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Discussion Starter · #1 · (Edited)
FMIC temp range is consistantly 15f variation vs 50f variation for the honda intercooler.
FMIC volumetric efficiency (%) is a measure of the volume airflow through the engine vs the expected airflow if the engine filled the cylinders.
VE is way down on the Honda item as is the resulting volume airflow (note the mass airflow is also much less though so is expected to some degree).
RAW power favours the Honda intercooler but when DIN corrected, the power/airflow favours the FMIC.
Question.
How can the FMIC be capable of higher DIN corrected power when it seems to be down everywhere else ?
Discuss.....
:D

ASSUMPTIONS
1. The Honda map will regulate the smoke level limits and hence Air Fuel Ratio will be controlled at any rpm.
2. The Honda map will regulate the torque level limits and hence control the peak corrected power the engine produces at any rpm.
3. The Honda map will attempt to keep the same torque/AFR limits no matter what the ambient pressure and temperature.
4. MAP (boost) and resulting MAF (airflow) will therefore be increased or descreased as necessary depending on weather conditions.

APPLYING DIN CORRECTION to RAW POWER...
DIN POWER = RAW POWER /((MBAR/1013.25)*((293/(TEMPC+273))^0.5))
Where
MBAR = ambient pressure in millibar
TEMPC = ambient temperature in centigrade
POWER = SEE BELOW..

OBTAINING RAW POWER FROM MASS AIR FLOW...
BHP = MAF/(AFR*(BSFC/60))
where
MAF = mass air flow in lbs/min
AFR = Air Fuel Ratio assumed to be 18:1 for a consistant comparison.
BSFC = Brake Specific Fuel Consumption ass umed to be 0.39 lbs/ bhp hour for a consitant comparison.

OBTAINING VOLUMETRIC EFFICENCY FROM RPM MAF IAT MAP
VE = (MAF*GAS*(RANKINE+IAT))/(MAP*(RPM/2)*INCHES)
where
MAF = mass air flow in lbs/min
GAS = the Gas constant R (639.6)
RANKINE = absolute freezing in Farenheit to 0f (459.67f)
IAT = Inlet Air Temp if Farenheit
MAP = Manifold Absolute Pressure in psi.
RPM = ;)
INCHES = engine displacement in Cubic Inches (134.2 cu.in)

BLUE DOTS...
6x 3rd gear wide open throttle runs combined to allow tolerance
DATALOG ON 04 08 2012
2.5" DECAT -SINGLE SILENCER - SINGLE EXIT EXHAUST
HONDA INTERCOOLER.
NO RAMAIR.
FINISHED MODIFIED AIRBOX.
AMBIENT TEMP = 27f (-3 c)
AMBIENT PRESSURE = 15.23 psi (1050 mbar)

RED DOTS...
6x 3rd gear wide open throttle runs combined to allow tolerance
DATALOG ON 08 08 2012
2.5" DECAT -SINGLE SILENCER - SINGLE EXIT EXHAUST
FMIC INTERCOOLER.
NO RAMAIR.
FINISHED MODIFIED AIRBOX.
AMBIENT TEMP = 34f (1 c)
AMBIENT PRESSURE = 14.79 PSI (1020 mbar)
 

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Premium Member
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ehhh you lost me, far to technical for me :facepalm: ,but the fmic does look good :D
 
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Cockup Specialist
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Discussion Starter · #5 ·
I made pictures for those that dont understand the text ;) ...pmsl
 

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Now that is some serious reading I have to do at work tonight. What's the short answer, or do we have to work it out for ourselves?
 

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Discussion Starter · #11 · (Edited)

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Relic,

I don't have a direct answer for you, but can share some musings with respect to gas turbine performance that may trigger some thoughts.

Quasi non-dimensional mass flow (NDMF) – essentially equivalent to your DIN power equation – is defined as:
NDMF = [W*(T_in / T_ISA-SLS)^0.5] / (p_in / p_ISA-SLS)

W = mass flow (kg/s) and the ISA values are sea-level static (SLS).

Typically, as altitude is increased the decrease in temperature is outstripped by the drop in pressure and so the NDMF increases. This leads to increased power. This increase in power is in spite of the real mass flow decreasing (the increase in air density due to reduced air temperature with altitude is insufficient to combat the commensurate fall in air pressure). In this case it helps to consider quasi non-dimensional rotational speed, defined as:
PCN = [N*(T_ISA-SLS / T_in)^0.5] / [N_DP*(T_ISA-SLS / T_in-DP)]

N is the rotational speed and the DP subscript references the design-point of the gas turbine. This shows that as temperature decreases the PCN value will increase, so whilst real mass flow reduces the engine rotational speed effectively increases, resulting in increased pressure ratio and so more power.

I wonder if there is a similar formula for PCN with respect to combustion engines that may help to explain the results you are seeing.

DISCLAIMER: I'm no expert, just sharing my thoughts!
 

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Discussion Starter · #16 · (Edited)
RAW ENGINE CFM = (INCHES/1728)*(RPM/2)

AIR DENSITY (USING AMBIENT PRESSURE AND MANIFOLD AIR TEMP) = 1.325 * (2.03625437 * (MBAR/1000*14.5)) / (459.67 + IAT)

RAW ENGINE MAF = RAW ENGINE CFM * AIR DENSITY.

GET THE MAF RATIO AT THE ENGINE = MEASURED MAF / RAW MAF

GET THE MAP RATIO AT THE ENGINE = MAP / AMBIENT PRESSURE.

VE % = MAF RATIO / MAP RATIO.


Well I was thinking initially theres a flaw in the way garrett apply the formula to calculate VE.
So I did the calculation the long winded way above and ended up with pretty much the same VE +-0.001%
:facepalm:

In fact I have been banging my head for the past few days.
As the FMIC efficiency is much better than the SMIC at 20c in the summer.

So my thoughts.
Yes at those Inlet air temps at that rpm the Honda intercooler is better.
And thats the crux of it.

but....the big butt....
What matters at the end of the day is how much manifold pressure or boost is required to give you the desired mass air flow at a specific ambient pressure and temp ;)
The lower the MAP is to give the same MAF = more power, more efficient engine, more airflow & less turbo load.

The FMIC sees much lower air temps to begin with so although it does not use the lower air temps as well as the Honda item would....then Honda item never sees such low air temps to make use of it.

;)
 

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Discussion Starter · #18 ·
who you calling big butt? ;) fmic wins then especially when temps go up
Yep...looks like it.
Its -2c and 1040mbar (15.1psi) at the moment.
So thats much closer to the -3c and 1050 mbar for the SMIC log.
I'll datalog now and see if the boost is still way lower.
If it is we have an answer.
 

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i've missed these type of threads :D
 
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