Allpar Forums banner
1 - 2 of 2 Posts

Premium Member
3,295 Posts
Why does the Supercharged Hellcat 6.2 Hemi have a clutched pulley?

by Patrick Rall

I have seen some discussions online about how Hellcat Challenger and Charger owners are looking to increase the output of their supercharged Hemi engines by increasing the boost. The two "simple" ways to do this are to replace the lower pulley on the crankshaft, or the upper pulley on the supercharger itself.

Vehicle Motor vehicle Engine Car Auto show

Changing the upper pulley is a common means of boosting boost levels, but unlike some engines, the Hellcat Hemi uses a clutch system in the upper pulley. That makes it harder to simply swap to a new pulley for increased boost levels.

Some people on Web forums insist that you can just swap to a pulley without the clutches without any short-term problems. They might be right, and swapping to a clutchless upper pulley on the Hellcat engine might not cause any short term problems, but before changing such a crucial component of your Mopar muscle car's supercharger, you should understand why the clutch system is there in the first place. Automakers don't spend money on unnecessary systems, after all.

Engine Auto part Electronics Technology Vehicle

Before the Hellcat Challenger hit the market, I had the opportunity to visit the Chrysler Headquarters in Auburn Hills for a close-up look at the most powerful American muscle car engine of all time. The engineering team was on hand to walk the small group of media through the most intricate details of the supercharged Hemi, and in addition to slides chock full of information, they had a Hellcat Hemi engine torn down into individual components.

The engineers discussed the development process of the Challenger and Charger with the IHI supercharger. The Hellcat Hemi supercharger requires around 80 horsepower of driving force from the crankshaft to achieve the internal revolutions-per-minute (RPMs) needed for full boost; that force causes the engine RPMs to drop dramatically when the driver lifts off of the throttle. In other words, the supercharger has a braking effect on the engine.

Engine Auto part Automotive tire Automotive engine part Tire

Engine RPM loss hinders performance, particularly when you lift off the throttle to bang from one gear to the next. What's more, in some cases, the change in the supercharger pulley speed would be too violent for the belt system, so when it didn't slow down the engine RPM, it would cause the drive belt to spin on the pulleys. That leads to increased belt wear and, over time, lower performance when the belt begins to slip under boost as well.

To prevent having the supercharger's rapid internal deceleration cause belt slippage or sudden engine RPM drops, the engineering team added the one-way clutched upper pulley system. This way, when you let off of the throttle in either of the Hellcat cars, the supercharger can slow down quickly without having any impact on the engine RPM or the belt system, since the clutch system allows the pulley and the blower internals to spin freely at different speeds.

Auto part Engine Vehicle

Swapping to a new upper pulley without the clutch system will most certainly lead to increased boost pressures and increased power levels, but it will also lead to increased internal supercharger RPMs. Because of this, the deceleration of the supercharger could be even more aggressive, leading to sudden RPM drops between gears or belt slippage and increased belt wear.

Chrysler 1904-2018

Spread the word via <!--Tweet or--> Facebook!

We make no guarantees regarding validity or accuracy of information, predictions, or advice - .
Copyright © VerticalScope Inc. All rights reserved. Dodge, Jeep, Chrysler, Ram, and Mopar are trademarks of Fiat Chrysler Automobiles.


1 Posts
This is incorrect.. the pully clutch is a sprag. Any time the crank shaft is driving the blower the clutch locks up and requires power from the crankshaft. The supercharger cannot slow down more quickly than the rotation of the blower pulley, this is the same relative movement that locks the clutch to make it operate.

The inertia from the blower rotors spinning at 14000 and 23000 continues during the 160ms transmission shift when the much higher rotational inertia of the engine is clutched down by the transmission and transferred to forward motion of the car. In other words, the blower clutch allows the bower to "gradually" reduce its RPM while the engine rapidly reduces it rpm during the very quick gear change. Simple inertia of the blower for that very brief period maintains manifold pressure until the blower slows back down to match the pulley speed when it locks back up again and requires power to drive.

When you remove the clutch (with an aftermarket pulley), the blower inertia itself ADDS instantaneous torque to the crankshaft through the blower belt drive, but on the tensioner side.

This is a reliability issue for sure.. but the money spent by Dodge on this was probably more due to not wanting the added manufacturing costs of a key or pin on the damper/crank for anti rotation. The diamond crusted washer would have probably slipped somewhat soon due to the sudden and repetitive torque reversals during normal (and boosted) driving, so a clutched pulley was the "cheap" solution that was marketed to look like more.
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.