318 Mopar vs. 340 Mopar

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My vote would be for a 360,either the La with magnum head conversion or the roller block magnum 360 converted to carb. Modern heads/combustion chamber will produce more across the rpm range power,but slightly less peak power than the la head. Better burn with the magnum also means better mileage
 
mooser said:
Am i the only person that realizes he has a /6 car so probably has a 7 1/4 rearend therefor if he gets a 340 or 360 he has to upgrade to at LEAST an 8 1/4 while if he gets a 318 he can use his 7 1/4.
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The old 273 4bbl cars came with a 7¼ and 904 tranny; 8 3/4 if 4-speed. I managed to find a 3.23 SG 7¼ SBP for the Demon. Since 7¼s are nearly falling out of trees, I put in BBP axles. The engine I have is a 318 with 302 heads and a .441 lift/270 deg cam conected to a 904. Rough estimate is 275 hp at the flywheel. I'm not planning a lot of burn-out or racing. I'll let you know how it holds up.

In the meantime, I'm saving $s and keeping my eyes open for an 8 3/4 or a Dana 44. I've never seen a max hp recommendation for the 8 3/4, but the Dana is good for 550 hp.
 
MOPEkidD-3 said:
I want to build a high-compression 360 Magnum for my '70 Duster in the future. Iron Ram Magnum heads (home-worked), flat-top zero-deck slugs (10.5:1 comp.), Lunati Voodoo cam, and other goodies, hooked to a Passon A-833 OD and an 8-1/4" rear. Of course you could go with something milder, but 360's are fantastic motors no matter what you do.
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That's basically the 360 I built and I have an A833OD with an 8.25. This engine makes ~370 HP based on 102 mph trap speeds in my car and has run a best of 13.7 in the 1/4. Its not the engine that is keeping the car from reaching the 12's, I have traction issues as shown by the misreable 2.2 60' time on the 13.7 run. I also get 17-18 mpg around town and 21-22 mpg on the hiway.
 
The 8 1/4 was used IIRC in performance cars after '72. I seem to recall seeing a couple 340 stick cars with 4.10SG 8 1/4s under tehm... In any event, the 7 1/4 wont last very long, even abusing it with a slant. Been there, done that... In terms of the differences, there are 22 cubic inches that are different if you rebuild both of them with performance in mind. Even with the smaller heads. No other difference really. I'd find a nice 318 core, stick some good pistons in it, and run a set of 308s on it with 1.88 valves. Cheap, easy, and will run with any equally built 340.
 
My ex had a 170/6 Valiant and she annilated 2 rear ends! .........
.....something about revving it to high heaven attempting to unstick car from snow bank and never backing out of it when dry pavement was found.
 
340's are getting hard to come by I myself own one 318, 340, and a 360. My dad has 6 340's 2 are stroked one is a standard bore together in his dart, one is standard bore but very rusty, bought a standard bore 340 short block at monster mopar for $100 and the last one is a 30 over complete engine that was bought for $250. We dont pay the high prices we wait for a deal to come along to make the right move. Just wait it out im sure one will show up.
 
it all depends on how much mmf you want. what kinda numbers do you want. if your compremising with econemy get a 318. you can find them in damn near any dodge truck. you dont need to upgrade rearends if your not plannin any major hp but if your lookin for something fast with 270 to 400hp id get a new rear
 
I've bought running 318's for as little as $50 bucks and running 360's for $200 and even a nice running 70K 400 for $700 (complete with Cordoba wrapper). Even if you find a smogger engine from the 70's it is pretty easy to swap on a better set of heads and make some decent power. You can even put magnum heads on the LA engines with a few modifications. So I suggest for cheap and easy, find a 318 with tranny, for more power, go with the 360.
 
I would run the 318. But I like building 318's because a lot of people think it takestoo much money or parts to make them run right,when it doesn't. I don't have that much into my 318 and it runs good.
 
340-360's have taller beefier main caps than the 318 hence the washers that come with the windage tray main bolt kit, cause 340,360 main bolts are longer.

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If you have time...wait out for a 340.If not the360 is plentiful.The 340 is a moparmans motor(high revs)plenty of power.Start looking for an 8 3/4 cause once you get the bug..your in.8 3/4 rears came in 426,440 automatic cars.I,ve snapped an axel in 8 1/4 rear with 4 speed.to much HP.Learning can be $$$$$.If I had known about this site earlier,I,d have saved enough money to purchase another car.
 
I am gonna hold out for the 340. I have a buddy that thinks his uncle might have one that he would be willing to trade tattoos for so that might work out really well. I love bartering. thanks for all the advice.
 
Given that you are looking for a driver, and not a race car, I don't see any reason why you would need more than a 318. A 318 is a good, solid foundation for a dependable motor. It sounds like that will be important. Cost wise, you would probably spend about the same money on a 360 as a 318, so that point would be moot. Do you need a 360? Probably not. Would it be fun? Yeah it would. Others have brought up a great point that your 7 1/4 will probably be toast if you put any kind of real power in front of it.

OTOH, a 318 can be pretty darn fun too :) I'm putting a 318/727 into my 68 Dart for a driver. There is no reason a 318 can't be a good all around runner.

I would just look for what you can find, and build a good motor. Keep in mind that you may have to upgrade that rear end. It might be a good idea to have at least an 8 1/4 rear standing by in case you grenade that 7 1/4 you have now.

As for swapping out the /6 to a V8, There are lots of components to replace besides the rear end. There is LOTS of good information here and on the web about what you need to do to do the swap.

Good luck and keep us posted. I'd love to see more pix of your car.

j
 
318 are dime a dozen ,340 like pulling hens teeth , 360 better choice if your not looking for that certain piece . 340 are still around but are you willing to pay the price . you can buy a junkyard 360 or 318 still for under 500 that runs an probably never even fine the block of a good 340 for that.best create motors are the best way to go if you want something that runs good an pretty much just bolt right in .plus you get the warrenty with them .
 
keep in mind,if you are not building a tire fryer,,a 318 uses way less gas then a 360.. speaking of 340 engines,, i sold my extra i owned it since i pulled it out of the junk car in 1978,i regret it now,,there is a guy at work,,has not driven in 12 years to many DUI, has a 1970 340 just stiing in his garage,,and another friend of mine has so much junk in his garage he cant get to his engines,, probable at least 4/5 340,s in there,,they are around but all seem to be getteing harder to find 318 340 360
 
340;s are still out i recently picked-up a '70 block still standard bore for $275.00....
 
goatboy said:
I am not going to rule out a 360 but I think I am leaning towards a 318. I am not looking to run the 1/4 for anything more than fun. I really want to just be able to have fun with it. I don't really drive much about 10 miles a day to work and back. and then to KC (about 1 hour) or St. Louis (about 3.5 hours) a couple of times a year. I am not worried too much about mileage but I still want to be able to run 65 for a couple of hours at a time without hurting it. I also know I will be replacing the rear end and the drive shaft. I know better than trying to use whats shes got.

If I look for a doner car are there any I should stay away from? I don't want a computer. thanks
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goatboy said:
I am not going to rule out a 360 but I think I am leaning towards a 318. I am not looking to run the 1/4 for anything more than fun. I really want to just be able to have fun with it. I don't really drive much about 10 miles a day to work and back. and then to KC (about 1 hour) or St. Louis (about 3.5 hours) a couple of times a year. I am not worried too much about mileage but I still want to be able to run 65 for a couple of hours at a time without hurting it. I also know I will be replacing the rear end and the drive shaft. I know better than trying to use whats shes got.

If I look for a doner car are there any I should stay away from? I don't want a computer. thanks
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360 is overall going to give you better cruising. 318 will work just fine, too. 8.25 diffs are easier to find for an A body than 8.75. Go up a cam size regardless of which engine U get. 3.23 gears are best for cruising with some zip. But 3.55 gets more punch at the light(s). Also depends on tire diameter. Do the math. And get a posi unit. Headers will breath best. A 600 vacuum secondary carb. Nothing bigger unless U R going to race it.
 
Better piston options out there for a 360 if you want to build the engine up later on. But for local cruising and light duty, 318 would be fine.
 
goatboy said:
I have a 71 dart with a 225 slant 6. I am thinking about putting a v8 in it. After looking at what it would cost to build the 225 I think I might be happier with something bigger. What I am looking at right now is going with a 318 or a 340. Could someone tell me the benefit or difference between the two. Thanks
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If you're going from a 225, never had a v8 before...build the 318 340 spec at 9.1 compression and you'll be happy. You can make within 25ish hp of a 340. And digging deeper in to potential power increase... its all about how much valve you can use and a bore that wont shroud it. Same head, bigger bore wins if both heads are worked to the bore size.
 
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