A little back story, I got my 74 HighBoy from the original owner 2 years ago, she's a little tired, was marking her spot every time I stopped and with 224,000 miles and being 46 years old, that is to be expected. On the other hand, this truck would start and run perfect, every time, with just a bump of the starter. Oil burn was minimal at worst, a very light puff of blue on startup from the right bank but nothing else. Plugs stayed fair given the mileage, no other issues.

I started off with the plan of "freshening up" the motor a little, new rear main seal, new gaskets on the rocker boxes, headers (to take care of the cold exhaust tick) and finally a new clutch because she still had the original. Original owner claimed the engine had never been "touched" other than tune-ups and a new water pump. I did find all the lower exhaust manifold bolts with silver anti-seize and one stripped out on the top side with a bolt through and nut on the back. So it has been "touched". Moving further into it, the bolts on the valve covers were barely finger tight as well.

The further I got into the motor the need for a full overhaul was revealing itself, the mains were showing copper, albeit not bad but definitely at the end of their lifespan. Upon pulling the heads I found deep grooves indicative of broken rings in 2 cylinders but found the rings in perfect shape on all 8 jugs so must have been sand or who knows what went through the motor at some point. Other than the grooves in 2 holes, the rest could use a quick hone and go right back with new rings, they are in phenomenal shape with very little taper wear, no ridge at the top as I was able to just bump the rods with the handle of a rubber mallet and pop them out.

VIN number and paperwork from original purchase both say I have a 360. I checked the stroke and it's 3.5 so definitely a 360. Reading the book "How to rebuild Big Block Ford Engines" by Steve Christ and now I'm stumped. My pistons are clearly 390 style with the reliefs for crank clearance however my stroke says its a 360. I'm going to make it a 390 with new crank, rods and pistons but I'm seriously wondering if I was told a little "farmer story" when I got the truck? He had nothing to gain or loose by telling me such as he did not sell me the truck, it was a gift with the promise when I'm done I'll pass it along to someone who wants it as badly as I wanted it.

My "long winded" question, was there ever a case where Ford put the 390 style pistons in the 360 or has my motor actually been "touched"?

 

360s use the 352 rod and crank and the 390 piston. This results in low compression via the piston down the hole. Not the best, but it worked.

So yes, your 360 has the 390 CAR look piston.

The pickup 390 uses the Mercury 410 piston on top of the longer stroke and "all other" shorter rod. Again, it results in a down the hole, low compression setup.

If you rebuild, if you want 9+ compression, you have to use the "car" piston.

This is discussed repeatedly here, but it does seem like a "story" when you first hear it.

More later, gotta go stuff my face.

 

Thank you for clarifying that. I have read plenty about the low compression and I want to go back together as a 390 but nothing hot-rod, just a decent engine that will get down the road. Having trouble finding anyone locally that can head me in the correct direction for pistons, rods etc. They either want to sell me $5k stroker kits or stock parts. When I ask about mild performance upgrades, they get a glazed look and mumble small block chevy or 351W or...... No interest or knowledge in FE truck motors.

 

Gotta remember you're dealing with an engine that was born 62 years ago. Your best bet is to find a 390 crank and rods, then buy new pistons. The 445 stroker kits are the most popular.

 

What you're looking for is a piston with 1.77 compression height along with 6.490 rods with a 390 crank (3.780 stroke). You can snag up some KB with rings for around $340 from Summit. Stock 390 rods reconditioned with some ARP rod bolts added should be had for $200. A reman 390 crank with bearings is $450 + shipping from Rockauto. So your already looking at a grand. Makes that stroker kit a bit more inviting.

 

The cost of a stroker kit itself is not the expensive part. It's everything down the line from that kit that starts to add up. Making a whole lot more power than stock (double the output of HP and Torque is relatively easy) suddenly requires a litany of upgrades between the end of the crank and the contact patch on the tires. Now once everything is upgraded to handle the increased output there comes the next problem, I can get it going fast but now I have to stop all of that. A 74 High Boy has drum brakes all the way around and no viable option for retrofitting disc brakes to the front axle (bulk of stopping energy) so have to find a new front end with disc brakes, make it fit the vehicle, rebuild it to match rear gearing etc.

I'm not opposed to a stroker kit, I am however realistic in my understanding that just upgrading the engine to a much higher output then moves the failure points further down the line all of which cost money and take time to bring up to par with the output of the motor.

However to your point, by the time I gather all the parts to make it a 390 I'm 2/3rd of the way to the price of a full on stroker kit. No matter which way I go, new timing gear, intake setup are needed, the machining price is the same so another 700-900 and it's now a big, bad motor. Absolutely tempting and with blinders on, a no brainier. Taking the blinders off and all of the sudden the cost of a "usable" stroker motor starts going up steep and fast.

Then I have to ask myself, do I need all of that for something I will drive a few times a month? Need, absolutely not, it did just fine before I started tearing into it to fix a small oil leak and exhaust leak. Want, I cut myself this morning and my blood is still red, so yes, absolutely want.

 

You're making the assumption that your right foot has a mind of it's own here. What comes out of the stroker in terms of power is controlled by your brain telling your foot what to do. And the total output is controlled by what else is used in the build (cam, intake, carb) You can build it with a mild cam, stock heads (provided your heads are salvageable and the cost to rebuild them doesn't make a new set of aftermarket heads more attractive) You'll get the increased torque, same as a 390 crank does, but without the topend horsepower. In short you don't neccessarily need to upgrade the rest of the drivetrain or brakes (not that disc brakes wouldn't be a bad idea, no matter what engine is there)

 

All true statements. I'm just saying the dollar amount spent towards "a little better" than stock components as opposed to no joke performance parts. That's all. I went with the upgraded stock parts on my 390 and just think I should have cried once instead of twice.

 

My machinist once went on a long dissertation about how the rod length made a HUGE difference between the 360 and the 390. Because the 390 has a shorter rod, the piston acceleration is a lot different at TDC and BDC. As the piston approaches TDC, and then leaves TDC, it's acceleration before and after TDC is a lot higher than it is with the longer rod on the 360. And not just the 30 cubes differences. The acceleration made a difference in how much exhaust could be expelled, or how much vacuum could be incurred to suck more intake in.

Also, because of the shorter rod, once the cylinder fired, the force of the explosion was sent to the crank at a more straight (for the lack of a better term) push against the crankshaft pin. More efficient.

Anyway, what it means is, there is a win-win when it comes to converting to a 390.

 

Maybe I'm thinking this wrong, but the force against the crank journal with a longer rod is straighter than with a shorter rod. The dwell of the piston at TDC gives the intake charge a longer burn time than a shorter rod. You might get a bit more torque with a short stroke in relation to the rod length than a shorter rod.

 

Think of the dwell of the piston at TDC as a "slower" piston and rod combo with a longer rod. Another way is- the longer rod has to make the piston travel further than a short rod so just because of that, it takes more time (slower). Changing to the car 390 piston takes advantage of this as well as closing up the deck height difference between otherwise stock dimensions.

I might have missed something there but that's how it work in my brain.

 

All things being equal, like where the piston is when the cylinder actually fires, if the rod is shorter (and the piston pin is lower), it will exert force against the crank pin at a lower angle. That angle being more lateral, acting more directly against the crankshaft instead of at a higher angle. That difference in angle equates to a more efficient "push" against the crank. It increases the lateral load on the piston, though, so increased friction, etc.

Anyway

 

Piston travel is the same regardless of rod length. The rod slows down more at either end of the stroke with a longer rod, hence the longer dwell time for a better burn. It speeds up in the middle of the stroke. A longer rod yields more torque with the same stroke. Steam locomotive designers discovered this 120 years ago. Railroads that ran in mountianous territory favored longer main rods connected to the third driver on 8 coupled locomotives. Those designed for speed chose shorter main rods shearly due to the lighter shorter main rod.

 

I'm realistic if nothing else about the connection between the right foot and the brain. If the power is there and available, there will be times the neurons fire in such a way that the power will summoned by the now mildly disconnected right foot.

I worked in the custom motorcycle industry for many years, I ran one of the show trucks for a custom bike manufacturer. Since all of our bikes were "production" bikes, they had to be sold with legal exhaust systems. The first thing every person who bought one of these bikes would do is change the exhaust. Now, if they changed it to an exhaust that was actually designed and engineered for the bike, they would see a gain in power. IF they continued to operate the bike the same they would also realize an increase in fuel mileage. The number one question I got at every show "I put these V&H pipes on, bike sounds awesome, makes more power but how come my fuel mileage went down?" Their mileage went down because of their right hand, more power and more noise so when sitting at the light, constantly burping the throttle to hear all that power, followed by full throttle through the gears to feel that new found power.

At the very least I will be building this as a 390. In all likelihood, I will buy a balanced stroker kit and I will, in all likelihood end up breaking something further down the line. However until I get the green light from the machine shop that the motor all checks out, I'm simply looking at options and adding stuff to shopping carts.

As for all the rest of the conversation regarding length of rods, the science behind how and where the power is made. Well, that's beyond my scope, however going back to my days as a teenager and later in life rolling around the country with 24 custom bikes in a semi trailer I recall the line, there is no replacement for displacement. My daily driver had a 460, my "company bike" had a huge stroker/big bore kit. As I'm now at that point in life where the kids are done sucking money, the ex wife has moved on and now my paychecks are mine and mine alone to spend in whatever frivolous ways I see fit, I will probably continue to spend said paychecks making this old High Boy into something a little beyond stock from the radiator to the rubber. This truck has absolutely no practical purpose for me, I have other vehicles capable of hauling things, other vehicles to commute around in, so in the end this is just a toy, no timeline to get it back on the road so no need to scrimp or rush to get it going again.

I appreciate reading the discussion on how the power is made and the science behind it.

 

You're correct about the right foot, but aside from the drum brakes, the rest of the drivetrain can handle what a stroker puts out, Ford didn't skimp on the FE's drivetrains. If you have a manual trans, then it should get a new clutch and pressure plate regardless of what engine you go with. If it's an automatic, it's got a C6 which are pretty bullet proof to start with. Ditto for the rear axle be it a half ton or 3/4 ton. Can't comment on the front axles, never had much to do with 4wd. Main reason I mentioned a stroker to start with is FE parts are getting hard to find in useable condition 45 years after production ended, and machinework costs are involved regardless of what route you take.