Aluminum heads on a "stock" B/RB engine

[Bad B-rad]

I have a question about aluminum heads, for arguments sake lets say the 440 source ones.

I picked these heads because they are a copy of the stock heads, so the ports and combustion chamber are closer to stock heads vs edelbrock, or Trick Flow ones


If someone installed these heads on a basically stock 68-70 B/RB engine, running the Magnum/Roadrunner cam, would any real noticeable power be gained?
Or will most of the performance potential of aftermarket aluminum heads come from the better flowing port design, and or combustion chamber design?



I have always gone by the rule that the aluminum heads disperse heat so much faster then cast iron, that when building an engine, if using aluminum heads you can go a full CR point higher then you would with cast iron.
If this is true, would a stock 68-70 B/RB engine, "act" like it lost a point of compression installing the aluminum heads in place of cast iron, again if not changing camshaft?

I

 

[Jerry Hall]

watching. I'm interested in the opinions and facts.

 

[Bad B-rad]

Side note: With aluminum intake manifold, and water pump + housing, and heads, you can drop 100+lbs off the nose, of car. Your can even paint them to match so it looks stock. Toss in headers vs the cast iron exhaust manifolds, if you don't care about stock look, and you can save some more weight.

All that is just an added bonus, but not why I was inquiring about the aluminum heads on a stock engine.

 

[Sahara]

I ‘m watching with interest because I’ve heard the same thing about compression re: aluminum heads.

 

[Jackpot50]

You will not loose a point on compression with aluminum heads, but you could bump up compression a point on an not get engine knock on lower octane gas.

 

[Bad B-rad]

Jackpot 50:
I understand you don't "LOSE" a point of compression.
(as long as chamber size is the same)
I am asking if a stock 68-70 B/RB would see any performance gains by just swaping heads, aluminum from cast iron, or would the engine preform as if it LOST a point of compression due to the rapid heat dissipation, of the aluminum heads.
Or perhaps it would act exactly the same as the cast iron?

Lets also clarify that in this theoretical scenario, the combustion chambers are the same size, between the iron and aluminum and ports are the same.

 

[Kern Dog]

Port flow means more of a gain than a 1 point loss of compression would cost you, just to make a comparison.

The aftermarket heads all seem to flow better than the stock NON Max Wedge heads. Even the 440 source heads. They are marketed as a stock appearing head but they do flow more air than a stock head.

 

[origcharger]

Not likely to use an OEM style steel shim gasket with aluminum heads either.....

I can tell you that my 76 low comp 440 with pistons down approx .140 in the hole, 440 source heads and composition head gaskets still gets the job done quite well.

 

[Bad B-rad]

Port flow means more of a gain than a 1 point loss of compression would cost you, just to make a comparison.

The aftermarket heads all seem to flow better than the stock NON Max Wedge heads. Even the 440 source heads. They are marketed as a stock appearing head but they do flow more air than a stock head.

Well that makes it a much harder thing to test.


Would a stock B/RB benefit from that added flow?
And what gains would one expect from them?
Anything one would notice, in MPG, or seat of the pants power?

I understand that a modern cam, or a bigger cam, then the stock one, would take a larger advantage of that flow improvement. But for this discussion, I was only talking about stock.

 

[Bad B-rad]

I can tell you that my 76 low comp 440 with pistons down approx .140 in the hole, 440 source heads and composition head gaskets still gets the job done quite well.

So then the added flow of the heads made a large change?
Did you keep the same cam?

 

[Kern Dog]

The numbers that I have heard being tossed around were around 30 HP on a stock 383 Magnum and between 35-40 HP on a 440 Magnum.
This is assuming a stock cam and manifolds. Obviously, the gains increase with more cam, compression and improved scavenging of headers.

 

[Bad B-rad]

Wow, This blows my mind!!
I was always told, that the 906/452 head flow fine for stock to mildly modified engines.
So I wrongly was assuming that on a stock(ish) engine, used on the street, that it really would not benefit from larger ports.

 

[Bad B-rad]

I even had read that when larger ports are used, on a stock engine, that it would slow down the velocity of the incoming air/fuel mixture, having negative results on power.

That blows that theory out of the water, LOL!!!

You really can loose some weight, and gain some good power, with these heads alone, on a STOCK B/RB engine, sounds like really no drawback to this mod.
I was worried about the heat dissipation pulling away more power then they would add.

 

[Lelo 500]

I was worried about the heat dissipation pulling away more power then they would add.

The EngineMasters show did a test showing that to be false and aluminum heads always making more power even with everything else about the head being the same.

 

[Cranky]

Wow, This blows my mind!!
I was always told, that the 906/452 head flow fine for stock to mildly modified engines.
So I wrongly was assuming that on a stock(ish) engine, used on the street, that it really would not benefit from larger ports.

Generally, aluminum heads will not 'help induce' ping as readily as cast iron since they do dissipate heat faster but they still run hot enough to not reduce power. Yes, heat helps make power too but too much can cause detonation but so does a lazy combustion chamber.....high heat and a lazy chamber together is even worse and that's where the better heads come into play. One down side is that you should run a composite head gasket so you are pretty much doubling the gasket thickness vs the stock steel shim gaskets. Thicker gaskets generally increases quench distance which isn't what you want do to but in many cases, it's not enough to make much of a difference unless your quench distance is already lousy. Pages and pages of info on all this technology (old and new) has been written and what little bit I stuck in here is a very small tidbit. And there are others here that make plenty of power using the old school stuff without ping issues and I have too in the past.....IQ52 is just one of the many here that know how to do it and DVW is another but you can go into the racers hangout and find many others too.

 

[cbodybob]

Not likely to use an OEM style steel shim gasket with aluminum heads either.....

I can tell you that my 76 low comp 440 with pistons down approx .140 in the hole, 440 source heads and composition head gaskets still gets the job done quite well.

What head gaskets are you using & what compression ratio did you end up with.

 

[BSB67]

If someone installed these heads on a basically stock 68-70 B/RB engine, running the Magnum/Roadrunner cam, would any real noticeable power be gained?
Or will most of the performance potential of aftermarket aluminum heads come from the better flowing port design, and or combustion chamber design?

You've given so little info. Please tell us a little more about this "basically stock" engine. After 50 years, there are very few stock engines. Usually someone has been in them before and made some changes. If you are not the original owner, or have not owned the car/motor for 35 years, be skeptical that the motor is stock.

What is the engine size?
What is the measured compression ratio?
What is the cranking cylinder pressure?

Generally speaking, factory heads with unknown detailed history are likely weak performance wise, and any new aftermarket aluminum head will give a noticeable boost in power.

 

[33 IMP]

My research says the stock 906/346/452 heads fl9w in the low 200s (215-225 cfm) and can be under 200 with a bad valve job. The source heads appear to flow around 255/265 and the rpm around 280 cfm. So considerable power increase is possible.
But... I don't know how well the stock intake flows, or how much the manifolds would cost power, compared to headers.
Imho, 25 to 30 up, with the stone stock stuff, 60 to 100 with a good intake and carb and headers, and maybe another 50 with a cam swap.

 

[451Mopar]

Most of the aluminum heads have smaller chambers than the stock heads which should boost compression. Look at the Edelbrock E-Street heads too.
They also have larger valve sizes than stock, smaller 11/32" valve stems, are stainless steel with single groove valve locks.
Being aluminum, they have hardened seats installed.
Springs should be OK for most mild hydraulic flat tapped cams.
You will need the matching cylinder head bolt kit (reduced wrenching size) also.

The original heads in untouched form don't flow very well, but can be modified to flow very well, but the cost can end up being more expensive than the aluminum heads.

 

[wish4hemi]

Relevant reading material from the Hughes Engines Tech Center. Several here have mentioned cylinder pressure and it’s something they detail pretty well.

https://moparconnectionmagazine.com/hughes-engines-tech-center-got-me-under-pressure/