Mopar LA question

Will 318 Magnum heads fit on a 273 block?

Will they physically bolt up, yes. You will probably have to notch the bore for valve clearance as the magnum valves are the same size as the 340/360 heads and you have to do that with those heads. Also, Valve to piston clearance will be close. 

The other issue is they just flow too much for the 273. It's too much head and will make an already dogged low end motor and make matters work. 

I would pass on it with the hidden costs involved. 

Yes, Magnum heads will fit, although you'll have to use Magnum style pedestal rockers instead of the LA shaft rocker setup (unless you do some oiling work IIRC).  But, don't bother with stock Magnum heads unless you really need to be cheap.  The vast majority are cracked between the valve seats in at least 1 cylinder.  The cracks don't usually go through to coolant, but occasionally they do.  Plus, there are better flowing and less crack prone aftermarket castings out there for not a lot of money. 

Stock valve sizes in a Magnum head are 1.92 / 1.62 IIRC.  Aftermarket stuff is usually either 1.92 or 2.02 intake valves, 1.62 exhaust unless you get into expensive stuff with really high flow numbers. 

Don't forget about Magnum intake manifold compatibility.  The heads that rsl mentions, the "Magnum replacements", all seem to be both traditional LA + Magnum compatible which gives a lot more options for intakes.  

pres589 (djronnebaum) said:

Don't forget about Magnum intake manifold compatibility.  The heads that rsl mentions, the "Magnum replacements", all seem to be both traditional LA + Magnum compatible which gives a lot more options for intakes.  

Good catch.  I forgot about the different intake bolt setups.  With Magnum heads, do not overtorque the intake bolts.  They don't angle outwards like an LA, they go straight down like a Ford 302, so if you over-torque, the manifold is basically wedging the heads apart.  I've seen head gaskets fail after an intake swap if things weren't done carefully enough. 

There's supposed to be some cast iron aftermarket heads that sell for like $300 each and are basically what the Magnums should have been from the factory; thicker decks, not crack prone, compatible with both Magnum and LA intakes, and the ports are a fraction better.  I wouldn't bother searching for Magnum heads in a yard unless I was doing working to the smallest budget possible and wanted to stick with small block Chrysler.

pres589 (djronnebaum) said:

There's supposed to be some cast iron aftermarket heads that sell for like $300 each and are basically what the Magnums should have been from the factory; thicker decks, not crack prone, compatible with both Magnum and LA intakes, and the ports are a fraction better.  I wouldn't bother searching for Magnum heads in a yard unless I was doing working to the smallest budget possible and wanted to stick with small block Chrysler.

You're probably thinking of the Enginequest heads.  They come in both a 1.92 and 2.02 intake valve version and both versions flow better than the stock Magnum heads (the 2.02 more so, as expected).  The Indy MA-X heads are the next step up flow wise for a bit more money (they also sell an LA-X version that's meant for LA engines). 

In reply to rslifkin :

That's the ones.  

rslifkin said:

pres589 (djronnebaum) said:

There's supposed to be some cast iron aftermarket heads that sell for like $300 each and are basically what the Magnums should have been from the factory; thicker decks, not crack prone, compatible with both Magnum and LA intakes, and the ports are a fraction better.  I wouldn't bother searching for Magnum heads in a yard unless I was doing working to the smallest budget possible and wanted to stick with small block Chrysler.

You're probably thinking of the Enginequest heads.  They come in both a 1.92 and 2.02 intake valve version and both versions flow better than the stock Magnum heads (the 2.02 more so, as expected).  The Indy MA-X heads are the next step up flow wise for a bit more money (they also sell an LA-X version that's meant for LA engines). 

I have heard on other forums that about three years ago the EQ heads changed from a performance casting that flows quite a bit better than the original Magnums to a different casting that much more closely mimics the stock Magnum head for flow (but is crack-resistant where all the stock heads crack).  

Even if that's true I think the stock Magnum heads flow better than almost all of the stock LA options except maybe the "X" heads.

And that is all of the hidden costs that I was mentioning. Great for a 318 motor where you can make good HP and the smaller CC head than factory.