OK, I was listening to some bench racers last night and heard one say that if alluminum heads were used on a motor, it actually drops a point or percentage in compression ratio. His engine builder is from Texas, so it is law to him. Am I missing the boat here or is this true? :beers:
nikkisdad
the material that a head is made out of will not effect compression ratio. combustion chamber volume, head gasket, piston shape and piston depth in the hole will.
Many feel that you can run higher static compression ratio with aluminum heads as compared to cast iron without detonation. IMO the jury is still out on that.
Many feel that you can run higher static compression ratio with aluminum heads as compared to cast iron without detonation. IMO the jury is still out on that.
Are you from Texas too?
"compression ratio" which refers to an engines static compression ratio, is a mathematical formula based on the volume.
The material used has NOTHING to do with it.
Even "dynamic compression" which puts the cam events into the equation, is not affected by materials used.
As Steve pointed out, some have said an alluminum headed engine may be more resistant to detonation due to more heat transfer, this (if true) has nothing to do with measured and calculated compression ratio.
As a general rule of thumb, engines with aluminum cylinder heads can tolerate one full point of compression more than an engine with cast-iron heads.
The reason for this difference is that compression ratio equates to heat, and aluminum heads tolerate and rid heat better and faster than cast iron.
The reason for this difference is that compression ratio equates to heat, and aluminum heads tolerate and rid heat better and faster than cast iron.
Well , ya cant always believe how Texans esplain dat, But I thank what he wus saying or meant to say, you could get away wif a point more due to alloy heads and heat dissapation. . Dats da way I learned it in ma Texas cowchip hand manual. Some times we think and talk in two differant minds.
On the other hand if that Texan in Utah was right, then the hotter i got the motor, the more compression I would have? Huh?
On the other hand if that Texan in Utah was right, then the hotter i got the motor, the more compression I would have? Huh?
i've noticed that a lot of aluminum small block heads seem to have a 70cc or so chamber volume- which would be a compression increase if you swapped out later model 76cc heads, and a decrease if you were replacing older 64cc heads.
personally, i want a set of 50cc aluminum heads to use with some flat tops and thin gaskets for a "flex fuel" E85/pump gas motor.
personally, i want a set of 50cc aluminum heads to use with some flat tops and thin gaskets for a "flex fuel" E85/pump gas motor.
OK not start a stupid argument but here are the facts. Compression Ratio is just that. I measure of the volume at BDC and TDC as expressed in a ratio. Asuuming the identical chamber the material is irrelevant. So basically the asnwer is NO the Material alone has no efffect on the actual compression ratio.
Now in support of what is being stated above the heat disapation that aluminum provides. will aloow for higher compression without denotation.
BTW I cant spell or type so please bear with me.
Now in support of what is being stated above the heat disapation that aluminum provides. will aloow for higher compression without denotation.
BTW I cant spell or type so please bear with me.
i've read that if you were to have 2 sets of heads with identical ports, valves, coolant jackets, and chambers- but one pair was aluminum and theo ther iron- the iron heads wuld make more power due to holding more heat in the chamber.
the advantages of aluminum heads are that you can run a higher static compression ratio, they are lighter, and they can be easily fixed by anyone that knows how to tig weld if they do crack or get otherwise damaged.
the advantages of aluminum heads are that you can run a higher static compression ratio, they are lighter, and they can be easily fixed by anyone that knows how to tig weld if they do crack or get otherwise damaged.
Aluminum cools how much faster than iron?
Heat both pieces to 300º take the heat off and grab them both 15 seconds later.
Aren't they both hotter than heck? Doubt you'd see 5º difference in temps.
Aluminum heads are not some NASA Ceramic that dissipates heat in nanoseconds!
An engine at 6,000 rpm is firing 50 times per second. Just how quickly does that heat in the cylinder dissipate? Aluminum vs Iron equals absolutely no difference in combustion efficiency, detonation suppression or the ability to handle more or less compression.
Heat both pieces to 300º take the heat off and grab them both 15 seconds later.
Aren't they both hotter than heck? Doubt you'd see 5º difference in temps.
Aluminum heads are not some NASA Ceramic that dissipates heat in nanoseconds!
An engine at 6,000 rpm is firing 50 times per second. Just how quickly does that heat in the cylinder dissipate? Aluminum vs Iron equals absolutely no difference in combustion efficiency, detonation suppression or the ability to handle more or less compression.
Disagree Tom. So did Smokey Yunik. (did I spell his name right) Anyway, back in the sixties he thought highly of BBC aluminum heads but he maintained that they didn't hold heat as well as iron so they didn't make as much power, all factors being equal. His solution was to seal the combustion chamber side of the water jacket with that stuff used to preserve eggs. I forget the name of it but it's sorta like a jell. When it setup, it would hold the heat in the chamber better than untreated heads. But he didn't say if it was equal then, to iron.
The heat "losses" from running the aluminum heads is far greater than when using the cast iron ones. This fact has been known by many of the best builders in the business for some years now.
Due to the "thermal-inefficiency" of the aluminum much of the "charge" is dissipated/absorbed by the heads instead of being retained/reflected as power gains.
This fact goes back to the days when Bill Mitchell (and some others) started the foundry to produce the iron heads. To this day it's the reason many of the aftermarket cylinder head manufacturers use the cast iron as their platform along with the somewhat lower pricing.
Again, this is the also the reason you can run some higher "static" numbers (with aluminum) as the material helps to reduce the point of detonation.
Thanks, Gary in N.Y.
P.S. Here's an interesting post from another forum putting this in a little "easier to understand" perspective: (the "highlighted red" pertains to this discussion)
(Quote) T/F blocks are billet blocks and are five time stronger than cast blocks. Its an apple and Oranges comparison.
And talk about Apple and Oranges comparisons.
Are we forgetting that the1000hp units are Turbo charged? The pressure rise in the combustion chamber with a turbo is much smoother, there is no overlap and the piston is always in compression. The dynamic forces in the crank case are so smooth and the loading is not as unidirectional so a block that would crack down he middle in a normally aspirated engine will make 500 to 600 more horsepower with a Turbo and live ten times longer! Hit one of those things with nitrous and make 1000hp and your block wont make it to half track. Nitrous has a pressure rise in the chamber that makes dynamite seem slow. I am kidding of course but you got the mental image didnt you. I have LITERALLY cut blocks in half with Nitrous. With a turbo on the same engine combination you can build another 500 to 800hp and never hurt the block.
What I am trying to say is whether the block lives or dies has more to do with way the power is being produced than the power level itself.
On another note,
A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power.
There are ways to help out the situation in order to minimize the losses but you will always be down a little with an aluminum block. Billet blocks seem to minimize the losses more than anything else. Thick cylinder walls will help but that limits over all power by limiting valve size so your really screwed coming or going.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
(End quote)
FAX-468-3147
Due to the "thermal-inefficiency" of the aluminum much of the "charge" is dissipated/absorbed by the heads instead of being retained/reflected as power gains.
This fact goes back to the days when Bill Mitchell (and some others) started the foundry to produce the iron heads. To this day it's the reason many of the aftermarket cylinder head manufacturers use the cast iron as their platform along with the somewhat lower pricing.
Again, this is the also the reason you can run some higher "static" numbers (with aluminum) as the material helps to reduce the point of detonation.
Thanks, Gary in N.Y.
P.S. Here's an interesting post from another forum putting this in a little "easier to understand" perspective: (the "highlighted red" pertains to this discussion)
(Quote) T/F blocks are billet blocks and are five time stronger than cast blocks. Its an apple and Oranges comparison.
And talk about Apple and Oranges comparisons.
Are we forgetting that the1000hp units are Turbo charged? The pressure rise in the combustion chamber with a turbo is much smoother, there is no overlap and the piston is always in compression. The dynamic forces in the crank case are so smooth and the loading is not as unidirectional so a block that would crack down he middle in a normally aspirated engine will make 500 to 600 more horsepower with a Turbo and live ten times longer! Hit one of those things with nitrous and make 1000hp and your block wont make it to half track. Nitrous has a pressure rise in the chamber that makes dynamite seem slow. I am kidding of course but you got the mental image didnt you. I have LITERALLY cut blocks in half with Nitrous. With a turbo on the same engine combination you can build another 500 to 800hp and never hurt the block.
What I am trying to say is whether the block lives or dies has more to do with way the power is being produced than the power level itself.
On another note,
A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power.
There are ways to help out the situation in order to minimize the losses but you will always be down a little with an aluminum block. Billet blocks seem to minimize the losses more than anything else. Thick cylinder walls will help but that limits over all power by limiting valve size so your really screwed coming or going.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
(End quote)
FAX-468-3147
On another note,
A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
(End quote)
FAX-468-3147[/quote
There you have it..courtesy of gofast and Reher -morrison.Add this to your rolodex of life.Good stuff.:thumbsup:
A cast iron block with cast iron heads will make more power than any other combination.
A cast iron block with aluminum heads will make less power.
An aluminum block with aluminum heads will make even less power.
_________________
Darin Morgan
R&D-Cylinder Head Dept.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
(End quote)
FAX-468-3147[/quote
There you have it..courtesy of gofast and Reher -morrison.Add this to your rolodex of life.Good stuff.:thumbsup:
The loss of power from the extra heat dissipation is less than the extra power you get from running 1 point higher compression ratio, this is ignoring the weight savings. This is assuming that the heads are exactly the same, but aluminum are usually considered higher end and there are more options from Dart/Brodix in aluminum than old iron.
I like thisun (that's Tex-Okie, y'all). I get to use a little of what happens in my line
of work here.
Some rambling preamble
Ramble 1. Aluminum dissipates heat faster than iron based metal.
Evidence A. The metal of choice for electronics heat sinking is aluminum
Evidence B. Try to cut a hunk of aluminum with a torch, better have plenty of gases cuz
you'll be there awhile.
Ramble 2. The objective of internal combustion is primarily pressure. Of course heat is
work, but a piston can't harness heat except to expand. Work= Force times Area. Increase
the Force(Pressure) on the same area and you do more Work.More inter-relationship than
that but I'm trying for brevity, and I suck at brevity so cut me some slack. I'll get back
to this anyway.
Ramble 3. I thought higher quality aluminum heads had thicker decks to handle increased
pressure from power adders. The cast heads don't have to do this because CI is stronger in
a same thickness scenario. But there may be a heat benefit to it as well, and I'll get
back to that too.
Ramble 4..... Time. Somebody brought that up and it is crucial, it plays a part in more than
just material selection. I don't know how to tie the two together but as alluded at 6000
RPM you fire 5 times per second, how much heat can exchange in that short window eludes me
but it comes back to what else happens at higher rpm. Our engines breathe different and
the affect of big cams has less affect on DCR. Like I say I don't know how to tie the 2
together or how much part either one plays, but both exist.
Done rambling now, and try to tie some of it together...
Anyhow, if we are after pressure how does temperature affect us?
In Gas Compression we use 3% as a rule of thumb for pressure loss in intercooling, and
that is from 300 to 120°F. It's just a rule of thumb and has some slop in it.
We use the Gas Laws to be able to predict what will happen inside a machine in regard to the relationship of Pressure/Volume/Temperature(PVT).
There's lots
of Gas Laws, Charles', Boyles', The Ideal Gas Law, and the one I normally use is called
the Combined Gas Law(but it becomes Gay-Lussac's Law and works if the piston is not
moved and the volume of the cylinder is constant).Y'all can look them up on the internet, they are fun to play with and I am
fortunate in that I get to see them in practice everyday at work. You have to convert to
Kelvins for temperature, which is just celsius plus 273. Idunno what a gasoline engine
runs temp wise so I used what I know from big natural Gas engine pyrometers under heavy
load, 1200° for T1 and 1100° for T2. And I just input 180# for pressure as P1. P2 is
calculated and is the affect of changing temp at a constant volume.
180/922= X/866
X= 169#
gay lussac Law p1/t1=p2/t2
Combined Law
(p1v1)/t1=(p2v2)/t2
This ASSUMES aluminum heads would lower your temp in the chamber by 100°.
Who knows. I think this is where TIME, and deck thickness would come into play.
At higher rpm you have less TIME to transfer heat, and if the head deck is thicker it will
exchange heat less effectively(to my head).
So, let's say we only knock 25°F off
180/922= X/908
X= 177.3#
I guess it depends on how much you think the aluminum sucks out of the combustion heat.
I've been windy enough for now. Time to get off my butt and go play.
No, I have to add this. Because it's where I was aiming to begin with.....As the volume of the cylinder increases as the piston travels, 2 important things happen. The pressure must fall or the temperature must fall, or one can change more than the other. But if volume increases something else WILL CHANGE. We know this intuitively but it is in the Laws.
The fact that we know our pyro temps can approach the melting points of metals, coupled with the knowledge that temp or pressure MUST fall as volume increases and that the exhaust port is not exposed to exhaust gases until AFTER the cylinder has attained close to full volume pretty much eliminates the heat transfer to the head having anything more than a few degrees difference in addition to telling us that temp couldn't have been much higher at the onset. Stands to reason we gained volume, lost pressure, and temperature stayed fairly constant.To my head anyway.
Of course the exhaust gas temp is not the piston, head, or liner temp. That's why we cool those pieces. If an aluminum piston hit much over 400° it would squeek.
of work here.
Some rambling preamble
Ramble 1. Aluminum dissipates heat faster than iron based metal.
Evidence A. The metal of choice for electronics heat sinking is aluminum
Evidence B. Try to cut a hunk of aluminum with a torch, better have plenty of gases cuz
you'll be there awhile.
Ramble 2. The objective of internal combustion is primarily pressure. Of course heat is
work, but a piston can't harness heat except to expand. Work= Force times Area. Increase
the Force(Pressure) on the same area and you do more Work.More inter-relationship than
that but I'm trying for brevity, and I suck at brevity so cut me some slack. I'll get back
to this anyway.
Ramble 3. I thought higher quality aluminum heads had thicker decks to handle increased
pressure from power adders. The cast heads don't have to do this because CI is stronger in
a same thickness scenario. But there may be a heat benefit to it as well, and I'll get
back to that too.
Ramble 4..... Time. Somebody brought that up and it is crucial, it plays a part in more than
just material selection. I don't know how to tie the two together but as alluded at 6000
RPM you fire 5 times per second, how much heat can exchange in that short window eludes me
but it comes back to what else happens at higher rpm. Our engines breathe different and
the affect of big cams has less affect on DCR. Like I say I don't know how to tie the 2
together or how much part either one plays, but both exist.
Done rambling now, and try to tie some of it together...
Anyhow, if we are after pressure how does temperature affect us?
In Gas Compression we use 3% as a rule of thumb for pressure loss in intercooling, and
that is from 300 to 120°F. It's just a rule of thumb and has some slop in it.
We use the Gas Laws to be able to predict what will happen inside a machine in regard to the relationship of Pressure/Volume/Temperature(PVT).
There's lots
of Gas Laws, Charles', Boyles', The Ideal Gas Law, and the one I normally use is called
the Combined Gas Law(but it becomes Gay-Lussac's Law and works if the piston is not
moved and the volume of the cylinder is constant).Y'all can look them up on the internet, they are fun to play with and I am
fortunate in that I get to see them in practice everyday at work. You have to convert to
Kelvins for temperature, which is just celsius plus 273. Idunno what a gasoline engine
runs temp wise so I used what I know from big natural Gas engine pyrometers under heavy
load, 1200° for T1 and 1100° for T2. And I just input 180# for pressure as P1. P2 is
calculated and is the affect of changing temp at a constant volume.
180/922= X/866
X= 169#
gay lussac Law p1/t1=p2/t2
Combined Law
(p1v1)/t1=(p2v2)/t2
This ASSUMES aluminum heads would lower your temp in the chamber by 100°.
Who knows. I think this is where TIME, and deck thickness would come into play.
At higher rpm you have less TIME to transfer heat, and if the head deck is thicker it will
exchange heat less effectively(to my head).
So, let's say we only knock 25°F off
180/922= X/908
X= 177.3#
I guess it depends on how much you think the aluminum sucks out of the combustion heat.
I've been windy enough for now. Time to get off my butt and go play.
No, I have to add this. Because it's where I was aiming to begin with.....As the volume of the cylinder increases as the piston travels, 2 important things happen. The pressure must fall or the temperature must fall, or one can change more than the other. But if volume increases something else WILL CHANGE. We know this intuitively but it is in the Laws.
The fact that we know our pyro temps can approach the melting points of metals, coupled with the knowledge that temp or pressure MUST fall as volume increases and that the exhaust port is not exposed to exhaust gases until AFTER the cylinder has attained close to full volume pretty much eliminates the heat transfer to the head having anything more than a few degrees difference in addition to telling us that temp couldn't have been much higher at the onset. Stands to reason we gained volume, lost pressure, and temperature stayed fairly constant.To my head anyway.
Of course the exhaust gas temp is not the piston, head, or liner temp. That's why we cool those pieces. If an aluminum piston hit much over 400° it would squeek.
Kelvins? What happened to Rankin? Still a good topic Tim. Been a long time since I messed with supercompressorablility issues. I am thinking , the temp and the time that it is exposed at each stroke, so its the same process on each stroke, from intake to discharge. Increasing compressor speed then moves the gas in and out quicker, i am thinking less time for heat to soak before discharge.
I think we have two differant processes here, making hp and using what the prime mover is applying. What ever, no need to get into this. Gonna mess up our readers.
Waited all week for you to chime in on this,,, In event you did not razzle/ dazzle the audiance (sp) with brillance, you may have baffled them with bs. You are good on your theories.
I think we have two differant processes here, making hp and using what the prime mover is applying. What ever, no need to get into this. Gonna mess up our readers.
Waited all week for you to chime in on this,,, In event you did not razzle/ dazzle the audiance (sp) with brillance, you may have baffled them with bs. You are good on your theories.
Ah bin watchin', Don.
The Gas Laws are not BS. They work. Driver or driven, don't matter. Gas is gas. The only wildcard is how far down the hole you think combustion continues.
The only way I'll back off on what their application provides herein is if I see a dyno result showing pyro temps falling when a cast to aluminum head swap of otherwise identical heads is performed. And then if I see that dyno comparison with EGT's I can tell you how much pressure was changed. Because on that apple/apple comparison length of combustion is negated. And that is the scenario I addressed.
Either that or I've left myself wide open for someone to come along and teach me something about engines. And that would be good too. I'm here to learn and share. Hope I don't come across wrong, I know I'm an aggressive bastard.
Kelvin is Rankin for Celsius, both are absolute scales.
F plus 460 = C + 273
I sometimes use units that are strange. Sorry, I wasn't trying to obscure or BS when I used Kelvins or applied the Gas Laws, it just didn't occur to me that people weren't used to it because I live in a world of pressure and temperature and volume.
The Gas Laws are not BS. They work. Driver or driven, don't matter. Gas is gas. The only wildcard is how far down the hole you think combustion continues.
The only way I'll back off on what their application provides herein is if I see a dyno result showing pyro temps falling when a cast to aluminum head swap of otherwise identical heads is performed. And then if I see that dyno comparison with EGT's I can tell you how much pressure was changed.
Because on that apple/apple comparison length of combustion is negated. And that is the scenario I addressed.Either that or I've left myself wide open for someone to come along and teach me something about engines. And that would be good too. I'm here to learn and share. Hope I don't come across wrong, I know I'm an aggressive bastard.
Kelvin is Rankin for Celsius, both are absolute scales.
F plus 460 = C + 273
I sometimes use units that are strange. Sorry, I wasn't trying to obscure or BS when I used Kelvins or applied the Gas Laws, it just didn't occur to me that people weren't used to it because I live in a world of pressure and temperature and volume.
eeek. I though this post was about compression ratio?
Now the engineers are getting in on the action, everyone duck!
Now the engineers are getting in on the action, everyone duck!
and what this post has really drifted into is deonation resistance, cause that's what it is all about. You see, our engines are better than our fuel, or at least they are limited by fuel. Look what happens when we remove that limitation:
How 'bout a fuel dragter? 5000 HP from 500 cubic inches. The fuel is the oxidizer, it's the coolant, AND it's the fuel! I gotta get me some o that stuff!
Do alluminum heads enhance the detonation resistance of a pump gas motor?
I dunno. But when I switch from iron to alluminum heads this winter,I'm gonna bump the static compression nearly a full point. Is that because I believe the magic alluminum will allow it? Is it because I believe my current combo is no where near the magic point where the heat / pressure generated by compbustion will cause the fuel to detonate? Or is it to make up for the additional 15 to 20 degrees of cam timing I'm gonna put in?
you pick. I dunno.
How 'bout a fuel dragter? 5000 HP from 500 cubic inches. The fuel is the oxidizer, it's the coolant, AND it's the fuel! I gotta get me some o that stuff!
Do alluminum heads enhance the detonation resistance of a pump gas motor?
I dunno. But when I switch from iron to alluminum heads this winter,I'm gonna bump the static compression nearly a full point. Is that because I believe the magic alluminum will allow it? Is it because I believe my current combo is no where near the magic point where the heat / pressure generated by compbustion will cause the fuel to detonate? Or is it to make up for the additional 15 to 20 degrees of cam timing I'm gonna put in?
you pick. I dunno.
I wanted to take it that direction with my first post, when I started talking about TIME.
Because they taught me many moons ago at Big Hairy *** Engine's That Break Expensive **** School, that time is the single easiest thing we can change to get out of detonation. Next is timing, load, heat, fuel, cr,etc.
Decrease TIME(by spinning faster) and detonation chances are lowered.
But like I said, I'm trying for brevity so cut me some slack.
Because they taught me many moons ago at Big Hairy *** Engine's That Break Expensive **** School, that time is the single easiest thing we can change to get out of detonation. Next is timing, load, heat, fuel, cr,etc.
Decrease TIME(by spinning faster) and detonation chances are lowered.
But like I said, I'm trying for brevity so cut me some slack.
Ah am watchin this answer too . We kinda got off topic base and Tim left me in the dirt on some of this as my knowledge on his bigger engines comes up to about his knee height.
But If all this really is true, on a curve, then why are we all switching to alloy heads? I can relate to Jim's question on the T/F or F/C engines as their compression is regulated by the blower or boost plus they burn a differant heated fuel.
So back to the the door slammer question, Are we not asking ourselves the right head questions when going to alloy? Could it be that most of us have gone to alloy for flow only and forgot about the heat issue? And thats something ready to install heads are made of, Aluminum? I can't recall many steel heads within our budgets that have been cast or Cnc'd to flow big numbers. Most all steel would have to be sent to a professional head porter. But then again , maybe its our duty to do just as Jim said, get the alloy head but work within the numbers to make up in compression for what we will lose in heat effeciencies?
But If all this really is true, on a curve, then why are we all switching to alloy heads? I can relate to Jim's question on the T/F or F/C engines as their compression is regulated by the blower or boost plus they burn a differant heated fuel.
So back to the the door slammer question, Are we not asking ourselves the right head questions when going to alloy? Could it be that most of us have gone to alloy for flow only and forgot about the heat issue? And thats something ready to install heads are made of, Aluminum? I can't recall many steel heads within our budgets that have been cast or Cnc'd to flow big numbers. Most all steel would have to be sent to a professional head porter. But then again , maybe its our duty to do just as Jim said, get the alloy head but work within the numbers to make up in compression for what we will lose in heat effeciencies?
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