[frbformula]

For a moderate hp build lets just say 800hp. Is it better to go with a set of e heads or upgraded cast heads? What is more cost effective?

[v869tr6]

I have $1200 into a set of iron heads, all new valves and a exhaust valve for the heat of a turbo. Lite porting to about 230 at 0.500" lift. I needed D port exhaust to match the hot side headers I have.
Car hasn't run yet but it should make 800 HP no trouble.

[frbformula]

I have a nice set of aluminum heads on my N/A engine. I would have to have the chambers machined to lower the compression for a turbo. I was just wondering if there would be any reason to use iron heads over aluminum.

[charlie66]

either one will be good for your hp goals. i think the iron heads would be a better choice for reliability. i put a lot of bucks in my aluminum heads when I started going high in boost.i never tried steel heads but I bet they will hold the heat better for making power and there more ridged for clamping them down...

[taff2]

Iron heads have better clamping on the headgaskets for sure,but at 800hp it probably isn't going to be an issue anyway.

[Interceptor]

The better heat dissipation of aluminum heads will delay the onset of detonation.

[RUDOLFSSON]

Originally Posted by charlie66

either one will be good for your hp goals. i think the iron heads would be a better choice for reliability. i put a lot of bucks in my aluminum heads when I started going high in boost.i never tried steel heads but I bet they will hold the heat better for making power and there more ridged for clamping them down...

x2..

[TimeWarp]

Originally Posted by charlie66

either one will be good for your hp goals. i think the iron heads would be a better choice for reliability. i put a lot of bucks in my aluminum heads when I started going high in boost.i never tried steel heads but I bet they will hold the heat better for making power and there more ridged for clamping them down...

When you say more "ridged" I assume you mean more rigid? I know aluminum has different stretch properties than iron, but in a piece as thick as a head I'm not sure theres a measurable difference in straight line rigidity at the head surface between the two. Pretty sure it would take a lot more force than combustion to flex a head. If anything, I think under high boost you can potentially stretch the steel head bolts.

I've heard of some engines getting thicker bolts installed. Wonder if that can be done with the pontiac blocks?

[v869tr6]

A quick look at thermo expansion shows alum. to be over twice that of cast iron.
The alum. expands, crushes the head gasket over and over and then the gasket lets go.
I believe all of the turbo Pontiac engines with start crushing the top of the bolt hole in on the bolt with alum.
heads and that also causes the bolts to loose their clamp force.

http://www.engineeringtoolbox.com/li...ents-d_95.html

[TimeWarp]

yes, all good reasons to let the engine reach full operating temp before boosting. But I dont think the difference in clamping force is that different between hot and cold...we tighten the bolts at cold temp. Heated they should hold the gasket fine. But you are right about the bolt holes near the exhaust...which is why people are sleeving them.

Plenty of people running aluminum heads with boost and not having repeated gasket problems. As Charlie was saying in another post, I think the problems happen for other reasons, and the gaskets fail as a result of those other reasons.

[BruceWilkie]

Cast iron at running temp IS far stiffer than aluminum. Stays stiffer at temps far beyond what aluminum heads can handle.
It takes approximately one full point of compression MORE for aluminum to make the same power(ALL ELSE EQUAL) as iron.
Marty P was over 1600 HP from a 406 with ported iron heads. That was around 1993..he switched to aluminum and et improved slightly but never went faster mph that I'm aware of.

Plenty of power to be had with iron smog heads just keep compression in the 8-8.5:1 range.

[TimeWarp]

I really doubt the heads are flexing enough to blow head gaskets. But theres a huge difference between a set of ported iron heads flowing 230-250 and say a set of KRE high ports flowing 400 cfm in the ability to EFFICIENTLY produce power with boost. But yes, the iron heads are plenty for the original poster's goals.

[charlie66]

Originally Posted by TimeWarp

I really doubt the heads are flexing enough to blow head gaskets. But theres a huge difference between a set of ported iron heads flowing 230-250 and say a set of KRE high ports flowing 400 cfm in the ability to EFFICIENTLY produce power with boost. But yes, the iron heads are plenty for the original poster's goals.

The problem with the aluminum heads are the towers fail. If that didn't happen there would be know problem. I don't really think its the studs failing because before I changed my towers I went through 2 sets of ARP studs with the same failing results. What happens is as the tower crushes, the space between the block deck and the head deck surface becomes smaller in-between so now the set point between the nut and the head is too large. so with that said the bolt needs to be tightened down to maintain its toque. so its not the bolt failing, its the bolt needing to be tightened further down to maintain its original toque setting..

As for what Bruce said, I think he is 100% right. The aluminum head is good for all out performance not that the iron is not good for that ,its just it is easier with compression so you can use pump gas at higher levels of boost verse race gas.

As for the stiffness of a iron head , I don't think you will ever crush a tower in one of those.

[charlie66]

Originally Posted by v869tr6

A quick look at thermo expansion shows alum. to be over twice that of cast iron.
The alum. expands, crushes the head gasket over and over and then the gasket lets go.
I believe all of the turbo Pontiac engines with start crushing the top of the bolt hole in on the bolt with alum.
heads and that also causes the bolts to loose their clamp force.

http://www.engineeringtoolbox.com/li...ents-d_95.html

I think the head gasket does get damaged after awhile by the head crushing and lose of clamp force. Not from the expansion of aluminum head.. I believe the gasket fails because it loses the clamp needed to do its job.....

[Tom Vaught]

Originally Posted by BruceWilkie

Cast iron at running temp IS far stiffer than aluminum. Stays stiffer at temps far beyond what aluminum heads can handle.
It takes approximately one full point of compression MORE for aluminum to make the same power(ALL ELSE EQUAL) as iron.
Marty P was over 1600 HP from a 406 with ported iron heads. That was around 1993..he switched to aluminum and et improved slightly but never went faster mph that I'm aware of.

Plenty of power to be had with iron smog heads just keep compression in the 8-8.5:1 range.

Agree with the lightly ported cast iron head deal. Marty had a set of #62 Heads with some moderate porting (240+ cfm) to keep the head port passages/water jacket passages thick. (Marty's NA cast iron heads leaked water on the dyno when they were over 280 cfm (maybe 290 cfm).

I was helping Marty in pre-1996 and the Keens in 1998 so the time line is somewhat close as far as when Marty first started looking at Boosting (Maybe late 93 or 94 time frame as he did a bunch of covert testing with the car (chassis builder driving the car that first year) and everyone keeping the info to themselves.
Kind of like what Fulton is doing today.

Tom V.

ps All heads grow somewhat. How well the gasket follows the head is a big deal in retaining the combustion seal. Marty ran NO HEAD GASKETS and used a special sealing ring system so using his combo to describe durability of the cast iron vs aluminum head might be a bit off-track, Bruce.

[mgarblik]

This is a great thread once again that cries out loudly for the need to have one of the Pontiac vendors make a decent pair of IRON heads for this exact application. A 300 cfm iron head would be perfect. You could get away from all the negative aspects of aluminum heads, and there are plenty, and have the flow of a decent out-of -the box aluminum head. The sealing ability and structure of an iron head and even the cost savings. We have what, nearly a dozen great choices in aluminum heads now and ZERO in iron. Don't you think it's about time?

[charlie66]

Originally Posted by mgarblik

This is a great thread once again that cries out loudly for the need to have one of the Pontiac vendors make a decent pair of IRON heads for this exact application. A 300 cfm iron head would be perfect. You could get away from all the negative aspects of aluminum heads, and there are plenty, and have the flow of a decent out-of -the box aluminum head. The sealing ability and structure of an iron head and even the cost savings. We have what, nearly a dozen great choices in aluminum heads now and ZERO in iron. Don't you think it's about time?

I like that idea. They also should make a aluminum head with steel towers built in as well...

[70 bird]

800 hp. Iron heads with studs.

[Tom Vaught]

I would be a fan of a proper 300 cfm iron head for a Pontiac.

It could make any power level that the typical street or race guy would want with the average Centrifugal or Turbo Boosting device. When you can break into the 6s at 194 mph with a 406 cid engine and 240-260 cfm iron heads, that gives you a really good comparison for the value of the iron head.

Tom V.

[mgarblik]

The support column in aluminum heads will certainly crush in and cause a loss of clamp load on the head gasket. Tried the steel tube pressed in the aluminum and it helped some but did not solve the problem. The column itself needs to have enough wall thickness to handle the load. Insert step washers help with the crushing in at the top of the hole but is still a band aid. Iron head actually solves the problem if it is cast properly with a decent column diameter. I feel the biggest obstacle to an iron head is vendors being concerned it will steal sales from the more expensive aluminum heads, even though for many applications they would be far superior. Heavier, more difficult to repair and port, are the only real drawbacks. With proper design and good fuel they would make more power than aluminum by helping to keep the cylinder bores more straight and round, better thermal efficiency, and better gasket seal.