Cubic inches and Boost Correlation
01-06-2020, 10:59 AM
#61
If its a guy that's maxed out his class turbo and needs more power, heads are a solid move. Or because they already made 1200 on stock heads and want to push further and paying for the thicker deck... maybe. But if its a guy starting out and just throwing money at a build blindly then absolutely true.
But when you're wanting to make 800 to 900 horsepower and are spending thousands and thousands on heads, intake, throttle body, custom fabbed intercoolers, all in the hopes of making the exact same amount of power on 6 PSI less, at least have a valid reason for wanting less boost. Most cant give a valid reason why it matters at all.
01-06-2020, 11:50 AM
#62
But when you're wanting to make 800 to 900 horsepower and are spending thousands and thousands on heads, intake, throttle body, custom fabbed intercoolers, all in the hopes of making the exact same amount of power on 6 PSI less, at least have a valid reason for wanting less boost. Most cant give a valid reason why it matters at all.
01-06-2020, 02:14 PM
#65
Anything below 160-180 doesn't need timing pulled at all, and how much/when above that is definitely debatable.
The boost number itself doesn't directly correlate with the temperature in your intake manifold.
You can do the math on heat of compression for an adiabatic process once you know your way around it:
Pi*Vi^K=Pf*Vf^K.
Simplify it down basically is Pressure*Volume^K=Constant. K is air gamma.1.4 is the Gamma for air.
You can go further down to TemperatureIn*PressureRatio^(K-Pi)=TemperatureOut. Pi is inlet pressure, so 1.
TempIn*(PressureRatio^0.4)=TempOut
100 degree inlet temps * [3.0 pressure ratio (or 300 KPA) ^ 0.4] = 155 degree temps from compression.
So from compression alone, running 300 KPA (29 PSI Boost) increases your inlet temps about 55 degrees.
So for you guys wanting to spend 4k on Heads/intake/intercooler to run 11 PSI of boost instead of 18 PSI:
11 PSI: 80 degree inlet temps * [1.76 ^ 0.4] = 100.3 degrees from heat of compression.
18 PSI: 80 degree inlet temps * [2.24 ^ 0.4] = 110.5 degrees from heat of compression.
You saved yourself 10.2 degrees F.
Most of the heat comes from passing the air through the extremely hot heat-sink of an aluminum compressor and heat soaked piping, not the amount of boost your running.
Stop wasting your money.
Run all of the boost.
01-06-2020, 02:20 PM
#66
This EXTREMELY handsome gentleman once posted something on running extra boost and its correlation with detonation as well, if you're still not convinced.
Boost and octane have no direct correlation to each other. I've tuned smaller engines that made 40 PSI on 93 octane before.
Higher pressure raises the boiling and flash points of gasoline.
Pressure DOES decrease the autoignition temperature, but we'll get to that at the end.
And boost being a measurement of restriction is a bit of a misunderstanding. It is a measurement of resistance on the compressor, not the engine. You could run heads/intake with 6" wide ports and a 10" throttle body that poses ZERO restriction to flow, but you're still going to be making boost if the compressor inlet is pulling in more CFM than the engine can pull in by itself.
THE MOST IMPORTANT THING: airmass determines power/torque production.
If boost was a measurement of restriction, it would be highest before the valve, and would drop afterwards once entering the cylinder.
Whether boost is 25 PSI in the intake manifold or 5 PSI in the intake manifold, if the end result is the same amount of power, its because the airmass and boost pressure in the cylinder was the same, regardless of what it was in the intake manifold (as long as the camshaft and static compression ratio are the same). Since autoignition doesn't occur in the intake manifold, pre-cylinder pressure is completely irrelevant to knock/autoignition/octane, etc. You might increase the chances of a tuning error using a wider spread of the fueling/spark tables, or complications involving excess heat, but that's easily dealt with.
Long story short, heads/intake or any other pre-cylinder flow restrictions you might have will have NO effect on chances of knock with pump gas, because the cylinder pressure will be the same for a given power level, meaning that pressure's effect on autoignition temperature doesn't apply.
You want to change something that will allow you to make more power on less boost with a direct effect on your chances of knock with pump gas? Camshafts are the exception to the rule.
Everything else, you're literally throwing your money away.
Higher pressure raises the boiling and flash points of gasoline.
Pressure DOES decrease the autoignition temperature, but we'll get to that at the end.
And boost being a measurement of restriction is a bit of a misunderstanding. It is a measurement of resistance on the compressor, not the engine. You could run heads/intake with 6" wide ports and a 10" throttle body that poses ZERO restriction to flow, but you're still going to be making boost if the compressor inlet is pulling in more CFM than the engine can pull in by itself.
THE MOST IMPORTANT THING: airmass determines power/torque production.
If boost was a measurement of restriction, it would be highest before the valve, and would drop afterwards once entering the cylinder.
Whether boost is 25 PSI in the intake manifold or 5 PSI in the intake manifold, if the end result is the same amount of power, its because the airmass and boost pressure in the cylinder was the same, regardless of what it was in the intake manifold (as long as the camshaft and static compression ratio are the same). Since autoignition doesn't occur in the intake manifold, pre-cylinder pressure is completely irrelevant to knock/autoignition/octane, etc. You might increase the chances of a tuning error using a wider spread of the fueling/spark tables, or complications involving excess heat, but that's easily dealt with.
Long story short, heads/intake or any other pre-cylinder flow restrictions you might have will have NO effect on chances of knock with pump gas, because the cylinder pressure will be the same for a given power level, meaning that pressure's effect on autoignition temperature doesn't apply.
You want to change something that will allow you to make more power on less boost with a direct effect on your chances of knock with pump gas? Camshafts are the exception to the rule.
Everything else, you're literally throwing your money away.
01-06-2020, 03:42 PM
#70
With a proper intercooler, I rarely see over 140 degrees of IAT tickling the top of a 3 bar MAP sensor. That is NOT spraying meth on the sensor.
Anything below 160-180 doesn't need timing pulled at all, and how much/when above that is definitely debatable.
The boost number itself doesn't directly correlate with the temperature in your intake manifold.
You can do the math on heat of compression for an adiabatic process once you know your way around it:
Pi*Vi^K=Pf*Vf^K.
Simplify it down basically is Pressure*Volume^K=Constant. K is air gamma.1.4 is the Gamma for air.
You can go further down to TemperatureIn*PressureRatio^(K-Pi)=TemperatureOut. Pi is inlet pressure, so 1.
TempIn*(PressureRatio^0.4)=TempOut
100 degree inlet temps * [3.0 pressure ratio (or 300 KPA) ^ 0.4] = 155 degree temps from compression.
So from compression alone, running 300 KPA (29 PSI Boost) increases your inlet temps about 55 degrees.
So for you guys wanting to spend 4k on Heads/intake/intercooler to run 11 PSI of boost instead of 18 PSI:
11 PSI: 80 degree inlet temps * [1.76 ^ 0.4] = 100.3 degrees from heat of compression.
18 PSI: 80 degree inlet temps * [2.24 ^ 0.4] = 110.5 degrees from heat of compression.
You saved yourself 10.2 degrees F.
Most of the heat comes from passing the air through the extremely hot heat-sink of an aluminum compressor and heat soaked piping, not the amount of boost your running.
Stop wasting your money.
Run all of the boost.
Anything below 160-180 doesn't need timing pulled at all, and how much/when above that is definitely debatable.
The boost number itself doesn't directly correlate with the temperature in your intake manifold.
You can do the math on heat of compression for an adiabatic process once you know your way around it:
Pi*Vi^K=Pf*Vf^K.
Simplify it down basically is Pressure*Volume^K=Constant. K is air gamma.1.4 is the Gamma for air.
You can go further down to TemperatureIn*PressureRatio^(K-Pi)=TemperatureOut. Pi is inlet pressure, so 1.
TempIn*(PressureRatio^0.4)=TempOut
100 degree inlet temps * [3.0 pressure ratio (or 300 KPA) ^ 0.4] = 155 degree temps from compression.
So from compression alone, running 300 KPA (29 PSI Boost) increases your inlet temps about 55 degrees.
So for you guys wanting to spend 4k on Heads/intake/intercooler to run 11 PSI of boost instead of 18 PSI:
11 PSI: 80 degree inlet temps * [1.76 ^ 0.4] = 100.3 degrees from heat of compression.
18 PSI: 80 degree inlet temps * [2.24 ^ 0.4] = 110.5 degrees from heat of compression.
You saved yourself 10.2 degrees F.
Most of the heat comes from passing the air through the extremely hot heat-sink of an aluminum compressor and heat soaked piping, not the amount of boost your running.
Stop wasting your money.
Run all of the boost.
01-06-2020, 04:10 PM
#72
Exhaust mass is based on power not boost pressure. A 1 liter engine at 100 PSI making 1000 HP and a 10 liter engine N/A making 1000 HP, as long as EGTs and air fuel ratios are the same, are moving the same exhaust mass. So if you have 2 identical turbo setups making identical power at different boost pressure, they are moving the same exhaust mass. They will have the same amount of heatsoak in the turbo and the compressor. The actual heat of compression will be negligible between the 2.
None of this has anything to do with actual boost pressure.
01-06-2020, 04:33 PM
#73
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01-06-2020, 04:57 PM
#74
Ever compared turbo IATs to forward facing procharger IATs? Reverse procharger IATs are higher because they heat soak from being under the hood. Low forward mounted prochargers have extremely low IATs.
The formula above is similar to what I've used before with industrial blower units used to compressor air for entire factories at 80+ PSI. The air coming out of them is considerably cooler than typical turbo IATs pre-intercooler at significantly lower pressures.
01-06-2020, 05:13 PM
#75
9 Second Club
ALL Compressors heat the air, including superchargers and it is from the compression of the air where most of the heat is generated. Any heat from the wheel/scroll itself is and will be negligible given it only spends milliseconds in there.......and when off the throttle....and the air can spend a few extra milliseconds in there, charge temps do not go sky high either.
Hell...even my small tyre inflator gets the brass fitting mid hose line hot pumping a tyre up ! And there's no hot turbine there lol
Hell...even my small tyre inflator gets the brass fitting mid hose line hot pumping a tyre up ! And there's no hot turbine there lol
01-06-2020, 11:42 PM
#76
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I think it also depends on how efficient the turbo is at the given power level and pressure ratio which dictates how hot the air is going to be and most of the heat comes from compressing the air not the exhaust ?? Lol
01-07-2020, 10:01 AM
#78
I botched an equation yesterday after a few beers and used Fahrenheit instead of Kelvin in the temperature of compression formula and forgot to divide the exponent by air gamma.
If I did it in Kelvin:
TempIn = 311 kelvin = 100 Fahrenheit
Pressure Ratio = 3.0 (~300 KPA or 29 PSI)
TempIn*(PressureRatio^[0.4/1.4])=TempOut
311*(3.0^0.2857)= 425 Kelvin
Temperature In = 100 Fahrenheit
Temperature Out = 305 Fahrenheit
This doesn't account for humidity, which might put it off a few %.
So yes, a lot of the temperature change comes from the heat of compression.
A lot of it still comes from compressor heat transfer. Remember, it DOES spend almost as much time in the compressor as it does the intercooler.
There have been studies done that show that the compressor heats the ambient air for the bottom 80% of most compressor maps.
Such as the one done by the Royal Institute of Technology specifically to determine the turbine heat's effect on compressor heat and compressor outlet temps.
http://kth.diva-portal.org/smash/get...801/FULLTEXT01
They kept everything constant. Eliminated as many variables as possible.
They increased the turbine gas temps from 1050*F to 1400*F to simulate low and high load conditions,
and the compressor outlet temperatures changed from 80 degrees to 170 degrees on a water cooled turbo.
The results also show that the water had a significant impact on stopping heat transfer from ultimately turbine to compressor,
so uncooled turbos likely have much greater temperature changes from heat transfer.
Stupidly long story short, heat of compression isn't nearly the only factor. It is less of a factor at low boost pressure and more of one at higher pressures, obviously.
If I did it in Kelvin:
TempIn = 311 kelvin = 100 Fahrenheit
Pressure Ratio = 3.0 (~300 KPA or 29 PSI)
TempIn*(PressureRatio^[0.4/1.4])=TempOut
311*(3.0^0.2857)= 425 Kelvin
Temperature In = 100 Fahrenheit
Temperature Out = 305 Fahrenheit
This doesn't account for humidity, which might put it off a few %.
So yes, a lot of the temperature change comes from the heat of compression.
A lot of it still comes from compressor heat transfer. Remember, it DOES spend almost as much time in the compressor as it does the intercooler.
There have been studies done that show that the compressor heats the ambient air for the bottom 80% of most compressor maps.
Such as the one done by the Royal Institute of Technology specifically to determine the turbine heat's effect on compressor heat and compressor outlet temps.
http://kth.diva-portal.org/smash/get...801/FULLTEXT01
They kept everything constant. Eliminated as many variables as possible.
They increased the turbine gas temps from 1050*F to 1400*F to simulate low and high load conditions,
and the compressor outlet temperatures changed from 80 degrees to 170 degrees on a water cooled turbo.
The results also show that the water had a significant impact on stopping heat transfer from ultimately turbine to compressor,
so uncooled turbos likely have much greater temperature changes from heat transfer.
Stupidly long story short, heat of compression isn't nearly the only factor. It is less of a factor at low boost pressure and more of one at higher pressures, obviously.
01-07-2020, 10:34 AM
#80
Dude it was a long day. I was several beers in when we had to head to the hospital to find out my gf had both the flu and pneumonia while being pregnant. Luckily (or unluckily?) I had my work laptop lol.