[cgeise]

Originally Posted by john marcella

Cast iron sucks, I want heat in the cyl not the head. JMO

Real question, why don't most OEM still use iron heads?

I think you will find that answer to be - WEIGHT

[cfmcnc]

Originally Posted by john marcella

Cast iron sucks, I want heat in the cyl not the head. JMO

Real question, why don't most OEM still use iron heads?

CAFE.Bill C.

[Aaron Quinton]

Iron keeps more heat in cylinder than aluminum. You like iron more than you think.

Oem's use aluminum for weight reduction to improve fuel economy. A good iron design can approach aluminum in mass.

Originally Posted by john marcella

Cast iron sucks, I want heat in the cyl not the head. JMO

Real question, why don't most OEM still use iron heads?

[mgarblik]

On an engine like our Pontiacs, a QUALITY GOOD FLOWING iron head would offer many advantages. The primary one being most head gasket sealing issues would go away due to the stiffness of the iron. We have been begging for a good iron head for over a decade! I think they would sell like the original run of Performer E heads. They would likely steal some sales from the aluminum heads though.

[Elarson]

Thermal conductivity of cast iron is in the range of 20-30 BTU/hr*ft2*degF.
Aluminum is 120-130 BTU/hr*ft2*degF.

So aluminum conducts heat away from the hot source 6 times as fast as cast iron.

If you want to retain heat (energy) in the chamber, cast iron wins.

Eric

[charlie66]

I think the aluminum is better for running pump gas at higher compression ratios...

[john marcella]

Originally Posted by Elarson

Thermal conductivity of cast iron is in the range of 20-30 BTU/hr*ft2*degF.
Aluminum is 120-130 BTU/hr*ft2*degF.

So aluminum conducts heat away from the hot source 6 times as fast as cast iron.

If you want to retain heat (energy) in the chamber, cast iron wins.

Eric

Hmmmm OK.

Seems like a lot when you look at it by percentages. BUT......................
There is 100 BTU/hr loss per ft2 with the aluminum. **OK** ,Ever check to see what that is really worth?

Well lets say a chamber has 18 square inches of surface area each ....X 8 =144 inch2
And 1 ft2 =144 inch2

100 BTU/hr = .03930 HP due to heat loss of the material. PER FRICKIN HOUR. LOL

I will take the 50lbs reduction from the aluminum thank you

[Elarson]

Originally Posted by john marcella

Hmmmm OK.

Seems like a lot when you look at it by percentages. BUT......................
There is 100 BTU/hr loss per ft2 with the aluminum. **OK** ,Ever check to see what that is really worth?

Well lets say a chamber has 18 square inches of surface area each ....X 8 =144 inch2
And 1 ft2 =144 inch2

100 BTU/hr = .03930 HP due to heat loss of the material. PER FRICKIN HOUR. LOL

I will take the 50lbs reduction from the aluminum thank you

Back to math class for you. You left out the calculation of temperature difference. Assume the combustion surface of the cylinder head runs at 400 degF. Select 150 degrees on the water side of the aluminum.

.03930 hp x (400-150) = 9.8 horsepower (an approximation since I had to guess at inner temperature)

Eric

[BruceWilkie]

Originally Posted by charlie66

I think the aluminum is better for running pump gas at higher compression ratios...

Thats because of the heat rejection... lower octane fuel, like pump gas... burns at a faster than race gas.
Less heat in chamber... slower burn rate...
Analogy...throw a log on a small pile of burning twigs... takes some time to get that log consumed...throw the same size log on a large hot fire and it is consumed quickly. Similar energy got released from similar log.

Octane itself is combustion control(burn rate) not energy content!

Early to mid fifties pump premium was 87 octane! 11:1+ compression was methanol territory. The early hemi's were a big step in that regular 77+octane fuels would work where typically only 85-87 octane would have been required at same compression. 8.5:1 compression WAS a big deal back then. (My 55 Starcheif 287 2 barrel... with automatic... premium fuel of 87 octane or better was what the owners manual recommended... compression was around 8.5:1!!!

Fast forward... some aluminum headed race motors on 116 octane fuel run 15:1 or more compression... if iron heads probably 14:1 or so would be pushin compression limit... octane is why.

With both materials at edge of octane tolerance... you are probably going to see same hp...

John gets the correct conclusion with the wrong math... Aluminum wins...because its lighter and easier to work.

[john marcella]

Originally Posted by Elarson

Back to math class for you. You left out the calculation of temperature difference. Assume the combustion surface of the cylinder head runs at 400 degF. Select 150 degrees on the water side of the aluminum.

.03930 hp x (400-150) = 9.8 horsepower (an approximation since I had to guess at inner temperature)

Eric

Ok, say we go with the 9.8. Isnt that loss per hour? And at constant energy input. Our motors have 4 events and only 1 of those is producing power or heat so......9.8 divided by 4 =2.45 and that's per hour correct?
And my math for 2.45/hr converted to a 10.00 run would be a loss of .00680556 hp.

Thinking about it, in sure both our math is incorrect as there are many variables and temp that are changing during each cycle.
But at the same time , logic and quick rudimentary math all points to.............look for power somewhere else other than energy lost do to heat. At least for me.
JMO

[Elarson]

No. Horsepower is already time-based so you don't divide by time again.

The assumed 400 degree material temp is a running average of all events in the 4 cycles. Combustion temps at 2500-ish. Exhaust stroke at 1400-ish. Intake event at atmospheric temp. Compression at a few hundred degrees. So the 9.8 hp heat loss rate is an a average rate. The heat sink ability of the head metal averages it all out.

The 9.8 is based on some temperature assumptions. Put a tolerance of +/- 50% on that and you have a 5-15 hp range. That might be important in some cases and not in others.

And the other factors mentioned (machineability and weight) have to be factored in. Every engine is a compromise.

Eric

[john marcella]

Originally Posted by Elarson

No. Horsepower is already time-based so you don't divide by time again.

The assumed 400 degree material temp is a running average of all events in the 4 cycles. Combustion temps at 2500-ish. Exhaust stroke at 1400-ish. Intake event at atmospheric temp. Compression at a few hundred degrees. So the 9.8 hp heat loss rate is an a average rate. The heat sink ability of the head metal averages it all out.

The 9.8 is based on some temperature assumptions. Put a tolerance of +/- 50% on that and you have a 5-15 hp range. That might be important in some cases and not in others.

And the other factors mentioned (machineability and weight) have to be factored in. Every engine is a compromise.

Eric

Hmmm, now this is making sense.
You are right about not not dividing by time again. My bad. After you explained your numbers I don't think I can disagree with anything in that post.

See I will admit when im wrong

[Elarson]

I enjoy a respectful technical conversation. And I have been wrong my fair share of times.

"Most good judgment comes from experience and most experience comes from bad judgment". author unknown

Eric

[cgeise]

Who is that posting stuff using Johns name - ??????????

[john marcella]

Originally Posted by cgeise

Who is that posting stuff using Johns name - ??????????

LOL

[john marcella]

Originally Posted by Elarson

I enjoy a respectful technical conversation. And I have been wrong my fair share of times.

"Most good judgment comes from experience and most experience comes from bad judgment". author unknown

Eric

This is the fast way to learn, have a discussion with multiple points of view. Throw in a calculator and different personal experiences and experiments and , WALA. We are all smarter ,until we figure out that we all had it all phucked up from the start. And then you do it again. LOL

[johnta1]

I think the aluminum is better for running pump gas at higher compression ratios...

It’s a fact that an aluminum head dissipates (gets rid of) heat much faster than an iron head. The rapid heat loss from the combustion chamber results in reduced combustion chamber pressures (heat equals pressure); similar to the effect that lowering the compression ratio lowers cylinder pressure.

If no compression ratio increase is used, the power (HP) from the aluminum head will be less. (with the same cfm flowed on head)

So, usually the CR is increased to get back to the efficiency that was lost from the heat loss.
If the head also flows more it will gain even more HP.

WHOA!

Now if that heat is kept in the combustion chamber where it can make more HP and not being lost to the cooling/exhaust system, one could gain significant HP.

Sounds about like that coating piston tops/chambers argument.

See I will admit when im wrong

Only if Stan or I didn't write it.

This is the fast way to learn, have a discussion with multiple points of view. Throw in a calculator and different personal experiences and experiments and , WALA. We are all smarter ,until we figure out that we all had it all phucked up from the start.

Kind of like I said before, I can lead one to the calculators/knowledge but I can't make him learn.

[charlie66]

So what do you guys say the compression ratio limit is with a iron head on e85?

It will be fun to hear the different opinions on this..

[Region Warrior]

Sounds like coating the chamber on aluminum heads would help make more power.

[mike leech]

Originally Posted by johnta1

It’s a fact that an aluminum head dissipates (gets rid of) heat much faster than an iron head. The rapid heat loss from the combustion chamber results in reduced combustion chamber pressures (heat equals pressure); similar to the effect that lowering the compression ratio lowers cylinder pressure.

If no compression ratio increase is used, the power (HP) from the aluminum head will be less. (with the same cfm flowed on head)

So, usually the CR is increased to get back to the efficiency that was lost from the heat loss.
If the head also flows more it will gain even more HP.

WHOA!

Now if that heat is kept in the combustion chamber where it can make more HP and not being lost to the cooling/exhaust system, one could gain significant HP.

Sounds about like that coating piston tops/chambers argument.





Only if Stan or I didn't write it.





Kind of like I said before, I can lead one to the calculators/knowledge but I can't make him learn.

Patch together an intelligible comment that supports your claim then. Still waiting for "someone" to post those "results". And no posting info from the company selling it doesn't count.

The only reputable support I've gotten for its use was as a friction modifier and for restoring piston skirt clearance.