318 cylinder head

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David Eldridge

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Ok I know there are a ton of posts like this, but all seem to go off topic. I'm sure this will like all others but worth a shot. I have a 1970 Dodge Dart with its original bone stock 318 with a 4 barrel. Heads finally need redone. Question is will 340/360 heads or an aftermarket head drop the compression ratio too much? Once again I know this has already been asked but it seems it's with all the super low compression 318's from the mid 70's. I'm not in that boat. And no no engine swap or pistons or anything. This is the original engine to the car and the bottom end is great! Might do a mild cam too.
 
A 340/360 head will drop compression about a half point. The bigger ports can help with flow but you need a bigger cam and some careful tuning to make it work and benefit you.
 
If nothing else is changed, putting on the 340/360 heads won't improve performance to any significant degree (and might even make it worse). Plus, you now add the mismatch head/manifolds port sizes to the mix and IMO not worth the change. Now, if you're going the do a complete makeover on that 318, that would be a different story.
 
  • I have always gained by replacing stock 318 heads with 340/360 heads, especially when milled .040. Always.
  • I've never had to cut the intake when I milled the heads that amount and never an issue. My experience, yours may differ
  • You can work with the 318 heads and get modest gains as well.
  • Yep, aftermarket heads work nice as well, though a set of (per say) edelbrock aluminum heads won't achieve potential sitting on a stock 318 long block with just a 4bbl carb. This would be my last choice if you plan on leaving the 318 otherwise stock.
 
Much like the post from 318willrun I have seen some great results going to 1.88 valve heads 340/360 on a 318 , Is seems everyone has different opinions but I have never had a bad result. I would add a small cam and dual exhaust and enjoy.
 
your 318 with the stock cam, cannot use the flow-potential of the big valve heads. and between the compression loss and the slower-moving airstream, I've never had good results with this, And even worse if the gearing is in the basement. Yeah the smoggers are even worse.
Ok, the top end might have potential, but the bottom end sucks. So if you are prepared to throw more stall and gears at it, you can fool yourself into thinking your car is faster, but until you change the cam, it's just the same old Dart with gears and stall.
So if you are gonna go down this road, get yourself some zero to 60 time trials, before and after, the head change, and smarten me up. Remember; NO other changes are allowed. After that's done, you can do whatever you want and document the change in zero-to 60 as you go.

When you're all finished, add up all the money you spent, and all the time you spent, and decide if the Change in zero-to sixty was worth it.Only you can answer that. As for me, the answer was no.
So after doing that twice;
on the third time
I installed a 2800 and 4.30s, BadaBoom!. Never looked back. Even the smogger is now fun.
Whatever you decide;
Happy HotRodding.
 
toolmanmike said:
A 340/360 head will drop compression about a half point. The bigger ports can help with flow but you need a bigger cam and some careful tuning to make it work and benefit you.
Click to expand...
David Eldridge said:
Ok I know there are a ton of posts like this, but all seem to go off topic. I'm sure this will like all others but worth a shot. I have a 1970 Dodge Dart with its original bone stock 318 with a 4 barrel. Heads finally need redone. Question is will 340/360 heads or an aftermarket head drop the compression ratio too much? Once again I know this has already been asked but it seems it's with all the super low compression 318's from the mid 70's. I'm not in that boat. And no no engine swap or pistons or anything. This is the original engine to the car and the bottom end is great! Might do a mild cam too.
Click to expand...


If you have the idea to change heads why not go with a 66-67 273 head (#178,234 or 920 or late 80's #302's) and bump your compression up a half point, add a little cam and with your 4 barrel it will be a nice combination. It's a lot of work for a little bump in compression though and no improvement in flow. Or do something different and go like AJ suggests and add a converter and or gears.
 
The 340/360 heads will get compression down into the sevens. I wouldn't do it.
 
Pick 2 and call me in the morning.

Black or Silver ??
(302 Closed Chamber Heads)
For the 318s, bolt right up.

1020161036.jpg


1020161100.jpg
 
RammerJammer75 said:
The 340/360 heads will drop the compression. Aftermarket will probably raise compression as the chambers are smaller that most (if not all) OE heads.
Click to expand...
Most 360 heads range in the 70-72cc ....318 heads like 675 open chamber heads are 68cc, later open chamber 318 heads are 72 cc, like the 163/593 castings.

What was the concern again?

Without a doubt, anything bigger than 68cc will lower the compression on the early pre 74 318s. The remedy is to mill .026-.045 off.

Point was in some cases it's no difference!
72cc 2.02 #915 j head or 72 cc 1.78 #163/593 heads...
 
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,@David Eldridge, i don't see anything wrong with just doing a nice valve job to your original 318 stock heads and leave all as is. Stock cam and all.

Here are a set of thin head gaskets to use with your fresh valve job to help keep the compression up. Made for the 318s.

Screenshot_20201026-063540_Chrome.jpg


One recommendation is to port match your intake manifold to the 318 cyliner head ports so that you don't have a square edge there coming off your 4 barrel manifold.

Here is a Stock 1969 318 with a 4 barrel added to the stock 318 intake and stock cam and single original exhaust system. Ran out really nice, great performance and gas mileage.

318 4bbl / 727 trans / 2.94 rear gears, one of my favorite stock drive line setups.

20200803_230827.jpg
 
David Eldridge said:
Ok I know there are a ton of posts like this, but all seem to go off topic. I'm sure this will like all others but worth a shot. I have a 1970 Dodge Dart with its original bone stock 318 with a 4 barrel. Heads finally need redone. Question is will 340/360 heads or an aftermarket head drop the compression ratio too much? Once again I know this has already been asked but it seems it's with all the super low compression 318's from the mid 70's. I'm not in that boat. And no no engine swap or pistons or anything. This is the original engine to the car and the bottom end is great! Might do a mild cam too.
Click to expand...
Looks like there are several suggestions/opinions, could you maybe share some info about your Dart , gears , trans (904) , other modifications like intake , carb , exhaust and intended usage. Do you manually shift at WOT or leave it in drive , where does it shift at WOT etc. Maybe you dont drive it hard and its more of a cruiser?
 
Not surprising. With a 273, you have to notch the block and/or overbore just to get 2.02 valves to open. Even when you do, they're shrouded so bad, the flow is terrible.
 
I have a 1970 Dodge Dart with its original bone stock 318 with a 4 barrel. Heads finally need redone.
Click to expand...

It sounds like if the heads didn’t need freshening you wouldn’t be touching it.

If the rest of the overall combo will remain unchanged, I’d go through the current heads and put it back together.
 
You have a 4 barrel. Add some nice dual exhaust and have @halifaxhops recurve the distributor for you. You might be surprised how good it runs. I would do a compression and cylinder leakage test first of all to see if you need to pull the heads or not.
 
After reading about magnum heads superior exhaust ports, rocker ratio and even the lower cc of the heads, i won't consider LA heads on a future build. Plus they are cheap. Grab George Jets offer and run with it for some good small chamber LAs
 
pishta said:
After reading about magnum heads superior exhaust ports, rocker ratio and even the lower cc of the heads, i won't consider LA heads on a future build. Plus they are cheap. Grab George Jets offer and run with it for some good small chamber LAs
Click to expand...
Those are LA heads. #302's
 
toolmanmike said:
You have a 4 barrel. Add some nice dual exhaust and have @halifaxhops recurve the distributor for you. You might be surprised how good it runs. I would do a compression and cylinder leakage test first of all to see if you need to pull the heads or not.
Click to expand...
It has duals on it. I pulled the heads when I got the car just to see. I know one of the exhaust valves is starting to recede. Stock heads are 60cc replacement Indy's I'm looking at are 62cc with 202 valves.
 
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