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-   -   Official Nissan 370Z Synchro Rev Match Transmission thread (http://www.the370z.com/nissan-370z-general-discussions/1107-official-nissan-370z-synchro-rev-match-transmission-thread.html)

AutoX Z 08-27-2009 06:22 PM

Quote:

Originally Posted by Philipp (Post 172292)
When lapping at the race track, I often hit the Rev-limiter will downshifting... Besides the "wheelhopping" effects, I do not understand why this will cause a blown engine???
Done this more than 300 times on my previous car without any engine issues... Is the Rev Matching disabling the engine cut-off sensors???

I think we're confusing down shifting with up shifting. 1-2 upshift, 2-1 downshift. Going from 2-1 it is possible to force the engine to over-rev because of the speed the wheels are turning. No amount of fuel cut will keep engine from exceeding the rev limit when there is a mechanical link to the wheels. That is a money shift and will definitely lead to major engine damage in some fashion.

Philipp 08-27-2009 09:44 PM

Quote:

Originally Posted by AutoX Z (Post 173121)
I think we're confusing down shifting with up shifting. 1-2 upshift, 2-1 downshift. Going from 2-1 it is possible to force the engine to over-rev because of the speed the wheels are turning. No amount of fuel cut will keep engine from exceeding the rev limit when there is a mechanical link to the wheels. That is a money shift and will definitely lead to major engine damage in some fashion.

AutoX
Sorry if i didn't translate properly my thinking... English isn't my first language.
Wheelhooping does occur under hard breaking when the rear of the car is going slower than the axle (due to brake compression on the wheels). It doesn't happen during acceleration...
Hope this clarify my comments. Also, hitting the rev-limiter is "NORMAL" when downshifting under braking before entering a tight corner/apex. This driving habit may also due to my rotary engine history where the power band was at high (very high) RPM levels.

Modshack 08-28-2009 03:10 PM

Quote:

Originally Posted by Philipp (Post 173352)
Also, hitting the rev-limiter is "NORMAL" when downshifting under braking before entering a tight corner/apex. This driving habit may also due to my rotary engine history where the power band was at high (very high) RPM levels.

It's not "Normal" unless you're downshifting too soon. Scrub off some speed with the brakes so your downshifts fall into the RPM range that the engine is happy with. Forcing an over-rev with gearing is a classic reason for Valve damage on the track. You could get away with it on the rotary because there are no valves to float. Downshifting, Wheel hopping and over-reving does not sound smooth at all. You can probably better your times if you get smoother... That, and you don't even want to know what it will cost to replace bent valves on a VVEL motor..

!xoible 08-28-2009 03:14 PM

Quote:

Originally Posted by Philipp (Post 173352)
AutoX
Sorry if i didn't translate properly my thinking... English isn't my first language.
Wheelhooping does occur under hard breaking when the rear of the car is going slower than the axle (due to brake compression on the wheels). It doesn't happen during acceleration...
Hope this clarify my comments. Also, hitting the rev-limiter is "NORMAL" when downshifting under braking before entering a tight corner/apex. This driving habit may also due to my rotary engine history where the power band was at high (very high) RPM levels.

actually wheelhopping is @ acceleration, burnouts, hardshifts 1-2, 2-3.

Modshack 08-28-2009 03:23 PM

Quote:

Originally Posted by !xoible (Post 174694)
actually wheelhopping is @ acceleration, burnouts, hardshifts 1-2, 2-3.

Actually it's very easy to do on deceleration too where engine braking exceeds tire traction. Since the rear wheels can't spin up due to engine drag they hop when they lose traction. High end performance motorcycles now employ "slipper clutches" that slip just enough to prevent this kind of thing, like an ABS for track deceleration..

AutoX Z 08-28-2009 05:52 PM

Quote:

Originally Posted by Modshack (Post 174705)
Actually it's very easy to do on deceleration too where engine braking exceeds tire traction. Since the rear wheels can't spin up due to engine drag they hop when they lose traction. High end performance motorcycles now employ "slipper clutches" that slip just enough to prevent this kind of thing, like an ABS for track deceleration..

I've seen it done on a solid axle firebird braking HARD with R-comps. The weight transfered to the front enough to severely unload the rear axle. This caused the rear brakes to lock and activate the abs. Everytime the wheels locked the axle jumped cause there was so little weight on it.

kannibul 08-28-2009 11:06 PM

FWIW, synchro-rev works on the 7AT, I noticed it today on both ends - downshift AND upshift.

shabarivas 08-29-2009 04:45 AM

synchro rev does not exist on the 7AT - you have a torque converter

kannibul 09-08-2009 01:11 PM

Quote:

Originally Posted by shabarivas (Post 176031)
synchro rev does not exist on the 7AT - you have a torque converter

LOL - ok, try again.

Matt 03-19-2010 07:03 AM

http://img367.imageshack.us/img367/9...2541034zi2.png

370Zsteve 03-19-2010 07:09 AM

Quote:

Originally Posted by AutoX Z (Post 173121)
I think we're confusing down shifting with up shifting. 1-2 upshift, 2-1 downshift. Going from 2-1 it is possible to force the engine to over-rev because of the speed the wheels are turning. No amount of fuel cut will keep engine from exceeding the rev limit when there is a mechanical link to the wheels. That is a money shift and will definitely lead to major engine damage in some fashion.

Not with the rev-limiter it won't. The damage you risk is to the clutch and the transmission.

370Zsteve 03-19-2010 07:15 AM

Quote:

Originally Posted by Modshack (Post 174705)
Actually it's very easy to do on deceleration too where engine braking exceeds tire traction. Since the rear wheels can't spin up due to engine drag they hop when they lose traction. High end performance motorcycles now employ "slipper clutches" that slip just enough to prevent this kind of thing, like an ABS for track deceleration..

:icon18: and my MV Agusta goes a step further and uses what they call an Engine Braking System. No slipper clutch needed! Rather than me try to explain it :icon14:, here's the official line:

The Magneti Marelli 5SM ECU manages the widely acknowledged EBS system (Engine Brake System) that is fitted to MV Agusta engines. The concept is based on a solenoid-activated by-pass valve on cylinder N° 2 intake duct. The by-pass is situated downstream from the feed throttle that has a suitably shaped air intake. This device allows cylinder N°2 to produce torque even under deceleration (when the feed throttles are closed) thanks to a signal sent by the Marelli ECU.

Matt 03-19-2010 07:19 AM

Be careful, Steve. This thread is like 9 months old, haha! Necro'd by a spammer.

370Zsteve 03-19-2010 07:22 AM

Quote:

Originally Posted by Matt (Post 454229)
Be careful, Steve. This thread is like 9 months old, haha! Necro'd by a spammer.

lmao I just saw it, reported :icon14:

SkyZ 03-22-2010 07:05 PM

Prepping for race wars i see. Well u'll need 2 of the big bottles.

Quote:

Originally Posted by Zlips (Post 16263)
Nope...LOL I need NOS haha.



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