72 340 build vs...other options

[Dartswinger70]

So since the 318 guys never want to have a civil discussion about anything other than converting a 318 into a race engine I got to thinking, how does the 72-73 340 stack up say as compared to a 360. If I was an aspiring small block Mopar guy

graduating from the depths of 318dom into something with a few more cubes, is it wise to pick up a 72 340 or opt for a 5.9/360 type build. I saw a Nicks Garage video where Nick ran a 72 340 with a Thermoquad and got 300-335 horse. Its interesting what these later 340s put out in actual numbers. Lets have a nice chat and... its a 340 thread

P.S. Ill list what I like about the later 340.
1. the heads - its a 360 casting but can have 2.02s put in fairly easy
2. the block -no matter how you slice it its a 340 block you can do whatever with it that you could do with the earlier block Id think swapping pistons would be on my mind.
3. The crank - depending on build date you may have a forged crank good for high rpm.
4. Pistons - even the later ones had valve releifs - can use high lift cam
5. That 72 Thermoquad setup right down to the trap door air cleaner- I don't know, it just worked...

What I dont like about later 340:

1. The heads - the J with the bigger combustion chambers, combined with the low comp pistons BUT that can be overcome with earlier style pistons.
2. The internal vs external balance forged vs cast crank by build date
3. it was getting to be the smog era.
4. the 8.5:1 compression ratio

My conclusion is I wouldn't sneeze at a later 340 yeah I know some are external balance but so is the 360 that's easy to over come and live with..

All things considered this engine is fairly easier to straight up mod into a strip screamer than a 318- just swap in parts from the 68-71 340

I saw a later 340 on here recently for 1500-1600 dollars to me that's a deal and a good starting point for a build. OR would you go 360?

see how easy that is? yeah I know "340s aren't available" but I see them on here regularly. Ante up...you are paying for convenience and performance.

What say you?

 

[toolmanmike]

The Later 340's lack compression, cam, and cylinder head. The stockers have more restrictive exhaust manifolds. I'm sure there are differences in distributor timing, carbruation and intake as well. The 73's did have electronic ignition and Thermoquad carbs which can be a plus. 240 net horsepower. the 318's made 230 horse up till 71. Net horsepower ratings started in 71 I believe so there's that.

 

[Dartswinger70]

Ah the cam, makes sense in the smog era.- Yes I believe the later 340s... the smog era killed them its actually a shame. But the 340 I beleive is easily moddable for the racer working at home the parts interchangeability I like the full floating pistons makes piston swaps easy etc.

 

[TrailBeast]

So since the 318 guys never want to have a civil discussion about anything other than converting a 318 into a race engine I got to thinking, how does the 72-73 340 stack up say as compared to a 360. If I was an aspiring small block Mopar guy

graduating from the depths of 318dom into something with a few more cubes, is it wise to pick up a 72 340 or opt for a 5.9/360 type build. I saw a Nicks Garage video where Nick ran a 72 340 with a Thermoquad and got 300-335 horse. Its interesting what these later 340s put out in actual numbers. Lets have a nice chat and... its a 340 thread

P.S. Ill list what I like about the later 340.
1. the heads - its a 360 casting but can have 2.02s put in fairly easy
2. the block -no matter how you slice it its a 340 block you can do whatever with it that you could do with the earlier block Id think swapping pistons would be on my mind.
3. The crank - depending on build date you may have a forged crank good for high rpm.
4. Pistons - even the later ones had valve releifs - can use high lift cam
5. That 72 Thermoquad setup right down to the trap door air cleaner- I don't know, it just worked...

What I dont like about later 340:

1. The heads - the J with the bigger combustion chambers, combined with the low comp pistons BUT that can be overcome with earlier style pistons.
2. The internal vs external balance forged vs cast crank by build date
3. it was getting to be the smog era.
4. the 8.5:1 compression ratio

My conclusion is I wouldn't sneeze at a later 340 yeah I know some are external balance but so is the 360 that's easy to over come and live with..

All things considered this engine is fairly easier to straight up mod into a strip screamer than a 318- just swap in parts from the 68-71 340

I saw a later 340 on here recently for 1500-1600 dollars to me that's a deal and a good starting point for a build. OR would you go 360?

see how easy that is? yeah I know "340s aren't available" but I see them on here regularly. Ante up...you are paying for convenience and performance.

What say you?

A lot of people are into the 340 just because of the nostalgia and ability to tell others they have a 340.
If I had one I would sell it.
Same with a Hemi.

 

[Dartswinger70]

A lot of people are into the 340 just because of the nostalgia and ability to tell others they have a 340.
If I had one I would sell it.
Same with a Hemi.

Now I have to say you are a smart man...I say to the wife all the time "if I was smart I'd just unload everything now and keep My Harleys...

But there's more to it than that have ya ever ran one or opened one up to rebuild it? Its really a testament to the Chrysler engineers and what they could come up with and no it isn't a warmed up 318 that's what people don't understand or refuse to believe. The sound of one idling is unique like how an 80s 5.0 Mustang GT is. Now I will say yes you can get a 318 "sounding good" with a cam but it won't rev... its in the heads. The powerband of the two engines is completely different.

 

[TrailBeast]

Now I have to say you are a smart man...I say to the wife all the time "if I was smart I'd just unload everything now and keep My Harleys...

I’d do the same with the Harleys.

 

[Dartswinger70]

I’d do the same with the Harleys.

Eventually... I don't have to sell any of it its paid for and I'm not a renter. I told the wife when Im gone let em come take it get grocery money for it.

 

[TrailBeast]

Eventually... I don't have to sell any of it its paid for and I'm not a renter. I told the wife when Im gone let em come take it get grocery money for it.

Pretty much the same here.

I’m a 5.9 guy because of the availability and low cost for good quality.
A 340 that needs parts and machining to be strong and reliable is going to cost a lot more just to be able to say it’s a 340.

Now if I had a rare car that originally had one, it would be different if I was concerned about resale value.

 

[65 Cuda 340]

The Later 340's lack compression, cam, and cylinder head. The stockers have more restrictive exhaust manifolds. I'm sure there are differences in distributor timing, carbruation and intake as well. The 73's did have electronic ignition and Thermoquad carbs which can be a plus. 240 net horsepower. the 318's made 230 horse up till 71. Net horsepower ratings started in 71 I believe so there's that.

318 net hp is 150. Going from gross to net, they lost 80 hp (rated, not actual) with the same compression, carb, etc. as it had before. The 340 went from 275 supposedly gross to 240 net after losing two full points of CR, getting smaller exhaust (edit - smaller intake) valve and (at least compared to 68-70) worse passenger side exhaust manifold. That's less loss (on paper) than any big block that lost the same amount of CR. Actually, I've always thought the early 340 275 hp rating was net from the git go.

BUT - a 360 has 20 more cubes. And it's easier and cheaper to find one. If I'm rebuilding the motor anyway and didn't already have a 340, I'd look for a 360. Since I do have a virgin 340 block, if I build one more motor before I croak, it will be the 340 - but with a stroker crank, so the 20 less cubes in original form won't matter.

 

[a-bodyguy]

Now I have to say you are a smart man...I say to the wife all the time "if I was smart I'd just unload everything now and keep My Harleys...

But there's more to it than that have ya ever ran one or opened one up to rebuild it? Its really a testament to the Chrysler engineers and what they could come up with and no it isn't a warmed up 318 that's what people don't understand or refuse to believe. The sound of one idling is unique like how an 80s 5.0 Mustang GT is. Now I will say yes you can get a 318 "sounding good" with a cam but it won't rev... its in the heads. The powerband of the two engines is completely different.

my 318 reved with the street hemi cam 2.02s torker door stop and a holley dp
it was the best sounding small block ive had
sounded better then my 11 to 1 340 gk243@50 108 lsa 508 lift cam torker door stop holley dp
most like because the rhoads lifters dumbed down that cam

 

[CFD244]

Definitely, positively, absolutely, unequivocally a 360...............If I was building a cargo van

 

[AJ/FormS]

On the street, with an A-body, not racing;
you do not need 2.02s
you do not need a long stroke
You do not need forged parts
Any top end will fit on any bottom end.
Allowing for cylinder-pressure adjustments;
A 318 with a cam one size bigger than a 340, will about match it for absolute-power, ie NOT torque
A 318 with max compression will match the bottom end torque of a stock lo compression 360.
A lo-compression 340 with a 318-cam will about match the 318 for fuel economy but have more bottom end.
The 340 burble was more from the rectangular tips and high-energy exhaust. The 44* of overlap is actually very modest.
For the street, I don't think much of the 340 cam and I have several of them packed away.
A 318 will happily rev to whatever a 340 can, and so will a 360. All any of them need is the right springs and lifters, plus the standard oiling mods.
KB107 pistons for the 360 are about 2/3rd the weight of the 340 forged slugs. After balancing, the 360 crank will go to 7200 as often as you like for more than 125,000 miles (mine)
A 360 can happily pull 65=1600 rpm (mine) all day every day. Try that with your 430 hp-340.
What a 340 can do with a 4-gear manual, a 360 can sacrifice one gear, and the 318 will like an extra gear. Or looked at another way, whatever the 360 likes each smaller engine will like 10% more rear gear.
If a city car; second gear will make or break your combo.
______________________________________________
As to second gear.
I have a manual trans with a GVod behind it, so I can run any street gear I want to, and I have run everything from 2.76 to 4.30 except I never had a 3.73. And for me, having the right amount of power in second gear, at any speed it will do, is everything. In my combo, I finally settled on 3.55s. and first gear is a 3.09, The only other gear I care about is overdrive, because I live an average of 15/20 miles from civilization, so every trip I make is 90% hiway. ..... and now, 65=2240rpm.
so that 3.09 gear tops out at 44mph@6000, and on the shift, the Rs drop to 3730, and that gear will hit the power peak at about 62 mph. And I'll stretch it out to 65 and stuff her into overdrive. Done.
So then Second gear is my go-to gear. Which means I need a chitload of torque at 44mph=3730 rpm.
A stock 318 is way past it's modest torque peak, and will not cut it.
a stock 340 @3730 is a almost to it's torque peak, but that peak is more like a speed bump, it's just not enough to thrill me.
But the stock 360 is right in the thick of it's peak torque. (No, mine is not stock)
And that is why the 360 was my choice; cuz it can and did put down more torque at any speed below 55mph with 3.55s than the chassis can handle, and the smiles just keep on coming.
____________________________________________

BTW
Let's say my 360 makes 380ftlbs at 3730; that's 270hp.
Getting a 340 to 270hp @ 3730, is gonna be a real adventure, and with a 318, it's never gonna happen

But you say, 380 @3730 for a 360 is impossible.
Meh, you're probably right, so I bored my 360 to 4.04 and now it's a stroked 340, measuring 367 cubes, and everybody knows 340s can out-pull anything so a stroked one should pull even harder....... lol..

The truth is it doesn't matter how much torque the 360 makes at 3730, the fact is that neither of the other two are gonna touch it, build for build. Which means, they will need more gear to match it, but that changes the operating rpm! There is only one gear combo that can hit 3730 at 44 mph, which is 6.8075. It's just simple math. and 1.92 x 3.55= 6.816, daymn close.

Sometimes, most times, the choice comes down NOT to preference, but to the application, and it's intended usage. My intent is to wear out tires and have maximum fun doing it.
If my intent was maximum mpgs, I would have built a 273.
If my intent had been to appeal to the car-show fans, I wouldda built a 340.
If my intent had been to drive a bazzilion trouble-free miles, well then, a 318 mightbin on my radar.
I mean I have a shed full of blocks to chose from.
How many 340s do you want me to ship.

 

[Divenut]

 

[Dartswinger70]

Pretty much the same here.

I’m a 5.9 guy because of the availability and low cost for good quality.
A 340 that needs parts and machining to be strong and reliable is going to cost a lot more just to be able to say it’s a 340.

Now if I had a rare car that originally had one, it would be different if I was concerned about resale value.

I can understand that .

 

[Dartswinger70]

How many old Mopars have you owned? and how many of those were NOT 318s?
The bores range from 3.91 to 4.04, a range of 3.3%
The strokes range from 3.315 to 3.58 a range of 8%.
the sizes have a range of 13.2%
For your application;
Case closed.

On the street, with an A-body;
you do not need 2.02s
you do not need a long stroke
You do not need forged parts
Any top end will fit on any bottom end.
Allowing for cylinder-pressure adjustments;
A 318 with a cam one size bigger than a 340, will match it for power.
A 318 with max compression will match the bottom end of a stock 360.
A lo-compression 340 with a 318 cam will about match the 318 for fuel economy but have more bottom end.
The 340 burble was more from the rectangular tips and high-energy exhaust. The 44* of overlap is actually very modest. For the street, I don't think much of the 340 cam and I have several of them packed away.
A 318 will happily rev to whatever a 340 can, and so will a 360. All any of them need is the right springs and lifters. KB107 pistons for the 360 are about 2/3rd the weight of the 340 forged slugs. After balancing, the 360 crank will go to 7200 as often as you like for more than 125,000 miles (mine)
A 360 can happily pull 65=1600 rpm (mine) all day every day. Try that with your 340.
What the 360 can do with a 3-gear manual, a 340 will need 4 gears, and the 318 will like 5
If a city car; the rear gears will need to be a least 10% greater between each engine. What the 360 can do with 2.94s, the 340 will need 3.23s and the 318 needs 3.55s.. As the engines get smaller, Second gear becomes very important, so that you always have the right amount of torque on tap.
_______________________________________________
From Experience, I can tell you that having 400 ftlbs on tap at 45 mph is seriously big fun, but 400 ftlbs at 90 mph is nothing to write home about and 400 at zero-mph is absolutely bonkers
You cannot get 400 out of a streetable normally aspirated 318

Thanks for that info. Very well presented / Let me run this by you. say someone picked up a standard bore 72 340 with a forged crank and flat tops. couldn't they switch the cam and pistons and in effect have an early high comp 340? In my mind I cant see why not but I ay be missing something. I think my point is a later 340 is worth something in parts although Id stay away from the external balance but that's not a show stopper either.

 

[missing linc]

I'm pretty much with @TrailBeast on this one, unless it's an original 340 car, I going with the 360 or 5.9 Magnum. I had more than one person tell me from the passenger seat of my 70 Dart 360 that it was just as fast if not faster than any 340. Timeslips more than proved it. And I did have a 340 block but sold it.

 

[Dartswinger70]

318 net hp is 150. Going from gross to net, they lost 80 hp (rated, not actual) with the same compression, carb, etc. as it had before. The 340 went from 275 supposedly gross to 240 net after losing two full points of CR, getting smaller exhaust valve and (at least compared to 68-70) worse passenger side exhaust manifold. That's less loss (on paper) than any big block that lost the same amount of CR. Actually, I've always thought the early 340 275 hp rating was net from the git go.

BUT - a 360 has 20 more cubes. And it's easier and cheaper to find one. If I'm rebuilding the motor anyway and didn't already have a 340, I'd look for a 360. Since I do have a virgin 340 block, if I build one more motor before I croak, it will be the 340 - but with a stroker crank, so the 20 less cubes in original form won't matter.

I've been watching Nicks garage and he's been getting 300 plus HP with 340s alot of times its 325-340 horse and they are supposedly stock. Or close to stock and its gross hp ( no accessories bolted on_ etc. Ill have to check out some 360 dyno pulls. I have a set of J heads with 1.88s Id like to find a home for i may acquire a 360 short block at some point.

 

[Garrett Ellison]

Cheap late model 360 magnum with good aftermarket heads. Well, I prefer a 340 with a longer than stock crank but that doesn’t really conform to the thread that well, either.

 

[Garrett Ellison]

How about a 340 from a 360 block? Overlook the spray preservative. Just saving up for some decent heads now…

 

[Dartswinger70]

Cheap late model 360 magnum with good aftermarket heads. Well, I prefer a 340 with a longer than stock crank but that doesn’t really conform to the thread that well, either.

All thoughts ideas and opinions are welcomed...

 

[Dartswinger70]

How about a 340 from a 360 block? Overlook the spray preservative. Just saving up for some decent heads now…

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interesting you mean the 3.31 stroke with .040 over and 340 rods? etc.

 

[340six]

Ah the cam, makes sense in the smog era.- Yes I believe the later 340s... the smog era killed them its actually a shame. But the 340 I beleive is easily moddable for the racer working at home the parts interchangeability I like the full floating pistons makes piston swaps easy etc.

My stock 1973 H code Ralley Challenger ran well. it took upgrades as any other 340 would. keep in mind 1971 340 rated at 275 was gross and 1972 was net with assy if ya did not know what net was. keep in mind both years had the same cam in the 340s. it did not loose that much HP with just lower compression. It was gross vs net
yes cast crank but worked fine until i rebuilded it with a steel crank, and heavy forged TRW pistons.

 

[273]

If just going by blocks (bore size) since most parts are interchangeable, would make 340 1st choice, 360 2nd, 318 3rd and 273 4th, cause 340 are expensive and hard to come by 360 would be the general best choice and if sticking with stock strokes makes a better streetable choice but 340 block with a 360 stroke be better. If looking to build an engine that revs but don't have money for crazy heads, 273/318 would make a good higher rpm engines.

To me you should be asking how much power and where (rpm) that tells you cid that's needed for the job.

 

[rumblefish360]

The Later 340's lack compression, cam, and cylinder head. The stockers have more restrictive exhaust manifolds. I'm sure there are differences in distributor timing, carbruation and intake as well. The 73's did have electronic ignition and Thermoquad carbs which can be a plus. 240 net horsepower. the 318's made 230 horse up till 71. Net horsepower ratings started in 71 I believe so there's that.

Ah the cam, makes sense in the smog era.- Yes I believe the later 340s... the smog era killed them its actually a shame. But the 340 I beleive is easily moddable for the racer working at home the parts interchangeability I like the full floating pistons makes piston swaps easy etc.

You two guys above, the low compression years of the 340 and all the HP 4bbl 360 engines (IIRC) used the same early 340.

350’s could be had with a smaller 2bbl cam and a 4bbl.

318 net hp is 150. Going from gross to net, they lost 80 hp (rated, not actual) with the same compression, carb, etc. as it had before. The 340 went from 275 supposedly gross to 240 net after losing two full points of CR, getting smaller exhaust valve and (at least compared to 68-70) worse passenger side exhaust manifold. That's less loss (on paper) than any big block that lost the same amount of CR. Actually, I've always thought the early 340 275 hp rating was net from the git go.

BUT - a 360 has 20 more cubes. And it's easier and cheaper to find one. If I'm rebuilding the motor anyway and didn't already have a 340, I'd look for a 360. Since I do have a virgin 340 block, if I build one more motor before I croak, it will be the 340 - but with a stroker crank, so the 20 less cubes in original form won't matter.

The exhaust valves for the 340 & 360 are and have always been a 1.60. The intakes for the later 340’s and all 360’s are the 1.88’s.
Is that what you meant?

 

[Garrett Ellison]

interesting you mean the 3.31 stroke with .040 over and 340 rods? etc.

RAMM Racing main bearing spacers for the larger diameter main bearing journal diameter and stock bore (4.04) TRW domed pistons. Rods are Eagle H beam.