I have read through this entire thread and have seen many opinions bantered about. If you are trying to determine increases a particular mod gives, you must have a baseline to compare. 1/4 mile times are not the baseline you want. There are too many variables to contend with temp, humidity, the ability of the driver to reproduce the same results is nearly impossible. There isn't a driver in the world than can register the same exact 1/4 mile time twice.

The answer to your question is the dyno. If you are concerned as to how accurate reproducing the same readings will be, then try this.

1) Use the same dyno each time.
2) Have the same tech work with you.
3) When positioning the car on the dyno ensure the same alignment as much as possible. To achieve this you can measure from the front or rear bumper to a fixed point in the shop on 2 corners
4) Record the temp and humidity the day you do the baseline run.
5) For subsequent tests, select days that are as close to the original temp and humidity as possible.
6) Do a minimum of 3 runs.
6) Allow for proper cooling between runs. Hot cars produce less hp. approximately 30 minutes is fine. If you want to get real technical bring a thermal imaging camera to read the surface temp of the engine. Select a temp that is equal to the temp the engine is after idling for 15 minutes. After each run wait until the engine temp drops back down to this temp.
7) Hp power should be measured in 3rd gear.

With a supercharger of the type in our vehicles, a flat torque and hp curve should be visualized. Unlike turbo chargers that increase thrust with the increase in rpm. The hp reading you will read is RWHP not brake hp. The difference is RWHP is the hp the car is putting to the ground. The brake hp(this is the one listed in the cars literature) is measure prior to the engine being installed in the car. Some refer to this as the hp at the flywheel. Hence it does not take into consideration the hp loss thought the drivetrain. The transmission, torque converter, and rear-end consume hp. Automatics lose between 18-22% of the hp from the fly wheel(brake hp number) to the ground(RWHP). So our cars list @ 330hp this roughly calculates to 264 rwhp using 20% loss through the drive train.

As for the debate over not needing to re-tune for the additional thrust when changing pulleys, that may be true if a very small increase in thrust is added. Remember more air equals requires more fuel. A crossfire does not use an MAF to measure air density/volume. It uses a fuel map. this fuel map is variable to a point but can not adjust for large changes. So if you increase the thrust and the ECU does not sense the increase, and increase the amount of fuel, your air/fuel ratio will drop and you will end up with detonation. The car will be running to lean. The AIT sensor reads only the air temp not CFM's or air density. You will need to increase fuel flow as air flow increases. This is what the tuning of the ECU does. Like I stated earlier you will get away with some additional thrust unaccounted for but at some point you will lower the air/fuel ratio low enough to create detonation.


I have rebuilt 7 cars. 4, 1/4 mile cars and 3 rally cars. Simply changing a pulley can give you additional hp but not monitoring fuel ratios can lead to a lot of engine damage. Have the ECU re-tuned for the pulley change as a soon as possible. The exhaust and other changes you make will less likely put the engine at risk. They make very small changes in most cases, surely not enough to damage the motor. The expected hp gain with a cat back exhaust is minimal, especially on a car that is already exhausting well like the srt6.

If you are interested in really big gains in hp install a NO2 kit with a 150 shot and hold on for dear life.

Leadfoot