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

Source: 2009 Nissan 370Z Touring: Brakes and Blips and Revs, Oh My! | Long-Term Road Tests Blog on Edmunds' Inside Line

The part about the revs falling is interesting. I've noticed that if I blip the throttle, the revs fall rather slowly. However, with SRM 'on' I've seen the revs fall very rapidly when upshifting. I don't know how to explain how the car can control its revs like this though...whether it's automatically modulating the clutch or has a way to engine brake and drop revs more quickly on command.

Hmmm, that's really interesting! Can anyone else comment on this?

Partially agree. With SRM on, RPM fall rapidly BUT stops at the optimum rpm for maybe about a second or two, then continues fall toward idle rpm if gas pedal is not pressed.

check out this video on how SRM upshifting works.
YouTube - synchr revmatch

I have been so busy lately, didn't get a chance to do a full SRM video (upshift and downshift).

Thanks AK. That video shows downshifting mostly, and does not illustrate what you said, that when upshifting it will rev match, then drop to idle if gas pedal not pressed. That last bit of information I didn't know, so thanks for sharing!

Yeah, it's a nice little feature that it will hold it at the next gear's revs. I just noticed that it can drop to the 'hold' point faster when SRM is on than when I just watch it fall after an engine blip on my own.

Correct me if I'm wrong, but isn't that BRAKE indicator a signal for the parking brake being engaged? I don't think it has anything to do with low brake fluid. More likely his parking brake linkage is loose and needs adjustment.

no actually, I have the same issue, im pretty sure its low brake fluid...

Owner's manual page 2-9:

"Parking brake indicator:
When the ignition switch is in the ON position,
the light comes on when the parking brake is
applied.
Low brake fluid warning light:
When the ignition switch is in the ON position,
the light warns of a low brake fluid level. If the
light comes on while the engine is running with
the parking brake not applied, stop the vehicle
and perform the following:
1. Check the brake fluid level. Add brake fluid
as necessary. (See “BRAKE AND CLUTCH
FLUID” in the “8. Maintenance and do-ityourself”
section.)
2. If the brake fluid level is correct, have the
warning system checked by a NISSAN
dealer."

Thank you sir. I should really do something about this...brakes feel fine though...they can hold for a bit longer until I decide what Im doing with them...

When test driving the 7AT, I notice the revs holding before falling back to idle. I'm not sure if they purposely do that to smooth things in between shifts.

Which makes it even more interesting to see what will happen with a lighter flywheel. If indeed the engine ECU is the one delaying the RPM drop during gear shifts, and not the stock flywheel, we might not see the results one expects from a lighter flywheel. travisjb might be the first one to find out.

I suspect the flywheel is the culpript not the ecu... no question our flywheel is heavy... and I struggle to think of why they would purposefully engineer-in a delayed rpm drop... but I could be wrong ! we'll find out soon

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...

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.

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.

Makes sense... In fact I wrote a similar explanation on my srm track thread a while back, here: http://www.the370z.com/track-autocro...rev-match.html where I wrote:

...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

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!

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.

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.

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

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...

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

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).

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

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

awesome. Rep for trying new flywheel for us all.

thank you ! will report back asap

Alright, I figured it out.

Aside from the sensor for each gate, there is a sensor in the center of each neutral position. If you take it out of gear straight up or down to the neutral position directly above or below the gate then the revs will hold where they are or fall slightly. If you move it from that neutral position to a neutral position further left then it will blip.

The easiest way to test it is to drive in 5th at a steady speed of 45-60 and drop it down to neutral above the various gates. If you drop it to neutral and let go, the spring will center it above 4th so the engine blips in anticipation. If you push it to the left the engine really blips thinking that you might stick it in 2nd. If you drop it out of gear but hold it to the right the engine doesn't blip at all.

Fascinating, and interesting solution to this problem. Thanks for finding out Chris!

One more annoying thing I experimented with a little is the reluctance of the rpms to drop when up shifting, for this test I had SRM disabled.

I found that the rpms will only drop quickly if you are 100% off the throttle before you touch the clutch, during normal driving you wouldn't do that as it makes for more jerky behavior. This could be attributed partially to the electronic throttle not sensing the load change quickly enough, compounded by the heavy flywheel.

Sounds right on to me, electronic throttle + heavy flywheel. I can't WAIT for travis' flywheel impressions!

There may be an additional factor at work here...If you read the VVEL expose over on the other forum (Posted today) it states that the throttle plate kind of plays second fiddle to the Cam actuation in determining some engine speed settings...

http://www.the370z.com/nissan-370z-g...potantial.html

Yes I read that one. It doesn't really matter what the throttle is controlling as long as whatever it is controlling reacts quickly. Given that the VVEL and throttle plate are both computer controlled this is potentially something that can be addressed by a software update (if Nissan determines it is a problem).