CR and pump gas question

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famous bob said:
I knew u were a pretty sharp guy , but ur full of **** when u say a hemi doesn`t have quench ! Its on the tapered sides of the tops--------
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Not enough quench to matter. And most guys don't even check it with a Hemi. What about a Hemi with a relatively flat top piston????

The quench a Hemi has is virtually none.
 
A physics observation (though I'm not a physicist). The whole idea of making more power in an internal combustion engine (is there an external combustion engine?) is to make more heat in the combustion chamber. That's the whole idea with nitrous, turbos, blowers, big cams and high CR, etc. The more fuel and oxygen you can burn in the chamber the more heat energy will be exerted onto the piston. Cooling the chamber takes away heat and thus power. However, if the mixture pre-detonates due to too much heat that can severely hurt power as well as parts. Bleeding off some heat will net more power but there may be better solutions than depending on the thermodynamics of aluminum.
 
dart_68 said:
A physics observation (though I'm not a physicist). The whole idea of making more power in an internal combustion engine (is there an external combustion engine?) is to make more heat in the combustion chamber. That's the whole idea with nitrous, turbos, blowers, big cams and high CR, etc. The more fuel and oxygen you can burn in the chamber the more heat energy will be exerted onto the piston. Cooling the chamber takes away heat and thus power. However, if the mixture pre-detonates due to too much heat that can severely hurt power as well as parts. Bleeding off some heat will net more power but there may be better solutions than depending on the thermodynamics of aluminum.
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Yes, there are EXTERNAL combustion engines.

Also, you assume that aluminum will wick away heat faster than the cooling system can absorb the heat. I suspect this isn't the case.

I have used Evans coolant and seen water temps go up. So there is more to it than saying aluminum absorbs heat better so therefore I can jack more timing and CR into my engine and be fine.

Look at all the aluminum headed engines out there that can't run full total timing because the CR is too high.

Again, head materiel is the LAST thing to look at for detonation suppression/resistance. And its contribution to either is very, very small.
 
"Look at all the aluminum headed engines out there that can't run full total timing because the CR is too high. YR says
amen to that
Just an old wives tale that an AL head can run "one more point" of compression
combustion chamber design (and splark plut location) has much more to do with it

BTW I worked on a Blown Fuel Hemi Bonneville motor- almost a flat top
and the one with just a little quench around the edge ran better than the one the didn't
However higher pressure injectors with smaller jets made more difference.
I think the Surfers were the first I saw doing this
 
yellow rose said:
Not enough quench to matter. And most guys don't even check it with a Hemi. What about a Hemi with a relatively flat top piston????

The quench a Hemi has is virtually none.
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Wrong , they just didn`t need as much due to chamber design . Street hemii`s or race hemi`s never had flat top pistons. The top fuel pistons were the only thing that would come close to a flat top, and they weren`t flat ! The tent roof pistons had to be machined to clear the heads, minimum clearance w/ steel rods was recommended at .060 , = QUENCH !! Good for gen 2 hemi combustion chambers. Still needed good to great gas tho.
I cut my tent roof " pent roof" as some were called down to s/s legal heigth in a lathe one time , later saw a special tool Jim Hale had made up for that , to fit the domes to hemi heads exactly , minum of .060 , QUENCH created .

I got a friend that runs 18 to one w/ with alcohol in a vega, that has an alum. block and heads------
 
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famous bob said:
Wrong , they just didn`t need as much due to chamber design . Street hemii`s or race hemi`s never had flat top pistons. The top fuel pistons were the only thing that would come close to a flat top, and they weren`t flat ! The tent roof pistons had to be machined to clear the heads, minimum clearance w/ steel rods was recommended at .060 , = QUENCH !! Good for gen 2 hemi combustion chambers. Still needed good to great gas tho.
I cut my tent roof " pent roof" as some were called down to s/s legal heigth in a lathe one time , later saw a special tool Jim Hale had made up for that , to fit the domes to hemi heads exactly , minum of .060 , QUENCH created .

I got a friend that runs 18 to one w/ with alcohol in a vega, that has an alum. block and heads------
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trying to show pic------------
 
dart_68 said:
A physics observation (though I'm not a physicist). The whole idea of making more power in an internal combustion engine (is there an external combustion engine?) is to make more heat in the combustion chamber. That's the whole idea with nitrous, turbos, blowers, big cams and high CR, etc. The more fuel and oxygen you can burn in the chamber the more heat energy will be exerted onto the piston. Cooling the chamber takes away heat and thus power. However, if the mixture pre-detonates due to too much heat that can severely hurt power as well as parts. Bleeding off some heat will net more power but there may be better solutions than depending on the thermodynamics of aluminum.
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FWIW.... The torque/power is produced by the DIFFERENCE in the temps/pressures through the cycle, NOT the absolute levels of temperature/pressure. Look at any thermodynamics P-V cycle diagram for the Otto cycle; if you lower or raise temps/pressures at the start of the cycle, and they are lower or higher at the ends of the cycle, you have not changed anything. So, everyone needs to get over the notion that taking away heat from the chamber necessarily takes away power.

And yes, a steam engine is an external combustion engine.
 
MOPAROFFICIAL said:
Don't ya hate when a thread goes a page or 2 sideways with an argument finally dwindling to "more heat slows combustion"
Too much fuel slows combustion as well when there isn't enough air density.
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If it is correct, what is wrong? (And note I say IF...) We've all accepted info that spark plug location and chamber size are factors in speeding/slowing the overall combustion time and thus are factors to tendencies to detonate, so why not the idea that there is maybe another factor in the mix? Too much fuel also cools the mixture, so that is not an apples-to-apples comparison to just changing temperature. But if that if the case, that does not conflict with the idea that excess heat slows the burn... there is nothing saying that there is not an optimum temp/mix for burn rate.

I agree that the tests of power production with AL vs iron have not concluding anything about detonation, but these articles just weren't looking for that. So they can't be used to say one way or another, and drawing a conclusion either way is erroneous, IMHO.
 
And that is why you can't make blanket statements like.. that you can run more compression with aluminum heads than iron on pump piss.
 
nm9stheham said:
If it is correct, what is wrong? (And note I say IF...) We've all accepted info that spark plug location and chamber size are factors in speeding/slowing the overall combustion time and thus are factors to tendencies to detonate, so why not the idea that there is maybe another factor in the mix? Too much fuel also cools the mixture, so that is not an apples-to-apples comparison to just changing temperature. But if that if the case, that does not conflict with the idea that excess heat slows the burn... there is nothing saying that there is not an optimum temp/mix for burn rate.

I agree that the tests of power production with AL vs iron have not concluding anything about detonation, but these articles just weren't looking for that. So they can't be used to say one way or another, and drawing a conclusion either way is erroneous, IMHO.
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Chamber size isn't a factor if the spark plug is located where it should be. The Hemi and SBM prove this.
 
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