Limbo
02-04-2009, 10:56 PM
Hopefully this will help others on which turbos will suit your application
This is test done a a MR2 motor(principles are still the same), from;
http://au.boostcruising.com/forums/lofiversion/index.php/t307267.html
This is how to choose the Garrett GT turbo that will rock you!
The clever turbine engineers at Garrett have shared with us their turbo and performance specifications in the form of measurements, and compressor and turbine maps, and with a little knowledge we can use them to find the right turbo for every application. As we collect more actual results we will be able to even more accurately predict performance on the 3S-GTE. But we already have the tools we need, and you can learn a lot of the nitty-gritty stuff from the section "Turbine Efficiency - Part 2...the missing piece to the turbo selection puzzle".
http://www.turbobygarrett.com/turbobygarre...bo_tech101.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html)
http://www.turbobygarrett.com/turbobygarre...bo_tech102.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html)
http://www.turbobygarrett.com/turbobygarre...bo_tech103.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html)
I'll just cover the highlights from that thread, and highlight the highlights in bold, to present this information in an easy to understand form, and use it to establish some general guidelines to finding the turbo of your dreams...the one that will provide the realistic best possible spool for the strongest bottom end, fullest mid-range, and extended top end.
A quick and dirty review of how a turbo works is essential as it is fundamental to understanding the tools we have to help us choose. A turbo is an air pump that’s powered by the energy contained in the engine's exhaust gas flow by spinning a turbine impeller wheel. That wheel rotates on a shaft that has a compressor wheel mounted to the other end that then also spins and forces more air into the engine's intake. It's the exhaust energy and turbine wheel that powers the compressor wheel to increase intake air pressure, and your boost controller that determines the amount of pressure (with the wastegate redirecting exhaust flow as required to prevent over-boosting). It's important to recognize that it's the compressor wheel that's in charge of reaching the desired boost pressure, and the turbine wheel’s job to spin it accordingly. When the turbine is struggling to do its job effectively the compressors ability to provide boost in a timely manner is compromised and we recognize this effect as turbo lag. When it's completely up to the challenge to power the compressor we recognize it as providing excellent throttle response.
In fact, our success in choosing the best turbo for our use rests solely on our ability to understand this relationship between turbine and compressor. And for our purposes of choosing among the GT line that relationship is primarily determined by (a) the relative diameters of those two wheels and (b) the aerodynamics of the turbine housing. The resulting performance is called Turbine Efficiency, and its measure is expressed as a percentage. A turbo whose turbine can efficiently power the compressor to produce quick spool and less restricted top end flow has a higher %, often close to or slightly exceeding 70%, while others are as low as 60%.
Here's what we're looking for in the Garrett specs:
(a) Garrett recommends a wheel diameter ratio range between 1.1:1 and 1.25:1 (compressor:turbine) to provide the best overall performance. As an example the GT28RS has a ratio of 1.1:1 (60mm/53.8mm) at the quickest spooling end of the range, and the GT3076R has 1.27:1 (76.2mm/60mm)…barely outside the other end of the range. The reason a large compressor wheel mated to a smallish wheel would not be able to spool as quickly is because a largish compressor wheel will need to turn slower to provide any given intake airflow than a smaller wheel would, and this in-turn forces the turbine wheel on the other end of the shaft to turn slower, and at speeds that it can’t operate as efficiently at. This is contrary to those that believe a comparatively small turbine wheel and housing will cause the largish compressor to spool more quickly. Dyno results confirm Garrett’s recommendations every time, while I have never seen evidence of a small turbine/large compressor spooling nearly as quickly.
Good examples to see this effect would be the GT28RS, GT2871R (or HKS GTRS), and GT2876R (or HKS GT2540R). All three share the identical turbine housing and wheel, but are mated with 60mm, 71mm, and 76 mm compressor wheels. The latter two compressor wheel diameters push the wheel ratio well outside of the recommended range to 1.32:1 and 1.45:1. Each larger compressor wheel causes a delay in spool of perhaps 750 rpm to ~17 psi and makes less top end power as well. The only way to make these wider spaced wheel combinations make more power is to significantly raise boost pressure. This however will not reduce lag, the restrictively small turbine wheel and housing will limit high rpm power as it reduces the entire engine’s VE, less ignition timing can be run at high rpm causing reduced power from the airflow, exhaust temps will be higher, and you’ll have to deal with all of the risks associated with higher boost levels. The solution is to follow Garrett’s recommendations whenever possible.
(b) The turbine housings are designed to maximize turbine efficiency. In some cases though a turbine housing will be made or modified to fit specific user applications like space constraints or the lack of suitable sized exhaust manifold turbine mounting flanges for some popular applications. This has led to small turbines modified to stuff in large wheels, large turbos with small turbines made to fit onto small exhaust manifold flanges, smallish turbos modified to fit onto large flanged manifolds, etc…and all of them have reduced the turbine’s efficiency to spool quickly and produce the strongest powerband. The impact of some twin scroll housings can’t be predicted because of their lack of turbine efficiency ratings by Garrett, but their impact will be seen in dyno results. In some of these cases the wheel ratio will appear to be ideal, but the modification to the turbine housing itself can negatively affect turbine efficiency. This is why it’s important to know the Garrett tested Turbine Efficiency % rating.
The various iterations of GT3071R is a good example of these variables. All models use the 71 mm compressor wheel, but some have a 56.5mm turbine wheel stuffed into a machined T28 turbine housing, some have the better matched 60mm turbine wheel fitted to a twin scroll housing of unknown efficiency, and the one that mates it with the 60 mm turbine wheel and T3 single scroll housing. The latter is surely the best of the bunch using Garrett’s specs and recommendations, and it’s very high efficiency rating of 72% and ideal wheel ratio of 1.18:1means that for this size of turbo you are unlikely to find anything that will out-spool or out-flow it. It also means that the similarly flow rated GT2871R models with less than ideal wheel ratio and as little as 60% turbine efficiency will not perform as well as the GT3071R at 72%. Some feel that the GT3071R versions that have been used on the 3S-GTE have been less than stellar performers, but these results I'd suggest are consistent with Garrett’s specs, ratings, and the recommendations presented here. Let’s choose the best model and set some powerband records!
I’d recommend that you first use the Garrett compressor maps to identify the compressor that can flow your requirements (see Garrett’s Turbo Tech section for these calculations), and then to consider the wheel ratios and the turbine efficiency ratings found on their turbine maps as a guide to matching that compressor with a suitable turbine wheel and housing. While efficiency actually varies with flow rate, pressure ratio (think boost level), and turbine wheel rotation speed, the stated maximum efficiency rating is going to be quite comparable among all models within the GT line.
Now you need to choose the turbine housing AR. You’ll notice on the turbine maps that the efficiency curves are different for the various available turbine housing AR. These shows that the lower AR housings are more efficient at lower flow rates generated at lower engine rpm, while higher AR housings are more efficient at higher rpm flow rates. These housing options will allow you to choose between maximum low rpm spool and power at the cost of a little high rpm peak power, or maximum peak power at the cost of a little lower rpm performance, or something in-between if there’s a 3rd option. Valendia and RickyB provided a good dyno comparison of this AR housing trade-off using a .64 and .82 AR on the GT28RS. The lower AR made for a significantly stronger powerband overall on this setup, and I believe we will see this trend with each turbo model and engine setup…if peak power is your goal the higher AR will likely provide that every time.
I hope this will help you better choose from the GT turbo options that are available.
Bruce Hadfield
Garrett specs, compressor and turbine maps can be found at http://www.turbobygarrett.com/turbobygarre...bochargers.html (http://www.turbobygarrett.com/turbobygarrett/products/turbochargers.html) , and
Compressor selection guidelines at http://www.turbobygarrett.com/turbobygarre...ech_center.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/tech_center.html)
Turbine Efficiency - Part 2...the missing piece to the turbo selection puzzle
Let’s quickly review the resources we’ve been using to choose a turbo so we can better appreciate our current needs:
1. Testimonials. While it may be entertaining to hear about how somebody smoked another car at a stop light, or how they got pushed back into the seat when the turbo kicked in, the general lack of useful information and the subjective nature of the comments leads us directly to #2.
2. Dyno Graphs. Dynos measure power at the wheels (or hubs) and that power is affected by many non-turbo factors. While dyno results have been widely regarded as the best tool we have to measure the difference certain modifications make, they are not a perfect tool. General engine condition, supporting mods, boost levels that can change during a run, aggressiveness of the air/fuel ratio and ignition timing, octane, 3rd vs. 4th gear, and a wide range of dyno equipment and testing factors and conditions can make it difficult to clearly see the impact of only the turbo, or compare one turbo to another. Throw in some mods that can greatly differ from car to car, such as the state of tune of an EMS, or mods that affect volumetric efficiency like a set of cams and cam gears, custom intake, and maybe a little head-work, and it becomes almost impossible to determine how much of the dyno results are the result of the turbo alone. At best you can see what is possible on a given set-up. If you want to research a turbo not yet dyno’d, or learn more about the ones you see in the dynos, you proceed to the dreaded step #4.
3. Turbo “Power Ratings/Estimates” Often around as useless as Testimonials and with all the limitations of Dyno plots (so many other things that effect power other than turbo by itself)
4. Compressor Maps. These are the turbo manufacturer’s graphic representations of the compressor’s ability to flow air across a range of pressure ratios. Compressor efficiency and shaft speeds are shown. We then need to “estimate” our engine’s airflow requirements throughout our desired powerband using a complicated formula designed by the devil him self, and then learn all about a compressor map so we can check to see which compressor “might” be able to provide the required amount of airflow. You really should struggle through the formula of estimating your engine’s airflow requirements to truly appreciate all the factors that affect it. While you may have been led to believe that finding a suitable compressor map will identify a suitable turbo, this isn’t necessarily true, and many members have discovered this the hard way. That’s because the ability of the compressor to deliver its indicated airflow is dependant on the turbos turbine section, and something called turbine efficiency…the subject of this article.
Turbine Efficiency
So what is turbine efficiency and why should we care? The compressor relies on the turbine to use the exhaust gas energy to power the shaft that spins the compressor wheel that pushes the air through the engine to create ungodly amounts of torque when mixed with fuel and a well-timed spark. And if the turbine goes about it’s job in a sloppy and inefficient way then the compressor won’t be able to do its job well, and performance will suffer. A turbine operating at high efficiency will be able to more quickly spool a compressor when called upon to make good low-end power, and/or will provide less back-pressure at high rpm to enable the turbo to make more top-end power by actually improving the engine’s volumetric efficiency. Turbine efficiency is the ratio of useful exhaust energy to total energy supplied, the flow at which it’s efficiency is the highest at all pressure ratios is plotted on it's “turbine map”. and it's maximum efficiency is stated as a percentage.
Turbine efficiency and maps are closely related to the compressor, and further discussion would be easier if related to an actual turbo. Only Garrett publishes turbine maps to my knowledge, and since I was able to use them to select my turbo and then acquire actual 3S-GTE results, let’s use my GT28RS for our example. It will then be interesting to see how we can carefully navigate through a staggering choice of 17 GT turbos models and predict their performance. I’ll make this clear by keeping it fairly simple…I promise!
Example - Crunching the numbers for a stock Gen 2 3S-GTE
This is test done a a MR2 motor(principles are still the same), from;
http://au.boostcruising.com/forums/lofiversion/index.php/t307267.html
This is how to choose the Garrett GT turbo that will rock you!
The clever turbine engineers at Garrett have shared with us their turbo and performance specifications in the form of measurements, and compressor and turbine maps, and with a little knowledge we can use them to find the right turbo for every application. As we collect more actual results we will be able to even more accurately predict performance on the 3S-GTE. But we already have the tools we need, and you can learn a lot of the nitty-gritty stuff from the section "Turbine Efficiency - Part 2...the missing piece to the turbo selection puzzle".
http://www.turbobygarrett.com/turbobygarre...bo_tech101.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech101.html)
http://www.turbobygarrett.com/turbobygarre...bo_tech102.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech102.html)
http://www.turbobygarrett.com/turbobygarre...bo_tech103.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html)
I'll just cover the highlights from that thread, and highlight the highlights in bold, to present this information in an easy to understand form, and use it to establish some general guidelines to finding the turbo of your dreams...the one that will provide the realistic best possible spool for the strongest bottom end, fullest mid-range, and extended top end.
A quick and dirty review of how a turbo works is essential as it is fundamental to understanding the tools we have to help us choose. A turbo is an air pump that’s powered by the energy contained in the engine's exhaust gas flow by spinning a turbine impeller wheel. That wheel rotates on a shaft that has a compressor wheel mounted to the other end that then also spins and forces more air into the engine's intake. It's the exhaust energy and turbine wheel that powers the compressor wheel to increase intake air pressure, and your boost controller that determines the amount of pressure (with the wastegate redirecting exhaust flow as required to prevent over-boosting). It's important to recognize that it's the compressor wheel that's in charge of reaching the desired boost pressure, and the turbine wheel’s job to spin it accordingly. When the turbine is struggling to do its job effectively the compressors ability to provide boost in a timely manner is compromised and we recognize this effect as turbo lag. When it's completely up to the challenge to power the compressor we recognize it as providing excellent throttle response.
In fact, our success in choosing the best turbo for our use rests solely on our ability to understand this relationship between turbine and compressor. And for our purposes of choosing among the GT line that relationship is primarily determined by (a) the relative diameters of those two wheels and (b) the aerodynamics of the turbine housing. The resulting performance is called Turbine Efficiency, and its measure is expressed as a percentage. A turbo whose turbine can efficiently power the compressor to produce quick spool and less restricted top end flow has a higher %, often close to or slightly exceeding 70%, while others are as low as 60%.
Here's what we're looking for in the Garrett specs:
(a) Garrett recommends a wheel diameter ratio range between 1.1:1 and 1.25:1 (compressor:turbine) to provide the best overall performance. As an example the GT28RS has a ratio of 1.1:1 (60mm/53.8mm) at the quickest spooling end of the range, and the GT3076R has 1.27:1 (76.2mm/60mm)…barely outside the other end of the range. The reason a large compressor wheel mated to a smallish wheel would not be able to spool as quickly is because a largish compressor wheel will need to turn slower to provide any given intake airflow than a smaller wheel would, and this in-turn forces the turbine wheel on the other end of the shaft to turn slower, and at speeds that it can’t operate as efficiently at. This is contrary to those that believe a comparatively small turbine wheel and housing will cause the largish compressor to spool more quickly. Dyno results confirm Garrett’s recommendations every time, while I have never seen evidence of a small turbine/large compressor spooling nearly as quickly.
Good examples to see this effect would be the GT28RS, GT2871R (or HKS GTRS), and GT2876R (or HKS GT2540R). All three share the identical turbine housing and wheel, but are mated with 60mm, 71mm, and 76 mm compressor wheels. The latter two compressor wheel diameters push the wheel ratio well outside of the recommended range to 1.32:1 and 1.45:1. Each larger compressor wheel causes a delay in spool of perhaps 750 rpm to ~17 psi and makes less top end power as well. The only way to make these wider spaced wheel combinations make more power is to significantly raise boost pressure. This however will not reduce lag, the restrictively small turbine wheel and housing will limit high rpm power as it reduces the entire engine’s VE, less ignition timing can be run at high rpm causing reduced power from the airflow, exhaust temps will be higher, and you’ll have to deal with all of the risks associated with higher boost levels. The solution is to follow Garrett’s recommendations whenever possible.
(b) The turbine housings are designed to maximize turbine efficiency. In some cases though a turbine housing will be made or modified to fit specific user applications like space constraints or the lack of suitable sized exhaust manifold turbine mounting flanges for some popular applications. This has led to small turbines modified to stuff in large wheels, large turbos with small turbines made to fit onto small exhaust manifold flanges, smallish turbos modified to fit onto large flanged manifolds, etc…and all of them have reduced the turbine’s efficiency to spool quickly and produce the strongest powerband. The impact of some twin scroll housings can’t be predicted because of their lack of turbine efficiency ratings by Garrett, but their impact will be seen in dyno results. In some of these cases the wheel ratio will appear to be ideal, but the modification to the turbine housing itself can negatively affect turbine efficiency. This is why it’s important to know the Garrett tested Turbine Efficiency % rating.
The various iterations of GT3071R is a good example of these variables. All models use the 71 mm compressor wheel, but some have a 56.5mm turbine wheel stuffed into a machined T28 turbine housing, some have the better matched 60mm turbine wheel fitted to a twin scroll housing of unknown efficiency, and the one that mates it with the 60 mm turbine wheel and T3 single scroll housing. The latter is surely the best of the bunch using Garrett’s specs and recommendations, and it’s very high efficiency rating of 72% and ideal wheel ratio of 1.18:1means that for this size of turbo you are unlikely to find anything that will out-spool or out-flow it. It also means that the similarly flow rated GT2871R models with less than ideal wheel ratio and as little as 60% turbine efficiency will not perform as well as the GT3071R at 72%. Some feel that the GT3071R versions that have been used on the 3S-GTE have been less than stellar performers, but these results I'd suggest are consistent with Garrett’s specs, ratings, and the recommendations presented here. Let’s choose the best model and set some powerband records!
I’d recommend that you first use the Garrett compressor maps to identify the compressor that can flow your requirements (see Garrett’s Turbo Tech section for these calculations), and then to consider the wheel ratios and the turbine efficiency ratings found on their turbine maps as a guide to matching that compressor with a suitable turbine wheel and housing. While efficiency actually varies with flow rate, pressure ratio (think boost level), and turbine wheel rotation speed, the stated maximum efficiency rating is going to be quite comparable among all models within the GT line.
Now you need to choose the turbine housing AR. You’ll notice on the turbine maps that the efficiency curves are different for the various available turbine housing AR. These shows that the lower AR housings are more efficient at lower flow rates generated at lower engine rpm, while higher AR housings are more efficient at higher rpm flow rates. These housing options will allow you to choose between maximum low rpm spool and power at the cost of a little high rpm peak power, or maximum peak power at the cost of a little lower rpm performance, or something in-between if there’s a 3rd option. Valendia and RickyB provided a good dyno comparison of this AR housing trade-off using a .64 and .82 AR on the GT28RS. The lower AR made for a significantly stronger powerband overall on this setup, and I believe we will see this trend with each turbo model and engine setup…if peak power is your goal the higher AR will likely provide that every time.
I hope this will help you better choose from the GT turbo options that are available.
Bruce Hadfield
Garrett specs, compressor and turbine maps can be found at http://www.turbobygarrett.com/turbobygarre...bochargers.html (http://www.turbobygarrett.com/turbobygarrett/products/turbochargers.html) , and
Compressor selection guidelines at http://www.turbobygarrett.com/turbobygarre...ech_center.html (http://www.turbobygarrett.com/turbobygarrett/tech_center/tech_center.html)
Turbine Efficiency - Part 2...the missing piece to the turbo selection puzzle
Let’s quickly review the resources we’ve been using to choose a turbo so we can better appreciate our current needs:
1. Testimonials. While it may be entertaining to hear about how somebody smoked another car at a stop light, or how they got pushed back into the seat when the turbo kicked in, the general lack of useful information and the subjective nature of the comments leads us directly to #2.
2. Dyno Graphs. Dynos measure power at the wheels (or hubs) and that power is affected by many non-turbo factors. While dyno results have been widely regarded as the best tool we have to measure the difference certain modifications make, they are not a perfect tool. General engine condition, supporting mods, boost levels that can change during a run, aggressiveness of the air/fuel ratio and ignition timing, octane, 3rd vs. 4th gear, and a wide range of dyno equipment and testing factors and conditions can make it difficult to clearly see the impact of only the turbo, or compare one turbo to another. Throw in some mods that can greatly differ from car to car, such as the state of tune of an EMS, or mods that affect volumetric efficiency like a set of cams and cam gears, custom intake, and maybe a little head-work, and it becomes almost impossible to determine how much of the dyno results are the result of the turbo alone. At best you can see what is possible on a given set-up. If you want to research a turbo not yet dyno’d, or learn more about the ones you see in the dynos, you proceed to the dreaded step #4.
3. Turbo “Power Ratings/Estimates” Often around as useless as Testimonials and with all the limitations of Dyno plots (so many other things that effect power other than turbo by itself)
4. Compressor Maps. These are the turbo manufacturer’s graphic representations of the compressor’s ability to flow air across a range of pressure ratios. Compressor efficiency and shaft speeds are shown. We then need to “estimate” our engine’s airflow requirements throughout our desired powerband using a complicated formula designed by the devil him self, and then learn all about a compressor map so we can check to see which compressor “might” be able to provide the required amount of airflow. You really should struggle through the formula of estimating your engine’s airflow requirements to truly appreciate all the factors that affect it. While you may have been led to believe that finding a suitable compressor map will identify a suitable turbo, this isn’t necessarily true, and many members have discovered this the hard way. That’s because the ability of the compressor to deliver its indicated airflow is dependant on the turbos turbine section, and something called turbine efficiency…the subject of this article.
Turbine Efficiency
So what is turbine efficiency and why should we care? The compressor relies on the turbine to use the exhaust gas energy to power the shaft that spins the compressor wheel that pushes the air through the engine to create ungodly amounts of torque when mixed with fuel and a well-timed spark. And if the turbine goes about it’s job in a sloppy and inefficient way then the compressor won’t be able to do its job well, and performance will suffer. A turbine operating at high efficiency will be able to more quickly spool a compressor when called upon to make good low-end power, and/or will provide less back-pressure at high rpm to enable the turbo to make more top-end power by actually improving the engine’s volumetric efficiency. Turbine efficiency is the ratio of useful exhaust energy to total energy supplied, the flow at which it’s efficiency is the highest at all pressure ratios is plotted on it's “turbine map”. and it's maximum efficiency is stated as a percentage.
Turbine efficiency and maps are closely related to the compressor, and further discussion would be easier if related to an actual turbo. Only Garrett publishes turbine maps to my knowledge, and since I was able to use them to select my turbo and then acquire actual 3S-GTE results, let’s use my GT28RS for our example. It will then be interesting to see how we can carefully navigate through a staggering choice of 17 GT turbos models and predict their performance. I’ll make this clear by keeping it fairly simple…I promise!
Example - Crunching the numbers for a stock Gen 2 3S-GTE