Jackson Racing Supercharger Owners Thread

[904FRSlow]

Originally Posted by Thorpedo

Please do, because there is NOT!!!!!! What you're saying is the equivalent of me throwing a baseball and it continuing to speed up after it has left my hand.

When you throw the ball, it will land and roll through the ground

[CSG Mike]

Originally Posted by Thorpedo

Please do, because there is NOT!!!!!! What you're saying is the equivalent of me throwing a baseball and it continuing to speed up after it has left my hand.

I'll do a less simple version.

First, each action has an equal and opposite reaction correct? When you load the car with acceleration, there is a tiny bit of twist in the metal components, rubber bits that deflect, etc.

Second, there is much more rotational inertia, in gear, with the clutch engaged, than with the clutch disengaged.

Third, as previously mentioned, there is a delay between throttle pedal input and actual ECU reaction, and then ECU action.

Now, lets combine the three.

You lift off the throttle. As you clutch. Momentarily, a few things happen. The force fighting the acceleration, which has now stored energy in the form of deflection, torsion, binding, etc, is released. As a result, load on the engine is also released. As this happens, the rotational inertia of the drivetrain also disappears, leaving only the engine itself and the flywheel. We'll revisit this later; lets handle accleration first.

While this is all happening, the engine is still firing. The observed delay is about 0.04s. At 7000 RPM, that is enough time for 4.67 rotations. Now combine that with the lack of load, and you can see how it turns into 5 rotations. A 4 cylinder engine fires every 180 degrees, or once per cylinder every 720 degrees. Thats about 9 combustion events assuming no acceleration, or more realistically, a bit over 10.

Now, the ECU has finally processed that you lifted on the throttle, and stopped firing.

Now lets address inertia/momentum. At 7000 RPM. You clutch in as you lift. Lets say this is a cable throttle, and the throttle is instantly closed. You still have 7000 RPMs of kinetic energy. Now, energy (momentum) is preserved. You clutch in, decreasing the rotational inertia of the system from engine/flywheel/pressureplate/clutch/transmission/driveshaft/axles/wheels to engine/flywheel/pressureplate. TO preserve that energy, you must spin faster.

Now, lets add that load. The ECU sees a certain amount of load. But wait, the ECU has a delay between its input, the time it takes to process the input, and then adjust what it's doing based on that input. As you lift the throttle and clutch it, it still think you're putting a heavy load on the engine...

[CSG Mike]

Originally Posted by Thorpedo

Please do, because there is NOT!!!!!! What you're saying is the equivalent of me throwing a baseball and it continuing to speed up after it has left my hand.

Technically, it will always continue to speed up (downward) until it's hit the ground... unless there's a crazy updraft...

[0351USMC]

@moto-mike and @CSG Mike back on a JRSC topic..... What are your guys opinions of stock vs upgraded injectors for e85 tuned JRSC. I know bigger injectors and pump will be more power but can I wait on the injectors for now?

[CSG Mike]

Originally Posted by 0351USMC

@moto-mike and @CSG Mike back on a JRSC topic..... What are your guys opinions of stock vs upgraded injectors for e85 tuned JRSC. I know bigger injectors and pump will be more power but can I wait on the injectors for now?

100% absolutely mandatory.

[Skegrider]

Wow. Somebody knows his shit. JR kit is looking better every time I get on here.

[0351USMC]

Originally Posted by CSG Mike

100% absolutely mandatory.

Thanks. Ended up going deatschwerks for 700cc squirted and 265lph pump.

[mfd1012]

Originally Posted by moto-mike

I'm fairly confident this is a data acquisition issue or stock like rev limit implementation. Acceleration has no momentum, so if you pull spark or fuel then it will stop accelerating. We've seen some of the devices out there (and even stock tachos) report a higher than actual RPM. It gives me that unsteady feeling when I spin a rotary to 10k indicated via the dash on the dyno when it is only hitting 8800 in reality.

This car that I drive has been beat to death with FI for over 30k miles, 40k total. I raised the revs to 7850 without finishing break-in. It has been to the dyno countless times. I prefer to use a dynojet with an actual spark pickup (vs calculated) and I've never seen a spike over my preset RPM. Again, data aquisition issue, or how the rev limit is being implemented. If they are using OEM style throttle cut, then it will overrev because you have to exhaust the plenum volume. Which when compressed will be substantial. But if you use an alternate method that is not an issue (all our tunes).

...

I have always wondered about the time it takes to exhaust the plenum volume with this type of FI design. Is it detectable when driving (throttle response)?

[bfrank1972]

Originally Posted by CSG Mike

At 7000 RPM. You clutch in as you lift. Lets say this is a cable throttle, and the throttle is instantly closed. You still have 7000 RPMs of kinetic energy. Now, energy (momentum) is preserved. You clutch in, decreasing the rotational inertia of the system from engine/flywheel/pressureplate/clutch/transmission/driveshaft/axles/wheels to engine/flywheel/pressureplate. TO preserve that energy, you must spin faster.

Now, lets add that load. The ECU sees a certain amount of load. But wait, the ECU has a delay between its input, the time it takes to process the input, and then adjust what it's doing based on that input. As you lift the throttle and clutch it, it still think you're putting a heavy load on the engine...

Ok I'll buy the stored torsional energy + the slight ecu lag concept, albeit I think it will be pretty much imperceptible.

The 2nd part about preservation of momentum when you disengage the clutch is incorrect.

It's like saying you have an airplane flying through the air, it splits in half and the front end starts accelerating. Momentum is conserved in the split airplane because the front half and rear half are still traveling the same velocity at the moment they split, even though each piece is 1/2 the weight.

When you decouple the driveshaft from the motor (clutch in), you're just creating two separate spinning 'assemblies'. Both with less angular momentum, but the sum of both is the same as the original combined angular momentum (at least at the instant when they are disconnected). The 'two piece' concept is oversimplifying it, but just to make the point.

[CSG Mike]

Originally Posted by bfrank1972

Ok I'll buy the stored torsional energy + the slight ecu lag concept, albeit I think it will be pretty much imperceptible.

The 2nd part about preservation of momentum when you disengage the clutch is incorrect.

It's like saying you have an airplane flying through the air, it splits in half and the front end starts accelerating. Momentum is conserved in the split airplane because the front half and rear half are still traveling the same velocity at the moment they split, even though each piece is 1/2 the weight.

When you decouple the driveshaft from the motor (clutch in), you're just creating two separate spinning 'assemblies'. Both with less angular momentum, but the sum of both is the same as the original combined angular momentum (at least at the instant when they are disconnected). The 'two piece' concept is oversimplifying it, but just to make the point.

You're talking a linear momentum with your airplane, vs a rotational inertia with an engine.

A more accurate analagy is a figure skater. When they go into a spin on the ice, if they pull in their arms and legs (lowering inertia), they spin faster. If they move their arms/legs away from the axis of rotation, they slow down.

Remember, this decreased inertia is also being combined with some more combustion events from the engine.

[*LongFella]

Mike - I didn't know you were a figure skater?!?!!! Man, the things I learn on the Internet... 😂

[bfrank1972]

Originally Posted by CSG Mike

You're talking a linear momentum with your airplane, vs a rotational inertia with an engine.

A more accurate analagy is a figure skater. When they go into a spin on the ice, if they pull in their arms and legs (lowering inertia), they spin faster. If they move their arms/legs away from the axis of rotation, they slow down.

Remember, this decreased inertia is also being combined with some more combustion events from the engine.

No, a figure skater is not a good analogy for the rotating parts in an engine and transmission. As a figure skater pulls his/her arms and legs inward, he/she is changing their moment of inertia - the mass of the arms and legs are changing with respect to the axis of rotation. The laws of conservation of momentum then dictate that the speed of rotation needs to increase.

Maybe a more straightforward way to think about it: imagine a tetherball wrapping around a pole. As it gets closer to the pole, the rate it orbits the pole increases dramatically... but in reality the ball is traveling roughly the same speed (in a perfect vacuum with an infinitely thin rope attaching it to an infinitely thin pole, in real world there are other forces slowing it down). As the ball's travel radius decreases, it has to circle the pole faster to cover the same distance (circumference by radius, pi * r * 2). The ball and the skater concepts seem different, but in reality they are the same principles.

Back to the motor/transmission - when you decouple the motor from the driveline via the clutch, there is NO change in the moment of inertia for any of the rotating components. The driveshaft doesn't get skinnier or fatter. The flywheel doesn't change shape. The crankshaft doesn't either. The only thing that is happening is you are disconnecting two 'components', but not changing their moment of inertia.

Think of it as your ice skater in a gentle spin, not changing the position of their arms/legs, and a big cleaver comes in and cuts her in half (gory, yes I realize). Her remaining lower torso won't just start increasing in spin velocity because she's now missing her upper torso.

[Xuningshen]

why don't you guys just think about it like an actual engine instead of all these analogies. they're giving me headaches.

for a simple minded guy like myself. I find it hard to believe that flywheel, crankshaft, whatever other crap is attached, would INSTANTLY stop climbing revs once you cut fuel/spark.

please... please... dont respond to me in analogies.

[sw20kosh]

Originally Posted by bfrank1972

No, a figure skater is not a good analogy for the rotating parts in an engine and transmission. As a figure skater pulls his/her arms and legs inward, he/she is changing their moment of inertia - the mass of the arms and legs are changing with respect to the axis of rotation. The laws of conservation of momentum then dictate that the speed of rotation needs to increase.

Maybe a more straightforward way to think about it: imagine a tetherball wrapping around a pole. As it gets closer to the pole, the rate it orbits the pole increases dramatically... but in reality the ball is traveling roughly the same speed (in a perfect vacuum with an infinitely thin rope attaching it to an infinitely thin pole, in real world there are other forces slowing it down). As the ball's travel radius decreases, it has to circle the pole faster to cover the same distance (circumference by radius, pi * r * 2). The ball and the skater concepts seem different, but in reality they are the same principles.

Back to the motor/transmission - when you decouple the motor from the driveline via the clutch, there is NO change in the moment of inertia for any of the rotating components. The driveshaft doesn't get skinnier or fatter. The flywheel doesn't change shape. The crankshaft doesn't either. The only thing that is happening is you are disconnecting two 'components', but not changing their moment of inertia.

Think of it as your ice skater in a gentle spin, not changing the position of their arms/legs, and a big cleaver comes in and cuts her in half (gory, yes I realize). Her remaining lower torso won't just start increasing in spin velocity because she's now missing her upper torso.

This.