CR and pump gas question

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I would always run the closed chamber Edelbrocks over the open unless you NEED the open chamber heads (like with stock 340 pistons).

Aluminum heads dissipate heat much better than iron, that is why you can run more compression with aluminum heads and not run into detonation. Typically, you can get away with premium pump gas and 10.7:1 (even higher compression depending on cam selection).

Also to note, stroker motors eat up cam duration...meaning, you can run a larger cam and it will "act" like a smaller cam...if that makes sense (max power will be at a lower RPM than advertised).


It has never been proven that aluminum will tolerate more compression that iron will. Chamber geometry, plug location, cam timing all have way more affect on detonation than does head materiel.
 
I also hear that the 60779 run closer to 65-66cc than the advertised 62-63cc.
Mine measured out right at 63 cc's. IMHO, some measuring setups are sloppy and result in 1-2 cc's larger-than-reality measurements. For exmaple, if the sealing between chamber and plexiglass cover is .010" thick, it will add almost 2 cc's to an open chamber measurement
 
It has never been proven that aluminum will tolerate more compression that iron will. Chamber geometry, plug location, cam timing all have way more affect on detonation than does head materiel.
Mmmmmm..... heating of the mixture DOES play into detonation and a lot of that heat comes from the head. I came across a research article recently that found that a hotter mix burned more slowly. A more extended burn time (like with open chambers or large recesses or the plug waaaay off to the side) is a known contributor to detonation tendencies, due to the longer burn times.

So anything that lowers heat transfer to the mixture in the chamber should help. That includes being AL instead of iron with the lower thermal resistance and lower chamber surface temps. Not wanting to be disrespectful at all, but the idea that it not been proven does not seem (to me) to hold water; the general experience with AL heads all points that way. IMHO, the same applies for polished chambers: less heat transfer to the mixture.....less tendency to detonate.
 
Ah okay, that makes sense. Thanks for clearing that up. I got in contact with Hughes and they actually recommended I go up one camshaft to this Hughes Engines which surprised me. Would you say this should be just as good to go with 93? I figured that would be too much for the low end power I want, but they said that would work better for a stroker. Thanks for the help.
You're welcome.... From a DCR standpoint, it will have a slightly lower DCR so should be fine.
 
Mmmmmm..... heating of the mixture DOES play into detonation and a lot of that heat comes from the head. I came across a research article recently that found that a hotter mix burned more slowly. A more extended burn time (like with open chambers or large recesses or the plug waaaay off to the side) is a known contributor to detonation tendencies, due to the longer burn times.

So anything that lowers heat transfer to the mixture in the chamber should help. That includes being AL instead of iron with the lower thermal resistance and lower chamber surface temps. Not wanting to be disrespectful at all, but the idea that it not been proven does not seem (to me) to hold water; the general experience with AL heads all points that way. IMHO, the same applies for polished chambers: less heat transfer to the mixture.....less tendency to detonate.


I'd like to read that article. It goes counter to everything I've seen.

I should have also mentioned fuel in my above comments, and booster design. All those things have a much greater affect on detonation resistance than does head materiel.
 
yr booster design- don't tell all the secrets but I have heard that before
yes on opening the heads around the intake
I gave you big hints twice about who grinds Hughes cams
it used to be Engle
nm- post a link
yr does point out a lot of factors that have to all work together
and why backing off the static CR makes sense unless you are going to consider all the factors together- and some of them- like the cam timing- you do not have
 
It has never been proven that aluminum will tolerate more compression that iron will........

Actually, this is rather in basic metallurgy and thermodynamics.....I suggest you do some reading.

.......Chamber geometry, plug location, cam timing all have way more affect on detonation than does head materiel.
You are correct, all of these factors impact detonation...along with the head material....and many other factors.
 
Actually, this is rather in basic metallurgy and thermodynamics.....I suggest you do some reading.


You are correct, all of these factors impact detonation...along with the head material....and many other factors.

I've done the reading. And also the testing. Again, head materiel is about the last factor in compression ratio.

I can run just as much CR on iron as I can aluminum. It's that simple.
 
I've done the reading. And also the testing. Again, head materiel is about the last factor in compression ratio.

I can run just as much CR on iron as I can aluminum. It's that simple.

So having seen the aluminum vs iron tests I wanted to click 'Like' above but I went 'Agree' seemed to fit better. So down here, 'Like' 'Like' 'Like' 'Like'!

I too have had no problem running the iron
 
I would always run the closed chamber Edelbrocks over the open unless you NEED the open chamber heads (like with stock 340 pistons).

Aluminum heads dissipate heat much better than iron, that is why you can run more compression with aluminum heads and not run into detonation. Typically, you can get away with premium pump gas and 10.7:1 (even higher compression depending on cam selection).

Also to note, stroker motors eat up cam duration...meaning, you can run a larger cam and it will "act" like a smaller cam...if that makes sense (max power will be at a lower RPM than advertised).
It seems more like the combustion chamber in the aluminum heads has more to do with less detonation than the iron heads. Tests with the same combustion chamber shape in iron and aluminum have not confirmed the ability to run more compression. Nor does it show that the iron heads will make more horsepower.
 
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I'd like to read that article. It goes counter to everything I've seen.

I should have also mentioned fuel in my above comments, and booster design. All those things have a much greater affect on detonation resistance than does head materiel.
I'll see if I can find it again.... I posted a link to it in another SBM thread about 4-5 weeks back. I was intrigued by the outcome, and was not sure it was 100% but IMHO it showed something worth pondering over. The slowed combustion process was what caught my eye.

What do mean by 'booster'? The auxiliary venturi? That word is not clicking in for me.....
 
Aluminum carries off heat faster than cast iron, helps with cooling the combustion chamber, there fore allowing more compression w/o using a higher grade octane , '' to a certain extent !" No way could I run 10.5 to 1 with cast iron heads on 91 , and have it tuned for all out h.p. Not sure on that tho, still tuning----.
 
Oh, if someone would site actual aluminum vs iron tests and not the heat transfer theory. You know, cylinder head tests with the same style combustion chambers and air flow figures on the same shortblock, intake manifold and carburetor combinations.
 
yr booster design- don't tell all the secrets but I have heard that before
yes on opening the heads around the intake
I gave you big hints twice about who grinds Hughes cams
it used to be Engle
nm- post a link
yr does point out a lot of factors that have to all work together
and why backing off the static CR makes sense unless you are going to consider all the factors together- and some of them- like the cam timing- you do not have
Old news.
Chris at engle told me this many many yrs ago. Hughes wanted them faster to the point the Jacks son said kick rocks, too many failures, grind your own or find another. There are only a couple few in cali who really grind cams, engle does their own and another guy ...cant remember his name...itll come to me I'm sure, he grinds for bullet,herbert, and few other cam brands.
 
I think there has to be value to using material that keeps the combustion chamber cooler just based off the way combustion and detonation work. Whether the benefit of switching from iron to aluminum alone is even enough for a tiny bit of measurable benefit is up for debate, but the concept has got to be accurate. I think the idea that "aluminum heads can handle higher compression ratios than iron" comes from all the improvements of a standard aftermarket aluminum head over the factory irons, though - material being just one part of it. Again, how much that part is I've got no clue. Could be an immeasurably small amount, could be a lot.
 
Does the aluminum really keep a "combustion chamber" cooler? Has anyone actually measured this? If you have iron and aluminum heads that make exactly the same horsepower and keep the water temperature the same in the jackets behind the combustion chamber, does the aluminum transfer heat better so you must have a better cooling system to maintain the water temperature?
 
Does the aluminum really keep a "combustion chamber" cooler? Has anyone actually measured this? If you have iron and aluminum heads that make exactly the same horsepower and keep the water temperature the same in the jackets behind the combustion chamber, does the aluminum transfer heat better so you must have a better cooling system to maintain the water temperature?
Aluminum transfers heat better, so it stands to reason it could pull heat out of the combustion chamber to the water jackets better. Who knows if it's enough of an improvement to make any difference in chamber temps, but in theory it is some kind of improvement. It'd be like moving the coolant closer to the combustion chamber.
 
Aluminum carries off heat faster than cast iron, helps with cooling the combustion chamber, there fore allowing more compression w/o using a higher grade octane , '' to a certain extent !" No way could I run 10.5 to 1 with cast iron heads on 91 , and have it tuned for all out h.p. Not sure on that tho, still tuning----.
I guess you're right. I've run iron '906 heads at 11.9:1 on 91 octane for maximum horsepower and never been able to make any more than 748 HP at our home dyno. I thought we were gonna make more on Comp Cams dyno, but the dyno operator forgot to turn the water on to the engine and we had to run a blown up engine, with bent valves and 56% leakdown, that only made 730 HP there.
 
Aluminum transfers heat better, so it stands to reason it could pull heat out of the combustion chamber to the water jackets better. Who knows if it's enough of an improvement to make any difference in chamber temps, but in theory it is some kind of improvement. It'd be like moving the coolant closer to the combustion chamber.
Human reasoning hasn't always worked out so well when evidence is presented........So we just keep repeating the old mechanic's tale even though we have NO PROOF?
 
So we just keep repeating the old mechanic's tale even though we have NO PROOF?
That's science, not an "old mechanic's tale". I said I don't know if it is enough to actually make any difference in combustion chamber temps, but aluminum DOES transfer heat better.
 
That's science, not an "old mechanic's tale". I said I don't know if it is enough to actually make any difference in combustion chamber temps, but aluminum DOES transfer heat better.
well known fact ^^^^^^^^^^
why do you generally have to run hotter plugs in an alum headed engine ?
 
I guess you're right. I've run iron '906 heads at 11.9:1 on 91 octane for maximum horsepower and never been able to make any more than 748 HP at our home dyno. I thought we were gonna make more on Comp Cams dyno, but the dyno operator forgot to turn the water on to the engine and we had to run a blown up engine, with bent valves and 56% leakdown, that only made 730 HP there.
Would have to see it to believe it , not just on ur dyno either -------- nuff said !
 
Regardless of head material, no matter the compression level, you need two things.

The correct octane and the ignition timing to be spot on.

I don’t care for the debate on head metal. I’ve gone fast & made some good power with each.
 
Fact.......Aluminum does transfer heat better.

What scientific tests have proven its quantitative effects in horsepower, combustion chamber cooling, detonation resistance. Some even claim it cools so much that you must increase the compression 1 full point to keep the same horsepower. Now, as I see it, there is an old mechanic's tale.
 
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