will have a slightly different carb, which works with the duraspark better, if you can, keep it & rebuild it. Obviously, if you have different plans for the intake/exhaust, disregard.
I'm kinda assuming with this responce that you snagged (or was given, whatever) the entire long block with all the accessories. If not, the main thing to keep in mind is the oil pan thing. Also keep in mind the local emissions, you may have to keep them happy.
I was pretty lucky when I put the '79 engine in my truck as I was also doing a intake/exhaust swap & getting the right oil pan was a minor deal (I was doing all of the work at a friend's place that was 40 miles away, one way) to everything else I was doing at the time. I was fortunate enough to have a garage to work in & a stand to put the engine on so I could set it all up first & then install it. Good luck.
Edwin

 

If you go with the '78 motor, you will need a distributor with advance weights, springs, and a vacuum advance.

If you decide to get a new distributor, consider our custom curved Duraspark Distributor built with our new Full Length Oil Impregnated Bronze Bushing. The full length bushing improves timing stability and spark scatter. If stock appearance is not an issue, take a look at our one piece D.U.I. Distributor. Whether you choose the Duraspark or the D.U.I., we curve each on a distributor machine based on your engine combination. Please see them at:

http://www.performancedistributors.com/forddistributor.htm

Also, there is now an excellent installation article on the D.U.I. Distributor on the Ford-Trucks.com site at:


https://www.ford-trucks.com/article/idx/0/358/article/DUI_Ignition_Installation_In_A_Ford_351W_V8.html

 

Interesting, Same screen name