Jackson Racing Supercharger Owners Thread

[Xuningshen]

Originally Posted by Massimopirrone

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

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because racecar (read ricer) Its before maf so I didn't feel that bad about doing it. Plus its on my bucket list to have that PSHH. its a continuous PSH though, because supercharger and not turbo. so dont expect a quick, short, sweet PSHH.

But looking at obdII torque app i'm not reaching 9 psi. which I think its supposed to be right? or is it 7 lol. I thought it was 7 until I saw someone post 9. So I'm thinking it might be opening for some reason. because you have to have the thing set super super super soft. otherwise you let off the throttle and it stays there for a few seconds before rpms simmer down. going to put the little plastic by pass valve or just plug up the VTA portion of the dual by-pass valve and see if i reach 9 psi.

[CSG Mike]

Originally Posted by Massimopirrone

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

You could vent it to atmosphere if you wanted to...

[mistressmotorsports]

Originally Posted by CSG Mike

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.

I am sorry, but this is just not correct. If there was no friction and you removed all forces from the engine, the rpms would stay at the same speed they were at. Think of it this way - the crankshaft has a certain speed at any time. I absolutely can not accelerate if there is no force acting on it. So with no force and no friction, it just stays at the same speed regardless of what was happening to it previously. The crank simply can not go faster if you don't put a force on it. If you roll a bowling ball and it is accelerating as you roll it, it immediately stops accelerating once you let go, regardless of how hard you were pushing it previously. There is no momentum to the acceleration, only the ball itself has momentum. Different things. On the ball throwing example, if there was no gravity or aero friction and you threw the ball, it would stay at the same speed it was at when it left your hand. The fact that your hand was accelerating the ball is irrelevant once you are not touching it anymore. However, since this is a supercharger thread, I am not going to debate it any further. I don't mean that out of spite or emotion, so please don't take it that way. I just don't want to get more off topic.

[CSG Mike]

Originally Posted by mistressmotorsports

I am sorry, but this is just not correct. If there was no friction and you removed all forces from the engine, the rpms would stay at the same speed they were at. Think of it this way - the crankshaft has a certain speed at any time. I absolutely can not accelerate if there is no force acting on it. So with no force and no friction, it just stays at the same speed regardless of what was happening to it previously. The crank simply can not go faster if you don't put a force on it. If you roll a bowling ball and it is accelerating as you roll it, it immediately stops accelerating once you let go, regardless of how hard you were pushing it previously. There is no momentum to the acceleration, only the ball itself has momentum. Different things. On the ball throwing example, if there was no gravity or aero friction and you threw the ball, it would stay at the same speed it was at when it left your hand. The fact that your hand was accelerating the ball is irrelevant once you are not touching it anymore. However, since this is a supercharger thread, I am not going to debate it any further. I don't mean that out of spite or emotion, so please don't take it that way. I just don't want to get more off topic.

Errr you're right. I need more coffee.

RPM would not keep climbing in a frictionless engine; it would stay constant. I'm confusing acceleration with decreasing rotational inertia. However, this doesn't change my diagram and what the datalogs show.

[mistressmotorsports]

I do not doubt your traces. RPM can continue to climb after releasing the throttle. I was just getting at the reason(s) why.

[tahdizzle]

[Xero-Limit]

Originally Posted by CSG Mike

Errr you're right. I need more coffee.

RPM would not keep climbing in a frictionless engine; it would stay constant. I'm confusing acceleration with decreasing rotational inertia. However, this doesn't change my diagram and what the datalogs show.

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).

But in the grand scheme I don't think anyone has to worry about revs of 8k or below. Above 7500 I recommend a smooth rev limit to minimize cam chain slap. The STX auto-x and track folks we've tuned (dozens upon dozens) usually go for 8000-8100 rev limit. When you auto-x you spend a lot of time at the rev limit. If they aren't floating valves or stretching rods it is a non issue. Durability long term will no doubt be affected, but when you spin a rotrex blower which maximizes power at the top, there's nothing wrong with going a few hundred RPM higher to maximize its advantages. If we got 40k miles on it, 30k supercharged with all the testing we do, then the average person is highly unlikely to have an issue within a typical 150k mile life of a motor.

[CSG Mike]

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).

But in the grand scheme I don't think anyone has to worry about revs of 8k or below. Above 7500 I recommend a smooth rev limit to minimize cam chain slap. The STX auto-x and track folks we've tuned (dozens upon dozens) usually go for 8000-8100 rev limit. When you auto-x you spend a lot of time at the rev limit. If they aren't floating valves or stretching rods it is a non issue. Durability long term will no doubt be affected, but when you spin a rotrex blower which maximizes power at the top, there's nothing wrong with going a few hundred RPM higher to maximize its advantages. If we got 40k miles on it, 30k supercharged with all the testing we do, then the average person is highly unlikely to have an issue within a typical 150k mile life of a motor.

We'll agree to disagree.

We cater to a few national level (and champion) drivers, and we've all reached the same conclusion that an increased redline is not the way to go without a huge budget. The guys that can have ultra aggressive final drive gears and further enhance the aggressiveness with specific tire sizing.

[wrussi]

to those guys that have had the JRSC for a while... have you guys upgraded the clutch? is it nescesary to upgrade the clutch with this kit? im about to go this route and im wondering if the stock clutch will hold or will i have to get one right away... thanks guys!

[ScionOfHorus]

Originally Posted by wrussi

to those guys that have had the JRSC for a while... have you guys upgraded the clutch? is it nescesary to upgrade the clutch with this kit? im about to go this route and im wondering if the stock clutch will hold or will i have to get one right away... thanks guys!

Stock clutch holds just fine, just don't go crazy with the abuse.

[Thorpedo]

Originally Posted by CSG Mike

We'll agree to disagree.

We cater to a few national level (and champion) drivers, and we've all reached the same conclusion that an increased redline is not the way to go without a huge budget. The guys that can have ultra aggressive final drive gears and further enhance the aggressiveness with specific tire sizing.

Whether the engine is speeding up and hitting 7400 where the acceleration is cut, or the engine is at 7400 steady and the acceleration is cut makes no difference. There are no further forces speeding the crank speed up, so it simply does not speed up due to any sort of momentum whatsoever.

It HAS to be a data acquisition/intake tract evacuation/electronic delay issue of some sort. There is no argument here, as you said, "it is physics". My vote (guess) would be the further expansion of the compressed gases in the intake combined with the delay of the electronics working out what is happening.

[CSG Mike]

Originally Posted by wrussi

to those guys that have had the JRSC for a while... have you guys upgraded the clutch? is it nescesary to upgrade the clutch with this kit? im about to go this route and im wondering if the stock clutch will hold or will i have to get one right away... thanks guys!

No clutch necessary unless you're going to be pushing E85 with a higher redline.

[CSG Mike]

Originally Posted by Thorpedo

Whether the engine is speeding up and hitting 7400 where the acceleration is cut, or the engine is at 7400 steady and the acceleration is cut makes no difference. There are no further forces speeding the crank speed up, so it simply does not speed up due to any sort of momentum whatsoever.

It HAS to be a data acquisition/intake tract evacuation/electronic delay issue of some sort. There is no argument here, as you said, "it is physics". My vote (guess) would be the further expansion of the compressed gases in the intake combined with the delay of the electronics working out what is happening.

The discussion up to this point, at least on my end, has been simplified down quite a bit, but yes, there is a momentum in the rise of the RPMs, which will cause it to continue to rise, even when the throttle is closed.

It is not a data acquisition issue. I've observed it on other cars.

I really should start a separate thread for this; when the evidence is laid out, it will make sense, as does the math.

I'm not the type to make random, wild claims, without empirical evidence to back up my findings.

[Thorpedo]

Originally Posted by CSG Mike

The discussion up to this point, at least on my end, has been simplified down quite a bit, but yes, there is a momentum in the rise of the RPMs, which will cause it to continue to rise, even when the throttle is closed.

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.