340 heads on a 318?

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72DodgeSwinger

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I've got 1975 318 with the smog heads and cam, and I've been putting together stuff to replace all of it. Got the factory four-barrel 340 manifold and a hotter cam, but I need heads. I've heard that certain 340 heads can be bolted onto a 318 to boost compression, but I've also heard certain castings will lower the compression. First off, is this true, and second, which casting/year/whatever would work to boost performance on a 318? Any help would be fantastic. Thanks.
 
good 340 heads will lower your compression. You would need new pistons to bring it up or have the heads milled. I would suggest new pistons as head can only be milled so much. Another choice would be to find some 360 heads with 1.88 valves. they were designed to flow better with the 8.6 compression your 318 has. not to mention they will be cheaper than 340 X heads. take the money you save on the heads and get them polished and ported. Your 318 will thanks you for it.
 
+1 to the above...

360 heads will perform just as good on a 318 but....you must have them shaved to get the compression up or the engine will be a complete dog.
If they are shaved properly, they run fantastic on a 318. You also gain larger
valves by using the 360 head. The 2.02 valves on a 340 head are complete overkill on a 318 unless you are running it constantly in the higher rpm's. The larger valves can actually hurt your low end.

Lots of people say to use the mid 80's 318 head (302 casting) with portwork.
I have heard this works well but I have always went with tinkered 360 heads.
Doing this, you are still stuck with the puny 1.78/1.50 valves.

It's really a trade off between flow and compression ratio.
 
You can also have the larger 360 valves installed in you 318 heads maintaining stock compression.
 
72DodgeSwinger said:
I've got 1975 318 with the smog heads and cam, and I've been putting together stuff to replace all of it. Got the factory four-barrel 340 manifold and a hotter cam, but I need heads. I've heard that certain 340 heads can be bolted onto a 318 to boost compression, but I've also heard certain castings will lower the compression. First off, is this true, and second, which casting/year/whatever would work to boost performance on a 318? Any help would be fantastic. Thanks.
Click to expand...

What is "A hoter cam?" Specs please.
All 340 and 360 heads will drop compresion. IF anybody else told you different, there stupid. Walk away from them.

IMO, depending on what cam and how the rest of the engine is built, would help me decide what head to run. In your case, since the infomation given leads me to think this is a mild build up, stay with the 318 heads. Use 360 valves and port the head. DO NOT POLISH IT!!!!!


74swingerlover said:
Another choice would be to find some 360 heads with 1.88 valves. they were designed to flow better with the 8.6 compression your 318 has. / take the money you save on the heads and get them polished and ported. Your 318 will thanks you for it.
Click to expand...
1st, the 1.88 was not designed to flow better with a low compresion.
2nd-ly, Poor advice, truly a step backwards


65Vart said:
You can also have the larger 360 valves installed in you 318 heads maintaining stock compression.
Click to expand...

Good advice, good train of thought.

Due note, that MoPar used to offer a ported 318 head that made more power than a 360 head, ported or not. Of course, there are limitaions to this.

By porting the 318 head, you'll save time and money over going to a larger 340 or 360 head. Because when you suddenly realize that the bigger head doesn't perform as good as the ported 318 head, you will have wasted lots of time and money on useless parts for your 318.

Has not anyone here read the MoPar engines book? OMG!!!!!!!!! :banghead:
 
318's run very well with 340/360 heads, intake valve size is not important. Magneflux any used heads to make sure they are not cracked first. Always mill them .020 on block side and .019 in intake side if they haven't been milled before. This gives you a flat surface to seal to the block and keeps about the same compression ratio. Clean up the bowls under the valve, see Wild and Crazy's thread on porting heads. Tighten the guides and get a Good 3 angle valve job. This is a cheap way to add horsepower to any 318. The ported 318 heads are no longer available from Mopar Performance and cost a lot of money. If you trust your porter, and the money is in your budget go for it. The "302" castings are the ones to use. Air flow makes more power than compression... Do you really think 22 cubic inches makes that much difference that 340 /360 heads won't work on a 318????
 
So what's the best choice 318 302 heads 188-160 ported

Or 360 heads I think 915 188-160 valve

Which one would overall be best for street performance
 
Street today its the small port 302 however big ports work well with 3.91-4.10 gearing.Does Eddy make a small port aluminum head, nope--enough said
 
Stock 318:
Pull head, clean casting flaws (don't port it!) and have a 3 angle valve job done on it.
power well increase nicely, with no bottom end loss.(aka stop light acceleration)

360 will require a lot more attention to details to make it work better.

340 cost to much for the same "Basic" head.
 
Just wondering, as the advice is verying so much, how many of you advising 72DodgeSwinger, have actually tested what you are saying? Are you just repeating what you have heard? 'Cause it seems to me, to be a bunch of bologna I'm seeing, with an occassional truth, thrown in.
 
What I see is a lack of information by the thread starter. Some spec's would help alot not to mention the over all want out of the build, performance wise. Is there a "Time" he wants to run?
 
If it was me, and I was camming up a little and not looking to spend anything, I'd use the 340/360 heads. Those that say "its a dog" havent had a good one I guess. Mine weren't dogs, even in an E body with 3.23s and the resulting 7-ish:1 compression. Overcamming will exacerbate the low end issues. So don't over cam it.
Now as for facts.. No 340/360 head will gain compression without machining, and to get the benefit, you'll end up doing more machining to make it all work together. In terms of the best budget option when you have some money... Stick a set of Engine Quest Magnums on it. Get them in the LA intake pattern, and plan on measuring and ordering pushrods and grabbing some stock Magnum rocker assemblies from the boneyard. You should be able to get the heads assembled with mild performance springs for $500 or thereabouts and they are perfect for a hot 318, and should gain you a little compression depending on the year of the 318 used.
 
Sorry about the lack of info. The Cam is a Comp 268H with a 268 duration and 454 lift. The reason I wanted to switch heads is because they're still the stock piece off the smog motor, and from what I've heard, they're far more restrictive than pre-EPA pieces.
 
As far as performance goals, I was just looking for a healthy setup that would make decent power. I'm not out to put together a car to thrash at the drag strip every weekend, but I'd like it if the car were capable of laying down a respectable time, or surprising a car two at the stoplight.
 
The 268 is about the largest you can run with the Magnum type springs because they runa 1.6 ratio and the lift is very limited. I think the EQ heads would be preferred over the 340/360s if you have to buy some anyway.
 
throw on some 360 heads, better mileage. Save up the money you saved on gas for a year and when you get bored with the lack of power install a turbo and it will thank you for the low compression with the ability to push more psi. Cost = $0

:---)
 
wow.lol

I agree the 340/360 heads should be milled to raise the compression, they are 72'ish cc's from the factory with 318 heads 'open chamber' version being 68'ish cc's. in that case 'if it were me'...I would be looking to remove about .050 from the decks, 'every .0048 removed is 1 cc' on a 340/360 head fwiw. food for thought, when going from a stock steel .019 thick head gasket to a felpro replacement style, you just added .026-.028 more to the gaskets thickness and just gained 4-5 cc's-'lower compression'
So with milling off .050...you end up with about 61cc's but thats also compensating for the thicker head gasket by doing so...so it's the effect of 65cc chamber based on a .019 gasket, if that makes sense.... after the decks have .050 removed, also do the intake face of the heads, remove .045..., there are diff thickness intake gaskets to work after that.

I also like the engine quest head idea if the money is there, i hear they flow about 10 cfm more than a 2.02 x/j head and still have a small'ish port volume, but wouldnt want them for more than a 318-330 cid in comparison to the other heads available.
 
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