Bluezone
Tailgaters will be prosecuted.
I've been thinking after my drag racing experience yesterday. What would it take to pre-activate the rear differential coupler on take off. So I have some questions and I'm looking for useful input. The idea is to engage the all-wheel drive system before wheel slip is detected. Hopefully improving the launch by providing four wheels for contact.
First does anyone know if the rear coupler is a direct electromagnetic coupler or is it a electromagnet coupler with a incline ramp and roller system? If it's the ramp and roller style, this would explain the time to activation on take off. You need rotation order for the ramps to lock up. In which case what I'm thinking about will not work.
From what I understand the coupler works on a 12-volt system with a relay sending 12 volts to activate the electromagnet. Pulse width modulation is used to achieve a semi locked condition to transfer torque from the drive shaft to the RDU. Also I read somewhere that maximum torque capacity of the stock clutch pack is something around 780 pounds torque. So you probably only want to apply roughly 75% of Max torque capacity. Now on launch, the engine is only turning around 2000 RPM. From looking at log data and different Dyno charts I would guess the engines only producing roughly a 150 lb torque. This is due to spool up not really taking place at this point. With my engine with the downpipes installed I've only got maybe 2 to 3 lb a boost at that that engine speed. When you go through the gear ratios you end up with roughly 1860 pounds of torque available. It must be remembered that that number is divided by 2 and there are losses going through the PTU and rear drive system. Now front drive system probably has a 15% loss from crank power. Whatever losses are incurred by the rear drive system are derived from what is left over from the front wheel drive system and then its own losses. So I'm guessing roughly 790 pounds of torque at the front differential available to be transferred through the rest of the powertrain to the rear differential. So knock another 10% off that and you end up with something like 712 lb of torque available with rear wheels with full lock up from a standing start at 2000 RPM. No wonder they use pulse width modulation. That's why I figure only a half second of torque loading for the 2 seconds relay run time. One and a half of those seconds is wasted at the lights.
Now what I'm thinking is setting up a system of electrical switches and possibly some sort of electronic black Box that contains a timer and possibly a oscillator to provide a pulsing signal.
The idea is to have an arm / disarm switch, a momentary contact switch mounted at the steering wheel plus the black box wired to a relay to send power to the electromagnet on the rear differential coupler.
The purpose of the timer in the black box is to set length of time for activation.
In operation you would hit the arm switch, pull up to the staging Lanes. When staged press the activation switch. The black box would countdown a time length of 1.5-2 seconds of activation. During this time a static or pulsed signal is be sent to the coupler to lock it up for takeoff. Problem with using a static signal is full torque is sent to all wheels. With a pulse signal the relay would be sending an on/off oscillating signal to prevent total lockup.
The second version of this does not send the pulsed signal to the coupler electromagnet. Instead you're sending a pulse signal to one of the wheel speed sensors to mimic wheel spin. This would be hopefully cause the system to automatically apply torque to the rear coupler Via interpreted wheel slip. The problem with this is that with the CAN bus system this may be interpreted as a system fault.
Anyone have any input or ideas to add to this?
First does anyone know if the rear coupler is a direct electromagnetic coupler or is it a electromagnet coupler with a incline ramp and roller system? If it's the ramp and roller style, this would explain the time to activation on take off. You need rotation order for the ramps to lock up. In which case what I'm thinking about will not work.
From what I understand the coupler works on a 12-volt system with a relay sending 12 volts to activate the electromagnet. Pulse width modulation is used to achieve a semi locked condition to transfer torque from the drive shaft to the RDU. Also I read somewhere that maximum torque capacity of the stock clutch pack is something around 780 pounds torque. So you probably only want to apply roughly 75% of Max torque capacity. Now on launch, the engine is only turning around 2000 RPM. From looking at log data and different Dyno charts I would guess the engines only producing roughly a 150 lb torque. This is due to spool up not really taking place at this point. With my engine with the downpipes installed I've only got maybe 2 to 3 lb a boost at that that engine speed. When you go through the gear ratios you end up with roughly 1860 pounds of torque available. It must be remembered that that number is divided by 2 and there are losses going through the PTU and rear drive system. Now front drive system probably has a 15% loss from crank power. Whatever losses are incurred by the rear drive system are derived from what is left over from the front wheel drive system and then its own losses. So I'm guessing roughly 790 pounds of torque at the front differential available to be transferred through the rest of the powertrain to the rear differential. So knock another 10% off that and you end up with something like 712 lb of torque available with rear wheels with full lock up from a standing start at 2000 RPM. No wonder they use pulse width modulation. That's why I figure only a half second of torque loading for the 2 seconds relay run time. One and a half of those seconds is wasted at the lights.
Now what I'm thinking is setting up a system of electrical switches and possibly some sort of electronic black Box that contains a timer and possibly a oscillator to provide a pulsing signal.
The idea is to have an arm / disarm switch, a momentary contact switch mounted at the steering wheel plus the black box wired to a relay to send power to the electromagnet on the rear differential coupler.
The purpose of the timer in the black box is to set length of time for activation.
In operation you would hit the arm switch, pull up to the staging Lanes. When staged press the activation switch. The black box would countdown a time length of 1.5-2 seconds of activation. During this time a static or pulsed signal is be sent to the coupler to lock it up for takeoff. Problem with using a static signal is full torque is sent to all wheels. With a pulse signal the relay would be sending an on/off oscillating signal to prevent total lockup.
The second version of this does not send the pulsed signal to the coupler electromagnet. Instead you're sending a pulse signal to one of the wheel speed sensors to mimic wheel spin. This would be hopefully cause the system to automatically apply torque to the rear coupler Via interpreted wheel slip. The problem with this is that with the CAN bus system this may be interpreted as a system fault.
Anyone have any input or ideas to add to this?
Last edited:
