GT Turbo Compressor Maps vs. L28ET Air Flow

[boardkid280z]

L28ET Engine Air Flow and Turbo Compressor Maps

Modified for Garrett ball bearing GT turbos by Matthew Brazle (boardkid280z)

Originally sourced from: http://www.mygen.com/users/dbruce/myz31/TurboMaps/L28ET%20Engine%20Air%20Flow%20and%20Turbo%20Compressor%20Maps.htm

Author: Daniel Bruce

Calculations (see source page)

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

Pressure - cfm______Pressure - lbs/min @ 6500rpm

1.68 bar - 424.73cfm - 10psi - 29.35lbs/min

2.09 bar - 527.90cfm - 16psi - 36.48lbs/min

2.36 bar - 596.69cfm - 20psi - 41.23lbs/min

2.70 bar - 682.50cfm - 25psi - 47.18lbs/min

cfm ----------- lbs/min @ 20% of Redline Flow

84.95cfm - 5.87lbs/min

105.58cfm - 7.30lbs/min

119.34cfm - 8.25lbs/min

136.50cfm - 9.44lbs/min

(Calculated L28ET air flow in lbs/min using Ev 0.80)

 

The plotted color lines show L28ET air flow in lbs/min at 10, 16, 20 and 25psi (1.68 / 2.09 / 2.36 / 2.7bar) of boost

• far right end points are at max boost and redline (6500rpm)
  
• "knees" are ~half way to redline when full boost hits (3750rpm). note: this is an arbitrary point and is dependent on A/R ratio. I moved it from 3250 to 3750 since this seems more realistic for full boost for these aftermarket turbos
  
  
• far left "start" point is 20% of redline flow and pressure ratio of 1bar. note: this is also arbitrary
  

Here is a list of the turbos and their compressor maps on this page:

Turbo____ (Ind ______Exd____ trim _A/R)____Application Recommendation

GT2876R (52.7mm 76.0mm 48 0.70) [Horsepower 280 – 480; Displacement 1.8L - 3.0L]

GT3071R (53.1mm 71.0mm 56 -) [Horsepower 300 – 460; Displacement 1.8L - 3.0L]

GT3076R (57.0mm 76.2mm 56 0.60) [Horsepower 310 – 525; Displacement 2.0L - 3.0L]

GT3582R (61.4mm 82.0mm 56 0.70) [Horsepower 400 – 600; Displacement 2.0L - 4.5L]

GT3788R (63.5mm 88.0mm 52 0.72) [Horsepower 440 – 675; Displacement 2.0L - 5.0L]

GT4088R (63.5mm 88.0mm 52 0.72) [Horsepower 400 – 700; Displacement 2.0L - 6.0L]

GT3271 (51.2mm 71.0mm 52 0.50) [Horsepower 200 – 420; Displacement 2.0L - 2.7L]

GT3776 (55.0mm 76.2mm 52 0.54) [Horsepower 320 – 500; Displacement 2.0L - 4.0L]

GT3782 (59.1mm 82.0mm 52 0.54) [Horsepower 350 – 550; Displacement 2.0L - 4.0L]

All this info is available on Garrett’s website: www.turbobygarrett.com

 

 

• 6500 rpm red line points for this compressor at all four levels of boost are in the 70-75% efficiency region.
  
• 3750 rpm "knee" points for this compressor at all four levels of boost are in the 70-75% efficiency region.
  
• At lower boost levels, 10 and 16psi, efficiency passes through the highest efficiency island.
  
• At higher boost levels, 20 and 25psi this turbo is outside of its maximum efficiency level, but is still in the 70%+ region of the map
  
• This turbo will do great at lower boost levels and will do OK at higher boost levels. Good for low RPM response, but will run out of air at higher boost or higher RPM and on higher flowing motors.
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says “great upgrade for a stock motor,with a little room to grow”
  

• 6500 rpm red line points for this compressor at 10, 16 and 20psi of boost are in the 75% +/- 1% efficiency region. At 25psi you’re getting close to the limit of this turbo, you’re close to the max speed of the turbo and efficiency is dropping quickly as you approach redline.
  
• 3750 rpm "knee" points for this compressor at all levels of boost are in the 72% +/- 1% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 78% area, thus performance is ideal during this period, especially at 16 and 20psi
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "great upgrade for a stock motor, with a little room to grow "
  

• 6500 rpm red line points for this compressor at all three level of boost are in the 70 to 77% efficiency region. Lower boost levels can go even higher on the flow axis without losing much efficiency since their redlines are right on the edge of the highest efficiency island
  
• 3750 rpm "knee" points for this compressor are close to the surge line, especially at higher boost levels there may not be enough flow to spin the turbo around the knee
  
• When accelerating towards redline, the efficiency passes through the maximum 77% area, thus performance is ideal during this period. 10, 16 and 20psi boost plots spend a lot of time in the high efficiency region; 25psi doesn’t and will generate a little more heat.
  
• It should be obvious that this compressor can handle only slightly more boost above the 25psi line.
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "great upgrade and good performance below 20psi with room for more flow”
   
  
  

• 6500 rpm red line points, for the three lower levels of boost, are just barely in the 76% "sweet spot"
  
• 3750 rpm "knee" points for this compressor, at 10 and 16psi, are pushing lower efficiency regions near the surge limit. This region is where the flow is not sufficient to spin the turbo wheels. At 20 and 25psi the knee points are outside the surge line, and this turbo would require a dual stage boost controller.
  
• This big compressor will give poor performance unless running full out near red line and beyond. Therefore; it is great for drag applications and higher flow motors and not so great for the street.
  
• Goldilocks says "too big for a stock motor, great for modified motors”
  

• 6500 rpm red line points for this compressor all fail to reach the highest efficiency region.
  
• 3750 rpm "knee" points for this compressor at all levels of boost are in the surge threshold region
  
• It should be obvious that this compressor will work better with a larger displacement or higher flowing engine as its sweet spot is far to the right where higher flows are required.
  
• Goldilocks says "too demanding and too big”
   
  
  

This GT40R is a large frame turbo and has a T4 flange:

• 6500 rpm red line points for this compressor all fail to reach the highest efficiency region.
  
• 3750 rpm "knee" points for this compressor at all levels of boost are in the surge threshold region
  
• It should be obvious that this compressor will work better with a larger displacement or higher flowing engine as its sweet spot is far to the right where higher flows are required.
  
• Goldilocks says "too demanding and too big”
   
  
  

Here are a few journal bearing turbos, first the GT32 (71mm) and then two GT37s (76mm and 82mm)

• 6500 rpm red line points at 10 psi and 16psi are in the 65 to 68% efficiency region. At 20 and 25 psi the red line points are off the compressor map where the turbo would be overspinning
  
• 3750 rpm "knee" points for this compressor at all four levels of boost are in the 76% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 76% area for 10, 16 and 20psi, thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle only slightly more boost above 16psi and it will run well from 10psi to 16psi of boost, or higher boost on a lower displacement motor
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "great for low end response like auto-X or daily driving but not much room to grow"
   
   
   
  
  
• 6500 rpm red line points for this compressor at 10, 16 and 20psi of boost are in the 75% efficiency region. At 25psi the compressor is nearing its maximum speed and is in danger of overspinning
  
• 3750 rpm "knee" points for this compressor at all levels of boost are in the 70% efficiency region. At 25psi the knee is near the surge threshold region
  
• When accelerating towards redline, the efficiency passes through the maximum 76-77% area, thus performance is ideal during this period especially at 16 and 20psi.
  
• It should be obvious that this compressor will work best up to the 25psi line. Up to 20psi it can handle more flow from porting, a cam, intake, displacement, etc.
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "just right, with room to grow"
  
  
  

• 6500 rpm red line points for this compressor at all four levels of boost are in the 74% efficiency region.
  
• 3750 rpm "knee" points for this compressor at all three levels of boost are in the 68% efficiency region.
  
• When accelerating towards redline, the efficiency passes through the maximum 76% area at 16 and 20psi, and through the 74% region at 10 and 25psi. Thus performance is ideal during this period.
  
• It should be obvious that this compressor can handle even more boost and more flow and remain quite efficient. "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, with room to grow"
  

Edited March 27, 2009 by boardkid280z
formatting

[boardkid280z]

Notes about the post:

• I feel like I wasn't very successful in formatting my post inside the constraints of a vBulletin forum format - if any moderators see changes they can make to the formatting to make the information more clear, please go ahead.
  
• If anyone sees anything that is incorrect/questionable, you can post to let me know, or you might just send me a private message so I can change it without cluttering up the thread.
   
  
  

Options for additional information:

• Making an adjusted graph for more efficient motors (higher VE = more displacement, cams to increase VE, more boost, more RPMs, aftermarket intake, ported head). These graphs would have both the "knee" point and the redline point shifted to the right on the map for each boost plot. I was thinking of using a VE of .90 instead of the .80 I used for the stock motor, what do you guys think of that?
  
• Trying to place the max torque point in the middle of the high efficiency island. (matching turbos to specific applications)
  
• Adding a higher boost line, or consolidating the boost lines to 10, 20 and 30psi – maybe not necessary because it seems these turbos lose efficiency above pressure ratios of 2.7 (25psi)
  
• Comparing the compressor maps to the different turbine maps available for each compressor and adjusting the plots according to the flow expectations for higher/lower flowing turbines – adjusting knees according to A/R and turbine flow. Smaller turbines, quicker spool, knees closer to the surge line, and vice versa.
  

[boardkid280z]

Buick Grand National 1986-1987 turbo compressor map: Garrett TBO-348.

 

There is precious little info on these turbos and this is the only compressor map I was able to find. Some sources said it was one of the biggest T3s Garrett ever made. Others said it will support 375-400hp (crank/wheels?).

(from: http://www.turbobuick.com/forums/turbos-turbo-related-parts/247569-stock-tbo348-compressor-map.html)

 

NOTE: This map is not like the other maps in that it seems to be focused on the highest efficiency regions (65%+ instead of 60%+) and the source mentions the map was limited to < 2.6 PR where the others would not be limited. I am not sure, but it seems like the speed line 120501 is not necessarily the max RPM for this compressor either, but on the other maps it does seem like the top RPM line is max.

 

• 6500 rpm red line points at 10 psi and 16psi are in the 60 to 65% efficiency region. 20 psi may still be in the 60% region too.
  
• 3750 rpm "knee" points for this compressor at 10 and 16psi of boost are in the highest efficiency region.
  
• When accelerating towards redline, the efficiency starts in the maximum efficiency area for 10, 16 and 20psi, thus performance is ideal during this period.
  
• It seems that this compressor can handle only slightly more boost above 20psi and it will run well from 7psi to 20psi of boost. The source says it is used up to 44psi, but it seems like it will just produce a lot of heat above 25psi
  
• This compressor will give great performance compared to the stock T3-60.
  
• Goldilocks says "great upgrade with good performance, not much room to grow."
  
  

[wigenOut-S30]

I hope Big Phil Chimes in here as he is running a GT35R right now on his Z. he states that he gets full boost at like 2800 RPMs. That doesnt seem to match what the graph there is showing for the GT35R. I was going to go with a GT30R but went with a precision non Ball bearing unit instead because of cost.. Very interesting information indeed.

[boardkid280z]

Thanks for pointing that out, I will try to PM bigphil to get more information from him.

 

I would really like to do the comparison of one compressor with several different turbine housings. This will mainly affect spool-up, and therefore would move the knee point left and right. With a smaller turbine housing, the knee point could be significantly farther left from where I placed them.

[TimZ]

FWIW, here's what my last dyno pull looked like with my GT42r:

 

 

Airflow was calculated using wideband afr readings, injector flow rate and pulsewidth and assuming E85 fuel. The pulls were done pretty close to the time of year when E85 gets switched over to E70 for cold weather startability, so I dont know exactly what the mix was. If the calculations are done assuming E70, the flow numbers get pushed farther to the right.

[jgkurz]

FWIW, here's what my last dyno pull looked like with my GT42r:

 

 

Airflow was calculated using wideband afr readings, injector flow rate and pulsewidth and assuming E85 fuel. The pulls were done pretty close to the time of year when E85 gets switched over to E70 for cold weather startability, so I dont know exactly what the mix was. If the calculations are done assuming E70, the flow numbers get pushed farther to the right.

 

 

I'm just seeing this thread.

 

TimZ, From my perspective, the GT42R is a great match for your car. Looks like James knew what he was talking about...: ) You have room to grow on the top end and are nicely inside the surge line. The spool up flows through the high efficiency island perfectly. If the car ran well on E70, I'm guessing E85 won't move your plot much farther to the right if any. BTW, on your airflow plot, how much bhp are you making for 10lb/min? In other words, do you think you are making 700bhp at 70lb/min? It's my belief that modern engines (4v per cyl, variable cam timing, cross flow head) can achieve over 100HP for every 10lb/min of flow. I don't think our L28's can get there unless the engine is running right at peak VE.

 

I am saving my penny's for a GT35R but according the thread it's not an ideal street turbo. That is if I trust the plots being shown. The GT3782 plots better but does not have the peak flow of a GT35R. I need a turbo that can flow 60lb/min. The GT35R has a great map until about 18psi then (according the the plots in this thread) surge would occur. My hope is that the plot on my car would pivot more to the right. In other words, I believe my plot on a GT35R would be inside the surge line at 22psi which I believe to be the max practical pressure for this turbo. My engine is 3.0L vs 2.8 and I have many flow enhancements leads me to believe that I will be moving more air sooner than the plots in this thread. Turbine size would also affect the plot. I suppose I could do my own plot based on my dyno pulls... hmmmmm

[Garrett76Zt]

I dont have any charts to post but from my experience with the turbo's I've run . . . The 60-1 t3/t4 option is a great one. I ran a stage V .63 A/R backside and a TO4E cover, 3" inlet. Its relatiively cheap (i ran a standard journal bearing version) and flows over 60 lb/min. On my L28 (.080 over 3.0liter) I got full boost(25psi) at around 3700rpms and made 440whp on a stock head/cam.

 

I ended up killing it with too many hot shut downs (DANG you DNI shootout! hahaha.) and decided to do a minor upgrade. I specifically asked for a slight bump in power without sacrificing spool and what I ended up with was a "blowzilla", basically a GT40 Compressor side, 4" inlet housing, and the same exact turbine setup from before. Same exact boost the car put down 460whp with no noticeable change in spool. Both of these are journal bearing and can be had brand new for less than $1000.

 

I thought both of these were a great compromise in streetability. Powerband was from 3700-6000rpms and then once I upgraded cams up to 7krpms. Certainly didnt spool like a stock t3, haha, but very reasonable in my opinion. Just my .02 hope it helps. . .

[Tony D]

JeffP is running GT35® I believe, and gets full boots at 3400rpms like clockwork. He will get 2-3psi at off-idle when going WOT, and becase of his porting and cam, the car pulls like a much larger displacement N/A engine below boost threshold, and since the cam comes on 'above' boost threshold, it REALLY starts pulling around 4500 (peak torque?).

He doesn't seem to get much over 17-18 psi, and has run it at 20psi, but with no great effects. I may be out-of-date with his latest testing after installing the stock L28ET bottom end for some testing compared with the Stroker, but these numbers should be good for that application as well from what I gathered talking with him.

 

One of his previous builds had a turbo that would get boost a 3K rpms, and the car would go from 150 to 450HP in like 500 rpms. At first he didn't like the 'soft aspect' of how the GT35R came on, but he's learned that it makes for much more useable horsepower, and if he wants spunky tricks, he just cruises in 4th...

[dpuma8]

Still haven't decided on a turbo but it is between a 3071R and a 3076R in either a .63 or .82 A/R.  What would goldilocks say about these trims?  What if I have my head ported?