Jackson Racing Supercharger Owners Thread

[Xero-Limit]

I'm puzzled why you're seeing that. We have never observed this in our testing on the road and on the dyno nor track logs from customers. Once combustion stops the motor can't spin any faster regardless of what the rotrex unit wants to do. May be how your tune is implementing the rev limit vs what we do? Data acquisition issues?

Originally Posted by CSG Mike

Here's some datalogs illustrating what's going on. This is a lap at WSIR (available in Gran Turismo 6) that shows the RPM plot, throttle position plot, and clutch position (on/off switch).

Now, lets zoom into that spike with the peak RPMs.

You can see clearly between the 2nd and 3rd graph, that I am COMPLETELY off throttle, before the clutch sensor is engaged. However, being an on-off switch, you can't see the exact position of the clutch.

Between 1.00.46 and 1:00.56, there is a surge of 554 RPMs, which occured from a WOT shift at 7209 RPMs.

As you can see from the first, zoomed out graph, there are a LOT of RPM surges at WOT shifts, which happens with any FI solution. You'll also note that all of my shifts, except for that one, occur at 7000 RPMs.

This wasn't even a record lap attempt at WSIR. You can imagine the RPMs with a 7850 redline...

[autograph]

Originally Posted by CSG Mike

I would never rev a stock engine that high. That's asking for an engine failure very, very quickly.

With a full cut at 7850, the engine will still have enough revs to easily hit 8250 RPMs, at which point, you'd actually be spinning the Rotrex to past it's spec as well.

The reason we (CSG) recommend shifting at 7000, is because the TPS and PPS have approximately a 0.04s delay in response. This is enough time where if you have well developed shifting technique (lifting the throttle right as you clutch in), there is a 0.04s long moment where the engine is essentially being free revved at WOT.

Now, you say, wait, there's a rev limiter at 7400! Yes, there is! However, RPMs also have momentum, and if your engine's rate of RPM climb is not zero or close to at 7400, the momentum will still take the RPMs higher.

Our datalogs show that at WOT, a 400-450 rpm rise is frequent.

That's why we recommend shifting at 7000. There's so much more power with the JRSC that you WILL overrev your engine if you're not careful. With a higher redline, the results are catastrophic.

Statements like that make us question how much testing has been performed by other Jackson Racing distributors.

Mike, would you suggest lowering redline to 7100-7200ish then on a JRSC 86? Sounds like it might be a nice safety option especially if someone else drives the car and hits the rev limiter

[CSG David]

Originally Posted by autograph

Mike, would you suggest lowering redline to 7100-7200ish then on a JRSC 86? Sounds like it might be a nice safety option especially if someone else drives the car and hits the rev limiter

I'm not Mike, but I'll chime in since he's working on some JR oil cooler kit installs right now.

Like I said earlier, tune for 7400, shift at 7000. If you are having serious trouble beating your competition at 7000RPM, then you sure as hell won't be beating your competition at 7400RPM. You can drop redline below 7400RPM, but it's essentially pointless. It's nice to have that overhead from time to time, but don't just repeatedly shift at that redline.

Something in motion has inertia and momentum. The engine just doesn't suddenly hit 7400RPM and stop when you let off the clutch. When you accelerate those pistons in motion and cut that energy source out, the engine freely spins above that cutoff point before slowing down. This is just pure physics.

[CSG David]

Damn it. I was being retarded. I thought about position rather than velocity. In other words, taking derivatives of constant velocity is zero acceleration.

The cause in the blipped RPM is delay between the pedal and what the ECU deems cut input. Because of that, we see overrunning in engine RPM from various drivers and various ECU datalogs.

*I just drank coffee and facepalmed myself after SHARTA trolled me.

[CSG Mike]

Originally Posted by moto-mike

I'm puzzled why you're seeing that. We have never observed this in our testing on the road and on the dyno nor track logs from customers. Once combustion stops the motor can't spin any faster regardless of what the rotrex unit wants to do. May be how your tune is implementing the rev limit vs what we do? Data acquisition issues?

Incorrect. This behavior has nothing to do with the Rotrex, although the Rotrex does amplify it a bit, as with ANY forced induction solution.

Once combustion stops, the motor's RPM's rate of acceleration goes from positive (torque output) to negative (engine braking from compression and friction). It doesn't mean the engine's RPMs instantly stop dropping. The momentum of the rising RPM will carry it upward, and the decrease in inertia from disengaging the clutch allows for that momentum to act upon engine RPMs even faster. Combine that with the tiny DBW delay, and a 400-600 RPM increase with a throttle lift and clutch in isn't unheard of at all.

An analogy to this would be throwing a ball up into the air. The ball's trajectory is analogous to engine RPM. The moment the ball leaves your hand, the acceleration force (combustion) disappears. There is no longer an acceleration force upward acting on the ball. However, gravity (compression and friction) is always acting on the ball, causing the ball's trajectory to become a parabola. Even through the acceleration force isn't acting on the ball, the ball's momentum carries it higher (the RPM spike), before it eventually stops dropping.

Velocity is the derivative of acceleration. Acceleration's force is not instantaneous.

I've observed this type of behavior on EVERY type of tune for this car. It's partially physics, and partially the relationship between TPS and PPS. You cannot eliminate either one, unless you've developed an ultra low friction, low inertia engine, and have completely upgraded the ECU hardware with a far faster unit.

I can post datalogs from @DeliciousTuning, @ptuning, JamesM, and, also you, that exhibit the same behavior.

[CSG Mike]

Originally Posted by autograph

Mike, would you suggest lowering redline to 7100-7200ish then on a JRSC 86? Sounds like it might be a nice safety option especially if someone else drives the car and hits the rev limiter

You don't need to lower the redline; just use the car intelligently

[*LongFella]

I feel like I'm back in college... Haha!

[CSG Mike]

Originally Posted by *LongFella

I feel like I'm back in college... Haha!

Practical motorsport applications of basic Newtonian physics!

I lied. I learned the concepts in high school. Now it's just putting together a complex system of variable inertia and multiple forces for something we use every day.

[*LongFella]

Originally Posted by CSG Mike

Practical motorsport applications of basic Newtonian physics!

I lied. I learned the concepts in high school. Now it's just putting together a complex system of variable inertia and multiple forces for something we use every day.

I was a band geek in high school, so I spent most of my time fooling around during "band camp" ... This one time, at band camp... Yes, those stories are true and exist... Haha!

[CSG Mike]

Originally Posted by *LongFella

I was a band geek in high school, so I spent most of my time fooling around during "band camp" ... This one time, at band camp... Yes, those stories are true and exist... Haha!

I went to a nerd high school.
www.troyhigh.com

Because of the Troy Tech Program, Troy High School was ranked #1 by U.S. News for Best STEM (science, technology, engineering and math) High Schools in the Nation in 2014 among high schools of over 2,000 students; we have ranked in the top six since 2012. Here is a link to the Orange County Department of Education's explanation of STEM.

[CSG Mike]

From a resulting discussion of what's at hand...

[mistressmotorsports]

I just went to a regular high school, and it was long enough ago that they hadn't invented physics or Isaac Newton yet. However, let's look a little more carefully at some of the past statements. Acceleration does not have momentum. When you throw the ball up, it only accelerates upward until you stop pushing on it. Then gravity and aero drag start accelerating it downward. It's speed immediately starts decreasing, no continued upward acceleration. No force = no acceleration, that is Newtonian physics. In fact, it's Newtons first law.

We can compare the ball's speed to piston speed, which is really what RPM's are. With the ball, eventually, velocity goes negative, and the ball falls - the parabola that David mentioned. Just as the ball starts slowing the minute you stop pushing on it with your hand, theoretically, piston speed starts slowing if you stop feeding it fuel and/or air. In a theoretical world, if you truly closed the throttle (meaning no air and no fuel) were getting to the combustion chamber, then revs would not continue to climb once the throttle was closed. But, looking at Mike's traces, we see that they do. It is not because climbing rpms have momentum (they don't, just like the acceleration of the ball doesn't.) Rather there must be other forces at work that are continuing to speed up the revs for a period of time. We all know that a closed throttle really isn't closed - why cars don't stall at idle. There is still air and fuel getting to the combustion chambers, so there is still some energy available. As previously mentioned, there may be some delay between foot/computer commands and what actually happens. There may also be some smoothing (I don't really know,just a possibility) in the control software that doesn't want to "dump" the throttle, meaning the actual throttle stays open for just a little while longer. There is also the fact that once the clutch is pushed in, it takes way less throttle to raise engine rpm's then it does under load. So, some combination of these possible reasons can explain why engine revs can climb after taking your foot off the throttle. There certainly could be more reasons that I am not aware of, but rpm will only rise if there is combustion energy available that exceeds the energy needed to hold the rpm's constant under whatever load is there. It's not because acceleration has momentum.

Sorry for the highjack, back to more practical discussions of forced induction.

[Massimopirrone]

Has anyone changed the bypass valve yet? Just looking to make it a bit louder

[CSG Mike]

Originally Posted by mistressmotorsports

I just went to a regular high school, and it was long enough ago that they hadn't invented physics or Isaac Newton yet. However, let's look a little more carefully at some of the past statements. Acceleration does not have momentum. When you throw the ball up, it only accelerates upward until you stop pushing on it. Then gravity and aero drag start accelerating it downward. It's speed immediately starts decreasing, no continued upward acceleration. No force = no acceleration, that is Newtonian physics. In fact, it's Newtons first law.

We can compare the ball's speed to piston speed, which is really what RPM's are. With the ball, eventually, velocity goes negative, and the ball falls - the parabola that David mentioned. Just as the ball starts slowing the minute you stop pushing on it with your hand, theoretically, piston speed starts slowing if you stop feeding it fuel and/or air. In a theoretical world, if you truly closed the throttle (meaning no air and no fuel) were getting to the combustion chamber, then revs would not continue to climb once the throttle was closed. But, looking at Mike's traces, we see that they do. It is not because climbing rpms have momentum (they don't, just like the acceleration of the ball doesn't.) Rather there must be other forces at work that are continuing to speed up the revs for a period of time. We all know that a closed throttle really isn't closed - why cars don't stall at idle. There is still air and fuel getting to the combustion chambers, so there is still some energy available. As previously mentioned, there may be some delay between foot/computer commands and what actually happens. There may also be some smoothing (I don't really know,just a possibility) in the control software that doesn't want to "dump" the throttle, meaning the actual throttle stays open for just a little while longer. There is also the fact that once the clutch is pushed in, it takes way less throttle to raise engine rpm's then it does under load. So, some combination of these possible reasons can explain why engine revs can climb after taking your foot off the throttle. There certainly could be more reasons that I am not aware of, but rpm will only rise if there is combustion energy available that exceeds the energy needed to hold the rpm's constant under whatever load is there. It's not because acceleration has momentum.

Sorry for the highjack, back to more practical discussions of forced induction.

RPM is an instantaneous measurement, but yes, RPM, not acceleration in RPM, does have momentum. The momentum is the slope of the RPM curve. Now, normally, the forces acting on the RPM curve are so large, that the changes are nearly instant; an example of this is lifting on the throttle while in gear. The drop in is essentially instantly observed, because the deceleration force is so huge.

However, when we remove those giant forces, and make it so that only friction and compression are the deceleration forces on RPM, the rate at which RPM decelerates is fairly small, and can be observed. When RPM is rising, the slope of that curve is positive. When the acceleration force is removed, the RPM itself is still rising, but the slope of that curve starts its downward trend, and ultimately becomes negative, as friction and compression continue to affect the engine.

If you had a frictionless engine with perfect efficiency, then lifting on the throttle, with the clutch disengaged, would result in the slop of the RPM unchanging (slope only changes when there is acceleration whether its power output, or friction), and RPMs would continue to rise.