In a previous thread I was perplexed as to what motor I actually have when tearing it down because it had what appeared to be 390 pistons in it. Another member answered the question, it's a normal "truck" 360.

So, block and crank are at the machine shop, getting bored in the next couple days to take care of a couple scores in 2 cylinders. Shop is certain that .030 is going to be more than enough. Took the heads in and at 224,000 miles, the exhaust valves are sunk way too far for a simple cleaning and valve job, looking at $1000 in machine work. This started off as a "replace the dripping rear main" and has turned into a giant hole I'm throwing money into. I have gone back and forth a hundred times, make it a 390, make it a stroker 445, keep it 360 and just put some different pistons in to raise the compression a little with an RV cam and headers. This truck had plenty of power for what I do before I ever took the first bolt out of it. I do not want or need this truck to be a hot-rod, I have other vehicles that fill those needs. I have decided against spending $5k to $6k on a motor in a $1500 truck, just doesn't make sense and no matter how much I spend on the motor, it will never make the truck worth more than it is now and might reduce the value to someone looking for an original High-Boy.

That being said, going to go back together as a mostly stock 360 with stock re-man heads but since it's getting bored I will need new pistons so what pistons should I go with to bring the compression up?

 

AFAIK you would be looking at custom pistons.

I doubt you can find 352 pistons for an .080 overbore. (If you took a .030 overbore to clean up) 352 pistons have a compression height of about 1.84". You have to do some measuring and figuring to see that would work CR wise with your heads. I can only find them to .060 over anyway.....

Of the two pistons said to be found in 360s, the flat top 390 4bbl piston would give you a marginal bump over the dished 390 2bbl piston. Both are going to be down the hole which is another can of worms that can't easily be fixed.

As for the cam, check with the cam maker and go with a grind that is made for low compression. Higher lift and duration that doesn't allow cylinder pressure to bleed off due to overlap. New springs will be required.

 

What about getting a 390 crank and rods, and ordering a set of passenger car pistons? They give higher compression than truck 390 pistons, and the "stroker" crank and rods are actually just commonly available factory parts. Nothing in this combo is custom. Or, you could simply find another engine, preferably an actual 390 car engine.

 

Look for pistons with a compression height of 1.76 instead of 1.66. Most flat top pistons with that compression height will land you in the 9-9.5 compression ratio area (verify deck height because it goes up if your block is milled). They do make a couple dish pistons that will drop you back down into the stock range unless you mill the block/ heads to bump it back up to where you want it.

 

OP wants to stay 360, second thread on this:
https://www.ford-trucks.com/forums/1...do-i-have.html

 

I apologize if I broke some rule about having more than one thread. The title of the first one is "What motor do I have" which was answered. After much discussion on that thread figuring out that my motor is exactly as advertised I started this thread "Keeping it a 360" in hopes of finding some information on how to keep my motor a 360 but increasing the compression.

 

No rules broken. I wrote my last comment because I figured you've already been over the 390 conversion process, no need to hammer you on that.

Back to making compression in the 360. It needs a piston with a compression height just north of 1.8", and the 4.080 bore you will probably end up with. Pin size can be "adjusted" via busings.

A Mopar 340 piston comes in 4.080, with a compression height of 1.84. Piston pin is .984, only .009 more than the FE. There must be something that prevents this "obvious" solution from being popular.

Maybe by the time you fiddle with them you might as well go custom piston.

 

Yeah, I see so many different options for "stock" pistons/rods in all the popular places I did not know if someone had gone the route of keeping a 360 and increasing the compression with "off the shelf" parts.

I have given a whole lot of consideration to going 390 but finding any of those in my area that have any usable parts are like finding hens teeth. Have spent 3 weekends trolling the salvage yards around here but as is the story of my life, I'm too late to the party and anything 390 related has long been picked and gone.

The "easy" route is to hit the checkout button on a couple sites and have a full blown 445 delivered in pieces over the next couple weeks. Keeping it a stock 360 is just as easy, something in between those two (360 with increased compression, 390 with a 4bbl etc) seems to be more work. The price difference between a 390 and 445 is not enough to justify the 390.

My block and 360 crank are back from the machine shop taunting me 100 times a day sitting in my warehouse. If I didn't have the top end off my 68 putting in a new cam to keep me off the internet, I'd probably have found some obscure reasoning to turn the want of the 445 into a need and have the lovely young lady in the big brown truck stopping by on a daily basis right now. On one hand I want to throw caution to the wind and just go for it, on the other I have and absolutely stock from the factory 74 that begs to be restored back to just that.

 

Because FE pistons already come in a compression height of 1.76. It was the "car" piston for a 390. The .04 extra compression height from Mopar pistons doesn't seem worth the extra hassle. I'm not sure if the wrist pin bushing would do well with the extra material removed anyways as they are pretty thin to begin with. On a 360 rod/ crank with pistons at the 1.76 compression height, you should be only .012 in the hole IF you are still at the stock deck height of 10.17 inches and somewhere around 9-9.5 compression ratio with most truck heads.

This is the piston I used for my 390 conversion, but as you can see, they are listed for 360s: https://uempistons.com/series-2275-s...-5-9-1131.html

 

Watch that decimal point.

1.75 + 6.54 + 1.76 = 10.05 This is a 360 crank & rod and a 390 "car" spec piston.

10.17 - 10.05 = 0.120.

.012 would be in the range of the 352, which uses the compression height of about 1.84".

.120 would be down the hole for low compression, which was what the 360 is and what Ford wanted.

Change to 390 crank and rods: 1.89 + 6.49 + 1.76 = 10.14, or .030 down the hole, which is the max spec for a car 390. (see link below)

It is probably easier to just swap out 390 parts and it's more bang for the buck with the extra displacement anyway.

Car specs, from which the truck specs are derived via careful mixing of parts:

http://www.fastfairlane.com/Engines/fespechart2.html