340/360 Heads on a 318

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sneke_eyez

sneke_eyez

1974 Dodge Dart 2dr 318V8
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Might have just found a great deal on some 340/360 heads from a friend of a friend.
Completely rebuilt and hes asking very little for them.

He told my friend to tell me that it would be a totally worthwhile swap for my 318, and I've heard of this before, but I'm simply curious:

What advantage is there to adding 340 heads to a 318?
My 318 runs great now, completely stock except for an Edelbrock Streetmaster 318 intake and Edelbrock 650 Carb, and I'm just curious what the difference will be if I pony up the cash for these heads.

Thanks FABO! :read2:
 
There is little to no advantage to running 340/360 heads on a 318. Reason is the ports are to big so it looses velocity. And the combustion chambers are so big you'll loose alot of compression. If your engine is stock 8 point something to one compression it'll drop into the 7's with big chambered 340/360 heads. So in essence on a stock 318 you'll probably just loose a bunch of low end torque and only gain a little on the top end power. It'll be slower and be worse on gas.

Use the search button and you'll find this subject has been brought up numerous times over the yrs.
 
Your compression ratio will drop and your stock 318 exhaust manifolds will probably not seal to the larger ports on those heads.
 
Alright, thanks guys!

I did attempt a search, but like the search on many forums, it came up with few relative results.
I always just find its better to ask a question outright in these situations, rather than try to wade through mounds of information that ends up not being relevant.

Like I said though, I appreciate you guys clearing it up for me.

I'll be sitting this one out and saving my pennies for new wheels and tires.

Anyone want a deal on some freshly rebuilt 340 heads? I can pass his info along. :D
 
They can work,but they need good compression and a loose torque converter,fairly big cam. On your otherwise stock 318 it's a drawback. You will lose big gobs of torque in the low rpm ranges where you need it the most!

I had a cop car 83 Plymouth Caravelle,came from the factory with a 318 4bll and 360 heads. compression was probably 7.5:1. Passed everything on the freeway...could actually keep up to my buddies 71 Demon 340 in a side by side race at 50 mph. No way could I catch him otherwise.
 
magnum heads have smaller combustion chamber then LA heads
 
YES,they can work..my friend has a smog motor 318,we switched over to a set of 1.88/1.60 j heads last offseason,with a set of headers and he went from a best of 14.51 to 13.95...
 
I'll say on a stock engine, I wouldnt bother. But with a mild cam and careful setup, they can be better than stock 318 heads. You just have to understand what you're losing, and design things to try and get some of that back. Simply bolting them on won't do much.
 
I think the big port heads on a small cube engine is something you have to actually experience for yourself. Some think they run like stink in mild form, some don't. I don't, but anymore just am to the point of saying, ya, go for it.
 
I agree with the Alaskan. The big port heads are not to terrible to run and drive with. I have done both heads on a 318. The stock heads provided more torque off the line and a great midrange over the 360 heads, while the 360 head did better up top and only showed a mild difference in MPH but not so much in actual ET at the 1/4's end.

The biggest difference in the builds was the 360 headed 318 had a Holley DP on top a Torker II and a 4spd trans while the auto 318 has a LD4B and a Carter 625, with lower compresion. Same exact cams used.

It was a 3 mph dif at the 1/4's end but only a few tenths in time. The auto is much better around town and off the line.
 
I had a 318 years ago I put in my Dart after I blew up my 340 it was a 70 318 with 60,000 miles and a mild cam it went 13.80s I put on a set of 1.88 valve fairly stock 360 heads and was going 13.20s with 3.91 gears and 1 5/8 headers it had a 904 with a 10 inch convertor. I put in an 8 inch convertor and went a best of 12.67. Every combo is different.
 
dodgetkboy78 said:
Are they closed chamber too? I have never got my hands on a set, my 67 LA truck motors had open chamber heads. I heard somewhere they were closed chamber, and had lots of meat for porting.
Click to expand...

Yes they are closed chamber, shaped like closed chambered big block heads but with the angled plug [better], BTW they use a weird big ford thread 5/8 and the plugs that I ended up using [cold] came listed for a like a sb motor home??

They are on the 318 340cam performer intake /carb still, so I pulled a valve cover and took a pick of the #'s, all letters/#'s are BIG as cast.

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