360 Aftermarket Heads on 318

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Mopar Millenial

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So I've seen some discussion on various forums about stock 360 heads destroying compression on a 318 because of the combustion chamber size being closer to 74-76 ish... instead of the stock 318 size which I have found, from research, to be anywhere between 60-66 cc's. This can of course be minimized by milling down the stock 360 heads somewhere around .040-.050 to fix that.

HOWEVER here's my situation... when I acquired the 67 barracuda (has a 318 from 1970 in it), I discovered it has the Edelbrock 7177 RPM Cam for 340 360 in it that recommends 340-360 heads. Why that was put in a stock 318 with stock 318 unported heads, your guess is as good as mine. I found someone selling various parts including aftermarket 360 heads from Edelbrock, I believe the part number is #60779, that have a 63cc combustion chamber. So the only difference I see between those and the stock 318 heads are the valve sizes.

QUESTION: because this combustion chamber is within stock range for a 318, shouldn't those heads (paired with either the 340 intake that I have now or the 360 intake that also comes with the heads) theoretically give me the airflow I need (per the cam's instruction) without causing the compression ratio to be absolute trash? That should allow me to leverage the better performance from the cam, so I think.... or will the larger valve sizes cause other issues.
Looking for a healthy discussion and to learn me a thing or 2.
attached some specs for the aftermarket 360 heads for quicker reference

Screen Shot 2022-09-20 at 12.18.36 PM.png
 
Go for it. A few things the 318 heads lack but can be overcome with work and $$$'s is small valves and small ports. The 340/360 heads have bigger of both when teemed with a good intake, 4 barrel. decent sized cam, headers and the like will produce good power. The cam will tell you when (RPM) . Thinking in a compression direction, a close to zero deck 318 with the closed chambered 920 heads can make more power as well but not as much as the big valve/big port heads do. This combination is better for a mild street engine where big HP/RPM numbers aren't wanted.
 
toolmanmike said:
Go for it. A few things the 318 heads lack but can be overcome with work and $$$'s is small valves and small ports. The 340/360 heads have bigger of both when teemed with a good intake, 4 barrel. decent sized cam, headers and the like will produce good power. The cam will tell you when (RPM) . Thinking in a compression direction, a close to zero deck 318 with the closed chambered 920 heads can make more power as well but not as much as the big valve/big port heads do. This combination is better for a mild street engine where big HP/RPM numbers aren't wanted.
Click to expand...
Thanks for the input. Also forgot to mention I have 675 heads on now. Was going to do a port job on those and still might to just clean up some edges but will likely try and use those for a future stock build. (and so the mopar hoarding begins) lol.
 
That 7177 is too big for a 318. The duration is 300/310, if it's a hi revving bracket car maybe. JMO 65'
 
Plymouth 65 said:
That 7177 is too big for a 318. The duration is 300/310, if it's a hi revving bracket car maybe. JMO 65'
Click to expand...
I agree it's too big, I'm hoping to combat that with better air flow that crams more air into the cylinder since the intake valve doesn't close until 44* ABDC. But I'm just trying to make some solutions with out swapping the cam completely. personally I think a 340 or 360 intake with 360 heads could solve most of that...hopefully. lol
Thanks for the response!
 
I've measured a 318 head at 66 cc, so the aftermarket heads may not need any milling to keep the same compression as the stock 318 head...
 
krazykuda said:
I've measured a 318 head at 66 cc, so the aftermarket heads may not need any milling to keep the same compression as the stock 318 head...
Click to expand...
That's what I was thinking! so even at 66 cc's the 63 would actually raise compression. I did some quick math on the standard 318 cylinder volume vs the quoted 63 cc combustion chamber and the math works out to around 10.3:1...ish
 
Performance is not really about compression ratio; rather it is about cylinder pressure.
You can install any number of different cams into a 9.5 Scr engine and get pressure ranging from in the basement to in the attic.
For a streeter;
The pressure is what makes a snappy street engine.
That 7177 Edelbrock cam may be fine in an 11.5/1 engine, but in a 8.0 engine she will be a slug.
This is why bolting on big open-chamber heads onto a stock low-compression engine is bad enough, but if you then add a big cam, Bam! you get a dog of a combo. Sure it might make half decent power once the RPM gets up, but now you are committed to running race-gears, and a hi-stall convertor.

Here's an example.
Say your 9.2Scr early 318, with the stock cam (240/248/112) pumps 158psi. That's getting up there, Street-Performance will be pretty good.
Now say you install heads that are 14cc bigger.
At 9.2, the total chamber volume was 79cc. So at 79+14=93cc your Scr is now 8.0 and with the same cam, your pressure falls to 131psi. This is about what a smog 318 pumps, which everybody will agree is already pretty lame.
Now install a 340 cam (268/276/114) and the pressure falls to 114psi which makes a really really lame low-rpm engine. Couple that with 2.76s and hang your head in shame. I did this so I know this. It took 4.10s and a 2800TC to get outta that hole, just to get back to a normal bottom-end performance.
The 7177 cam is; 308/318/112, 234/[email protected], .488/[email protected] arms
But they don't publish the lift at 308* so it's sortof a useless number to work with;
The Wallace Calculator has been pretty accurate for me using the .006/.008 tappet rise numbers that most popular camshaft grinders supply. But in the case of the Edelbrock, not having those, I can only guess. Typical hi-performance cams will have acceleration ramps of 46 degrees or more, some as high as 53. Lets say I guess 50*. That would make the comparative numbers to be 284/294/112 advertized at .008 tappet rise. which is typical for this size of cam. From those numbers;
YOUR pressure in a 9.2 318 comes to ~130psi.
but if you install heads with 14 more cc, making your 9.2 engine into an 8.0 engine, then the pressure drops to
get this;
108psi.
And that's if I guessed at Edelbrocks .008 advertised correctly. The pressure could be lower.
At this low pressure, this 318 will have bottom-end power that is similar to a 225 slanty. This 318 will not wake up until deep into the 3000s rpm.
Now, all these examples come from the Wallace Calculator, input to 1000ft elevation..

So, as you can see, or should be able to see, pressure is a really really big deal.
However it has a downside, the more you run, the more likely the engine is to detonate, which breaks engine parts. So there is a limit as to how much you can run.... at WOT.
Typically, with iron heads, and on the street, the limits are; 165psi for 91gas, 160 for 89, 155 for 87octane.
Closed-chamber heads running a tight Quench, may go a lil higher.

My message to you is this; that if you bolt on big chamber heads, and then install a performance cam; you will be in for a very rude awakening.
There are way better things to do to that combo, that do not involve going into the engine.
 
Those edelbrock heads have larger ports and the exhaust port is raised as well. The eddy cam is considered mild but matched to those heads and works best with an airgap or rpm intake. Your dynamic compression is never exceed static compression, but dynamic can be much less dependent on valve overlap.
 
I just read AJ’s post and I concur. You need more static compression to begin with.
 
Plymouth 65 said:
That 7177 is too big for a 318. The duration is 300/310, if it's a hi revving bracket car maybe. JMO 65'
Click to expand...
Look at the duration @.050 & you’ll change your tune. If not, I don’t know what to say. IMO, the cam is NOT big.
Mopar Millenial said:
I agree it's too big, I'm hoping to combat that with better air flow that crams more air into the cylinder since the intake valve doesn't close until 44* ABDC. But I'm just trying to make some solutions with out swapping the cam completely. personally I think a 340 or 360 intake with 360 heads could solve most of that...hopefully. lol
Thanks for the response!
Click to expand...
WhT you really need is a better cam.
ch1ll said:
I just read AJ’s post and I concur. You need more static compression to begin with.
Click to expand...
Disagree. In a major way. AJ can write out all the math in the world and make me look bad but until you have actually been there and done that, please move aside.

I have a question for you!

If he doesn’t have enough compression, how did the Dodge NASCAR trucks make over 700 hp with only a measured 9.0-1 compression ratio?

OK…. Moving on…..
 
AJ/FormS said:
Typically, with iron heads, and on the street, the limits are; 165psi for 91gas, 160 for 89, 155 for 87octane.
Closed-chamber heads running a tight Quench, may go a lil higher.
Click to expand...

You can go much higher than that. There's more to detonation than just octane ratings. That said you need to pay attention to the details to make it happen. Would you run 11-1 comp with a 218 @ 0.050 hydraulic cam?
 
Last edited:
rumblefish360 said:
WhT you really need is a better cam.
Click to expand...
I definitely recognize the cam isn't what it should be. Having read all the information in the last few posts i'm definitely still learning about why all of that is. But I'm approaching this backwards to try set up the engine so the cam is leveraged best, but the best way is to set everything up, flow the heads, and then choose a cam.
 
AJ/FormS said:
Performance is not really about compression ratio; rather it is about cylinder pressure.
You can install any number of different cams into a 9.5 Scr engine and get pressure ranging from in the basement to in the attic.
For a streeter;
The pressure is what makes a snappy street engine.
That 7177 Edelbrock cam may be fine in an 11.5/1 engine, but in a 8.0 engine she will be a slug.
This is why bolting on big open-chamber heads onto a stock low-compression engine is bad enough, but if you then add a big cam, Bam! you get a dog of a combo. Sure it might make half decent power once the RPM gets up, but now you are committed to running race-gears, and a hi-stall convertor.

Here's an example.
Say your 9.2Scr early 318, with the stock cam (240/248/112) pumps 158psi. That's getting up there, Street-Performance will be pretty good.
Now say you install heads that are 14cc bigger.
At 9.2, the total chamber volume was 79cc. So at 79+14=93cc your Scr is now 8.0 and with the same cam, your pressure falls to 131psi. This is about what a smog 318 pumps, which everybody will agree is already pretty lame.
Now install a 340 cam (268/276/114) and the pressure falls to 114psi which makes a really really lame low-rpm engine. Couple that with 2.76s and hang your head in shame. I did this so I know this. It took 4.10s and a 2800TC to get outta that hole, just to get back to a normal bottom-end performance.
The 7177 cam is; 308/318/112, 234/[email protected], .488/[email protected] arms
But they don't publish the lift at 308* so it's sortof a useless number to work with;
The Wallace Calculator has been pretty accurate for me using the .006/.008 tappet rise numbers that most popular camshaft grinders supply. But in the case of the Edelbrock, not having those, I can only guess. Typical hi-performance cams will have acceleration ramps of 46 degrees or more, some as high as 53. Lets say I guess 50*. That would make the comparative numbers to be 284/294/112 advertized at .008 tappet rise. which is typical for this size of cam. From those numbers;
YOUR pressure in a 9.2 318 comes to ~130psi.
but if you install heads with 14 more cc, making your 9.2 engine into an 8.0 engine, then the pressure drops to
get this;
108psi.
And that's if I guessed at Edelbrocks .008 advertised correctly. The pressure could be lower.
At this low pressure, this 318 will have bottom-end power that is similar to a 225 slanty. This 318 will not wake up until deep into the 3000s rpm.
Now, all these examples come from the Wallace Calculator, input to 1000ft elevation..

So, as you can see, or should be able to see, pressure is a really really big deal.
However it has a downside, the more you run, the more likely the engine is to detonate, which breaks engine parts. So there is a limit as to how much you can run.... at WOT.
Typically, with iron heads, and on the street, the limits are; 165psi for 91gas, 160 for 89, 155 for 87octane.
Closed-chamber heads running a tight Quench, may go a lil higher.

My message to you is this; that if you bolt on big chamber heads, and then install a performance cam; you will be in for a very rude awakening.
There are way better things to do to that combo, that do not involve going into the engine.
Click to expand...
Thanks for all of the information! This is a lot for me to chew on, I'll definitely take this to learn some more. Seems there's some agreeing and disagreeing with this but I'm absorbing it all and will keep this in mind when making some parts decisions in the future!
 
Mopar Millenial said:
I definitely recognize the cam isn't what it should be. Having read all the information in the last few posts i'm definitely still learning about why all of that is. But I'm approaching this backwards to try set up the engine so the cam is leveraged best, but the best way is to set everything up, flow the heads, and then choose a cam.
Click to expand...
If your going to just keep the cam and add parts to be used as is for now, the Edelbrock cylinder head will work just fine.

Do so make sure you have a stall converter to allow the engine to perform best with the cam and your rear gear ratio as well should be part of the combination. Also as AJ/FormS mentions, the cam timing is super important since it can make or break an engine. The normal 110 centerline of cams will work well with the 318 and the Edelbrock heads. See if you can’t find a cam with an earlier intake valve timing closing event to help with keeping dynamic cylinder pressure as high as possible.

Everyone screams about the 318 being to small, super weak, etc…
(Basically) Treat it the same as if it were a 340 and let’er rip.
 
Last edited:
rumblefish360 said:
If your going to just keep the cam and add parts to be used as is for now, the Edelbrock cylinder head will work just fine.

Do so make sure you have a stall converter to allow the engine to perform best with the cam and your rear gear ratio as well should be part of the combination. Also as AJ/FormS mentions, the cam timing is super important since it can make or break an engine. The normal 110 centerline of cams will work well with the 318 and the Edelbrock heads. See if you can’t find a cam with an earlier intake valve timing closing event to help with keeping dynamic cylinder pressure as high as possible.

Everyone screams about the 318 being to small, super weak, etc…
(Basically) Treat it the same as if it were a 340 and let’er rip.
Click to expand...
Yea the 107 centerline advances it about 5* but to err on the side of keeping this as good as it can for what I actually have, I was going to look at advancing it several degrees more. obviously a newer cam would be the ultimate answer. But yes determining what converter I have and what I need, i'm learning, is going to be a fun game to play. And as a longer term upgrade, the 7.25 rear end has got to go.
 
Seems to me that you have a good idea of what you want to do. Your path, IMO, is a bit more lit up now and your head is in the right place. I think you just needed to bounce this off the forum members.
 
rumblefish360 said:
Seems to me that you have a good idea of what you want to do. Your path, IMO, is a bit more lit up now and your head is in the right place. I think you just needed to bounce this off the forum members.
Click to expand...
Yea even with just this question I've learned more. it's such a good source of information. And once you get to a certain level of depth, some questions just cannot be answered by looking something up, which is why I decided to make an account here for my super specific questions lol.
But I'm still learning little by little, just regurgitating stuff that I've heard or read and as I learn my ideas/plans change. I still remember about 6 months ago I was confused with "if you set your initial timing, wouldn't adjusting total timing change that?" and now knowing mechanical advancement can be changed with various methods I understand that and much more.
 
That’s the key! Know your routes and why. The old adage of “There’s more than one way to skin a cat” apply in cars and engines.
 
toolmanmike said:
Go for it. A few things the 318 heads lack but can be overcome with work and $$$'s is small valves and small ports. The 340/360 heads have bigger of both when teemed with a good intake, 4 barrel. decent sized cam, headers and the like will produce good power. The cam will tell you when (RPM) . Thinking in a compression direction, a close to zero deck 318 with the closed chambered 920 heads can make more power as well but not as much as the big valve/big port heads do. This combination is better for a mild street engine where big HP/RPM numbers aren't wanted.
Click to expand...
What are 920 heads and what do they come from (model/years)?
 
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