I lost an engine to detonation last year (not my tune). I am learning to do my own tune and have left the OEM knock retard settings in place. How do I safely move up the timing during the tune to a reasonable and safe level? Engine safety is more important here than 10 horsepower.
One degree at a time, until it begins to knock or you don't feel safe any more. In either case, back it down a few degrees at that point.
One degree across the board or just high end?
Wherever you want an additional degree of timing. There is no single answer for it, it all depends on the vehicle. But I would not add it to the entire table.
Factory Ls1 and Ls6's can take 32 degrees starting at .70 g/cyl to 26 degrees at wot 6500 rpm's and approx .90-100 g/cyl comfortably on 91 oct gas.Originally Posted by futuretech
Knowing how much timing to add can be different based on your location and altitude. Add 2-3 degrees at a time (1 degree increments take to long) till you see some KR activity then pull our 1-2 degrees in the area of knock. I like to use 1 degree when fine tuning wot.
After you start adding timing to the spark table and adjusting for knock you will begin to see the trend when viewed in 2d or the 3d table.
Detonation can also be caused by to lean of an AFR mixture under heavy load rather than to much timing. More often than not I see this situation.
Well said. I have an Z06 motor with headers. I am using the stock Z06 spark tables. I am using 93 gas. Where to start additions in your opinion?
I'd start by reading the sticky in this section on how to tune. It's basic info that will get you familiar with using the vcm editor and the vcm scanner.
It all boils down to making the parts (or additions) on the engine work correctly by giving the ECU the "correct" information.
I hate hearing of people adding timing till it knocks then backing off a few degrees. Definately not how it should be done in my opinion.
Cheers
Benno
It works in most cases where there isn't a huge amount of power being made. Anybody who is making enough power where even a small amount of knock will cause damage isn't likely to be running cheap fuel anyway. There are better ways to add timing, but the methods are often very math intensive.
You can take a factory tune throw it on a dyno and watch it go into KR most every time. Adding timing till you begin to see KR is perfectly fine. I'm saying "when you go into KR) meaning when you see the knock sensors being tickled. Don't add so much timing where the ecu begins to pull max amounts of retard out........that's just foolish.
If you're going to add timing and never hit KR then you need to be on a dyno to verify peak torque and when you lose it.
During my tuning and doing some WOT runs there are times I get no KR and other times is shouw up around 4K rpm. Most of the time the KR is not in the same area of cells. Seems strange.
In the vcm scanner histogram (i believe tab 2 is default for KR) you will see at what g/cyl vs rpm the KR will appear. You can cut / paste special into your spark map or you can manually remove the timing. If your in to tall of a gear and loading the engine hard you can promote KR.
In other words, putting the hammer down in fourth forcing a downshift? Different that a straight WOT run from an idle launch?
Find a good long straight road. In the scanner under vcm controls you can command the trans to stay in any one gear. Pick 3rd and, get to about 40 mph or so and use that gear to check your timing in those areas that you see kr.
Ideally you want to be on a dynamometer in a steady state load for this because it is much easier and safer to accomplish.
NOw that makes sense! Thanks.
This is about as foolish as it gets. Adding timing until you get KR has no scientific merit. Without quantitative methods to measure torque output, how do you know the power increasing with timing changes? The butt-o-meter? I use a dyno everyday and I see cars loosing power way before they register KR. I make various runs tweaking one parameter at a time measuring the output. AFR has a HUGE impact on dialing in spark advance and VERY difficult to perform on the street with any kind of accuracy. Once you start moving into high compression or FI setups, you are playing with fire.
2008 Corvette Coupe
Atomic Orange, 3LT, NPP, F55, CC3 and MN6
Thanks for the words of wisdom.
I've heard of people looking for the timing that gives the most vacuum at part throttle positions as a guide to how close to MBT you are. In your opinion is this a good method that will get you close without the use of a dyno?
Cheers
Benno
Would you mind expanding on the math intensive ways to do this?
Cheers
Benno
Not everyone can get on a dyno or live near a dyno. Just as you I'm on a superflow everyday. It is not foolish to add timing till you get some KR activity.
If your AFR is fine at say 12.6 - 13.0 your going to keep adding timing till when? When torque falls off, loss of power or you hit KR simple. Hitting KR and having the ECU pull max retard is foolish and I never condoned doing that.
What I said was add timing till you see activity i.e. .5 to 1 degree of KR, than pull timing out in the area of KR activity. Sitting there adding one degree at a time is not efficient especially if your an individual who claims to be sitting on a dyno all day, then you would know first hand how much you can safely get away with on the first run.
It appears you have grossly misunderstood what I told the OP. My method is perfectly safe given he has a wideband and a long road to do the testing.
Remember in tuning it's about "optimizing" the engine calibration for it's intended purpose, and there is more than one procedure for accomplishing that.
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