Hello all,

I've currently got a 78 f100 2wd with a 302 and c6 trans with an unknown amount of miles.

I recently did an intake swap to a 4V and some other minor upgrades and discovered that the 302 is just plain wore out and has zero power. Poor thing couldn't even muster a one legger but with a 2.73 gear that isn't all that surprising.

​​​​​​My plan for the truck is to be a nice Home Depot runner but still have enough power to go down the road and tow my 70 mustang around on occasion.

My thoughts have been to build a healthy 351w motor at around 400 HP. I want to avoid stroking the thing since I won't be going to the dragstrip. I've got a 96 roller block out of a bronco lined up but I am having a hard time committing as I am not up on my 351s in terms of speed parts.

However, I have also spotted a very decent used 5.0 that would end up with new heads and cam should I buy it to get me to my HP goals.

I plan on keeping the C6, despite wanting to have OD, and driving it till it breaks and upgrading later. Or the other option is to keep a tall gear (like a 3.25 or 3.50) and rebuild the C6.

i am just starting to build this truck and don't plan on winning races or restoring it completely. Just looking for a nice weekend too.

My budget is exactly 0-3000 bucks.

Your thoughts, criticisms and more importantly your sarcasm is always appreciated.
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Do the gearing first, related to the tire size.
No amount of horsepower or torque that you can reasonably get out of a 302 or 351 will overcome too tall gearing. Period...

Ok, so I'm being a bit dramatic maybe, but it's very true if you have just a bit too tall a tire, or too tall a gear for any tire. And your 2.73's in a truck are pretty much right there no matter what.
Your engine in fact may not be as tired as you think, if it's trying to fight the gear ratio the whole time. You could put a 460 in it and still swear it's underpowered.

On the opposite side of that coin, I have a '68 EB with a stock Explorer engine (right down to the cam and exhaust manifolds and all smog stuff intact) with 30 tires and 4.56 gearing and it's a flippin' rocket ship!
I can cruise along at 65 in overdrive at just over 2300 rpm (I'm used to much higher rpm with larger tires but no overdrive) and get almost 20mpg, but can barely keep the tires from spinning when I accelerate from a stop.
It's that huge of a difference with gearing.

So that's my recommendation. Do the gears first.
Be great if you can find a local buddy or car/truck enthusiast that's not using their 9" chunk with 3.50 gears and would let you pop it in for a test! That way you're only out a weekend of futzing around with your truck, rather than the few hundred dollars for getting one built.
Then again... A local junkyard might still have some 9" rears available in trucks and big cars from the early sixties to about '85 or so. Might be able to pick one up relatively cheap with something in the 3's already build.

Good luck.

Paul

 

I won't be of much help to you deciding on what engine to go with, but I can confirm that your 302 probably isn't as tired as you think. I have the same setup, factory 2bbl 302 with an auto and 2.75 rear end gear and I would have to say my engine runs great for as old as it is and I can only spin the inside tire when the road is wet and I'm turning. LOL Other than that, it takes off relatively quickly, especially if you let it spin up the rpm a bit. My '75 F-150 had a factory 460 with 3.25 rear end gear and would "spin the tires all day long" before it got a rebuild and doubled the hp it came with in '75, so I'd say the 302's of this era are just under powered in general and not necessarily tired out.

I wouldn't imagine a 351 would have too much different as far as "speed parts" goes compared to a 302. Sure, it has more deck height and needs a wider intake, but what else would keep you from modifying it similarly to a 302?

 

Thanks for the replies guys.

To answer and asking some questions:

Tires are currently 275/60/15 on a 10 inch wide slot mag wheel and aren't bald but have some flat spots due to sitting for a little while. My plan is to run them until they pop and replace them with a Cooper cobra of similar size.

With that size of tire I am not too worried about MPG or RPM.

As far as the engine having more power, you could be right. Changing the gears was my first thought. Does anyone know if 78s came with 31 splines exclusively? I know there could be a couple of possiblities throughout the years. I havent crawled under the truck to check and see if there is an axle tag yet. I want to stay pretty tall to keep RPM down but still have enough oomph to pass someone. If I had an AOD I would go with a much lower gear like a 4.11

As far as speed parts, I know an AFR 165 head is pretty much dead nuts on for instant upgraded power for a 302 but I don't know what the tried and true heads are for a 351. I can't imagine they are too different but I just have no idea. Not to mention would I be better off with a port and polish of the stock 96 head or going with an aftermarket one?

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For now, I'd start by doing a compression/ leak down test on the motor to see what condition it's in and if it's worth doing anything with. If you're gonna tow occasionally, go with the 351, or larger. You're going to want the torque.

 

So I went with a 96 351w roller motor out of a bronco. I tore it down today and took some pictures. Looks like two burnt valves but cylinders look ok. Hoping to avoid boring them.

My plan is to invest in the heads, pistons, and possibly camshaft. I want to make about 400 rwhp with about the same amount of torque.

Thoughts?

 

I wouldn't consider those valves burnt but just those cylinders running hotter than the others.

It seems to be penny wise and pound foolish to invest in new pistons on a stock XXXXX bore.

Unless of course you mic the bores and they are OK for the piston you intend to use.

I would do more than a dingle hone on my hand drill though to seat the new rings.

400rwhp out of 351ci and towing don't go well together. Add in an automatic and tall gears and you really have an under-performer.

You would be better to realisticly identify what the truck will be used for, and then build to that.

You'll be happier in the end.

 

I agree with 1Ton's earlier post, case in point, I have a 66 F100, 240/I6, T18, w/265/60/15, from the get go with original skinny tires he couldn't pull a hill, (mountain, I live by Yosemite) in 4th, had to drop to 3rd. rear end was making a little noise, so I decided to pull it and check, turns out I had 3.00's gearing, I found a 9" with 3.70's,, WOW totally different truck! I had bought a 302 to put in so I could rebuild the 240, 5-6 years later I'm still running the stock 240 and getting 15-18 mpg out of it. The key is getting the engne into it's happy zone rpm wise. I would look for a chunk with 3.50's or so, spend 45 mins rplcing it and see what you get, you will be pleasantly surprised.

 

 

IMO, tow rig engines should be built for torque, not hp. Look for a '96 Explorer with a V8 and grab the heads, they are GT40 heads. Also, look for a rear axle from a '78 or '79 4WD F150/Bronco, they came stock with 3.50 gears. They can be found for under $200 and will be a direct replacement.

 

You are gonna want the 351 for sure. 400 hp shouldn't be too tough. Blueprint aluminum heads are supposed to be good value for the money. Some good aluminum heads, edelbrock performer RPM intake, headers, comp XE262 cam and a good ignition should get you there and make a nice cruiser.

 

Hivolt,

I went with a 96 roller 351. Tore it all down and everything is junk. Cam and lifter wear timing chain slop. Cylinders looked ok but I haven't measured them. Pistons are DEEP dished and very low on compression. Plan is to go with Edelbrock e street heads. I haven't looked at a cam yet. As far as ignition goes I would like to keep the factory duraspark that I have and just swap the gear out. Exhaust wise I have a set of 1 1/2 inch Patriot headers that I am thinking of running single exhaust out of.