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No forged pistons in stock 340s.

In my opinion either motor is going to cost the same to rebuild.

The 340 has a higher initial by in. The 360 core is much cheaper and the longer stroke will give you a bit more low end grunt.

If you have a motor to start with build it, If not either one is capable of making a good street motor so buy which ever one you can get the better deal of. Most likely a 360.

Matt if I had the extra cash I would pick that motor up from you.

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He doesn't have an engine yet, so it looks like he'll be building a 360 since they are easier to find. An earlier poster mentioned using a Magnum over an LA, how can we tell the difference? Is there a good book on building smallblack mopars?

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Magnums have there pros and cons.

Hyd roller cam, Better heads but you will need a center sump oil pan, a LA timing cover and water pump, The cam isnt set up for mechanical fuel pumps but that cant be fixed with an aftermarket cam or bolt on snout. You also have to check the heads for cracks between the valves.

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I can understand the need for a center sump pan but why an LA timing cover and water pump?

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I can understand the need for a center sump pan but why an LA timing cover and water pump?

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To make room for the extended snout on the camshaft. when Chrysler did away with mechanical fuel pumps they also shortened the cam and on the Magnums they shortened the timing chain cover. The pump was redesigned for th enew Magnum cover and won;t work properly on an LA cover.

Don;t forget accesories. You are not likely to want to run the Magnum accesories, especially if you run the LA cover. You may have alignement issues running LA accesories on a Magnum block, just check them when you build the engine.

As for 340 vs 360, assuming both need rebuilt, r both don't, my recommendation is this. Street - 360, strip - 340.

360 has a longer stroke, builds more torque, all else the same. Torque is better for a street car.

340 has a shorter stroke, will rev up quicker and be happier higher up making more HP, all else equal. HP is the ticket for the strip.

Be an interesting dyno test if you took a 340 and a 360, built them the same (compression, heads, cam, etc) and see what they did.

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360 everytime!!!

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I can understand the need for a center sump pan but why an LA timing cover and water pump?

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To make room for the extended snout on the camshaft. when Chrysler did away with mechanical fuel pumps they also shortened the cam and on the Magnums they shortened the timing chain cover. The pump was redesigned for th enew Magnum cover and won;t work properly on an LA cover.
...
Don;t forget accesories. You are not likely to want to run the Magnum accesories, especially if you run the LA cover. You may have alignement issues running LA accesories on a Magnum block, just check them when you build the engine.

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awwhhh...the old 340 is going to rev faster theory again...ever weight a stock 340 piston and pin....together they weigh over 800 grams...

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When push comes to shove, the 360 is only 5.88% larger than a 340, so they're essentially equal if they're both operating at a given VE. Now, the more power a package makes, the bigger that 5.88% becomes. With the same cam & upper end on both engines, the 360 will probably peak at a marginally lower RPM, but output will reflect the extra cubes. That's 23.5 free HP on a 400HP package.

Clair

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I'm a little confused as your post seems to be saying on one hand the 5.588% isn't significant, but on the other hand it'll make more power because of the 20 extra cubes.

Bottom line for me is that 20 extra cubes is 20 extra cubes and as you say, that's 23hp on a 400hp engine......all from a core that cost significantly less to buy in the first place. Seems like a no-brainer to me unless you already have a 340 or it's a legitimate 340 car and you're concerned about originality.

Dave

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Dave, you're right, what I said could be taken either way. Of course if 20hp isn't a big deal, then so be it. Folks running manifolds vs. headers leave that on the table every day. HOWEVER, to get to the point, I say run what you have. If you gots nothin', go get a 360. If my Barracuda project didn't come with a 340, I wouldn't have gone out of my way to get one for my Valiant. Built equally, the 360 is almost certainly going to come out on top every time.

Clair

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I can agree with all of that



Dave

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awwhhh...the old 340 is going to rev faster theory again...ever weight a stock 340 piston and pin....together they weigh over 800 grams...

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(Shameless plug)or you could forgo the whole la stuff on a mag motor and use painless efi perfect managment system for the 5.9 when it comes out. (shamless plug.)

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on the 360. i don't know a lot about small blocks and A bodies so i don't know how much work it would be.
but with a 360 you can buy a newer motor from a modern car. you can have fuel injection, much better drivability and better mpg, serpentine fan belt, and modern alternator. without that much hassles and extra expense other than some wiring mods.

to do those mods on my hemi i figure it will cost 3-5K to it the way i want.

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on the 360. i don't know a lot about small blocks and A bodies so i don't know how much work it would be.
but with a 360 you can buy a newer motor from a modern car.

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you can have fuel injection, much better drivability and better mpg, serpentine fan belt, and modern alternator. without that much hassles and extra expense other than some wiring mods.

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