360 Magnum vs 340 mild street build - my experience

[318willrun]

36 years of owning many small block Mopars. Yes, 340's were among the many LA's that included 273-360's.
My first hand experience of 340's vs 360 magnum is just this: 360 magnum hands down wins in the typical "add camkit and headers, " mild street build using the long block.
This is NOT a bash 340 thread. I love 340's. << Re-read that, I LOVE 340's. I'm also a realist. I'm not comparing the low cost of the 360 mag vs the collector value of the 340. I'm talk'n the performing of the two in the typical "Add your cam and headers" to the mild street guy out there. I'm very impressed with the 360 magnum, and I've built both in mild street builds.

 

[318willrun]

Adding this: I was one of those that bulked at the pedestal rockers (I like the rocker shafts) and lack of intake choices for the magnum, especially since the MP version for the magnum is no longer in production. For years I owned magnums in Durangos, and such, but turned away from building them. Now that I've played around with a couple, I can say what I said in the first post.

• LA 360's are getting less and less common to find complete and in decent condition for sale, I highly recommend the 360 magnum to anyone looking to replace their tired 318 or their leaning tower of power with a V8.

 

[replicaracer43]

I've said this so many times and been criticized for it, but your correct in every aspect

 

[TT5.9mag]

I’ll take a 340 over a magnum 5.9 for one reason. To sell it to a collector and buy 3 more 5.9s. All day long and twice on Sunday.

 

[Andrew vanman87]

You are Comparing a engine with a better flowing head ( which the magnum has over 2.02 x heads) you could put a magnum head on a 340 and the hp numbers will jump or a cheap speed master head ( which would still outflow stock) . Apple to apple comparison would be comparing a la 360 with x heads .... In my eyes the only real value is in cost rather than performance 360 Magnums are just way cheaper and plentiful. People are not giving up their la blocks anymore ...

 

[318willrun]

You are Comparing a engine with a better flowing head ( which the magnum has over 2.02 x heads) you could put a magnum head on a 340 and the hp numbers will jump or a cheap speed master head ( which would still outflow stock) . Apple to apple comparison would be comparing a la 360 with x heads .... In my eyes the only real value is in cost rather than performance 360 Magnums are just way cheaper and plentiful. People are not giving up their la blocks anymore ...

Interesting points.

• First, I bet some will argue that point about the magnum head being superior to the "X" head in stock form or if they both were even "home ported". I will say I think if the magnum head has an advantage in performance (which I think it does), it's not much.
• To your second point, the LA 360 is almost always going to have factory dished pistons (eww) and in most cases the piston being in the hole a tad more than the magnums. This will give the magnums a better compression ratio, and that's not including the closed chamber heads boosting compression as well if the LA 360 had X heads.
• Though I haven't weighed the components, there are enough folks out there stating the magnums have a lighter rotating assembly and better ring placement on the pistons.
• My opinion is the magnum would outperform the LA 360 with X heads if the same size cam, intake, and carb was used on both stock short blocks.
• Oh, I have a LA 360 with the cheap speedmaster heads in one of my Dusters.

 

[rumblefish360]

You are Comparing a engine with a better flowing head ( which the magnum has over 2.02 x heads) you could put a magnum head on a 340 and the hp numbers will jump or a cheap speed master head ( which would still outflow stock) . Apple to apple comparison would be comparing a la 360 with x heads .... In my eyes the only real value is in cost rather than performance 360 Magnums are just way cheaper and plentiful. People are not giving up their la blocks anymore ...

It would have been nice if the LA 360 came with X heads. So since that’s not stock…. Your loading the LA stack up against the Magnum. How is that apples to apples?
It’s not….

 

[fishmens67]

The only argument you will get from me, is Chrysler designating them as Magnum engines. lol
The true Magnum engines died over 50 years ago.
Sure would have been nice if Chrysler built a big block roller engine for trucks.
I can't see any reason to build anything other than a modern 5.9 or 5.2 if you're building a small block.

 

[318willrun]

The only argument you will get from me, is Chrysler designating them as Magnum engines. lol
The true Magnum engines died over 50 years ago.
Sure would have been nice if Chrysler built a big block roller engine for trucks.
I can't see any reason to build anything other than a modern 5.9 or 5.2 if you're building a small block.

Yes, a roller 440 up through the '90's would have been a wonderful thing. I know they turned to the V10 and Cummins for the pull rigs, but now that 440 would have been a sought after piece !!

 

[RandyB]

So I have a line on a 1997 360 magnum with low mileage and maintenance of oil being changed every 3,000 miles. For $300.
Into my 65 Plymouth Barracuda that has a 273 dual exhaust in already, that would be a good thing?
Automatic transmission.
And yes, I will be keeping the 273 for my kids if they want to chamois back.

 

[Andrew vanman87]

I'd love to see a 340 with Magnum heads and LA heads ported to the flow numbers of a magnum head throw it on the dyno ... ( Dyno them both on the 340) Magnum 360 never cam with 10.5 to 1 compression pistons that the 340 did ..my bet with equal flowing heads of the magnum 360 the 340 higher compression would be a leg up on 360 Magnum ( this being that you left the 360 Magnum piston stock ) only giving the 340 had equal flowing heads as the 360 . My guess is they would be super close... I am coming at this from a performance perspective and not cost... 360 obviously wins the cost argument given the cost of 340 is currently of course there's the argument for potential power... 360 vs 340 bore diameter 340 has the largest bore of Mopar small blocks there will arguments for Valve shrouding in smaller diameter bores especially when adding 2.08 valves or larger on a cylinder head how much does valve shrouding come into play with a 2.08 or larger valves .... No idea but it's worth a Dyno run and adding a stroker kit to 340 vs 360 ... Would the 340 block have more potential?? I say certainly possible given what kits are available for 340 vs 360 blocks . The 340 will always more cubic inches in a stroker situation

 

[Garrett Ellison]

I can't see any reason to build anything other than a modern 5.9 or 5.2 if you're building a small block.

If I’m throwing the $ at one to perform,
I’ll keep with my ‘90 model roller cam 318 Industrial engines, thank you very much! I’m fairly confident this joker can go to stock 340 bore without issues. Being that it has blind head bolt holes, I’m looking forward to what I find under the oil pan.

 

[318willrun]

So I have a line on a 1997 360 magnum with low mileage and maintenance of oil being changed every 3,000 miles. For $300.
Into my 65 Plymouth Barracuda that has a 273 dual exhaust in already, that would be a good thing?
Automatic transmission.
And yes, I will be keeping the 273 for my kids if they want to chamois back.

That sounds like a great engine for the money. I'd verify the oil pressure and run the long block as it is

 

[318willrun]

I'd love to see a 340 with Magnum heads and LA heads ported to the flow numbers of a magnum head throw it on the dyno ... ( Dyno them both on the 340) Magnum 360 never cam with 10.5 to 1 compression pistons that the 340 did ..my bet with equal flowing heads of the magnum 360 the 340 higher compression would be a leg up on 360 Magnum ( this being that you left the 360 Magnum piston stock ) only giving the 340 had equal flowing heads as the 360 . My guess is they would be super close... I am coming at this from a performance perspective and not cost... 360 obviously wins the cost argument given the cost of 340 is currently of course there's the argument for potential power... 360 vs 340 bore diameter 340 has the largest bore of Mopar small blocks there will arguments for Valve shrouding in smaller diameter bores especially when adding 2.08 valves or larger on a cylinder head how much does valve shrouding come into play with a 2.08 or larger valves .... No idea but it's worth a Dyno run and adding a stroker kit to 340 vs 360 ... Would the 340 block have more potential?? I say certainly possible given what kits are available for 340 vs 360 blocks .

When we start to throw 2.08 valves, stroker kits, we begin to lose the "mild" or "cam kit and header" type of backyard build.

 

[RandyB]

That sounds like a great engine for the money. I'd verify the oil pressure and run the long block as it is

Thank you, it’s from my MoPar ‘dealer’ so I trust him.

 

[318willrun]

Thank you, it’s from my MoPar ‘dealer’ so I trust him.

If you aren't aware, there are just a few things to be aware of when installing a 5.9 magnum... it really helps if you get the flexplate with it. You can buy one, but saves money. Then you can run the neutral balanced converter. Also, you'll need a car 360 oil pan and pickup. You can run either LA front or Magnum front. If going LA, you can get a damper for the 5.9 magnum. If you are going to run a mechanical fuel pump, you can get the kit from Hughes for about 30 bucks to work on the magnum cam. If you change the cam, you can get a long snout cam so running a mechanical fuel pump is no issue. It's really not much to all of it, pretty simple swap.

 

[Andrew vanman87]

When we start to throw 2.08 valves, stroker kits, we begin to lose the "mild" or "cam kit and header" type of backyard build.

I was coming at it from a purely performance perspective not cost which is what I stated in the post potential power is always going to be an argument when throwing out the cost perspective in building an engine. If we add to the cost perspective then obviously there's no argument for 340 given the cost for them.

 

[RandyB]

If you aren't aware, there are just a few things to be aware of when installing a 5.9 magnum... it really helps if you get the flexplate with it. You can buy one, but saves money. Then you can run the neutral balanced converter. Also, you'll need a car 360 oil pan and pickup. You can run either LA front or Magnum front. If going LA, you can get a damper for the 5.9 magnum. If you are going to run a mechanical fuel pump, you can get the kit from Hughes for about 30 bucks to work on the magnum cam. If you change the cam, you can get a long snout cam so running a mechanical fuel pump is no issue. It's really not much to all of it, pretty simple swap.

Great information. It’s still in the vehicle so we will have to take it out. He say’s we can take it out and it will fit right in if I remember correctly, but I’m still kind of new to this

 

[318willrun]

I was coming at it from a purely performance perspective not cost which is what I stated in the post potential power is always going to be an argument when throwing out the cost perspective in building an engine. If we add to the cost perspective then obviously there's no argument for 340 given the cost for them.

I understand, and I was throwing out the cost as well. I was just saying once we start putting strokers and 2.08's on the 340 or 360, then we lose the mild backyard rodder... might as well say Trick Flow heads ... on a 440? If

 

[318willrun]

Great information. It’s still in the vehicle so we will have to take it out. He say’s we can take it out and it will fit right in if I remember correctly, but I’m still kind of new to this

"size wise"... it's the same as the 273. You'll have to use spacers on the driver's side mount between the block ears and mount. Only thing I question, and not because of the Magnum, but your car is a '65 and I think the hub on the Torque Converter may be different sized ??

 

[Oldmanmopar]

My experience in front of members on this site.

red 70 Duster 340 4spd all original with AC and manifolds. Carter 750 391's old L60 x15's

Side by side up hill, Dead stop and Rolling kick

white 71 Duster 360 380 horse crate motor 4spd with headers Edelbrock 750 391's with 275x60 radials

The 340 would pull on the 360 so hard on the bottom the 360 could not make up the ground on the 340 on the top

We tried switching drivers . Timing, with and without air cleaners . The 360 could stay with the 340 on the level or down hill only. Neither would hold ground to the multi color 68 340 4 spd GTS

We had other cars we would toy with but theses were all 4 spd's with 391's

The brown 72 Duster 360 magnum crate auto 355's went 13.40's in a quarter. It was a fun street car but no comparison to a 10.5-1 comp. 340. The early 340's pulled like BB's in the little cars

 

[RandyB]

"size wise"... it's the same as the 273. You'll have to use spacers on the driver's side mount between the block ears and mount. Only thing I question, and not because of the Magnum, but your car is a '65 and I think the hub on the Torque Converter may be different sized ??

I’ve got the spacer. And I think I’ve read that yes, I’ll have to get a different sized Torque converter. He’s trying to talk me into putting in a manual transmission and bigger rear end since we will be taking it apart anyways lol which I’m leaning towards that

 

[pishta]

So I have a line on a 1997 360 magnum with low mileage and maintenance of oil being changed every 3,000 miles. For $300.
Into my 65 Plymouth Barracuda that has a 273 dual exhaust in already, that would be a good thing?
Automatic transmission.
And yes, I will be keeping the 273 for my kids if they want to chamois back.

Do it, but get the 5.9 crank drilled for the 273 trans (manual or auto) and get the proper balance plate. Youll have to fab the new headpipes and MAYBE clearance the steering linkage but youll almost double the HP. You can even put the old 5 bolt LA valve covers on the 10 bolt magnum heads

 

[318willrun]

My experience in front of members on this site.

red 70 Duster 340 4spd all original with AC and manifolds. Carter 750 391's old L60 x15's

Side by side up hill, Dead stop and Rolling kick

white 71 Duster 360 380 horse crate motor 4spd with headers Edelbrock 750 391's with 275x60 radials

The 340 would pull on the 360 so hard on the bottom the 360 could not make up the ground on the 340 on the top

We tried switching drivers . Timing, with and without air cleaners . The 360 could stay with the 340 on the level or down hill only. Neither would hold ground to the multi color 68 340 4 spd GTS

We had other cars we would toy with but theses were all 4 spd's with 391's

The brown 72 Duster 360 magnum crate auto 355's went 13.40's in a quarter. It was a fun street car but no comparison to a 10.5-1 comp. 340. The early 340's pulled like BB's in the little cars

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What did the '70 Duster "all original" run in the 1/4 ? ever try it ? I know people that bought them brand new and tried to get into the 13's with 3.91's and couldn't with the only thing changed from show room was slicks.

 

[RandyB]

Do it, but get the 5.9 crank drilled for the 273 trans (manual or auto) and get the proper balance plate. Youll have to fab the new headpipes and MAYBE clearance the steering linkage but youll almost double the HP. You can even put the old 5 bolt LA valve covers on the 10 bolt magnum heads

Awesome