A Good, Quick Read on VE % vs. Boost Pressure

[motorhead]

http://speedtalk.com/forum/viewtopic.php?f=1&t=37811

[Tim Hensley]

I can't believe I read that
I can't hardly  read can't spell
I'm hoping the new Champion heads and intake make my car faster at the same boost

[Steve Wood]

I can't believe I read that
I can't hardly  read can't spell
I'm hoping the new Champion heads and intake make my car faster at the same boost

It's is completely apples and oranges.  If the heads and intake have less restriction, then the boost number is no longer related to your prior boost number.  And, it gets further complicated in that aluminum is thermally less efficient than iron so it takes a higher level of heat within the combustion chamber to produce the same amount of power as the iron heads.  That is why we raise the compression a point on average to try to make up for the thermal weakness of the aluminum head.

[Tim Hensley]

will i read enough to get Irons

[earlbrown]

I got 6 or 7 posts in before I was too stupid to work the mouse wheel and had to give up.

[Charlief1]

I'm with Earl on this one. The more I read either I got a lot dumber or the posts did. Just couldn't tell which.

[Top Speed]

LOL!!!

[Steve Wood]

I quit reading because I am usually in a state of confusion to begin with....I don't need any more

[Forzfed]

Aluminum is a much better conductor than iron.  Aluminum has a coefficient of thermal conductivity of 206 W/m'C (watts per meter celsius) compared to iron at 70 W/m'C.

[Steve Wood]

Aluminum is a much better conductor than iron.  Aluminum has a coefficient of thermal conductivity of 206 W/m'C (watts per meter celsius) compared to iron at 70 W/m'C.

Thanks for verifying my statement.

Engines run on the heat from the combustion process.  Aluminum bleeds more heat out of the combustion chamber than does iron.  This reduces power and makes it more inefficient than iron when it comes to power production.

We raise the compression to build more heat during combustion to make up for the loss.  We can also use thermal coatings on the piston tops and combustion chambers to keep the heat within the cylinder to drive the piston down harder and coat the inside of the exhaust port to try to keep the heat out of the coolant which may aggravate detonation

[Forzfed]

I have to do a government exam on this stuff right away.  One of the good things about aluminum being a good conductor is on the exhaust stroke it helps expel more heat so when the compression stroke occurs it is compressing denser gas because it isn't as hot.  The down side is you don't want to dissipate the heat on the power stroke.  You want to convert as much heat energy to mechanical energy as possible, ie. efficiency.

[Forzfed]

Okay might not have come out right.  I was kind of referring to the Carnot cycle, which is the ideal cycle.  Replace the cylinder head with basically a hot body, non-conductor, and cold body.  But you are correct we want to keep as much of the heat in the cylinder as possible and not reject it.

[Steve Wood]

I never had any doubt

The advantage that aluminum has over iron is that it is cheap to cast in smaller numbers, and it weighs a lot less.  In a racing environment, it is also easy to repair.  You have to look at the entire elephant and not just its ears or trunk.  This topic is really relevant to performance and not general science.  Else, we will soon be touting the wonders of electric power

[ttipe]

I read this thread and had to hurl! 1) In the specific case of aluminum heads for LC2 the valves and seats are larger, and unshrouded, therefore more charge air per intake stroke. The flow data from both Champion & TA support the fact that untouched Aluminums will out flow most (if not all ported irons). Since aluminum heads likely flow more air (at 28 inches on the water monometer) than iron, does boost (or unusable intake air quantity go down???) Yes if all other conditions are equal. If a greater amount of air by volume (aluminum) and a greater mass density due to cooler temperature (aluminum) makes it to the combustion chamber is more gas required to meet the commanded air/fuel ratio? YES!! Since the spark plug location (aluminum) is closer to the intake and exhaust valve might the thought occur that the chamber burn rate is faster?( Less octane req'd??). This is somewhat verifiable by the fact that aluminum head cars with higher static compression ratios run pump gas (without alky) at higher boost levels than iron head motors. Temperature is only one part of the Carnot cycle. You have mass density, potential energy/unit of mass and temperature. These factors combine uniquely in most situations. Folks with aluminum heads that I know without exception say they make better power and have better response than their irons. Is it more expensive to change over to aluminum? YES!!!! Do aluminums have different torque requirements for fasteners? Are aluminums good for newbies?? Probably not!       

[Forzfed]

I read this thread and had to hurl! 1) In the specific case of aluminum heads for LC2 the valves and seats are larger, and unshrouded, therefore more charge air per intake stroke. The flow data from both Champion & TA support the fact that untouched Aluminums will out flow most (if not all ported irons). Since aluminum heads likely flow more air (at 28 inches on the water monometer) than iron, does boost (or unusable intake air quantity go down???) Yes if all other conditions are equal. If a greater amount of air by volume (aluminum) and a greater mass density due to cooler temperature (aluminum) makes it to the combustion chamber is more gas required to meet the commanded air/fuel ratio? YES!! Since the spark plug location (aluminum) is closer to the intake and exhaust valve might the thought occur that the chamber burn rate is faster?( Less octane req'd??). This is somewhat verifiable by the fact that aluminum head cars with higher static compression ratios run pump gas (without alky) at higher boost levels than iron head motors. Temperature is only one part of the Carnot cycle. You have mass density, potential energy/unit of mass and temperature. These factors combine uniquely in most situations. Folks with aluminum heads that I know without exception say they make better power and have better response than their irons. Is it more expensive to change over to aluminum? YES!!!! Do aluminums have different torque requirements for fasteners? Are aluminums good for newbies?? Probably not!       

SUCCESS!  I hope you puked on yourself.

My buddy's Stage II heads, have a 10' valve, flow 335 cfm@.5 lift, he runs a .680 lift cam.  What aluminum heads will out flow these?  Yes I know your talking LC2, but what aluminum head matches the Stage II?  The car ran a 7.9@179 with 24psi of boost on an old T-88 and not on alcohol.  Yet you have to listen to all these pros chirp about how that isn't even possible to run. The funny part was the car was built by turbo pros and kept blowing up, because they messed up in a few areas which they never should have.  He laughed when he fixed it, but he got the car at a good price.

I don't claim to be an expert, like yourself.  I have friend that works for a top NHRA team that does heads.  They do things that defy logic all the time, but if they go fast that is the only thing that matters.

I knew with "Volumetric Efficiency Nut"  you'd chirp in!