Timing values
06-06-2003, 03:55 PM
#1
Race Car
Thread Starter
Timing values
I've gotten conflicting values for timing on a 944 Turbo. I'm interested in two values:
1. Number of degrees the timing is drawn back on a 944 Turbo Vs. an NA 944.
2. Number of degrees timing is retarded if knock sensors are triggered. Are there different detection levels or just one response no matter how much knocking is heard by the sensors?
If anyone knows I'd appreciate having this information. Thanks.
1. Number of degrees the timing is drawn back on a 944 Turbo Vs. an NA 944.
2. Number of degrees timing is retarded if knock sensors are triggered. Are there different detection levels or just one response no matter how much knocking is heard by the sensors?
If anyone knows I'd appreciate having this information. Thanks.
06-08-2003, 08:30 AM
#2
Race Director
"1. Number of degrees the timing is drawn back on a 944 Turbo Vs. an NA 944."
"2. Number of degrees timing is retarded if knock sensors are triggered. Are there different detection levels or just one response no matter how much knocking is heard by the sensors?"
Do you mean the amount when knock is detected? And by 'NA 944' you mean the S2 right?
This isn't an amount so much as a crank-position. Both cars will dial back ignition in 3-degree increments with it detects knock that's above its threshold level and it will continue to retard until knock stops. The maximum position is 4.7-degrees ATDC. This means if you're currently running 20-degrees ignition BTDC and knock is detected, the maximum amount of retard is 24.7 degrees. However, if you're running at a different operating zone on the map at 45-degrees ignition BTDC, then the maximum amount of retard is 49.7-degrees.
One quick note on knock-detection, it's not a binary yes/no type of thing. What a knock-sensor is, is really a microphone that listens to the noise-level in an engine. Some knock-sensors features a mechanical filter to home in on the specific knock-characteristics of that particular engine. Some engines like ours, use a general Bosch sensor with filtering done in the electronics. In both cases, the amount of noise that enters the computer is an analog range of greys. Typically as engine-RPMs increase, the noise-level increases as well. The computers are then set to listen for sudden noise-level increases above this background ambient level (at high-RPM). Any sudden noise activity is then considered knock and the ignition is retarded. The critical factor here is what's the minimum/maximm amount of normal operating background noise that's rejected and what's the rate-of-rise and peak values that constitutes a knock event.
"2. Number of degrees timing is retarded if knock sensors are triggered. Are there different detection levels or just one response no matter how much knocking is heard by the sensors?"
Do you mean the amount when knock is detected? And by 'NA 944' you mean the S2 right?
This isn't an amount so much as a crank-position. Both cars will dial back ignition in 3-degree increments with it detects knock that's above its threshold level and it will continue to retard until knock stops. The maximum position is 4.7-degrees ATDC. This means if you're currently running 20-degrees ignition BTDC and knock is detected, the maximum amount of retard is 24.7 degrees. However, if you're running at a different operating zone on the map at 45-degrees ignition BTDC, then the maximum amount of retard is 49.7-degrees.
One quick note on knock-detection, it's not a binary yes/no type of thing. What a knock-sensor is, is really a microphone that listens to the noise-level in an engine. Some knock-sensors features a mechanical filter to home in on the specific knock-characteristics of that particular engine. Some engines like ours, use a general Bosch sensor with filtering done in the electronics. In both cases, the amount of noise that enters the computer is an analog range of greys. Typically as engine-RPMs increase, the noise-level increases as well. The computers are then set to listen for sudden noise-level increases above this background ambient level (at high-RPM). Any sudden noise activity is then considered knock and the ignition is retarded. The critical factor here is what's the minimum/maximm amount of normal operating background noise that's rejected and what's the rate-of-rise and peak values that constitutes a knock event.
06-08-2003, 06:02 PM
#3
Race Car
Thread Starter
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Danno:
<strong>Do you mean the amount when knock is detected? And by 'NA 944' you mean the S2 right?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">In my first question I'm asking what the timing differences are between a normally aprirated 944 and a 944 Turbo. In addition to lower compression/intercooling there's a difference in the spark timing of the turbo in order for the engine to boost safely. I received a timing map from Russ [THANKS!] and am wondering how much different it is than a 944 whether it's normally aspirated 8 valve, S, or S2 [non-turbo basically].
Thanks for the info on the knock detection. I'll save those values.
<strong>Do you mean the amount when knock is detected? And by 'NA 944' you mean the S2 right?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">In my first question I'm asking what the timing differences are between a normally aprirated 944 and a 944 Turbo. In addition to lower compression/intercooling there's a difference in the spark timing of the turbo in order for the engine to boost safely. I received a timing map from Russ [THANKS!] and am wondering how much different it is than a 944 whether it's normally aspirated 8 valve, S, or S2 [non-turbo basically].
Thanks for the info on the knock detection. I'll save those values.