Piston Discussion (Was - Re: Building my 360/390 for towing)

[sideoilerfe]

Here's some piston information...

[fomocoguy]

I believe that photo is correct for early model engines but not so much later. The 360 I tore down for my build was in a 93k mile truck (1976 I believe) and had never been rebuilt. The pistons are std size and are stamped "360" but are identicle to the ones on the right with the partial skirt. I think at some point Ford realized it was a little silly to use different pistons for a 4v car and a 360 truck motor when they are exactly the same pin height and bore. Do you mind me asking where that pic is from? Any ideas when it was published?

[sideoilerfe]

Do you mind me asking where that pic is from? Any ideas when it was published?

How to rebuild big block Ford engines by Steve Christ

C. 1983 Well after FE's production stopped .

I believe that photo is correct for early model engines but not so much later. The 360 I tore down for my build was in a 93k mile truck (1976 I believe) and had never been rebuilt. The pistons are std size and are stamped "360" but are identicle to the ones on the right with the partial skirt. I think at some point Ford realized it was a little silly to use different pistons for a 4v car and a 360 truck motor when they are exactly the same pin height and bore.

They stopped putting FE's in cars in 1971. 360's have a 1.776 pin height and the longer 6.54" rod. 390's have 1.68 PH with a 6.488" rod. 360/390 have the same deck height so how was a 360 piston the same as a 390 piston when different length rods were used?

[fomocoguy]

Because 390 car 4v pistons sit at zero deck and have the identicle pin height as a 360 piston. Some original 360 pistons are even stamped "4v 390" right on the side. 390 truck pistons have the shorter pin height and are slightly recessed into the block at TDC. That is why a truck 390 has a much lower cr than a car 390 of the same year. Here, check out the compression distance on these TRW's: http://cgi.ebay.com/ebaymotors/360-390- ... ccessories
Note they are labled as 360 -390 pistons. Also look at the compression distance on these: http://cgi.ebay.com/ebaymotors/Speed-Pr ... ccessories
Now note the compression distance on these 390 truck pistons: http://cgi.ebay.com/ebaymotors/390-FORD ... ccessories
Original truck 390 pistons have the shorter pin height, 4 valve reliefs, and a dish. 2v car pistons have the taller pin height, 4 valve reliefs, and dish. 4v car pistons have just the valve reliefs, no dish.

I am not trying to argue, just stating facts. The picture in Steve's book is wrong; I will be happy to take pictures on the pin height, partial skirts, fomoco stamping, 360 stamping, C8*** casting number, and standard bore of the 360 pistons I have if you would like to see them.

[DuckRyder]

390 truck pistons ARE 410 mercury pistons.





My 360 had the slipper skirt pistons when it was torn down, it did not appear to have ever been apart. I didn't measure them and I don't still have them.

[sideoilerfe]

390 truck pistons ARE 410 mercury pistons.

After market ones are. Factory 410 pistons had a compression height of 1.687" as factory 390 truck pistons had a height of 1.680" 0.007" difference; very close but still different. Factory 360 pistons had a compression height of 1.776 as the factory car 390 4V piston had a compression height of 1.7919; 0.0159" difference. The car 390 2V had a height of 1.787. The car 390 2V pistons and the 360 pistons have a difference of 0.011" in compression height. Aftermarket 360 pistons have the slipper skirt.

So, there is a difference in the factory pistons. The aftermarket 360 and the 2V car 390 pistons are probably the same as Fomoco stated. Same goes with the aftermarket 390 truck and 410 Mercury pistons. Fact is, you can get any piston custom made for anything so it really doesn't matter.

Because 390 car 4v pistons sit at zero deck and have the identicle pin height as a 360 piston. Some original 360 pistons are even stamped "4v 390" right on the side. 390 truck pistons have the shorter pin height and are slightly recessed into the block at TDC. That is why a truck 390 has a much lower cr than a car 390 of the same year. Here, check out the compression distance on these TRW's: http://cgi.ebay.com/ebaymotors/360-390- ... ccessories
Note they are labled as 360 -390 pistons. Also look at the compression distance on these: http://cgi.ebay.com/ebaymotors/Speed-Pr ... ccessories
Now note the compression distance on these 390 truck pistons: http://cgi.ebay.com/ebaymotors/390-FORD ... ccessories
Original truck 390 pistons have the shorter pin height, 4 valve reliefs, and a dish. 2v car pistons have the taller pin height, 4 valve reliefs, and dish. 4v car pistons have just the valve reliefs, no dish.

Well, the 2nd link you provided are 460 pistons.

I am not trying to argue, just stating facts. The picture in Steve's book is wrong;

You shouldn't make untrue accusations. I've torn apart two 360s find full skirted pistons. Just because yours had slipper skirts does not mean the book is wrong. You think it had never been torn apart but people lie all the time to sell things.

[fomocoguy]

360's have a 1.776 pin height and the longer 6.54" rod. 390's have 1.68 PH with a 6.488" rod. 360/390 have the same deck height so how was a 360 piston the same as a 390 piston when different length rods were used?

This was the statement that started all this, implying that 360 pistons and 390 pistons were not interchangeble becasue of rod length.

After market ones are. Factory 410 pistons had a compression height of 1.687" as factory 390 truck pistons had a height of 1.680" 0.007" difference; very close but still different. Factory 360 pistons had a compression height of 1.776 as the factory car 390 4V piston had a compression height of 1.7919; 0.0159" difference. The car 390 2V had a height of 1.787. The car 390 2V pistons and the 360 pistons have a difference of 0.011" in compression height. Aftermarket 360 pistons have the slipper skirt.

So aside from splitting hairs of .007", .0159", and .011" I am correct and they are interchangeable.

You shouldn't make untrue accusations. I've torn apart two 360s find full skirted pistons. Just because yours had slipper skirts does not mean the book is wrong. You think it had never been torn apart but people lie all the time to sell things.

The book is wrong. My pistons are stamped 1968 (C8***) and have the std bore, fomoco stamp, and correct pin height. The book should say SOME 360's, period. Tonight I will take pictures of it all.
Steve's book is great, but nobody is perfect. He has other mistakes in it too, like the notion of high nickle content blocks, an old wives tale.

The 460 pistons were my bad. I was typing in duress of a fussy baby and an even fussier woman...

[DuckRyder]

I would like to see actual measurements. ALL of the books on FE's are riddled with mistakes, Steve Christ's book is no exception despite its overall goodness.

I do not recall how my 360 pistons were marked, I do know that they were slipper skirts and were in horrible shape. There are however way too many reports of people taking apart 360's and finding pistons marked "390" and truck 390's and finding pistons marked "410" for it to all be fantasy.

I do not know for sure what the "truth" is here, but where Ford production in the late 60's and early 70's is concerned I would be very careful about making statements of absolutes...

[fomocoguy]

I would like to see actual measurements. ALL of the books on FE's are riddled with mistakes, Steve Christ's book is no exception despite its overall goodness.

I do not recall how my 360 pistons were marked, I do know that they were slipper skirts and were in horrible shape. There are however way too many reports of people taking apart 360's and finding pistons marked "390" and truck 390's and finding pistons marked "410" for it to all be fantasy.

I do not know for sure what the "truth" is here, but where Ford production in the late 60's and early 70's is concerned I would be very careful about making statements of absolutes...

Absolutely! Not only do I have pictures, but I have some concrete evidence. First the pics:

Notice these are stamped "360" and "4V". No 4v 360's were built to my knowledge, so that would have to be for the 390.

Stock bore


Stock pin height

FOMOCO stamp

Casting stamp- C8AE6110AA
According to silvolite this crosses to the OE ford number for 360 truck engines. Look at the last one on the page. http://webpages.charter.net/beckracing/slvpg49.htm
These were caked in carbon and had every indication that they were original. I've already cleaned them a bit and cleaned the grooves.

[sideoilerfe]

That's very accurate I could angle the camera any way I wanted to get any reading I wanted. Why don't you start with measuring things correctly.

These were caked in carbon and had every indication that they were original. I've already cleaned them a bit and cleaned the grooves.

Big deal. Lot's of rebuilt engines have carbon on the pistons after years of usage. There's carbon in my exhaust pipes too I guess that means they're original.

[fomocoguy]

That's very accurate I could angle the camera any way I wanted to get any reading I wanted. Why don't you start with measuring things correctly.

These were caked in carbon and had every indication that they were original. I've already cleaned them a bit and cleaned the grooves.

Big deal. Lot's of rebuilt engines have carbon on the pistons after years of usage. There's carbon in my exhaust pipes too I guess that means they're original.

Sorry I don't have any other means to measure it, but why oh why on gods green earth would I fake the pin height? HOW could I fake the pin height when the pistons are stamped 360 and we all already know and agree that 360's have the taller pin height???
One thing my camera can not fake is the oem casting number. It speaks for itself.
This is not an attack on you, so I'm really not sure why it sounds like it's turning personal. I have no reason to pull underhanded dirty tricks like faking measurements. There is a pleathora of misinformation out there and I was under the assumption that we are all here to learn from one another. This is all good, pertinent information. I'm sorry if you are offended by it.

[sideoilerfe]

I think Ryan has most of his answers by now.

There is a lot of bad information out there. Best thing to do is to talk to an FE expert at a reputable machine shop about your build and they can help you from there.

[DuckRyder]

As you fellows can see I've split this off so the piston discussion can continue as long as it remains civil, any more personal attacks and the thread will be gone. It might take a member with it.

In short discussion is healthy and encouraged, accusations and personal attacks are not.

[JEF199]

one ? or mabey two...Can you use the 352/360 rods along with the 390 crank? And just mill piston tops to get propper deck height? would that lighten the bob weight to much trowing the ballance off? I guess thats three

I know that the rods are weaker but for a truck engine under 5000 rpms they should be fine. I was just thinking that the longer rods would help build torque.

[fomocoguy]

one ? or mabey two...Can you use the 352/360 rods along with the 390 crank? And just mill piston tops to get propper deck height? would that lighten the bob weight to much trowing the ballance off? I guess thats three

I know that the rods are weaker but for a truck engine under 5000 rpms they should be fine. I was just thinking that the longer rods would help build torque.

I wouldn't just because I wouldn't want to compromise the tops of the pistons. They are under an awful amount of heat and pressure and it would make it much more vulnerable to burning a hole in one under the right or wrong conditions. You could have a good machinist check and see if there is enough material there for you, but I would think you could buy all the proper parts for less than it would cost to have all the pistons machined. As for the stroke, that is dictated by the throw of the crank, so the longer rods wouldn't really affect it. Wether you have a longer rod with a shorter piston or a shorter rod with a longer piston, the overall rod+piston length will be the same.