Is a 1991 360 balanced like an la no matter what

[Sirsmiley9]

I ordered a refurbished magnum 360 from Jegs. However looking at the stamped numbers it seems to be a 91 which means it isn’t a magnum. However, if it is an la the loss of power is alright because it should bolt up easier but I need to know if it will be balanced like an la even if the engine has magnum heads and all of the subsequent changes.

 

[krazykuda]

It's balanced like an LA 360...

It doesn't have magnum heads...

However, you can bolt up any LA intakes and exhaust parts to it, so it has more choices...

 

[Professor Fate]

'91-'92 were the changeover years from roller LAs to Magnums. Magnums were probably being cast in '91. To be sure if the block is a Magnum, look on the sides of the block to see if it has the truck mounting bosses. If it does, it's a Magnum. LAs never had those style bosses. From the factory, roller LAs were balanced just like their standard LA counterparts. But since it's a refurb, (especially if it's got a mix of LA block and Mag heads and who knows what else), all bets are off as far as balance. I would contact Jeg's / the rebuilder and find out exactly what you have before moving forward.

 

[mod5v]

The diffrence in ballance is in the rods/pistons. La and magnum use the same crankshaft. so you really need to find out what rods and pistons are used to get the proper damper and flex/flywheel

 

[AJ/FormS]

@mod5v
good to know

 

[Professor Fate]

The diffrence in ballance is in the rods/pistons. La and magnum use the same crankshaft. so you really need to find out what rods and pistons are used to get the proper damper and flex/flywheel

Agreed. That's why he needs to contact the rebuilder and find out what he actually has in his engine and what the balance is.
OP- "even if the engine has magnum heads"? It doesn't sound like you're sure if you have Magnum heads or not...? If the rockers are shaft mounted, they are LA. If stud mounted, they're Magnum. Or just count the valve cover bolts- LA=5, Magnum=10

 

[pishta]

Mag rods have an 8 digit casting number, LA's had a 7 digit. Mag rods are thinner on the little end. Found this out by installing magnum stroker pistons on LA rods...they didnt fit! The LA is about 1.08 IIRC, the mags were like .980? YMMV.

 

[93ragtop]

Actually the 5.9 magnum didnt come out until 93, the 5.2 was 92

 

[Professor Fate]

Actually the 5.9 magnum didnt come out until 93, the 5.2 was 92

Yeah, I should have been clearer; when I said "changeover years" it would have been better to say "final years" of '91 and'92 respectively for the roller LAs.

 

[Bobzilla]

Magnum engines used the same casting number rods as the LA engines produced in later years of production with roller camshafts.
I don't know the exact year of change, but I have personally verified this myself. Casting number 53005798 is the one I am referring to.
So, the casting number alone may not help with determining final engine family balance.