Nissan 370Z Touring: Brakes and Blips and Revs, Oh My!

spearfish25 · 05-25-2009, 11:19 AM

Quote:

Originally Posted by OWSIU

The hanging revs/blips could be for emissions purposes. My brother's 09 WRX would sometimes blip (rpms rise when clutch is pressed) and revs hang. Searching online, the explanation we found is that it's for emissions purposes by burning off the extra gas.

Seems to me that 'burning off extra gas' would only increase emissions.

OWSIU · 05-25-2009, 11:46 AM

The extra gas causes a rich condition which when unburned would release more hydrocarbons than it would when burned. Remember in a perfect combustion reaction; Hydrocarbon + Oxygen = CO2 + water, of course it's never perfect, which is why we have emission standards and testing. Unburned, vaporized octane is going to increase hydrocarbon output which makes the car dirtier emissions wise, and the simplest solution car makers can do is just to burn it off.

travisjb · 05-25-2009, 12:22 PM

Quote:

Originally Posted by RCZ

I think the ECU is programmed to do a blip even when you go to neutral...

The system can't perfectly predict if you are going to upshift or downshift so the engineers designed it to always bleep when you go into neutral. Don't believe me? try it. I think they did this to make downshift bleeps even faster/smoother. It may have actually be done to work around a heavier flywheel...its a pre-bleep to the real downshift bleep, like a jump start. Maybe the flywheel is so heavy that if they didnt use the pre-bleep, then it wouldn't feel as quick.

I think the lighter flywheel will make the pre-bleep even more noticeable. However, it will help the system overall...

Makes sense... In fact I wrote a similar explanation on my srm track thread a while back, here: syncro rev match where I wrote:

Quote:

I have no data to confirm that SRM would hold the revs higher when up-shifting but it makes some sense. imagine you are accelerating and in the next second you will go from 55 to 60 in 2nd, as that's happening, you press the clutch and start moving the shift lever... SRM sense that you are 'passing the gate' for second gear and b/c you are now going 60 as you 'pass the gate' out of the gear it momentarily thinks you may be going into that gear and ups the revs... then you're on your way to 3rd and SRM targets a lower RPM but the damage was done...

...an 'electronic gate' that is located at the entry/exit point of every gear... if so, with srm on, we're going to hit that gate even when going out of gear on an upshift

miguez · 05-25-2009, 01:00 PM

So, since I only get my Z in August, I have to ask instead of trying:

When upshifting, RCZ mentions the RPMs will blip when passing neutral, before selecting the higher gear. If you don't select the hgiher gear, and leave it in neutral, are the RPMs maintained? And if so, what RPM is it? Does it change or is it always the same target until you tell the car what gear you are indeed going for next?

Thanks guys, this forum is the best school on this car there is!

ChrisSlicks · 05-25-2009, 05:39 PM

I haven't seen the RPM's blip in neutral, they don't blip until you hit the entrance to the next gear. He might have just seen over-rev from hitting the clutch which is pretty common in this car. Basically it doesn't blip until it knows what gear you're heading for, but it is easy to accidentally brush the entrance to the wrong gear and send the revs sky high.

RCZ · 05-25-2009, 05:53 PM

I'll make a video of later. When I move it from 3rd to neutral, being careful not to touch anything but neutral (either way it would touch 4th and a blip would be unnecessary) it still does a blip. I find it extremely annoying actually because i want the revs to drop, instead I get a blip. It does it when i go from any gear into neutral.

I know what you are saying Chris and it makes sense, but in practice, it bleeps when I go into neutral. Which as I said above, I can only guess is for faster matching during aggressive driving.

travisjb · 05-25-2009, 06:04 PM

it happens when you are accelerating... by the time you're coming out of a gear, you're 5'ish mph faster than you were when you were in gear and had just pushed in the accelerator, and therefore the SRM (when the shifter passes through the 'gate' leaving the gear) blips just like it is programmed to do whenever exiting / entering a gear... my theory anyways

miguez · 05-25-2009, 06:16 PM

Another theory, in agreement with Chris: What if it is just that the flywheel is relatively heavy in mass, and its inertia brings the engine revs up a bit once the tranny load is removed by clutching in? That sounds feasible.

imag · 05-25-2009, 07:09 PM

Quote:

Originally Posted by miguez

Another theory, in agreement with Chris: What if it is just that the flywheel is relatively heavy in mass, and its inertia brings the engine revs up a bit once the tranny load is removed by clutching in? That sounds feasible.

The flywheel mass will never make the motor spin *faster* - it will only maintain revs. Think of spinning a plate - no matter how hard you push it, it won't accelerate (faster, for those pedants among you) when your hand stops touching it.

However, I do think the friction point on this clutch is encouraging us to put the clutch in slightly before letting off the throttle in order to maintain smooth declutching of the gear. That extra throttle time is raising the revs. At least that feels right in my case. I think the lightweight flywheel is going to do wonders...

RCZ · 05-25-2009, 07:09 PM

Travis, you are agreeing with me then if you are saying it bleeps on the way OUT of a gear as well?

Miguez, I can see what you mean and it makes some sense, however to add revs you would have to add energy. When it is under load it would take the energy away, it wouldnt "spring" when you take the load off. You know what Im saying? You aren't adding any force by taking the load off.

Imag, I do that as well so that I dont get the "shudder", however thats not the case here. It happens even when Im completely off the gas.

Driving > foot off gas > clutch in > lever to neutral > Blip

ChrisSlicks · 05-25-2009, 08:00 PM

The over-rev I'm talking about seems like it is reluctance of the electronic throttle to fully lift off as you hit the clutch, it would act a lot like a blip.

I'm going to do some testing tomorrow with the SRM on and off and see if I can reproduce the behavior RCZ is seeing. I might even try seeing what it does if I knock it out of gear without touching the clutch (steady slow speed in 4th).

miguez · 05-25-2009, 08:39 PM

Quote:

Originally Posted by imag

The flywheel mass will never make the motor spin *faster* - it will only maintain revs. Think of spinning a plate - no matter how hard you push it, it won't accelerate (faster, for those pedants among you) when your hand stops touching it.

However, I do think the friction point on this clutch is encouraging us to put the clutch in slightly before letting off the throttle in order to maintain smooth declutching of the gear. That extra throttle time is raising the revs. At least that feels right in my case. I think the lightweight flywheel is going to do wonders...

Hey imag, you're right, guess I wasn't thinking things through.

travisjb · 05-25-2009, 10:23 PM

rcz, yes i'm agreeing 110%... there's no question it happens, imo
i think a lot of this will be resolved once i can test drive my car w/ new jwt gear... i should be able to share comments this week and maybe video next weekend... fingers crossed

RCZ · 05-25-2009, 10:49 PM

awesome. Rep for trying new flywheel for us all.

travisjb · 05-26-2009, 01:45 AM

thank you ! will report back asap

05-25-2009, 06:04 PM	#22 (permalink)
travisjb A True Z Fanatic Join Date: Jan 2009 Location: GSO Posts: 2,803 Drives: VIR Rep Power: 188	it happens when you are accelerating... by the time you're coming out of a gear, you're 5'ish mph faster than you were when you were in gear and had just pushed in the accelerator, and therefore the SRM (when the shifter passes through the 'gate' leaving the gear) blips just like it is programmed to do whenever exiting / entering a gear... my theory anyways __________________ 2009 370Z #104 For Sale

05-25-2009, 07:09 PM	#25 (permalink)
RCZ A True Z Fanatic Join Date: Nov 2008 Location: Miami Posts: 6,403 Drives: '09 370Z Rep Power: 1118	Travis, you are agreeing with me then if you are saying it bleeps on the way OUT of a gear as well? Miguez, I can see what you mean and it makes some sense, however to add revs you would have to add energy. When it is under load it would take the energy away, it wouldnt "spring" when you take the load off. You know what Im saying? You aren't adding any force by taking the load off. Imag, I do that as well so that I dont get the "shudder", however thats not the case here. It happens even when Im completely off the gas. Driving > foot off gas > clutch in > lever to neutral > Blip Last edited by RCZ; 05-25-2009 at 07:11 PM.

05-25-2009, 10:23 PM	#28 (permalink)
travisjb A True Z Fanatic Join Date: Jan 2009 Location: GSO Posts: 2,803 Drives: VIR Rep Power: 188	rcz, yes i'm agreeing 110%... there's no question it happens, imo i think a lot of this will be resolved once i can test drive my car w/ new jwt gear... i should be able to share comments this week and maybe video next weekend... fingers crossed __________________ 2009 370Z #104 For Sale

05-26-2009, 01:45 AM	#30 (permalink)
travisjb A True Z Fanatic Join Date: Jan 2009 Location: GSO Posts: 2,803 Drives: VIR Rep Power: 188	thank you ! will report back asap __________________ 2009 370Z #104 For Sale

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05-25-2009, 11:46 AM	#17 (permalink)
OWSIU Base Member Join Date: Apr 2009 Location: California Posts: 40 Drives: 06 Infiniti G35 Rep Power: 16	The extra gas causes a rich condition which when unburned would release more hydrocarbons than it would when burned. Remember in a perfect combustion reaction; Hydrocarbon + Oxygen = CO2 + water, of course it's never perfect, which is why we have emission standards and testing. Unburned, vaporized octane is going to increase hydrocarbon output which makes the car dirtier emissions wise, and the simplest solution car makers can do is just to burn it off.

05-25-2009, 01:00 PM	#19 (permalink)
miguez Enthusiast Member Join Date: Apr 2009 Location: Columbus, Ohio Posts: 359 Drives: '04 Cavalier Rep Power: 181	So, since I only get my Z in August, I have to ask instead of trying: When upshifting, RCZ mentions the RPMs will blip when passing neutral, before selecting the higher gear. If you don't select the hgiher gear, and leave it in neutral, are the RPMs maintained? And if so, what RPM is it? Does it change or is it always the same target until you tell the car what gear you are indeed going for next? Thanks guys, this forum is the best school on this car there is!

05-25-2009, 05:39 PM	#20 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	I haven't seen the RPM's blip in neutral, they don't blip until you hit the entrance to the next gear. He might have just seen over-rev from hitting the clutch which is pretty common in this car. Basically it doesn't blip until it knows what gear you're heading for, but it is easy to accidentally brush the entrance to the wrong gear and send the revs sky high.

05-25-2009, 05:53 PM	#21 (permalink)
RCZ A True Z Fanatic Join Date: Nov 2008 Location: Miami Posts: 6,403 Drives: '09 370Z Rep Power: 1118	I'll make a video of later. When I move it from 3rd to neutral, being careful not to touch anything but neutral (either way it would touch 4th and a blip would be unnecessary) it still does a blip. I find it extremely annoying actually because i want the revs to drop, instead I get a blip. It does it when i go from any gear into neutral. I know what you are saying Chris and it makes sense, but in practice, it bleeps when I go into neutral. Which as I said above, I can only guess is for faster matching during aggressive driving.

05-25-2009, 06:16 PM	#23 (permalink)
miguez Enthusiast Member Join Date: Apr 2009 Location: Columbus, Ohio Posts: 359 Drives: '04 Cavalier Rep Power: 181	Another theory, in agreement with Chris: What if it is just that the flywheel is relatively heavy in mass, and its inertia brings the engine revs up a bit once the tranny load is removed by clutching in? That sounds feasible.

05-25-2009, 08:00 PM	#26 (permalink)
ChrisSlicks A True Z Fanatic Join Date: Mar 2009 Location: North East Posts: 6,203 Drives: 09 370Z Sport M6 Rep Power: 653	The over-rev I'm talking about seems like it is reluctance of the electronic throttle to fully lift off as you hit the clutch, it would act a lot like a blip. I'm going to do some testing tomorrow with the SRM on and off and see if I can reproduce the behavior RCZ is seeing. I might even try seeing what it does if I knock it out of gear without touching the clutch (steady slow speed in 4th).

05-25-2009, 10:49 PM	#29 (permalink)
RCZ A True Z Fanatic Join Date: Nov 2008 Location: Miami Posts: 6,403 Drives: '09 370Z Rep Power: 1118	awesome. Rep for trying new flywheel for us all.