Does synchro-rev really matter??

kailua · 04-06-2009, 12:17 AM

Funny thing, I've had a bunch of 4 cylinder, manual cars (06 STI, 09 Speed3, 09 STI) and never really needed nor wanted the synchro rev match. With the V6, the synchro rev match helps alot, and without it, it is less forgiving when you down shift.

semtex · 04-06-2009, 07:45 AM

Quote:

Originally Posted by kailua

Funny thing, I've had a bunch of 4 cylinder, manual cars (06 STI, 09 Speed3, 09 STI) and never really needed nor wanted the synchro rev match. With the V6, the synchro rev match helps alot, and without it, it is less forgiving when you down shift.

That's due to the heavy dual-mass flywheel. Has nothing to with 6 vs. 4 cylinders. Heavy flywheels have more inertia, which means it takes more energy to change the revs (in either direction). When you downshift, if you don't blip the throttle in advance (either manually or via SRM), the revs will climb as soon as you re-engage the clutch as a lower gear revs higher than the preceding higher one. In other words, as soon as you re-engage the clutch, the clutch will 'grab' the flywheel and force the rpms up. Because a high-mass flywheel has more inertia and it takes more energy for the revs to climb, it's jerkier. This would be true regardless of how many cylinders the engine has. And it's also why they offer lightweight flywheels on the aftermarket (one of the most popular for this car is from Jim Wolf Technology.)

kailua · 04-06-2009, 02:54 PM

Quote:

Originally Posted by semtex

That's due to the heavy dual-mass flywheel. Has nothing to with 6 vs. 4 cylinders. Heavy flywheels have more inertia, which means it takes more energy to change the revs (in either direction). When you downshift, if you don't blip the throttle in advance (either manually or via SRM), the revs will climb as soon as you re-engage the clutch as a lower gear revs higher than the preceding higher one. In other words, as soon as you re-engage the clutch, the clutch will 'grab' the flywheel and force the rpms up. Because a high-mass flywheel has more inertia and it takes more energy for the revs to climb, it's jerkier. This would be true regardless of how many cylinders the engine has. And it's also why they offer lightweight flywheels on the aftermarket (one of the most popular for this car is from Jim Wolf Technology.)

What are the benefits of a heavy flywheel? Does it smooth out up shifts because of more inertia, but when you down shift there's too much inertia, hence the synchro rev match to smooth things out? Any benefits for the Z to not have a lightweight flywheel from the factory? I assume it wouldn't cost Nissan more dinero to put in a lightweight flywheel as opposed to one that is heavy?

Also, how come the 4 cylinder vehicles I mentioned do not come with a heavier flywheel, just overkill for a 4 cylinders I guess? Is there a simple rule of thumb that says, if you have a specific type of engine or output then there would be an optimum weight flywheel for that engine, etc?

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04-06-2009, 12:17 AM	#1 (permalink)
kailua Base Member Join Date: Feb 2009 Location: Earth Posts: 82 Drives: 09 STI Rep Power: 18	Funny thing, I've had a bunch of 4 cylinder, manual cars (06 STI, 09 Speed3, 09 STI) and never really needed nor wanted the synchro rev match. With the V6, the synchro rev match helps alot, and without it, it is less forgiving when you down shift.