Whats the deal with 340s?

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Punisher66j

Punisher66j

Dart Swinger
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I know that 340s were a strong running little small block but really is the difference? I am curious because I am looking at buying a 73 dart parts car with a 340. I currently have a 99 360 magnum and want to know the real performance advantage to a 340 than a 318, 360, or even a big block. Thanks and sorry for my ignorance.
 
I bet the 360 Magnum has more power then the 340. Just thinkin...
 
I think it was just a great stroke to bore ratio matched with a decent cam and decent lungs from the factory. Very stout combination for factory effort. I pesonally love the way the little guys scream.. could a teen or a 360 be made to do the same? Certainly. It was just factory badass in its day...
 
340 was rated 275 gross hp and give or take 280-290 gross in reality. Magnums are advertised 250 net hp. The MP crate 360/300hp (gross rating) was a stock Magnum longblock including the camshaft only with a carburetor. The 360 Magnum is the better engine. More torque. More horasepower when rated similarly.
But - the aura around the 340 is much stronger. And as YR said - once you rebuild them as street performers they are very similar, with the 360 getting the knod for torque, and the 340 for horsepower.
 
If 340 was dropped when the 360 was introduced in 71 and 360 got 2.02, high CR and cam 360 would be thought of as top dog.

But really all 3 are very capable engines
 
273 said:
If 340 was dropped when the 360 was introduced in 71 and 360 got 2.02, high CR and cam 360 would be thought of as top dog.

But really all 3 are very capable engines
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360 Magnum, Lots better than 360 LA.
 
I don't really see magnum as a different engine sure there is differences but it's basically just the heads and most that build LA are throwing aftermarket magnum heads on anyways. Only down side of LA heads it's more work to build quench.
 
273 said:
I don't really see magnum as a different engine sure there is differences but it's basically just the heads and most that build LA are throwing aftermarket magnum heads on anyways. Only down side of LA heads it's more work to build quench.
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And the roller valve train, And the increase in compression, Much better tolerances from the factory. And the magnum heads are not bad factory heads.
 
The 68-71 340s were special in that they WERE quench engines. They achieved quench with the pistons instead of the heads. Not the most optimal way, but they did it. Since the pistons were positive deck height, there was some quench being made. Some might argue just how much, but in my mind, something was helping them make so much power for such a mild engine and I think that was it. Plus, like Ben brought up, they have a pretty big bore for a small block, along with a short stroke. Pretty good combination for the street.
 
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Yep. There's no substitute for cubic inches... longer strokes make more torque. .. advanced heads flow better... one could build a near 'perfect' engine... but with all the compromises the factory made, they still had a stout small block. Kudos to the engineers of 40+ years ago. Even in 72 and 73, they were a 'decent' motor... not the badass they were in 68/69/70.. but they still made a statement. Today's strokers with high flowing aluminum heads will smoke them, but 40ish years ago they held their own...
 
moper said:
340 was rated 275 gross hp and give or take 280-290 gross in reality. Magnums are advertised 250 net hp. The MP crate 360/300hp (gross rating) was a stock Magnum longblock including the camshaft only with a carburetor. The 360 Magnum is the better engine. More torque. More horasepower when rated similarly.
But - the aura around the 340 is much stronger. And as YR said - once you rebuild them as street performers they are very similar, with the 360 getting the knod for torque, and the 340 for horsepower.
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240 net on the low CR 340s, about the same as a 5.2 Magnum. The '68-'71 340s did have more power, probably at least 275 net.

Mopar Tim said:
360 Magnum, Lots better than 360 LA.
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Old E58 was rated about the same and ran about the same in a similar weight truck as the 360 Mag.

A 1971 340 ran better than a 1974 360, same with a 1971 383, a 1971 440, but in 1974 that wasn't the case. The big blocks and 340s were seriously at a disadvantage compared to 360s in the emissions environments. The big blocks were still faster on the top end, but it was increasingly less relevant. Your '73 340- it'll run about like a 5.2 Magnum. Not a bad motor, add good value to a car it's in, but not a pinnacle in any way. A '73 should be externally balanced too.
 
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The 340 really deliver high rpm. They loved to wind up. Every freaking body in the world tells me " Great car! What's it got, a 340?" That said, I run a 98 360 block 408 stroker. Next time it'll be a 340 just to shut up the gawkers.
 
but a 340 decal on your air cleaner...99.999999999999999999999 wont know the difference....
 
Ben Drinkin said:
Yep. There's no substitute for cubic inches... longer strokes make more torque. .. advanced heads flow better... one could build a near 'perfect' engine... but with all the compromises the factory made, they still had a stout small block. Kudos to the engineers of 40+ years ago. Even in 72 and 73, they were a 'decent' motor... not the badass they were in 68/69/70.. but they still made a statement. Today's strokers with high flowing aluminum heads will smoke them, but 40ish years ago they held their own...
Click to expand...


I know this upsets the in crowd, but torque means nothing unless you are worried about smoking the tires.

That is why, decades ago, Chris Alston wrote, and I quote "Horsepower is KING. To dispute this is STUPID".

Every day, at tracks around the world, Chris Alston is proven correct.

Unless you are an OEM who has to make a car for girls.
 
Mopar Tim said:
And the roller valve train, And the increase in compression, Much better tolerances from the factory. And the magnum heads are not bad factory heads.
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You can put a roller valve train in a 340.

They hydraulic roller is pretty much useless any more. If my customers want a roller tappet for a performance engine. They get a solid roller.

A hydraulic lifter, is a hydraulic lifter.
 
I don't get this 360 is a torquer and 340 is a revver. 360 is gonna make 20-30 lbs-ft more which is about equal to one step up in gear and a 340 powerband is gonna be 300 rpm ish higher than a similar 360.
 
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340s were all performance engines. Until the magnum came out there was not much in the way of factory performance 360s.

In my opinion the biggest advantage the 340 had was by average Joe hot rudders who would either build a basically stock short block with stock replacement pistons. Cylinder heads were basically stockers most of the time. The most porting a set of heads got was a gasket match. Guys would throw cam of there choice and hit the streets. Most mods were bolt ons. Different carb and intake. 360 ran well but couldn't hold a candle to a 340 in this state of tune.

Today there are more piston choices. People almost never install stock pistons in a performance build. Head choices are out there now. You don't have to hope you come across a set of x heads. Magnum parts open it up further.
The performance gap has closed if not completely eliminated.
I still love 340s though.
 
Punisher66j said:
I know that 340s were a strong running little small block but really is the difference? I am curious because I am looking at buying a 73 dart parts car with a 340. I currently have a 99 360 magnum and want to know the real performance advantage to a 340 than a 318, 360, or even a big block. Thanks and sorry for my ignorance.
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It doesn't matter any more because you just build it to GO! And it will.

On the street driven car and a mild performance one, I like a 360. A little more torque and the same HP at a lower rpm. (Or very close to it.)
 
Mopar to ya said:
The 340 really deliver high rpm. They loved to wind up. Every freaking body in the world tells me " Great car! What's it got, a 340?" That said, I run a 98 360 block 408 stroker. Next time it'll be a 340 just to shut up the gawkers.
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Stock they wouldn't turn much harder than an HD/HP 360 but it was a better platform to build to turn RPMs. That reminds me of hearing that 318s love to turn- even though most stock ones will be declining in power after a hair over 4000RPM. More to a motor than its size alone...

Perfect answer would be "just a small block", followed by "it's a dodge motor" (in the event of the dumbass chevy comment), then in the face of further questioning- "360 block"- finished off with "408" if the questions persist. That has been my favorite answer to that question ever.

340dartley said:
340s were all performance engines. Until the magnum came out there was not much in the way of factory performance 360s.

In my opinion the biggest advantage the 340 had was by average Joe hot rudders who would either build a basically stock short block with stock replacement pistons. Cylinder heads were basically stockers most of the time. The most porting a set of heads got was a gasket match. Guys would throw cam of there choice and hit the streets. Most mods were bolt ons. Different carb and intake. 360 ran well but couldn't hold a candle to a 340 in this state of tune.

Today there are more piston choices. People almost never install stock pistons in a performance build. Head choices are out there now. You don't have to hope you come across a set of x heads. Magnum parts open it up further.
The performance gap has closed if not completely eliminated.
I still love 340s though.
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The biggest advantage they had was factory forged cranks. That's why people who were going to turn 8k used 340s, and if you didn't have to then a 360 did as well or better. I'd think the advantage was really exaggerated in the late '70s when the W2s came out. Even the '72/3 340s still had the same main journal size as the factory forged crank motors so it was easy to change with a 273 or 318 crank. That wasn't usually Chrysler's concern, they typically used Hemis if they were gonna turn that hard.
 
The 340 was one of the very few engines then, that delivered in stock trim actually more net horsepower as officially advertised.
And it was a strict HP - engine, never available with 2-bbl.

Even the NHRA recognized this fact and put a higher HP factor on it for Stock Eliminator Class,
That's how legends were made...
 
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Limited production
Only came in high horse trim
Beat the 383's, could wrestle a 440, and chased more than a few 426's
Responded well to bolt on's
Loads of potential from the factory
Cheap easy access to power

There are obviously other reasons. But if you want to get into the technical reasons they are different?

360
Bore: 4"
Stroke: 3.580"

340
Bore: 4.04"
Stroke: 3.313"

In the end. With what can be done today. They are practically the same. You can pull just as much power out of either to a point. Not including R3 blocks bored to big block size of course. There are some 440-500 R3 engines out there. In fact a kid here just had a ritter R3 engine built. I wanna say 440 CI. I could be wrong. Dynoed 780HP fresh off the build stand before any kind of tuning at all. Builder figures he can squeeze another 40-50 horse out of it with a good tune.
 
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