Re: Knock. A question for Graham or Marc

[XfireZ51]

Originally Posted by Ccmano

Come to think of it, if we assume for the moment that shift knock is a real thing on a stock car, which means gear clash is being picked up by the knock sensor, it begs the question, are Fidanza single mass Flywheel equipped cars more likely to experience false knock? The transmission noise of a single mass equipped car is well documented up to about ~2k rpm. Is that noise, under various load and speed parameters, generating false knock throughout the rpm range as we shift and move on and off throttle without the dampening affects of Dual Mass Flywheel? Food for thought.
H

Yep, think that's the question I was asking before. The problem is, false or not, it affects the performance of the motor. And that brings up the issue of the correct trans fluid.

[jss06c6]

Guys, I recorded data through engine shutdown. At shutdown, our motors clatter quite a bit. The knock sensor on the '93 definitely picked up the shutdown noise. It is 100% stock with Dual Mass FW setup..

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[XfireZ51]

Steve,

Do u normally pickup any noise at startup?

[jss06c6]

Not as much.. it's the rattle at shutdown that I pickup mostly. I'll rap the motor on Monday so I can see the response.

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[Hib Halverson]

I can't remember, did the LT5 cal use "burst knock retard"?

Also, I can't speak to false knock because I never had trouble with that, but when I had Barney there was a time when I did a lot of on-road and chassis dyno testing while logging KR. I found that the only way I could run "KR-free" in most conditions was to be burning 94.5-95-oct fuel. I'd get that by mixing pump gas with Rockett Brand 100-oct. racing gasoline.

[XfireZ51]

Thx Hib. No “burst knock” in the LT5 cal. Think that came w the LSx motors.
When u were datalogging, how stock was Barney?

[rkreigh]

the LT5 seems to have fantastic knock resistance. I enjoyed Marc's presentation about the knock events and how they drastically affect timing and very slowly return timing so the car feels very lazy


When I got the LSV, Larry left the race chip in it and it had 31 deg timing and ran around 12 to 1 compression and ran just fine on pump 93 gas. I ran some high octane unleaded at the track and saw no improvement and indeed no knock issues data logging with Ease.


Cam timing of course helps as the cyl pressure doesn't spike up at lower rpms and the high rpms as Graham mentioned are pretty forgiving


I got a bit "knock paranoid" from my old days of buick turbos as we "drove over the crank" every now and then from knocking the bottom end clear through the oil pan.


I'm very impressed at the efficient combustion chamber and knock resistance of the lt5. It allows much higher compression ratios on stock pump gas than other engines.

[Hib Halverson]

Originally Posted by XfireZ51

Thx Hib. No “burst knock” in the LT5 cal. Think that came w the LSx motors.

Copy that. I was wondering about that because back in my Barney days, I was not a calibrator.

When u were datalogging, how stock was Barney?

Auto Masters Street Skinner engine with Marc Haibeck cal.

I mixed 91 oct gas with Rocket Brand 100-unleaded to get about 95-oct R+M/2.

[XfireZ51]

Bringing this one up again because I continue to play around w it. A couple of questions come to mind, ideally for the likes of Graham and/Marc. But please chime in if u have 'played" around w this as well.

I have attached a pic w the stock Knock Retard values for the 92 LT-5.

My questions are:

1. Given that many of us have modified our motors, drivetrain, clutch etc., as Graham has stated, we have introduced other "noise" for the knock sensor to detect. How much from stock values would it be prudent to reduce the sensitivity of the sensor and still retain a level of protection from knock?
I believe Marc feels comfortable w modifying the attack and decay rates by +/- 50% depending on the parameter.

2. In the pic I have attached, the parameter for SA v MAT is displayed.
Just to clarify, this is showing that beginning at a MAT of 43C, the ECM is
retarding timing by 3*, correct?

The pic also shows that MAX Retard in PE for the 405hp motors is 4.92*
while the 375hp motors may retard timing by a minimum of ~7* in PE.
What changed to bring that about? Would it be ok to use the 93-95 settings
for the 375hp motors?

[Marc Haibeck]

Yes Dominic, the spark advance is retarded by 1 degree when the air horn is at 89 degrees F. And -3 degrees when the air horn is at 110 degrees F. This can take the edge off power on the dyno or at the drag strip. At peak power one degree of spark advance can change the HP by 10 on a 500 hp engine.

To avoid this loss, the table can modified. I recommend relocating the Manifold Air Temperature sensor out in front of the radiator to avoid the negative effect.

When the sensor is relocated the table values are a good feature. I think that it is good for engine safety to retard the timing when the ambient air is 90 degrees or more.

Long ago someone from GM told the group at the Gathering in BG that the sensor was placed in the compromised location to satisfy a requirement to be able to test the engine with all of the sensors that will be used with that engine. Rather than rely on a sensor located on the chassis that is installed at a different time and place.