Lightweight flywheels and SyncroRev Match
 

I've been driving around this weekend with SynchroRev turned off (as I do like to heel & toe just for the pleasure of it) and I got to thinking that the 370 could use a lighter flywheel. But then I started to wonder -- how exactly does SynchroRev work? More specifically, is the weight of the stock flywheel programmed into the computer algorithm that determines how much to blip the throttle in order to achieve the correct revs? If so, then won't getting a significantly lighter flywheel screw up SyncroRev Match? Because any given amount of throttle will rev a lighter flywheel higher than a heavy one. Any thoughts? Anyone understand the technical intricacies of how SynchroRev Match works?

You are absolutely correct. I am curious myself to see what happens. It all depends on what parameters are actually read by the system and which are calculated.

Its very funny that you put this thread up. I mentioned this to DDM earlier in a PM. I thought about the same thing you did, however I had a different take on it. I have no technical information about this, but if you ask me... I think I remember hearing in the Nissan videos that the car uses throttle position, sensors in the shifter and speed and G sensors to calculate the optimal RPM. I think it just blips the throttle and gets it to a predetermined RPM (as a function of data from the sensors) rather than taking the weight of the flywheel into account. If I'm right, a lighter flywheel would mean even quicker rev matches. If you think about it from Nissan's point of view, its much easier to calculate the necessary RPM's and then just say "100% throttle until you reach that RPM, then hold and revise every millisecond using data from the sensors"

There is another thread about this on this board. I'd bet my money that the light-flywheel will NOT screw up the rev matching. The rev-matching is done by realtime math calculations, not a predefined table of speeds.

^^ I hope that's how it works! It would be awesome if that's how it works. Even quicker blips? Oh yeah, I'd be all over that!

Nissan would be crazy to use a static table for that. If one motor is even slightly off from what the factory specs are (which is VERY common) then there would be endless issues with the system. The only way to achieve what they have is to use real-time calculations.

+1 we agree.

I'm sure they have a feedback loop in the control system that operates the rev-matching. IMO, changing the flywheel would not cause any issues.

Agreed. The resolution on the RPM sensors are so high now that they don't need even a quarter of a rotation to detect the RPM. The computers are fast enough to control the motor's fuel and air to some serious precision. It's actually very impressive. Something as clumsy as a combustion engine with less than predictable fuels and explosions can be controlled with such automation... Very cool technology.

Thread revival!

You're pretty much on the mark.
Here are the sensors that make it happen:
1- Clutch pedal sensor (the same one that allows you to start the car, ie. detect pedal is fully depressed)
2- Crank angle sensor (on the bell housing)
3- Neutral position sensor/gear lever position sensor
4- Input speed sensor (on the rear left hand side of the gearbox. Not far from the reverse sensor)
5- rear wheel speed sensors (on the diff). This one i'm not 100% sure about as #4 should suffice for smooth shifting.

1 tells the system to wake up
3 tells the system what gear you are currently in & what gear you are entering
4 tells the system how fast the (output i think) shaft in the gearbox is rotating. Automatic gearboxes use an input speed sensor for the same purpose - to enable smooth shifting.
2 is obvious - i tells the system what RPM the engine is rotating at and the system calculates the target engine speed based on the signal from #4 and #3.

Since the ECU can respond to throttle inputs that quickly, i'd assume if you swapped in a lightweight flywheel and lightweight underdrive pulley, the system would not overrev the engine. It will back off once the target RPM is reached.

PS. I'm not an expert.

Well I know for a fact that a UD pulley that is lighter than factory does not mess with the SyncroRev. I'd be willing to wager that a lighter flywheel would not cause issues either.

It doesn't.

Source? Clutch pedal switch is not used.

Nissan's SynchroRev Match System Explained - The Heel and Toe Robot

I guess the easy way to test would be to disconnect the lower clutch pedal sensor and go for a drive.
The upper sensor tells the cruise control to cut.

I might be wrong about which of the two sensors but in theory, it should be the lower one.

Have used the JWT 16lb Flywheel, and the Southbend DXD Race 19lb Flywheel. Currently still have the latter installed.

If anything, I'd say Synchro-Rev performance actually improved, the most with the JWT. It was easier to trick with the Stock Flywheel. And it's actually easier now to bounce between gears, up or down with the lighter Flywheel. The VQ37VHR itself is incredibly responsive and 'zippy', but just due to it's high level of NVH, Nissan chose to just dampen the heeeell out of it with a 32lb Dual-Mass Flywheel.

Downside to going Single-Mass Flywheels though still exist, the horrible chatter at idle in neutral (can largely be combated with thicker Gearbox Oil, and the reason I swapped out from the JWT to the DXD), slight rattle on standstill take-off (you'll learn to very slightly adjust how you take-off), and difficulty taking off uphill without adding to Clutch-riding.

JWT Install, when I first drove it home and first learned of this 'cement mixer' noise:
370Z Gearbox/Transmission Rattle Noise - YouTube

Still on JWT at this point, but I learned that thicker Gearbox Oil could help. I went with full Redline MT-90 and got this:
370Z Gearbox/Transmission Rattle Noise Improvement (Cold Start) - YouTube
However, be warned, thicker Oil does take a toll on shifting ability. Expect to use significantly more force to select gears for a couple of minutes on cold starts.


MoulaZ

I'm not sure why this thread got bumped to speculate, we already know for a fact that flywheel and pulley does not affect SRM. the only thing that affects SRM is final drive ratio (and transmission ratios if one were to actually change those out). ecutek has a mechanism to adjust the SRM offset, uprev currently does not.

/endthread

Heel to toe FTW.

Folks- I just had the stage 3 Southbend clutch kit (w/ 19lb flywheel) installed on my 370Z. It's an amazing clutch kit by the way- it really holds all 500 ponies that I'm laying down on the concrete.

As for the synchro rev functionality I can say from my experience that it still works 100% with the lighter flywheel.


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I have the lightened flywheel and lighter under drive pulley and rev-match has no problems with either of them

MoulaZ, do you have an OEM clutch or has that been upgraded as well?