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How Your Drive Train Handles Boost

“Roots and Twin-Screw superchargers are known for the higher low-end torque they provide. Are they harder on the drive train components than a centrifugal supercharger is?”


Written by James Bertok - Guest Tech Guru

The short answer to this question is both yes and no, so let's start with the basics. (See a comparison of supercharger types here!)

Drive train defined:
The system that transfers power from the engine to the wheels is known as the drive train or driveline. It includes the clutch or torque converter, the transmission, differential, ring and pinion gears, axles, and where applicable drive shaft(s) and transfer case, universal and/or CV-joints.

Power train defined:
The complete system of the engine and the drive train.

Understanding Factory Drive Train Limitations

The drive train in your car or truck is designed, by the manufacturer, to be strong enough to handle full engine power at the vehicle’s load and gross weight limits. Safety margins are factored into each component so that the entire powertrain will survive moments of particularly strenuous conditions. (ex: Shifting an automatic transmission into “Drive” and applying power while the vehicle is rolling in reverse). In some cases, the vehicle’s Powertrain Control Module (PCM) is programmed to identify stressful drive train conditions and take actions electronically to reduce them. One such example of this is where power is reduced during down or up shifting to extend the life of the transmission.

Many systems can also limit torque taking off from a stop. Abusive situations can also be identified by the PCM, such as a driver shifting back and forth between reverse and drive to create a rocking motion, or a high throttle position when putting the vehicle into gear - also known as “the drop shift.” The manufacturer knows exactly how much stress each component can handle under various conditions before it fails. The onboard computer (PCM) provides a way to extend the safety margins of the drive train without installing larger, heavier components. This contributes to higher fuel economy and lower cost.

Are Supercharger Kits Designed With Drive Train Limitations in Mind?

A Supercharger kit is the single best power upgrade you can make to your vehicle. Every supercharger manufacturer goes through extensive design, prototyping, testing, tuning, and qualification of each system before it can ever be brought to market. Most kits are tuned to be installed on otherwise factory-equipped engines. Power levels are specifically tuned not to exceed the critical thresholds of the OEM drive train components. An example of the Supercharger industry’s engineering confidence in their products' effect on powertrain lifespan is MagnaCharger’s 3-year/36,000 mile limited powertrain warranty.

What Affect Do Other Upgrades Have?

As explained, a supercharger kit installed to the manufacturers' specifications will not exceed the factory power train’s capacities. Problems will start to appear as other engine parts are upgraded to increase power even more. There are a few upgrades that will have an adverse affect on the drive train when combined with the supercharger. Here are some examples:

1. High-Stall torque converter. A torque converter multiplies torque from the engine to the transmission by a factor proportional to the rotational speed difference between them. Basically, a higher stall converter alone will cause the transmission to experience momentary input torque levels much higher than a stock converter would.

2. Boost Upgrade. Installing a smaller pulley on the supercharger is an easy way to get more power if detonation can be controlled. This extra power may be in excess of the drive train’s capabilities.

3. PCM Reprogramming. A popular performance modification to the PCM is to remove the Torque Management subroutines that reduce power in favor of drive train preservation.

4. Wider or larger diameter tires. From a drive train’s perspective, larger tires or wider high-traction tires have a similar effect when launching from a stop. Either tire upgrade will reduce wheel spin. Wheel spin actually reduces stress on the entire drive train once it begins. Increasing traction with a tire upgrade will increase driveline stress if the previous tires were able to break traction before.

These upgrades are so effective that together, with the supercharger, failure of a major drive train component is just about guaranteed to happen sooner or later if these components are not also upgraded to handle the additional torque.

Back to the Original Question:

In the never-ending quest for more power, it is this torque that ultimately dooms the weak link. Twin Screw and Roots superchargers make full boost right off idle when you jab the gas. At this instant, the engine may reach its torque peak just as the vehicle begins to move forward. The torque peak of a centrifugally supercharged engine would be seen in the higher end of the RPM range. Launching a centrifugal vs. twin-screw or roots with the same peak boost is therefore less stressful on the drive train and less likely to cause a failure for that reason.

It takes lots of torque to break parts, and twin-screws and roots superchargers make more of it. It is typical to see peak boost levels of centrifugal supercharger kits calibrated and tuned to one or two pounds greater than a roots or twin-screw kit for the same engine. The centrifugal supercharger kits do not have to be de-tuned to keep power levels manageable at low RPM.

Conclusion

Adding power, in excess of what the supercharger kit provides on a stock vehicle, is possible as long as attention is paid to the limitations of the transmission and the rest of the drive train components. If you’re building a torque-monster for towing and the best possible hole shots, driveline upgrades will be required.

For information on maximizing the lifespan of your power train, see our Maintenance Tips.
For some ideas on a rear axle differential upgrade click here.

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