I agree that knock control is useful in some situations when the threshold table is properly set up. In the case of overboost, I feel that an overboost fuel cut is key in addition to knock control. At least set it around 25 psi when the car is tuned to 20. That leaves plenty of headroom for unaccounted atmospheric changes and spikes. You can't expect knock control to save an engine when you make more than 30 psi on a 20 psi tune for pump gas.

Knock control may be set up to pull timing and add fuel, but if you're running a boost controller (whether it be manual or electronic) that is external to the AEM, you're going to continue running those dangerous boost levels despite knock and skyrocketting engine temps. Pulling timing may reduce knock voltage, but it increases cylinder head temps, which are already at dangerous levels when you overboost that badly. For example, knock control may reduce the likelyhood of ringland failure while increasing the probability of bearing failure or piston meltdown in an overboost situation.

This all happened while the car was in a shop's hands and AEM monitoring was at their fingertips. When overboost happens while the customer is off on their own, they might not even know it. Knock control, by design, is often transparent to the driver. A fuel cut is abrupt and obvious. It alerts the driver that something is seriously amiss, so they know to fix it.

just my 2c

-Mike

 

My friend boosted 37 psi on pump fuel and knock control saved his motor. Obviously you will feel knock control kicking in because when the car pulls timing there is a noticable plateau or loss of power. Only problems I have with it is it kicking in under false knock conditions like clutch rattle. But it isn't that bad.

 

What i did is i ran Straight C16 on 19lbs for 3 consecutive pulls to establish what the engines normal "noises" where including false knock after i determined that, i set the sensor to read anything above .75 volts to be real knock and pretty much cut the timeing table in half just to be safe.

 

wtf? I dunno about most cars but my cars normal engine noise is certainly above .75 volts in the higher rpm range. Cutting the timing in half that is just crazy. My timing between pump and race fuel is almost not any different because the extra boost creates plenty more activity for me to worry about. I am sure on race fuel I could get away with a lot more timing at 19psi though than the 30psi I run at the track. I think boost is a better way to make power on evos though.

 

how do you adjust knock control on the AEM EMS

 

Setup->sensors->knock sensor-> then there is a table that is for knock calibration it is a 2d graph representing rpm vs. knock threshold.

 

Good write up, prolly why my motor didnt grenade on bushurs dyno.. Great tuner

 

If your not using knock control on the AEM, you haven't tuned your car imo. It is one of the best things about the AEM. The thing is you have to properly set it up to use it.

I have run my car at 24 psi for 30k miles now and over 30 roadracing track events on days where the weather got to be over 100 degrees and my motor is still going strong.

I can think of at least a dozen separate events where knock control saved the day...

 

Ok I gotta question about that, it sure saves engines but when...? Here my question: In the Knock Sensor Cal table, the graph shows straight line at 0.30v all the way to 4000 rpm, then it gets up straight from 4000rpm/0.30v to 8000rpm/1.39v then again is straight to max 12800rpms.

In my options setting Knock Retard/Volt is set to 2.73, Knock Spark advance is 1.76, Knock Fuel Max is 5.08%, etc...

So my motor pulls timing at anything over 0.30 at 4000rpms at a rate of 3.16 degrees (as set in Knock Ign Rtd Max under options/Ign Control, or does it pull when 2.73 Retard/Volt is reached)?

man this is heavy, heheheh...

 

The EMS pulls timing whenever current knock voltage is over the threshold line in that cal table for the current RPM.

The amount of timing pulled is calculated based on how far over the threshold the voltage is X your "Knock Retard/Volt" setting. Knock restore rate and knock spark advance determine how quickly the EMS adds back in the timing it pulled due to knock.

Fuel control works the same, only it's adding fuel during what it considers to be knock based on your cal table, and then subtracting it back to the normal values after the knock event ends.

-Mike

 

Disclaimer:
1.) Don't flame me or blame me if you grenade your motor after reading this. As far as I know everything I'm writing is sound.
2.) RTFM.

Okay, first, IMO you shouldn't really be using the base map calibration for the knock sensor, nor should you be using anyone else's cal table. The base map cal is probably pretty safe to use since the knock thresholds are set so low. Probably too low and they would result in false knock being detected, needlessly dumping fuel and pulling timing. Having said that, it's safer to have the threshold set too low rather than too high. Every motor's knock sensor calibration is different. My stroker motor with forged pistons is going to be much noisier than some dude's stock short block. What passes for knock free readings with my motor would likely roach the next guy's.

Second, as Juiced described, you need to build a knock sensor profile for your particular motor. Similar to the way Juiced did, I logged Knock #1 Volts while running 19 psi of boost on 117 octane fuel while at the track. This allowed me to collect a whole lot of knock sensor data across a wide range of rpm breakpoints under full load with little or no real knock. Then I took this data and did a scatter plot with knock voltage on the Y-axis and RPM on the X-axis. Once you've plotted your knock profile you can then go into the knock calibration graph and create a threshold curve that matches your motor's characteristics.

It's important to note that you should use Knock #1 Volts to log the knock sensor data. Knock #1 Volts gives you the voltage reading from the knock sensor at the ignition event and not in mid-stroke where piston side loads or piston slap may be creating some noise. Also, you should use the internal data logger within the EMS to collect this data. PC logging does not have the high sampling rate needed to capture the voltage readings at the right times while running at high RPMS.

The amount of ignition retard or fuel dump is determined by the amount of voltage indicated by Knock #1. Don't confuse Knock #1 with Knock #1 Volts. Knock #1 gives you the amount of knock voltage ABOVE the knock sensor cal threshold. The EMS looks at the amount of voltage over threshold and applies the specified correction.

For example: If Knock Retard/Volt is specified as 3 degrees per volt and Knock #1 is measuring 1.5V, a total of 4.5 degrees of timing will be pulled. The timing will be restored at the rate specified by Knock Restore Rate & Knock Spark Advance.

 

I would have to check what my actual voltage is i just tossed .75 volts as an example.

The reason i cu the table in half was because i rather be safe than sorry, i rather lose the power instantly and take some time to figure out why by looking at the datalog than melt my motor, i guess i'm just paranoid.

 

Here's a plot of the voltage output from my knock sensor at various RPMs. My motor is pretty noisy since it's a built stroker. I see voltages as high as 3.75-4.0V at 7400 RPM. Click the image for the full size graphic. Note: this was collected during a road race event running the boost at 19psi on 117 octane fuel.