5.2 Magnum Piston Question

70DartCustom

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I’m pretty new to Mopar engines and ended up with a 5.2 Magnum out of a Ram 1500 and then another 5.2 short block (rebuilt) im going to pick up.


The used engine seems to be in good condition. I popped off a head and I can see cross hatch, the cylinder walls look great, had about 100k miles.

I noticed the pistons are flat on top. Is that what a stock magnum piston looks like? I am not too sure on the year but I believe it wa a 98-2000 5.2.


Now the short block was rebuilt 4 years ago but has been sitting in storage wrapped.

The pistons do look different. The owner says it’s for a 96-2000 truck.

Are these stock pistons or aftermarket? I’m leaning. Towards using the new short block and using the used heads on it after some clean up.

This will be going into my 69 Dart paired up with a 904, and 7 1/4 rear. Just a daily. Will be adding Doug’s headers and a sniper efi system to top it off. Replacing the slant 6.

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Max1196

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No #'s stamped on the crown? They look like a UEM 1266c or a Sealed Power 285np (these are for a earlier 318), which have valve notches. Not a UEM 3234H or Sealed Power H526AP or H814P,for a Magnum, which have no piston notches. Differences also are ; ring thickness, weight, compression distance, cost and no full float pin for the Magnum choice.
They sure look like these, S/P 285ncp's stuffed in a 350 Pontiac.
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70DartCustom

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No #'s stamped on the crown? They look like a UEM 1266c or a Sealed Power 285np (these are for a earlier 318), which have valve notches. Not a UEM 3234H or Sealed Power H526AP or H814P,for a Magnum, which have no piston notches. Differences also are ; ring thickness, weight, compression distance, cost and no full float pin for the Magnum choice.
They sure look like these, S/P 285ncp's stuffed in a 350 Pontiac.
View attachment 1715991090

Ah okay thanks!

I haven’t picked up the rebuilt short block. I will take a closer look at it and look for numbers.

I am guessing they might have used older LA 318 pistons in the magnum then.

I’m on the fence now after looking up those part numbers, this could be lower compression than the motor I’m currently taking apart.

I take it the piston rings might not be as good as the magnum ones as well. Here’s a picture of the Magnum I have.

It could also be that it’s not a magnum engine then huh.

I’ll take some pictures when I go take a looks mad I’ll add some of what Incurrently have.

Sounds like my Stock magnum might be a better choice for the swap?
 

408 swinger

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My experience is that all the 5.2 Mag engines used the straight, flat top pistons. Those four valve relief pistons are more than likely from an LA.
 

70DartCustom

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My experience is that all the 5.2 Mag engines used the straight, flat top pistons. Those four valve relief pistons are more than likely from an LA.
Only other pistons I also found while trying to do research were the MAHLE/ Clevite pistons from JEGS.

Wondering if this will affect the rest of the build. Was planning on swapping over the heads and air gap intake onto the rebuilt short block. Of course timing cover etc as well.

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txstang84

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Factory slugs for the 5.2 were indeed flat top with no valve reliefs. I have a 98 Dakota 5.2 in my 72 Scamp. The LA 318 in my Dad's 85 Ramchager also has flat tops too, but if I were to guess, they'd be a little lower in the hole than the magnum.
 

408 swinger

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The thing to look for is compression height of the pistons. Probably the same. No harm, no foul. Some LA had a higher height, therefore, a tick more static compression.
 

70DartCustom

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Brought it home and took some quick pics of it.

I’ll try to get some measurements later on but looks solid. It appears they reused the lifters and cam.

I was originally gonna swap those items over but might just run it as is and bolt in the heads.

I’m guessing magnum heads are interchangeable?

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408 swinger

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Magnum heads interchange on Magnum engines. Magnum heads will bolt on an LA block also. There's a bit to deal with to make that work, so, let's keep it simple and not worry about that aspect. Mag heads on a Mag engine, yes. Those pistons look kinda high up in the bores? That would be groovy. Maybe it's just the pics....
 

70DartCustom

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Magnum heads interchange on Magnum engines. Magnum heads will bolt on an LA block also. There's a bit to deal with to make that work, so, let's keep it simple and not worry about that aspect. Mag heads on a Mag engine, yes. Those pistons look kinda high up in the bores? That would be groovy. Maybe it's just the pics....
I’ll take some closer pictures when I get home later on tonight but they do seem to sit up high. Would be great!

Paid $500 for the short block , figured it would be worth it in parts.
 

txstang84

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They look like 285AP or possibly silvolite 1266 pistons...if they are, they're a low compression piston with either a 1.72 or 1.74 CH respectively. Assuming all other measurements are indexed and nominal, those pistons would be 0.102" in the hole at TDC. Even with magnum heads, that puts your compression approx 8.2~8.5:1
 
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