I have noticed that ECU blips the throttle wheel you disengage clutch briefly for down shifting, this is a cool feature for manual transmissions. Anyone notice this ?

Love the Z more everyday single day I own it.

 

See, I've noticed that but I just figured it was the clutch disengaging and the RPM's rose because there was less resistance? I don't know why it does that though. Anybody?

 

I believe thats for smoother downshifting, or upshifting if you are slow shifter.

 

Fletch figured it right. If you unload the engine by pressing in the clutch, the RPM's are going to shoot up if you don't let up on the throttle. Nothing magical about the ECU, it's basic physics.

 

I do let up on the throttle, its not me believe me, I tried to completely let go before pressing the clutch, it still blips.

 

One word:

momentum

 

momentum of what ?

 

hahaha now ive heard it all

my old Alfa with its semi Manual box blipped the throttle when u downshifted, i looked like a mad kent pulling up at traffic lights going down through the gears, and double blipping into first with high revs. But i liked it so much i wore out my first gear synchro within the first year

 

i noticed this too....and i must say when it happens its annoying cuz i am wanting to upshift quickly and i have to wait a lil bit longer for smooth shift. however, i have also noticed that if i rev to 3500+ before shifting and release the gas BEFORE engaing clutch the rpms dont seem to go up and quickly drop immediately

 

Nothing happens instantaneously. As KingTut pointed out - momentum. When you let off the gas, the engine slows. When you press in the clutch, the engine speeds up because it's been "unloaded". The rates at which those two things happen are not exactly the same so you see a "blip" in the RPM.

Here's a little test... put the car in neutral and hold the gas at a constant RPM, say 2000. Let off the gas quickly and see if it blips up a little bit or not. My guess is that you will see it drop without the blip.

 

Isn't this due to the momentum of the flywheel and not the ECU? I thought the purpose of the flywheel in an MT is to smooth out the power pulses from the engine. Even if you totally let off on the throttle the flywheel would still carry some momentum. If you disengage the clutch there is less load on the engine allowing it to rev faster. You would need an automatic tranny with an electronic clutch, like in a F1 or Tiptronic transmission, to have the tranny automatically blip or rev match. Where are the control units on a standard MT that allow them to blip or rev match automatically?

 

Stored in the flywheel. Try it with a Tilton lightweight flywheel and I bet you won't see it.

 

The 2005 Auto tranny will blip on downshifts, but not the MT.

 

If that is because of the momentum of the flywheel, then increase in momentum needs some energy, that needs fuel, that in turn means throttle was blipped.

I dont buy that being an engineer that momentum will increase without an energy imbalance, and when unloaded the rpm will increase only if you are still supplying fuel, thats mean throttling it, which is not what is happenning.

 

The momentum is carried in the flywheel which continues to spin with the motor after the clutch is disengaged. Once you take the load off the motor by pushing the clutch pedal in, the momentum of our monster dual mass flywheel can continue to push the motor up a few hundred rpms.

 

+1

Once you disengage the clutch the engine is no longer loaded with the force necessary to turn the rest of the drivetrain.

RPM=(HP/Torque) * 5252

A decrease in torque load will increase the RPMs. This is the RPM blip that you see the moment you disengage the clutch. That blip wasn't caused by the ECU.

 

I have never experienced this in my Z. I manually rev match. I thought rev matching only came in autos.

 

Well, I dont agree. Basic physics is in effect here, change in momentum in a certain time is a function of torque = so if momentum increases, that means rpm increases, increase in rpm means there is angular acceleration, that means engine is producing power, torque or energy to cause that acceleration and engine can only produce power when throttle is pressed, meaning fuel is supplied.

So the jist of this is that change in momentum needs fuel or throttle opening.

So when I take the foot off the throttle, there is no more fuel supplied except for idlling amount, the rpm should not increase. So if I take my foot off the throttle and press the clutch, the rpm should not increase.

And since we have drive by wire throttle systems, ECU might lag the throttle position compared to the pedal position and thus blip the throttle.

 

If I held the gas pedal steady and depressed the clutch, the RPMs would shoot up, probably to redline. If I let off the gas pedal then waited a second or two before the depressing the clutch, the RPMs would drop significantly because of the braking effect of the engine.

Maybe you're a little late is letting off the gas before depressing the clutch and the engine RPMs are blipping because of that? Maybe it has nothing to do with the ECU.

 

I think I know what your talking about and my 05 enth. does it too. When i clutch in with my foot completely off the gas, my tach dips down like a hundred rpms, goes back up those hundred rpms, and then fully drops down.

In other words, the rpms do a slight double pump when i shift from mid range. No it won't do it in "test mode" like suggested.