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

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

http://blogs.edmunds.com/roadtests/370Zbrakelight.gif

Quote:

In a fortuitous twist of fate, I scored the keys to out 370Z last night, and in the brief time I spent behind the wheel I have some observations as well as a simple maintenance issue.

Brakes:
Accelerating off the line with a bit more aggression than needed, I noticed that the "BRAKE" light appeared in the left instrument pod, then disappeared a few seconds after feathering the throttle. This was repeatable at every green light I encountered. Fortunately, I've come across this before in one of my own rides (when pulling serious lateral G's instead of longitudinal, though). My diagnosis: slightly low brake fluid level.

Another issue that caught my eye was the "VDC OFF" light remained lit during my morning commute. The VDC relies on the brake system to maintain stability, so I'm assuming this is related to the low brake fluid level. The light went away after I shut-down and restarted the engine (maybe it's powered by Microsoft?).

http://blogs.edmunds.com/strategies/370Z_BrakeFluid.jpg

Pop the hood, find the brake fluid resevoir, and there's it is -- the level's right between the high and low marks. I'll bring this to the attention of the Mikes and hopefully this is the actual culprit of the intermittent BRAKE light.

Blips and Revs:
I've spent the better part of the last decade honing my heel-toe downshift craft, and, I can confidently say, "Yeah, I've mastered it." I'm also fairly proficient at traditional, and more complicated double-clutch downshifts in vintage racecars. With that self-aggrandizement out of the way (bow down to the master of soon-to-be obsolete skills!), I am completely enamoured with the Z's Synchro RevMatch system.

I challenged myself to do it better and failed. **sigh** I've been replaced by a machine...but wait, something's not adding up here. A good heel-toe downshift requires a strong throttle blip that shoots the tach past the point of the matched revs of the next lowest gear. The clutch isn't re-engaged until after the revs begin to fall.

Here's what I discovered about the Z that makes me feel better about being beat by a computer: With the Synchro RevMatch off, I executed the typical heel-toe and noticed that the revs didn't fall as quickly as I'd expected. Using my normal downshift tempo, I was dumping the clutch while the revs were too high. So the solution was to pause before clutch re-engagement (not at all racy), or attempt to blip precisely to where the revs are in the next lowest gear (difficult, but not impossible).

I now contend that Synchro RevMatch is necessary in the Z because of the drivetrain's inability to affect a proper heel-toe downshift without the aid of a computer. That's my story, and I'm sticking to it, anyways.

Mark Takahashi, Associate Editor @ 6,533 miles

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?

Quote:

Originally Posted by spearfish25 (Post 77427)

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..

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!

Quote:

Originally Posted by AK370Z (Post 77447)

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.

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.

Quote:

Originally Posted by spearfish25 (Post 77427)

Quote:

Originally Posted by DIGItonium (Post 77761)

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.

Quote:

Originally Posted by miguez (Post 77857)

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.