About the 340

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340 Dart

340 Dart

I don't know ****.
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I am the kind of guy that likes to learn everything I can about something before I start on it. I know almost nothing about this engine. How does it differ from the 360?

I did a search and found a little info on allpar but there wasn't much there.

I have heard that this is a desirable engine. Why?

Does anyone have any links to info, or can you share you knowledge.
 
340s have a smaller stroke, 3.313" to the 360s 3.58". The 340s have a larger bore 4.04" to the 360s, 4.00" bore

The 360 at a lower rpm then the 360 will.

The 340 is more desirable because they were all performance motors were as the 360 started out as a passenger car motor. The 360 was offered as a performance motor in 74 after the 340 was killed but because it was an emissions era motor it made less power then the early 340s which kinda earned it a bad rep.
 
hi, the rod/ stroke ratio is better in the 340. the ratio is 1.85. the 360 is 1.71.
when the crank is at 90 degrees to the bore, the 360 rod angle is more compared to the 340. more angle pushes harder on the cylinder wall, causes more friction. the 340 will take more RPM ever the 360. the bore to stroke ratio is better in the 340. larger bore with shorter stroke. both are good motors, depends on what you prefer. personally, I like the 340, it's a tough motor, makes very good power! In running a stocker, have found that a cam profile that works in a 360 doesn't work very well in a 340.
 
Thanks for the replies so far gentlemen.



have found that a cam profile that works in a 360 doesn't work very well in a 340.
Click to expand...

Can you explain what would work? Eventually it will have to be redone and I would like to pick a correct cam.

Are the 340's harder to find parts for or more expensive to rebuild?
 
perfacar said:
hi, the rod/ stroke ratio is better in the 340. the ratio is 1.85. the 360 is 1.71.
when the crank is at 90 degrees to the bore, the 360 rod angle is more compared to the 340. more angle pushes harder on the cylinder wall, causes more friction. the 340 will take more RPM ever the 360. the bore to stroke ratio is better in the 340. larger bore with shorter stroke. both are good motors, depends on what you prefer. personally, I like the 340, it's a tough motor, makes very good power! In running a stocker, have found that a cam profile that works in a 360 doesn't work very well in a 340.
Click to expand...


As stated the rod to stroke ratio is better generally and is better in the examples given but not in all situations. The rod to stroke ratio of the 360 is better than the 340 in a 1/4 mile oval track application. In a short track application the car will lap time faster with a motor that comes off the corner well as opposed to a motor that pulls stronger towards the end of the straightaway. A motor with a rod to stroke ratio of 1.65 to 1.75 is ideal in this situation of coming off the corner. A 350 chev has a rod to stroke ratio of 1.63, a 360 Mopar comes of the corner much better because the chev is under the ideal rod to stroke ratio.

Also perfacar is spot on with the cam thing, you wouldn't think that just because of a rod to stroke ratio change would make a difference but it does.


Chuck
 
Wow, thanks.

This is the kind of stuff I was looking for.

Any hints or tips on future cam selection?
 
I have been shifting my 360 at 5,800RPM.
With a rebuilt, but stock, bottem end how high can you regularly spin the 340's?
 
My stock low compression 340 would spin to 6500rpms.

We need lots of info to pick a cam. Tire size,gearing,carb,intake,compression,exhaust.
 
The engine will spin/rev to it's limits via 3 items. You can spin past the max point, but theres no point in doing so, and do it at your own risk of engine damage.

1. The engine will make power up to a certain point (Combo dependent) and then the power falls off. Even though you press the go pedal and it will pull hard, the engine is past peak.

2. Valve spring limits. After the spring has reached it's limit on controling the valve.

3. Oiling system has limits. You can spin the engine faster, but then theres a lack of oil. Presto, damaged engine.

If, in example, your engine makes peal HP at 5800 rpm, theres no pint in pressing onward unless your crossing the finish line or getting to your wedding, baby's birth or makeing a mad get away from a bank robbery.

The valve spring can control the valves only so much. After that point, the valves will ethier and or bounce when the hit the valve seat or the valve spring can not keep everything tight and the lifter starts to jump like a skier of a ramp when the lifter goes over the top of the cam. This is called valve float. Power drops like a rock.

The stock oiling system is fine for most performance engines. Perhaps a hi-volume oil pump to help and a deep pan for it as well. But the system should be upgraded if your going past 6500 rpm's.

Most engines will peak around 6000 or so. Give or take 500 rpm. combo dependent again.
 
AdamR said:
My stock low compression 340 would spin to 6500rpms.

We need lots of info to pick a cam. Tire size,gearing,carb,intake,compression,exhaust.
Click to expand...


AND in addition, what you want out of the car or expected to do with it.
 
My 340 (ring and bearing '68 with stock everything except cam and headers) pegged the tach in my '73 Cuda (reads 7K, really about 6600) on several occasions. (not on purpose...lol) I shifted it at 6500 by that tach and dropped the clutch at 3500. I drove it daily fro 3 years, and ran 175hp NOS plate on it for the last 2. Amazing little engines really...lol. But you can save more than a few hundred going with a 360, and it will make better power where a street car needs it.
 
You sound just like me and my '73 Cuda. Minus the N02.
I like the 360 because it is easy to get, cheaper and has a longer stroke. A longer stroke engine vs a shorter stroke engine built with identical parts will peak in torque and HP sooner than the short stroke engine.
 
Sorry, I thought this was here. I got my threads mixed up.

I didn't build this, it is just the way it is coming.

340 engine
dcc 4120231 purple shaft 284 duration, 484 lift
Keith black 10 to 1 pistons
bored .030 over
2.02 intake valves in iron heads with mild port
edelbrock performer intake
750 eddie carb
Heddman headers
Cam was broke in yesterday! :headbang:

That is all I know for now. It is attached to a 71 swinger.

I am adding:

8 3/4 suregrip
3.55 gears
Stall 3,000-3,500??? (you tell me)
 
what kind of head gasket did ypouuse the 10.1 may only be 9.1 what is the com.ht of your piston
 
I don't know Mark.

I am torn between really wanting to know for sure and tearing apart a perfectly good zero mile engine for curosity's sake.

If I was snowed in or something I might do it.
 
The 340 is the BEST small block ever. Floating pins, long rods (as compared to brand X), valves located on bore center line, cam located higher in the block, best rod ratio of ALL small blocks. And..very good flowing heads (stock) as compared to the others. Best kept secret in the industry. Got zero print in the 'Chevy" mags. But a good one would run with just about ANY thing built in the day, big or small block. About 2800.00 for a Duster 340 or Dart Swinger 340 and you were in business... Terry.
 
:lol: :toothy7: I think it was the summer of 1968 when my buddy picked me up in his new dart GTS. 340 4 speed. There was one other in town with a factory 383. yes they did put big blocks in A-bodies. THis engine had it all, the early ones would run with anything chevy or ford produced big or small block. I think most of it was the compression ratio!!! That car would put you through the windshield when he down shifted. IT WAS HARD TO GET A RACE AFTER A WHILE, MANY BIG BLOCKS WERE SHAMED BY A WELL TUNED 340 a-BODY. That 275 horse advertisement was a Joke, more like 350. NUFF said if you can buy one get. Recently in my local trader an unbored 340 bare block was selling for 1000.00 firm. Your Mopar Brother Walt :coffee2:
 
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