Changing 390 Pistons

Reply Subscribe

Thread Tools

Search this Thread

Feb 26, 2024 | 08:49 AM

casetruck1

Thread Starter

Mountain Pass

Joined: Jul 2020

Posts: 178

Likes: 44

Changing 390 Pistons

I have a 76 390 and am in the process of deciding how I want to rebuild it. Do I want to put the stock truck pistons back in? They are the silvolite 1139. Or do I want to go with the earlier car 2 barrel piston? They are 1116. The compression height as everybody probably knows is different between the two. The truck pistons show 8.2 compression and the car pistons show 9.7. They also offer an 1130 that shows 9.5 compression. Can I change to any of these pistons with the stock truck heads and maybe a different camshaft. Or should I leave well enough alone and go with the stock pistons. The cam I am looking at is .486 and .512 lift.

Feb 26, 2024 | 10:12 AM

AZSCAWPION

Fleet Mechanic

Joined: Dec 2016

Posts: 1,259

Likes: 713

My choice would be the 1116. Speed Pro (I think) used to make another piston with slightly smaller valve reliefs (8cc IIRC). Would be a good choice as well. Makes no sense to use the truck pistons. Sounds like an RV cam you're going with? The boost in compression plus that cam will wake that motor up quite a bit.

Feb 26, 2024 | 10:23 AM

casetruck1

Thread Starter

Mountain Pass

Joined: Jul 2020

Posts: 178

Likes: 44

Yeah just an RV cam. I was just wanting to make sure that the .100 compression height would still have valve clearance with the RV cam.

Feb 26, 2024 | 10:49 AM

AZSCAWPION

Fleet Mechanic

Joined: Dec 2016

Posts: 1,259

Likes: 713

Unless the block has been decked beyond anything reasonable I wouldn't worry. You can confirm with whoever will be doing the machining tho.

Feb 26, 2024 | 10:53 AM

casetruck1

Thread Starter

Mountain Pass

Joined: Jul 2020

Posts: 178

Likes: 44

Thanks for the help. I am getting everything cleaned up now to see where I am at and what all i am going to have to have done.

Feb 26, 2024 | 12:48 PM

85e150

Super Moderator

Joined: Apr 2004

Posts: 34,503

Likes: 2,817

OEM car pistons with the approximate CH of 1.76" showed a nominal .030 piston to deck spacing iirc. I'll look it up later. OEM pickup pistons were the same spec as thr 410 Mercury. CH was approx 1.66. See what compression the cam likes.

Feb 26, 2024 | 07:39 PM

85e150

Super Moderator

Joined: Apr 2004

Posts: 34,503

Likes: 2,817

Chart for the car engines. Numbers above are off a little. I think Ford used. .020 steel shim head gaskets, based on some posts from others, but I don't recall what was in the '66 390 we tore down.....

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

Every 2026 Ford Engine Explained

Brett Foote

10 Ugly Ford Trucks That We Still Kinda Love

Joe Kucinski

10 Things Every Truck Owner NEEDS (2026 Edition)

Michael S. Palmer

Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath

Verdad Gallardo

Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer

Joe Kucinski

2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)

Brett Foote

Top 10 Ford Truck Tragedies

Joe Kucinski

AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make

Brett Foote

Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!

Michael S. Palmer

Ford's 2001 Explorer Sportsman Concept Looks For a New Home

Verdad Gallardo

Feb 27, 2024 | 12:28 PM

cleatus12r

Butt-Head

Joined: Apr 2004

Posts: 9,453

Likes: 2,936

From: Reed Point, MT

Quote:

Originally Posted by 1pump

. It's also the stock piston for the 360. It was a lot of compression in a 390, but no one seemed to have an issue.

Before Ford started making the 360 for pickups in 1968, those stock 360 pistons would have been cast with "390 4V" near the pin boss.

With today's nominal .040" thick head gaskets and piston manufacturers casting pistons with a shorter compression height for clearance after decking the block during a rebuild, 360 pistons work very well in 390 rebuilds.

Feb 27, 2024 | 12:52 PM

#10

casetruck1

Thread Starter

Mountain Pass

Joined: Jul 2020

Posts: 178

Likes: 44

Quote:

Originally Posted by 1pump

I had read somewhere that when building the truck engine you could use the 2v car piston instead of the 4v car piston to up the compression but not up it as much as the 4v. This truck is just going to be a good cruiser or that is the plan. I don't want to run into issues starting or pinging.