LA vs Magnum: What's Actually Different on a Small Block Mopar
Nothing burns small block Mopar money faster than the LA-vs-Magnum parts trap. The two engines share a bore spacing, a displacement, and a family resemblance — and differ in exactly the places that decide whether a part bolts on or goes on the shelf. Here's the split, once and for all.
The short version
The LA-series 360 ran from 1971 to 1992. The Magnum 5.9 replaced it from 1993 to 2003. Same basic block casting lineage, very different top end. If you remember only one sentence, make it this one: heads, intakes, rockers, and pushrods must all match the pattern of the engine you have — LA parts with LA parts, Magnum with Magnum, unless a part is specifically built to cross over.
Difference one: intake bolt pattern
This is the one that catches everybody. LA intake bolts angle into the head at roughly 45 degrees. Magnum intake bolts go in vertically. An LA intake will not bolt to Magnum heads, and a Magnum intake will not bolt to LA heads — no adapter, no shortcut. The aftermarket knows it, which is why Edelbrock casts the RPM Air-Gap both ways: 7576 for the LA pattern, 7577 for the Magnum. Buy for your heads, not your engine's birth year — because head swaps scramble the rule (more on that below).
Difference two: how the rockers get oil
The LA oils its shaft-mounted rockers through passages in the block and heads. The Magnum deleted those passages and oils its rockers through the pushrods, like a small block Chevy. That means Magnum builds need oil-through lifters and hollow pushrods, and it means you can't casually mix valvetrain hardware between the families. It's also why a Magnum-head swap onto an LA block is a package deal: heads, lifters, pushrods, and intake all change together.
Difference three: the heads themselves
The Magnum head is the prize of the family — 60cc closed chambers and about 209 cfm of intake flow, meaningfully better than the open-chamber LA smog heads. Bolting Magnum heads onto an LA 360 is a classic budget upgrade precisely because the chambers add about a full point of compression on the same pistons while the ports add flow. And if you want the best of both worlds without the intake headache, EngineQuest casts the clever one: the CH318B, a Magnum-style head drilled for LA intake bolts.
Difference four: crank balance
Every factory 360 crank — LA and Magnum both — is cast and externally balanced. But they are not balanced the same: the LA and Magnum use different external balance weights, so dampers and flexplates/converters don't swap casually between them. And the moment you build a 408 stroker with an aftermarket forged crank, the kits are internally balanced — which means neutral damper, neutral flexplate, and your old external-balance parts become scrap. Bolting an external-balance damper on an internally balanced rotating assembly makes a vibration you will never tune out.
The part-number minefield
Small block Mopar shopping punishes the careless, because the catalogs mix LA, Magnum, and big block listings freely. A few real examples from building our calculator's parts database: Lunati's small block Mopar cams live in the 10200-series — the 10230-series right next to them is big block. Comp's LA-pattern XE cams are the 20-22x series. Harland Sharp's small block rocker kits carry different part numbers per family. None of this is hard once you know to check — it's just unforgiving if you don't.
Why we built the gating into the tool
Our Dodge 360 calculator tracks which pattern every head, intake, and valvetrain part belongs to, and it simply won't let you build an impossible combination — pick Magnum heads and the LA intakes drop off the menu, with a note explaining the conversion parts. That's not a gimmick; it's this article, enforced in software. The parts catalogs won't stop you from buying wrong. The tool will.