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This topic has ben discussed on occasion but I was just reviewing the running options for the GT R running stock turbos.
With stock turbos, RENNtech, Eurocharged, Velocity AP, and PTG all have about the same HP rating of around 650-660. But RENNtech vs the others is way behind in torque. They are showing 614 on the dyne vs the others at 700ld ft.
The real difference is in the curves. RENNtech has maintained the nearly flat torque curve with the 614 delivered broadly while all the others are steadily increasing to the 700ft lb peak and then dropping off.
Has anyone driven the different types of tunes back to back? The RENNtech approach would seemingly give the same predictable power band as stock (just more of it) and should be well suited for track use.
The others are pushing maximum power from the stock package and I would expect much more of a shove in the back from the extra 85lb ft of torque as that is a BIG number. It has been established that the gearbox can hold 700ft lbs without needing to increase the operating pressures but a TCU tune is probably a good option for hard use with the bigger torque numbers.
Here is a copy of some perspective that may answer your questions. I hope this will help:
..."If you're a dedicated track enthusiast, dragster, street racer, professional motorsport driver with no budget constraints or warranty concerns, then this discussion may not resonate with you. You'll probably find yourself disagreeing with many points. However, if you primarily use your AMG GT for daily commuting with occasional track outings, and you're looking to sensibly enhance the power and torque of your car, here's a perspective:
Should I upgrade my turbos?
The AMG GT series utilizes bi-turbos, with one turbo unit dedicated to each bank of 4 cylinders. Each turbo provides compressed air to power a "smaller engine," corresponding to half of the 4-liter GT engine, allowing for the use of smaller-sized units. The primary advantage of smaller turbos lies in their ability to spool up faster, significantly reducing turbo lag. Additionally, they are designed to spin at a higher rate per exhaust pressure volume, resulting in substantial boost pressure. However, this design also leads to the disadvantage of generating more heat.
When dealing with OEM or small turbos, there's room to adjust the ECU's fuel tables, timing, and boost levels to notably enhance performance at lower RPM ranges (<5000), albeit with less impact at higher RPM ranges (>5000). Boosting the lower RPM range with smaller turbos is relatively straightforward, delivering a palpable surge at the starting line, noticeable as increased pull. This adjustment typically alters the torque curve from its original flat shape between 2100-5500 RPM to a bell-shaped curve within the 2500-5000 RPM range, followed by a flat or declining curve thereafter. Your tuner can fine-tune the peak and shape of this torque curve to align with your performance goals and driving style. However, it's essential to note that excessive torque at lower RPMs can strain the drivetrain significantly (see the black curve in figure 1). Therefore, it's critical for your tuner to carefully manage power delivery and safeguard the clutch and transaxle, particularly in 1st and 2nd gears.
Figure 1: OEM turbo tune sample. Blue – OEM Tune. Black – boost increase 2500-5500 RPM
Enhancing performance in the higher RPM range using OEM or smaller turbos comes with its set of challenges. Car manufacturers typically incorporate a safety margin to ensure engine and turbo longevity, including factors driven by economic and regulatory compliance. For instance, the AMG GTR boasts a margin of approximately +/-100 crank HP. While it's feasible to tune the OEM turbos to spin faster and increase intake boost, there are limitations to their spin speed. Operating without these safety margins, particularly considering the potential heat buildup and its dissipation, can ultimately result in turbo failure and potentially damage other components such as the intercooler, engine, exhaust system, and transaxle. Based on the experiences of numerous GT owners, it appears that the maximum horsepower achievable with the GTR's OEM turbos typically peaks between 650-670HP at the crank, regardless of the tune applied.
To achieve higher horsepower in the higher RPM range using OEM turbos while ensuring they remain within recommended speed specifications, modifications can be made to the intake side of the turbo. This involves increasing the impeller fan size and intake turbo cavity volume. By enlarging the intake side volume, a greater amount of air is generated per turbo spin at the compressor/impeller, resulting in higher boost for the same impeller spin speed, regulated by the wastegate. This approach is exemplified in turbos such as the PURE 900 or 1000. While these turbos can be tuned for higher torque and horsepower, it's important to note that this doesn't resolve the heat issue. In many cases, addressing heat dissipation may require removing the catalytic converter using new downpipes to facilitate better exhaust flow, particularly at higher horsepower levels.
If your goal is to retain the catalytic converter (or opt for a higher-flow cat replacement) and safeguard your engine, exhaust system, and transaxle, all while achieving a substantial increase in torque and power, larger turbos may be the ideal solution.
Larger turbos feature larger impellers and exhaust turbines, which enable a slower turbine spin while increasing boost compared to smaller turbos. This results in greater power output and reduced heat buildup. Large turbos can deliver a substantial increase in torque and power, with examples like the PTG 1000 or PTG-X turbos showcasing this capability.
Nonetheless, there's a prominent drawback associated with using larger turbos: turbo lag. Turbo lag refers to the delay between pressing the throttle and experiencing the surge of torque from a turbocharged engine. This delay stems from the time it takes for the engine to generate sufficient exhaust pressure to spin the turbo and deliver compressed intake air into the engine. Turbo lag is most noticeable during low-RPM, low-load driving scenarios. Consequently, during daily driving, you may experience a diminished response when demanding power at lower RPMs. However, at higher RPMs, the performance characteristics will be notably different, resulting in a distinct driving experience.
Figure 2: PTG-X sample. Max torque is reached past the 4500 RPM line
As depicted in the chart, maintaining high RPM, typically above 3000 RPM, notably reduces turbo lag, facilitating rapid power delivery and substantial power gains.
Regardless of your decision, there's another crucial factor to consider: the maximum torque capacity of the transaxle. The AMG GT series employs the Getrag/Magna 7DCL750 DCT transaxle, which is manufacturer-rated to handle up to 750nm or 553 Ft-Lb of torque at the crank. Accounting for a safe margin, the ultimate maximum torque could be around 820nm or 605 Ft-Lb before risking permanent damage to the transaxle. It's highly advisable not to surpass the transaxle's specifications when tuning the ECU. In addition, modifying the TCU to increase line pressure doesn't necessarily enhance the car's performance, especially with the moderate increase in horsepower we're aiming for. Elevating line pressure or upgrading the clutch to eliminate clutch slippage removes the transaxle protection provided by clutch slips, thus exposing it to potential damage from excessive torque bursts. Its easier and more cost effective to replace clutch then the entire transaxle.
Is there a turbocharger available that delivers power across all ranges without experiencing lag or heat-related issues? The answer is affirmative, and such solutions do exist, known as e-turbos. E-Turbos are new and not widely available. I have yet to find one suitable for the GT line.
Conclusions:
Ultimately, the decision on which turbo to choose and how to tune it should align with your driving habits, whether on the track or daily street. If you're not particularly focused on maximizing power and don't frequently track your car, the OEM power provided by AMG original tune is generally sufficient. However, if you desire a bit more power while maintaining safety, a canned tune like the one offered by Renntech can be a suitable option. Such tunes typically offer moderate power and torque increases and mimic the OEM torque curve well, providing a flat torque line from 3000-5500 RPM.
Should you seek even higher levels of performance, custom tuning and/or turbo unit modification may be necessary. To effectively communicate your power demands to the tuner, consider utilizing the car's built-in Track Pace program or other reliable third-party recorders to capture data while racing on your favorite tracks, providing the tuner with track layouts, speeds, and RPMs at various segments and track-out sections. This information can help the tuner tailor the power curve to suit your needs across all tracks used into a single tune map or create multiple maps, so you can have different performance curves for each application.
Ultimately, prioritize your perceived fun factor when making your decision, while also considering the engineering facts outlined above.
Here is a copy of some perspective that may answer your questions. I hope this will help:
Conclusions:
Ultimately, the decision on which turbo to choose and how to tune it should align with your driving habits, whether on the track or daily street. If you're not particularly focused on maximizing power and don't frequently track your car, the OEM power provided by AMG original tune is generally sufficient. However, if you desire a bit more power while maintaining safety, a canned tune like the one offered by Renntech can be a suitable option. Such tunes typically offer moderate power and torque increases and mimic the OEM torque curve well, providing a flat torque line from 3000-5500 RPM.
Should you seek even higher levels of performance, custom tuning and/or turbo unit modification may be necessary. To effectively communicate your power demands to the tuner, consider utilizing the car's built-in Track Pace program or other reliable third-party recorders to capture data while racing on your favorite tracks, providing the tuner with track layouts, speeds, and RPMs at various segments and track-out sections. This information can help the tuner tailor the power curve to suit your needs across all tracks used into a single tune map or create multiple maps, so you can have different performance curves for each application.
Ultimately, prioritize your perceived fun factor when making your decision, while also considering the engineering facts outlined above.
Thanks. That is a good read.
There is also a good thread around here somewhere on the limits of the gearbox and clutch in the GT R. They were found to be sufficiently high for most upgrades.
If I'm reading the larger PTG Turbo graph vs. the stock graph above it seems that at every RPM from 3500 on up torque is greater with larger turbos. I assume this is at WOT max power. So realistically when getting on it the car would downshift putting the car in the correct rev range above 3,500 for power, and the Torque up there is always greater then a car with stock turbos.
As for non-WOT under 3,000 RPM - when I look at my HP and Torque meter while driving around it never goes above 200-300 ft-lbs. And if I floor it to get more power the car downshifts and the rev's are up right in the powerband where the larger PTG turbos destroy stock turbos.
Y/N?
I've been following these PTG1000 threads as that is the route I think I want to go and to me it seems lag would be a non-issue. I'm also scared of wrecking my street car driving around town. What am I missing?
If I'm reading the larger PTG Turbo graph vs. the stock graph above it seems that at every RPM from 3500 on up torque is greater with larger turbos. I assume this is at WOT max power. So realistically when getting on it the car would downshift putting the car in the correct rev range above 3,500 for power, and the Torque up there is always greater then a car with stock turbos.
As for non-WOT under 3,000 RPM - when I look at my HP and Torque meter while driving around it never goes above 200-300 ft-lbs. And if I floor it to get more power the car downshifts and the rev's are up right in the powerband where the larger PTG turbos destroy stock turbos.
Y/N?
I've been following these PGT1000 threads as that is the route I think I want to go and to me it seems lag would be a non-issue. I'm also scared of wrecking my street car driving around town. What am I missing?
You're absolutely correct. By maintaining the larger turbos spooled and controlling the RPM and shift points, you'll consistently have more power than with the stock setup. The only instance where you might notice a slight delay (lag) is during casual starts at traffic lights or when accelerating from lower RPMs. However, in my experience, I've found this to be a non-issue.
You're absolutely correct. By maintaining the larger turbos spooled and controlling the RPM and shift points, you'll consistently have more power than with the stock setup. The only instance where you might notice a slight delay (lag) is during casual starts at traffic lights or when accelerating from lower RPMs. However, in my experience, I've found this to be a non-issue.
Here is mine. I have 200 cell sports cats with a stage 2 tune.
I'm using a track map from OPUS (ex Renntech Europe) as the mapper Lukas has founded OPUS after stopping Renntech Europe. He did a perfectly smooth map with ZERO torque spike. Numbers are maybe lower than some other names, but the curves are perfectly flat, no hardware is damaged even on track and the usability is perfect, even on the Nurburgring !
From memory, it's about 655hp and 890Nm, fully flat and clean.
I'm using a track map from OPUS (ex Renntech Europe) as the mapper Lukas has founded OPUS after stopping Renntech Europe. He did a perfectly smooth map with ZERO torque spike. Numbers are maybe lower than some other names, but the curves are perfectly flat, no hardware is damaged even on track and the usability is perfect, even on the Nurburgring !
From memory, it's about 655hp and 890Nm, fully flat and clean.
That sounds impressive. If the torque remains consistent at 890 Nm all the way to the 6200 -6500 rpm range, it eliminates the necessity for precise gear change timing based on rpm or speed, while on the track. Does OPUS offer this tune map for remote upload? Also, do you have a dyno chart illustrating this map?
That sounds impressive. If the torque remains consistent at 890 Nm all the way to the 6200 -6500 rpm range, it eliminates the necessity for precise gear change timing based on rpm or speed, while on the track. Does OPUS offer this tune map for remote upload? Also, do you have a dyno chart illustrating this map?
I'm anyway shifting around 6000 usually and use more the torque, except on the longer straights of the Ring.
I'll look for my graph, but I know they do work remote too, if you have a dyno.
03-15-2024, 11:31 AM
