Could someone explain how changing from the stock setting of 6 degrees BTDC will affect performance? Will advancing the timing improve performance?


[Modified by geezel, 9:33 AM 12/23/2003]

 

Most often, it does. Try advancing your timing 2* at a time and compare 1/4 mile, MPHs. Not ETs, MPHs. Stop and/or back off when you reach the max MPH or experience ping. Every car is different and will respond differently. Mine is set at 14* BTDC. Most won't want to go that high. The track opens for test and tune April 10th. Good luck, and...

RACE ON!!!


[Modified by CFI-EFI, 9:42 AM 12/23/2003]

 

Since your '86 L98 has an adjustable TPS I suggest you first follow the method on my site (link in sig. below) to set base idle and then tweak the TPS min/max values. A more agressive TPS setting will give crisper throttle response due to advanced spark curve and fuel.

Each engine performs best with the timing setting that it "wants"; follow the instructions above to find the setting that gives best power, i.e. trap speed.

 

Here is a great techincal write up

"A number of factors play into optimum timing. What you are trying to achieve is maximum cylinder pressure at ~14-18 degrees after TDC. Sometimes, you can't add enough timing to do this without causing detonation. With a higher compression ratio, the motor will tolerate less timing before detonation occurs. Ditto for high intake air temps. A combustion chamber which is smaller, and more efficient combustion chamber (the GMPP "Fast Burn" is a good example) needs less timing to achieve max pressure at the correct time as does a smaller bore. Fuels which burn faster need less timing. The higher the rpm, the more timing is needed. A leaner mixture needs less timing (it burns faster), and so on.

In any case, no matter what, optimum timing has to be determined empirically and can't simply be calculated in advance. I doubt even the OEM's have a sufficiently detailed model of each combo to simulate it. Contrary to what you often see on the board, optimum timing cannot be determined by simply continuing to advance the timing until you experience knock and then backing off. More timing, even without detonation, is not good if it advances max cylinder pressure too far towards (I used the misleading word "beyond" in the other thread) TDC.

This is one of the many reasons why tuning is best done on a dyno. You can tell if you are making more hp or less with each change and you also can instrument so you know what the conditions are (IAT's, etc.).

One other point just FYI. The less timing needed to achieve max cylinder pressure at the optimum point the better. That's one reason why those GMPP "Fast Burn" heads work well, they need very little timing to make hp. The earlier the spark, the earlier the cylinder pressure starts to rise. Keeping in mind that this begins before the piston reaches TDC, you can see how power is lost as the piston is forced up against the already igniting fuel/air mixture. In an ideal world, instanteous complete combustion would occur with the piston at ~14-18 degress ATDC. Of course, this is impossible. But the closer you can get, the better."- Dr. Rich Krause

http://web.camaross.com/forums/showt...hreadid=176734

 

My 86 is set at 8*, you just have to experiment with it.

 

My 87 ;s at 8 also...

 

When I dynoed my car it didn't seem to care whether it was at 2 or 12 degrees. HP varied only 2. That is just my car though and your results may vary.

 

How do you ajust the spark timing? is this by simply turning the cap rotor in one or the other direction? and how do you know at what degree it was set?

 

Look near the brake booster and you should see a small connector(1 lead)..unplug it. Next get a timing gun(any auto parts stores have them). Read the instruction on how to hook it up. It involves look down at the harmonic balancer when the motor is running and turning the distributer until you get it to the desired setting. Remember to re-hook the connector!
Good Luck

 

:iagree:

The connector is a brown wire with a black stripe (on my car)

 

Tray 28's post is very informative.

For additional reading on timing, primary/secondary spark control, lag angles, burn angles, spark control systems, etc, try "How to Build Horsepower" by David Vizard, ISBN0-931472-24-5.

Somwhat dated but a good primer. Haven't read Volume 2.

Again, if you are just getting into this issue, head for pages 88-109.

Available and Barnes & Noble, Amazon, etc.

dlmeyers 90 coupe zf6 3 speed shocks.

 

Every car is different, you will have to experiment. Even if doing this on a dyno don't always focus on peak # gains. Focus on total area under the curve and also how long it takes the engine to go through certain RPM points. The quicker the pull the stronger she is.

 

I have always thought that once base timing is set (just a ballpark #), the computer will retard or advance to where it needs it and not necessarily going to use the base timing setting. Or is the ECM timing range relatively small? Also keep in mind it takes some miles for the ECM to relearn.

 

Yeah, I also though the ECM did a part of the controls for this? :confused:

 

The ECM does do all the timing after base is set, but it doesn't KNOW where base is set at. The ECM assumes base is 6* all the time and goes from there. If you set base to 8* you've just added 2* to the entire spark curve.