Basic question

[pauly24]

I know with timing, best way to tune is on a dyno, you want as much spark as possible, either until you get MBT, or until knock occours and then you'll have to back off a safety margin.
When tuning on the street, all you can really do is increase timing till knock sensors kick in and then back off.
Is this correct so far?


But what about AFRs?
During power modes, do you want them as lean as possible upto some point?
I guess on the dyno you can experiment for what gives you best power.

But what do you do on the street? do you just keep leaning the AFRs out until you get knock and back off?

[WeathermanShawn]

I know with timing, best way to tune is on a dyno, you want as much spark as possible, either until you get MBT, or until knock occours and then you'll have to back off a safety margin.
When tuning on the street, all you can really do is increase timing till knock sensors kick in and then back off.
Is this correct so far?

Mmm. Somewhat of a risky strategy. If you are really good and can hear pinging or knocking (and also logging), I usually tune at least 2-4 degrees below the KR threshold. It is far easier (and safer) to begin low on spark and avoid any KR. All KR is mechanically destructive.

But what about AFRs?
During power modes, do you want them as lean as possible upto some point?
I guess on the dyno you can experiment for what gives you best power.

Again, pretty risky. Anecdotally, I have found that even if I can do 13.0 AFR's on the street, the car starts feeling weaker as I go leaner. Since a wideband reads ~.3 lower than a dyno (tailpipe location), that equates to ~12.7 on the street. Personally, I rarely go leaner. 95% of the time a N/A car will do just fine at ~12.5 AFR. Plenty of TQ and fuel. If that equates to a 1-3% HP loss from 13.0 AFR..far more safer.

But what do you do on the street? do you just keep leaning the AFRs out until you get knock and back off?

If you tune for 12.5-12.7 AFR on the street..then work on spark. Again, I would never go leaner until a dyno proved it was worth it..



Thats my perspective. Good luck..

[joecar]

+1 risky on both timing and AFR strategies.

Trying to set the best timing/AFR on the street is very risky to engine (and compromises safety of car/driver/public).

You might be able to do it empirically on the drag strip, but it will take many passes and the conditions will vary between passes...

Conditions can be strictly controlled/repeated on the dyno and the engine more easily monitored for knock and other problems.

Advancing timing and/or leaning AFR may or may not produce more torque... it depends on various things... remember the LSx head designs promote fast burn so less timing is required compared to say SBC designs... the faster burn means cylinder pressure peaks earlier, and you want it to peak when the crank is at the most advantageous position (any earlier means cylinder pressure opposes the crank, any later means cylinder pressure does less work).

Advancing timing and leaning AFR also creates higher combustion chamber temperatures... so even if you don't get knock, you still get damage due to elevated temperatures... and when it does knock, then all that aluminum is now nice and soft... have you seen pistons with a nice clean looking hole thru them.

[pauly24]

Ok makes sense, but how do you know where the knock threshold is without hitting it? If MBT isnt before the knock threshold then you would always have to induce knock to know where the threshold is correct?

I've got a Holden Commodore VE SS (L98 motor 6.0L)

In the E38 ecu, udner PE commanded fuel. from 0-2304 rpm it commands 13.3, Then upto 3320 it commands 12.95, and it doesnt drop below 12.5 until 4096.
In this scenario, would you guys change EVERYTHING to 12.5? or would you only change the richer values to 12.5

[WeathermanShawn]

I've got a Holden Commodore VE SS (L98 motor 6.0L)

In the E38 ecu, udner PE commanded fuel. from 0-2304 rpm it commands 13.3, Then upto 3320 it commands 12.95, and it doesnt drop below 12.5 until 4096.
In this scenario, would you guys change EVERYTHING to 12.5? or would you only change the richer values to 12.5

Wow, that is a really good question.

I have done PE Tables utilizing both methods. One where I step in at 13.4 AFR at 2400 Rpm's and richen it to 12.5 at Peak TQ (~4800 Rpms), then lean it to 13.0 AFR at 6400 Rpms.

For the last year I have kept it at 12.6 - 12.7 AFR for all Rpms. For me, its easier to hit Commanded AFR vs Actual AFR utilizing one number. The other reason could be in my head..it just seems like my setup accelerates quicker and with more TQ when I start it a little richer.

I can't see it making a difference on my logs or on the dyno. Dyno I went straight 13.0 AFR (12.7 at wideband) from 3000-6600 Rpms.

Thats my current line of thinking..

Edit: Additional Comments..

On spark..I see your point, but that is where a dyno is superior. You have to really work on spark past .40 g/cyl +, especially WOT. I have gotten pretty good at hearing pinging on my vehicle. If I ping, KR is usually just 2-3 degrees of spark away. I never let it ping. Unless your ear and car are in that kind of sync, I still think a dyno is superior. Your overall premise is generally correct...

[pauly24]

I guess I have to really start playing with it and see what works best for me while being safe about it all.

Ok ping and knock retard, and you saying that you can hear the car knock before the knock retard of the system kicks in?

[WeathermanShawn]

I guess I have to really start playing with it and see what works best for me while being safe about it all.

Ok ping and knock retard, and you saying that you can hear the car knock before the knock retard of the system kicks in?

Pauly, I can but that does not make me Superman. Its only because I ride with windows down and have become highly aware on my tune and vehicle. I would never recommend that as standard procedure. I am sure the destructive effects of pinging/KR start way before a human ear can even hear it.

No, my car had been dyno tuned for Best AFR & Spark, and then I tweak the Spark Tables for the street. If you do it that way, you'll have a nice-running car.

Good luck..

[pauly24]

Ok what I was getting at, isn't there a PID to watch the signal from the knock sensors?
Cant you use the knock sensors as the first point of knocking onset?

Instead of waiting for the system to pull the timing and then you say "hey the system pulled the timing it must of knocked"
cant you watch the actual sensors yourself? This way your not relying on your ears which for new people like myself would be dangerous.

Even when tuning on the dyne, how do you watch for knock? do you just wait until the system pulls timing or like i mentioned before can you watch the actual sensor?

[joecar]

The pid is GM.KR.

Some knock is audible and some isn't... also, sometimes, in some cases the knock sensors can miss hearing a knock event.

[pauly24]

Awesome, thanks everyone for the help.

Have cleared up this area greatly for me.

[gmh308]

Ok what I was getting at, isn't there a PID to watch the signal from the knock sensors?
Cant you use the knock sensors as the first point of knocking onset?

Instead of waiting for the system to pull the timing and then you say "hey the system pulled the timing it must of knocked"
cant you watch the actual sensors yourself? This way your not relying on your ears which for new people like myself would be dangerous.

Even when tuning on the dyne, how do you watch for knock? do you just wait until the system pulls timing or like i mentioned before can you watch the actual sensor?

There are per cylinder KR PID's. There is also a per cylinder true/false knock PID (Dashdaq has this) which seems to be applied before any filtering/thresholds are applied.

Best way to listen for knock if you dont want to invest in a "knock box" is to use the age old stethoscope method and use a piece of 3/8 ID plastic pipe and sit it on the engine somewhere and get used to what knock sounds like at part throttle and then hope you hear it through the background noise at WOT. Though only the knock box method with head phones will let you focus in on the WOT knock through the background noise. :)