Compression Braking

markesc · 06-14-2017, 02:39 AM

Didn't see this posted anywhere:

So I like to downshift prior to corner entry and use the engine to help maintain constant speed and/or slightly slow the vehicle in that mid turn area.

On a few occasions the car is predictable and you get a linear sense of compression braking from the motor...that's about as best as I can describe it.

Every now and then it's like someone is hitting the gas for me, and there's no more resistance from the engine, even though I'm not actually touching the gas pedal, this results in unexpected weight transfer.

Just wondering if anyone else has experienced this, and it doesn't even have to be in an extremely tight/at the limits turn situation. Happens about 1 out of 15 turns under off throttle deceleration/slight decel or nearly constant, usually in the upper rpms. Has done this since new.

Thoughts? Is this normal?

BGTV8 · 06-14-2017, 05:50 AM

Brakes is for stopping and gears is for going ..............

Modern OEM ECU's have a bunch of nannies to minimise emissions and will attempt to moderate rev decay which your bum (*** for USA) might interpret as acceleration.

This old fart brakes on corner entry (including trail braking where necessary) and uses SRM to ensure rev-matcing on downshift, and at/just before apex goes for progressively increased throttle percentage once the car has accepted its set and will tolerate torque inputs, hitting WOT as soon as traction circle rear grip dictates can be tolerated.

Spooler · 06-14-2017, 07:30 AM

Quote:

Originally Posted by markesc

Didn't see this posted anywhere:

So I like to downshift prior to corner entry and use the engine to help maintain constant speed and/or slightly slow the vehicle in that mid turn area.

On a few occasions the car is predictable and you get a linear sense of compression braking from the motor...that's about as best as I can describe it.

Every now and then it's like someone is hitting the gas for me, and there's no more resistance from the engine, even though I'm not actually touching the gas pedal, this results in unexpected weight transfer.

Just wondering if anyone else has experienced this, and it doesn't even have to be in an extremely tight/at the limits turn situation. Happens about 1 out of 15 turns under off throttle deceleration/slight decel or nearly constant, usually in the upper rpms. Has done this since new.

Thoughts? Is this normal?

Yes, this is normal. It happens to me from time to time. It always appears to be too much throttle input during Rev matching/braking.

Hotrodz · 06-14-2017, 09:12 AM

Quote:

Originally Posted by BGTV8

Brakes is for stopping and gears is for going ..............

Modern OEM ECU's have a bunch of nannies to minimise emissions and will attempt to moderate rev decay which your bum (*** for USA) might interpret as acceleration.

This old fart brakes on corner entry (including trail braking where necessary) and uses SRM to ensure rev-matcing on downshift, and at/just before apex goes for progressively increased throttle percentage once the car has accepted its set and will tolerate torque inputs, hitting WOT as soon as traction circle rear grip dictates can be tolerated.

Agreed...engine braking is not what you want to do if you want to be fast. Get all your braking done then down shift and then on the throttle as explained above!

Sent from my SM-N910P using Tapatalk

B&W_Evader · 06-14-2017, 09:37 AM

Agreed, the 370z does not do a good job compression braking. My belief is that this is so the car remains quiet and does not do the rumbling/backfire noises during deceleration. I'd bet it can be tune in but the car will start making more noise when you compression brake. Personally I'd accept a little noise from the exhaust pipes for better braking. It's a sports car, it should be able to compression brake.

cv129 · 06-14-2017, 11:13 AM

OP has a 7at. That's what happen when Nissan paired the slow shifting torque converter AT with rev match. I have the same 7at on my G and FX, it's that 1/4 of a second "emptiness", definitely not a good feeling during any fast driving.

Faster box like DSG doesn't have this sensation.

Spooler · 06-14-2017, 07:19 PM

Quote:

Originally Posted by cv129

OP has a 7at. That's what happen when Nissan paired the slow shifting torque converter AT with rev match. I have the same 7at on my G and FX, it's that 1/4 of a second "emptiness", definitely not a good feeling during any fast driving.

Faster box like DSG doesn't have this sensation.

Ah ha, I didn't see the 7AT. I never even thought a 370z came with one.....

06-14-2017, 02:39 AM	#1 (permalink)
markesc Enthusiast Member Join Date: Apr 2014 Location: Utah Posts: 380 Drives: 2014 370z M.B. 7AT Rep Power: 3366	Compression Braking Didn't see this posted anywhere: So I like to downshift prior to corner entry and use the engine to help maintain constant speed and/or slightly slow the vehicle in that mid turn area. On a few occasions the car is predictable and you get a linear sense of compression braking from the motor...that's about as best as I can describe it. Every now and then it's like someone is hitting the gas for me, and there's no more resistance from the engine, even though I'm not actually touching the gas pedal, this results in unexpected weight transfer. Just wondering if anyone else has experienced this, and it doesn't even have to be in an extremely tight/at the limits turn situation. Happens about 1 out of 15 turns under off throttle deceleration/slight decel or nearly constant, usually in the upper rpms. Has done this since new. Thoughts? Is this normal?

06-14-2017, 05:50 AM	#2 (permalink)
BGTV8 A True Z Fanatic Join Date: Dec 2009 Location: 03350 Australia Posts: 1,514 Drives: 09 Nissan 370Z M6 Rep Power: 39973	Brakes is for stopping and gears is for going .............. Modern OEM ECU's have a bunch of nannies to minimise emissions and will attempt to moderate rev decay which your bum (*** for USA) might interpret as acceleration. This old fart brakes on corner entry (including trail braking where necessary) and uses SRM to ensure rev-matcing on downshift, and at/just before apex goes for progressively increased throttle percentage once the car has accepted its set and will tolerate torque inputs, hitting WOT as soon as traction circle rear grip dictates can be tolerated. JARblue, Rusty, Hotrodz and 1 others like this.

06-14-2017, 09:37 AM	#5 (permalink)
B&W_Evader Track Member Join Date: Aug 2011 Location: CA Posts: 972 Drives: slower than before Rep Power: 387	Agreed, the 370z does not do a good job compression braking. My belief is that this is so the car remains quiet and does not do the rumbling/backfire noises during deceleration. I'd bet it can be tune in but the car will start making more noise when you compression brake. Personally I'd accept a little noise from the exhaust pipes for better braking. It's a sports car, it should be able to compression brake. __________________ \|RIP\|6spd-sport\|OSG-LSD\|XP8\|RBF600\|Eibach Sways\|RE-71R\|FI-34Row\|Gen3-CAI\|Yaw P.S.\| Last edited by B&W_Evader; 06-14-2017 at 09:40 AM.

06-14-2017, 11:13 AM	#6 (permalink)
cv129 A True Z Fanatic Join Date: Jul 2011 Location: Dallas, TX Posts: 3,222 Drives: 09 Nismo, 16 Nismo Rep Power: 163995	OP has a 7at. That's what happen when Nissan paired the slow shifting torque converter AT with rev match. I have the same 7at on my G and FX, it's that 1/4 of a second "emptiness", definitely not a good feeling during any fast driving. Faster box like DSG doesn't have this sensation. __________________ Setrab \| RE-71 \| SPL \| JRZ \| Nismo \| ARK \| Whiteline \| RacingBrake \| CJM Oil Pan \| Ti shield

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