J Heads vs Aluminum Heads

[340inabbody]

How much better is it having aluminum heads over Iron J’s with respect to thermal performance.

I know they will flow more but here in Phoenix we have shitty gas and very high temps.

 

[rumblefish360]

You can get away with another point to point and a half of compression and still run pump fuel.

In example, I run a 11.5-1, 360, Trickflow heads and a Hyd roller @226@050 on 93 octane.

Watch your timing. You will not require a lot of total timing under load.
(Floored gas pedal)

 

[Newbomb Turk]

How much better is it having aluminum heads over Iron J’s with respect to thermal performance.

I know they will flow more but here in Phoenix we have shitty gas and very high temps.

There is absolutely ZERO difference. I mean none.

If you have shitty fuel fix your tune up.

 

[340inabbody]

You can get away with another point to point and a half of compression and still run pump fuel.

In example, I run a 11.5-1, 360, Trickflow heads and a Hyd roller @226@050 on 93 octane.

Watch your timing. You will not require a lot of total timing under load.
(Floored gas pedal)

Another thing against me is that the best gas I can readily get is 91 Octane.

 

[340inabbody]

There is absolutely ZERO difference. I mean none.

If you have shitty fuel fix your tune up.

What about the larger exhaust port?

 

[Newbomb Turk]

Another thing against me is that the best gas I can readily get is 91 Octane.

That’s all I can get.

 

[Newbomb Turk]

What about the larger exhaust port?

I meant in how much compression you can use or detonate resistant.

Engine Masters did a test and to make the iron head look like it’s detonation prone they had to load an engine to the point it rattled and wouldn’t shut down.

Go watch it if you haven’t seen it.

When you are done if that’s how you drive your maximum compression ratio is 10:1.

I don’t drive like that. I don’t teach people to do that. If guys had to drive with a pyrometer and watch the EGT’s while they are driving and understood it they would never do what they did on the show.

 

[Oldmanmopar]

You'll get just as much money into freshening up your iron heads as the cost of new aluminum. I am going to run Iron X heads because it won't cost me anything to freshen and port them. Most of the customers that come here we tell them to buy new heads. Especially if they have no history of the heads they have. If you are doing a restoration then Iron it is. But make sure your heads were never surfaced past their limit to change intake angle.

 

[Newbomb Turk]

You'll get just as much money into freshening up your iron heads as the cost of new aluminum. I am going to run Iron X heads because it won't cost me anything to freshen and port them. Most of the customers that come here we tell them to buy new heads. Especially if they have no history of the heads they have. If you are doing a restoration then Iron it is. But make sure your heads were never surfaced past their limit to change intake angle.

Thats wasn’t exactly the OP’s question but you are correct. If you have nothing or the iron is worn out you just buy aluminum and don’t look back.

 

[rumblefish360]

Another thing against me is that the best gas I can readily get is 91 Octane.

A 10-1 ratio with an aluminum or iron head will be just fine with 91 octane and provide enough compression to use with some pretty hot cams for the street.

 

[rumblefish360]

What about the larger exhaust port?

The larger exhaust port is a plus
(and great if it flows well.)
If this is on a performance 5.9, I would suggest 1-3/4 headers with a performance cam.
1-5/8 will work very well for stock to moderate builds.