L28ET Engine Air Flow and Turbo Compressor Maps

Calculations:

280z Displacement = 2.753 litres = 168.00 cubic inches

Air flow equals:  Cid X  RPM X 0.5 X Ev
                                     1728

For 6500 redline and Ev = 0.80: 

Air flow equals:  168 X  6500 X 0.5 X 0.80   = 252.78cfm
                                     1728

1lb/min = 14.472 cfm 

so 252.78cfm = 17.47 lbs/min

air flow at boost = stock air flow X pressure ratio

Pressure Ratio = (boost + 14.7)
                               14.7

So for 20psi of Boost @ 6500rpm:

Air flow = 252.78 X (20+14.7) = 596.69cfm  or  41.23lbs/min 
                               14.7

Air Flow Data in Table Form for different levels of boost: (both cfm and lbs/min)

Calculated L28ET air flow in CFM using Ev 0.85 to 0.80

Calculated L28ET air flow in lbs/min using Ev 0.85 to 0.80

Air Flow Data Plotted Against Different Boost Levels (Pressure Ratio vs. lbs/min)

L28ET air flow in lbs/min at  10, 16 and 20psi (1.68 / 2.09 / 2.36BAR) of boost

• far right end points are at max boost and redline (6500rpm)
• "knees" are half way to redline when full boost hits (3250rpm)  note: this is an arbitrary point and is dependent on A/R ratio.
• far left "start" point is 20% of redline flow and pressure ratio of 1BAR  note: this is also arbitrary
  

Air Flow Data Plotted Against Different Boost Levels and Transcribed to "Stock" Garrett T3-60 Compressor Map (Pressure Ratio vs. lbs/min)

• 6500 rpm red line points for this compressor at all three levels of boost are at the 60% or lower efficiency range. This means the compressor is making a lot of heat in these regions. The boost range from 10 to 16psi holds near 60% at redline but it quickly gets worse as the boost is increased toward 20psi.
  
• Since the "knee" is ~3250 rpm, and it is in the 74% efficiency "sweet spot" this compressor will work well between 3250rpm and 4500rpm
  
• This compressor is optimized for low boost small displacement engines
  
• Goldilocks says "too small, too hot"
  

Air Flow Data Plotted Against Different Boost Levels and Transcribed to Garrett T61 Compressor Map (Pressure Ratio vs. lbs/min)

• 6500 rpm red line points for this compressor, for all three levels of boost, are in the 76% "sweet spot"
  
• 3250 rpm "knee" points for this compressor, for all three levels of boost, are in the 66% area near the surge limit. This region is where the flow is not sufficient to spin the turbo wheels.
  
• This big compressor will give poor performance unless running full out near red line. Therefore; it is great for drag applications and not so great for the street.
  
• Goldilocks says "too big"

Air Flow Data Plotted Against Different Boost Levels and Transcribed to Garrett T04E-50 Compressor Map (Pressure Ratio vs. lbs/min)

• 6500 rpm red line points for this compressor at all three level of boost are in the 75% +/- 1% efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three level of boost are in the 74% +/- 1% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 78% area, thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle even more boost and remain very efficient above the 20psi line. "It can grow with your need for more speed"
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "just right"

Air Flow Data Plotted Against Different Boost Levels and Transcribed to Garrett T04B-60-1 Compressor Map (Pressure Ratio vs. lbs/min)

• 6500 rpm red line points for this compressor all fail to reach the highest efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three levels of boost are in the surge threshold region
  
• It should be obvious that this compressor will work better with a larger displacement engine as it's sweet spot is far to the right where higher flows are required.
  
• Goldilocks says "too demanding"

• 6500 rpm red line points for this compressor at all three level of boost are in the 60-75% efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three level of boost are in the 76% +/- 1% efficiency region.
  
• When accelerating towards redline, the efficiency drops out of the maximum 76% area, thus performance decreases as rpms increase though this is not as bad as the T3-60 above
  
• It should be obvious that this compressor will work best for lower flowing engines with boost between  8 and 12psi.
  
• This compressor will give slightly better performance performance to the stock T3-60.
  
• Goldilocks says "not a significant change from stock"

• 6500 rpm red line points for this compressor at all three level of boost are in the 45-60% efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three level of boost are in the 69 to 72% efficiency region.
  
• When accelerating towards redline, the efficiency drops out of the maximum 73% area, thus performance decreases as rpms increase though this is not as bad as the T3-60 above
  
• It should be obvious that this compressor will work best for lower flowing engines with boost between  8 and 12psi.
  
• This compressor will give slightly better performance performance to the stock T3-60.
  
• Goldilocks says "not a significant change from stock"

• 6500 rpm red line points for this compressor at all three level of boost are in the 70 to 76% efficiency region.
  
• two of the 3250 rpm "knee" points for this compressor are below the surge limit so a dual stage boost controller is needed to only let the high boost at higher rpms's
  
• When accelerating towards redline, the efficiency passes through the maximum 78% area at 10psi and 76% at 16 and 20psi, thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle only slightly more boost above the 20psi line. 
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "ok but not most efficient and needs dual stage boost controller"

• 6500 rpm red line points for this compressor at all three level of boost are in the 65 to 72% efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three level of boost are in the 73% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 76% area, thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle only slightly more boost above the 20psi line. 
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "ok but not most efficient"

• 6500 rpm red line points for this compressor at all three level of boost are in the 65 to 68% efficiency region.
  
• 3250 rpm "knee" points for this compressor at all three level of boost are in the 77% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 76% area for 16 and 20psi, thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle slightly more boost above the 20psi line and 10psi boost is just OK.
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "ok but not most efficient"