FAQ: Spark Advance (Timing, Retard)

Is there an optimal/max timing value we want to hit rather than going as high as possible with no KR?

I was told by someone (a friend who tunes for INTENSE) who spoke to an engineer from GM claiming 26º BTDC was optimum for max torque in a 3800. I don't know if it was specific for heavy throttle, cruise, WOT, high RPM or low RPM. There are probably ideal values for each condition, but I think he meant under "heavy throttle".

I don't know if that value was optimized for NA or SC engines, either. Honestly, I don't know if it's even 100% legit.

Under throttle, go as hot as you can without KR - you probably won't come close to 26º BTDC with any real amount of boost. I'd think 15º BTDC at WOT is a good target. Higher (closer to TDC) from 10º BTDC is pushing things, imo.

For cruising, our engines will tolerate 45º, even 50º BTDC without KR, however, there is a point I think around 40º BTDC where it doesn't produce any torque gain, so no benefit to MPG. The downside to pushing hot timing is raised exhaust gas temperature (EGT), which is bad news. I wouldn't go down this road unless you have an EGT meter installed. I have never been able to get KR at cruise even at 48º BTDC, which is kind of scary, so I decided not to press any further.

You're not going to be able to advance timing at all with a 3.4" pulley. You might get away with it right now, but the second it gets hot outside it's knock city.

AA, I read the same. 26 to be optimal and if you can't get more than 13 with 0 KR you need to go up in pulley size.

I was running 33-37 in the 'hot' zone (where the larger timing #s are) with the 3.6" pulley with 0 KR.

I dropped to the 3.4" pulley and I have nearly eliminated all KR and still have an awesome looking timing table.

I am going to experiment and start reducing timing even if not needed to stay around 26 in these areas and then tune from there.


I read somewhere on the net that back in the day the trick to tuning was to advance timing as high as possible until KR happened then reduce by a couple degrees. But this is not the case with the 3800 SII.
I read there is optimal values and higher is not better. In fact, lower than stock can create more power in some areas.

I doubt i can find the source I read that from but it's something to consider?

Anyone want to share their timing tables with current mod list? Please?

Here's stock 05 GTP timing table. Looks hot!

Quote :

I read somewhere on the net that back in the day the trick to tuning was to advance timing as high as possible until KR happened then reduce by a couple degrees.

This sounds correct, but the whole concept of advancing spark by 40-50º BTDC is sort of freaky, especially at low RPM & high-load. At some point, even if you aren't reporting KR, it can't be a good idea to start the burn while the piston is still on the upstroke. It qualifies as "pre-ignition" in my book.

AA wrote:

Quote :

I read somewhere on the net that back in the day the trick to tuning was to advance timing as high as possible until KR happened then reduce by a couple degrees.

This sounds correct, but the whole concept of advancing spark by 40-50º BTDC is sort of freaky, especially at low RPM & high-load. At some point, even if you aren't reporting KR, it can't be a good idea to start the burn while the piston is still on the upstroke. It qualifies as "pre-ignition" in my book.

AA, are you saying the stock 05 GTP table looks freaky?

It's a hot table, for the gen III engine. This is why the gen III was rated 260 HP, and also why it was typical to see significant KR on a stock engine.

You kinda have to ignore all the low throttle/load areas of the Slll base timing maps because of something to do with the throttle-by-wire I guess. That whole section of the table has ridiculously higher advance than Sll tables. I would not use it as a template or anything

Good point, Codith. I didnt consider that.  I was going to use it as a template with the 3.6" pulley but not anymore.


I am seeing KR with my 3.4 pulley from 2k-3.6k RPM in the .08 and .12 columns. Nothing beyond those 2 columns! What does this mean? Why am I KR free after those columns but I see KR in the first 2 columns of the cylinder airmass?

Here's the timing table I'm working with right now. You will notice my KR area as that little green oasis in the spots I noted above. That's the only spot I see KR. Any advice?

Quote :

I am seeing KR with my 3.4 pulley from 2k-3.6k RPM in the .08 and .12 columns. Nothing beyond those 2 columns! What does this mean?

I don't see how you are getting that. the .08 and .12 columns represent very low air flow - like between idle and engine not running. Why would you see KR there?

Check page 2 of this thread for how to calculate MAF to mg/cyl (or g/cyl). Remember HPT timing chart is flipped from DHP, and HPT uses g/cyl, so consider the values are different by a factor of 1000.

Also there are so many other factors that cause KR besides spark timing and RPM (load, A/F, gear, etc.).

AA wrote:

Quote :

I am seeing KR with my 3.4 pulley from 2k-3.6k RPM in the .08 and .12 columns. Nothing beyond those 2 columns! What does this mean?

I don't see how you are getting that. the .08 and .12 columns represent very low air flow - like between idle and engine not running. Why would you see KR there?

Check page 2 of this thread for how to calculate MAF to mg/cyl (or g/cyl). Remember HPT timing chart is flipped from DHP, and HPT uses g/cyl, so consider the values are different by a factor of 1000.

Also there are so many other factors that cause KR besides spark timing and RPM (load, A/F, gear, etc.).

AA, that's what I want to discuss. What would cause KR there? I will get some scans posted soon.

Checking page 2 now.

What I meant is, how are you concluding you're getting KR "there"? What parameter are you looking at that makes you think knock is occurring at .08 & .12 g/cyl?

With DHP, we would need to derive g/cyl from MAF. I couldn't tell you where KR is occurring in the spark table until doing that. Does HPT have a g/cyl parameter that you're able to log real time?

I am using this:
http://www.theblattners.com/projects/tablemodifier/main_timing.html

and inputting my scans, MAF table, and spark table. Then using that program to adjust my timing where KR is appearing.

It has worked very well in zeroing in my fuel trims and eliminating KR on my 3.6" pully tune while increasing timing where applicable.

I'm sure the modifier program works if the instructions are followed, and if the info is entered correctly. I suspect something is wrong, but I don't use that program so can't say for sure.

Using your max g/cyl and RPM values for example:

.12 g/cyl = 0.0042328754 oz/cyl

0.0042328754 x 3 = 0.012698626 oz/rev

0.012698626 x 3600 rpm = 45.7150536 oz/min

45.7150536/16 = 2.857 lb/min


And for your minimum values:

.08 g/cyl = 0.002821917 oz/cyl

0.002821917 x 3 = 0.008465751 oz/rev

0.008465751 x 2000 rpm = 16.931502 oz/min

16.931502/16 = 1.058 lb/min

So to check this, look at MAF (lb/min) in your scans where there is KR, and the RPM. If you see close to 1 lb/min at 2000 rpm, or 2.8 lb/min at 3600 rpm, then the program is working correctly. If not, there's an error.

I think it's an error.

For KR, these MAF values seem low to me. 1 lb/min is what my scans usually show at ~800 RPM @ 0% throttle (idle, around 2900 Hz MAFF). You shouldn't see KR here. Not sure if 1 lb/min is even possible at 2k rpm.

For reference, from my scans in 4th and 2nd gears:

@ 15% throttle, 2000 RPM, MAF = 4.7 lb/min (5250 Hz MAFF)

@ 94% throttle, 3600 RPM, MAF = 20.9 lb/min (8650 Hz MAFF)

So looking at your "KR there", it's not correct, imo. The values aren't realistic. I'd figure this out before using this program to modify your spark table any further.

You're definitely right that there's something weird going on.

Check this out.

When I load my scan and timing table into the Table Modifier program, here's where it says my KR is..


Now here is the KR histogram of my most recent scan out of HPT. They don't match!
This is avg KR per cell. I am going to start tuning with this info and try to to figure out what's up with the table mod program. If I am not setting something right or what..

Ok. I am going back to the 3.6" now. WOT timing is weak with the 3.4". Here is my current timing table for the 3.4" followed by average KR then max KR.

I want to test both at the quarter mile and see which gets the best time though. I think the 3.4" pulls harder off the start but the 3.6" might make HP in the higher RPM range.

3.4" timing table


Average KR


Max KR

Couple of things -
1) optimal timing is different based on cylinder pressure, fuel mixture and RPM. There is not one optimal timing setting. Those variables all add up to how long the mixture takes to ignite.
2) I believe the blattners program is made to work with output from DHP. HP Tuners may have different scanning/logging output. The idea is the same though - look at the histogram of KR from your scan and make adjustments accordingly. Once you understand what that automated tool is doing, it's easier to do it by hand.

A regal gs dude at the track last week said he's running 24* WOT with intercooler/xp cam and 2.7" pulley. First ive heard of anyone pushing over 20* WOT?

Anyone else advancing >20* WOT?

Sounds to me like this guy needs to drop pulley size?

That's an awful lot of timing at WOT, but I suppose it's possible. I question his claim without seeing some proof and scans. Would also need heads and more.

Also just saw that there's an "XP HOT" and an "XPZ" cam, I don't know anything about the XPZ.

Years ago, I was told once by a respected someone in the 3800 tuning community that 26º spark advance is the point for generating optimum torque in our engine. This information supposedly came from an engineer at GM with many years of tacit knowledge. I don't know the validity, but I figured 15º would be a good target, and soon after that I stopped trying for boost and instead on breathing and timing (power).

I updated  my timing table and hit as high as 44* at cruise now. I bumped timing up in cruise cells and power cells as well. (trying to get as close to 26 as possible) Havent touched WOT in a few weeks but currently running 17-18* WOT with 0 KR. Going to see if I can get 20 next time at the track. Need to pulley drop asap but i need that dang snout mill tool.

I will post screenshots when I get home.

Put that 3.6" pulley back on there and warm up timing advance!

AA wrote:

Put that 3.6" pulley back on there and warm up timing advance!

uhhhh what?