FAQ: Spark Advance (Timing, Retard)

You weren't the only one that missed that part Deek...lol

I know it's also available on the HPT site.

wow, that is a hot timing table!
taking the car over to the moms house for intake project tomorrow (she has a huge flat driveway) and am gonna test out the new table on the way.

I'll set it back to stock to retune the fuel after the project is done.

deekster_caddy wrote:

oh well. already in the mail

naw, still saved me some time since you added the CSV timing file by itself as well.

whoa! mad KR off of that GTP file. saw 9* !
anyways, the cruise settings are good (and will surely help my gas mileage) so Im just gonna work on adjusting the GTP file in the upper RPM ranges.

I'm going to be trying some timing experiments in the near future, so reviving this thread. I have some basic questions about spark advance, and programming it with DHP. If anyone has any experience in this area, please chime in.

My biggest interest is timing advance at cruise in 4th gear. I'm getting about +38.5º max in the 70-80 MPH range with the DHP 1.5 BIN, and I've read at the DHP forums they are seeing as high as +47º. I am really interested in seeing similar numbers.

To me, it's obvious the "Good Spark" table is the one to tune. However, there is a "Mean Best Spark" table that I have to wonder about. It's values are hotter than the Good Spark table, but the values on the 1.5 BIN are all stock, so they seem to be unimportant. I found a good thread (a long read) on this at DHP, but the consensus seems clear as mud:

http://www.powrtuner.com/index.php?showtopic=4247

Eddie, who rights the timing calculators, seems to know his stuff. He says quite confidently that the Good Spark table is all that matters, and that there are modifiers that impact spark advance, most that are not visible or editable with DHP. Tiny Tuners software may give access to some or all of these modifiers.

My situation is slightly different than most in that I'm currently not using TC lock-up in any gear (my TC clutch has been gone for some time) until the next transmission rebuild. The shifting and reliability of the trans seems good, so this could be a few years down the road. With TCC inactive, my typical cruise RPM and MAF values are different (higher) than everyone else. Even so, the car doesn't do do badly with fuel economy. I continue to average 21.5 combined, and as high as 26 MPG on the highway. I'm looking to improve that number.

DHP bases spark advance based on RPM vs. Mg/cyl, which can be derived from MAF values. In order to calculate Mg/cyl, I will need to do some math using some numbers logged in a scan:

Typical MAF @ 1200-2200 RPM: 2.5-4.5 lb/min

For this example, using 3.5 lb/min @ 1800 RPM: 3.5 x 16 = 56 oz/min

Divide 56 by 1800 RPM = .03111 oz/rev

Being that each cylinder's intake stroke is every other revolution, this would mean only 3 cylinders fire per rev:

Divide .03111 by 3 cyl = .01037 oz/cyl

.01037 oz/cyl = ~294 mg/cyl

This should mean that the 280 mg/cyl cells in the Good Spark table are the ones to target at 1800 RPM. Does the math seem correct? I wanted to run this by anyone who may have done this - before I program the table and see lots of knock because I did it wrong. Seems right, but not sure.

Using the same formula, I get ~303 mg/cyl at 2000 RPM and 4.0 lb/min MAF, and ~267 mg/cyl at 1700 RPM and 3.0 lb/min MAF.

Thoughts?

Guess the math was right. I added several degrees of timing advance (roughly +10º) to the 240, 280, and 320 mg/cyl cells between 1200-2200 RPM, and some around the fringe to smooth out the edges. The result is +40 to +45º spark advance in 4th gear when cruising at 45-80 mph. No KR so far. I think I will fill up and see if there is any MPG improvement over the next week, then maybe push a little hotter and see what happens.

Here is the old 1.5 BIN's "Good Spark" table, as it comes from DHP:



And here is the new 1.5 BIN Good Spark table with advanced timing adjustments:

Interesting stuff. How does the car seem to be running? Has it changed the exhaust note at all?

No change to exhaust sound. The type of effect you notice with timing advance is more power/torque with less throttle %. The idea is that advancing spark optimizes torque of the piston stroke. This can also give better MPG at cruise RPM. In my case the change isn't that noticeable because it's being measured over a tank of gas, not the 1/4 mile.

The design of the L67 is unique because its static compression is a rather low 8.5:1, whereas under boost this changes to a much higher number, perhaps ~17:1. Our engine runs well in boost at +9 to +12 deg spark advance, and more advanced as RPM increases. When out of boost, our engine runs like a low compression NA motor on premium, which means extreme spark timings are possible with no knock. At the DHP tuning forums many are running +45 deg, and some + 50 deg advanced. Mid 30s to 40 MPG is not unrealistic on the highway. Timing maps play a big part of it.

The beauty is, the same car that achieves 40MPG on the freeway can also push out a healthy amount of power & torque with just a quick change in throttle, if the timing is optimized. GM finally came close with the '04/'05 GTP, and one popular tuning mod is to load the GTP's hotter timing maps. Instead, I'm modifying the DHP 1.5 BIN's timing map with similar values in hopes of seeing a slight MPG improvement.

That's awesome. So are you experimenting with just changing the timing when the engine is not receiving any boost in order to improve gas mileage? Are you changing the timing at all during boost to add more power/torque?

For now only cruise timing, or when not in boost. The boosted timing cells have already been optimized by DHP for the 1.5 BIN, If you look at the maps on the previous page, you'll see an area of red, orange and yellow in the middle. This is where DHP modified the stock timing.

If you look at the 2nd map on the previous page, you'll see a 2nd narrower patch of red/orange above the first one. Those are the cruising spark cells I've recently changed. DHP gave me a pretty good cruise map, but I want to know what happens if the values are pushed even more, like with the '05 GTP. If I can gain even 1-2 MPG, it will be worth it. What I'm seeing so far, the spark settings are applied independent of gear and speed, it's all about air flow vs. RPM. This means I see the added timing advance in 1st, 2nd, and 3rd as well as 4th, but only when not in boost. In city driving, my numbers are +10º higher than they were before whenever my throttle is between 5-15% in any gear, at any speed.

Advancing spark seems to be a forgotten part of modding with our cars, because the focus is on the blower and building boost. Swapping a pulley is easier and less expensive than tuning the PCM. What many end up doing is creating a strong low-end torque engine at WOT, but still sluggish at-tip in and when cruising. It makes the car feel slow when you aren't off the gas. Low MPG is another symptom. Hotter timing fixes that, and it's the main reason people appreciate a PCM swap or tune, because the car just feels so much stronger with everyday driving. You don't need to go WOT nearly as much. It can make a Buick engine drive exactly like a Pontiac GTP's (not that I want a Pontiac, but GM gave them a much better performance tune, being it was their "Driving Excitement" brand).

Sorry to come in late. I'll export my timing table for you to look over, but keep in mind I started with the 05 GTP table and tuned it for a VS cam, GenV blower and 3.2 pulley. but cruise timing in the 40s sounds very familiar.

Right now I'm using a stock timing table with a few degrees added in the cruise spot of the table, per Paul. I think I want to try out the 05gtp table though and get more familiar with timing. I really didn't want to mess with it because the different tables that I looked at from other bins just seemed all over the place compared to mine but I was kinda just looking at the numbers, not so much the curves. As soon as I saw values that were higher for some and lower for others when comparing the other tables to mine, I was put off to the idea of messing with timing at all. I have the timing knob that I use to deal with WOT timing and it works great but I want to get a feel for adjusting idle and cruise timing because I might need to change that once I get the higher compression motor in the car.
This 1997 timing thing still confuses me though...

Recently scanned my Riv I was looking at the timing and it read -33 degrees at regular driving doing about 65 it. I don't know what exactly to look for I need the baseline of what timing the Riv should run at. I'm using dash command for iPhone for data logging

SuperRivL67 wrote:

Recently scanned my Riv I was looking at the timing and it read -33 degrees at regular driving doing about 65 it. I don't know what exactly to look for I need the baseline of what timing the Riv should run at. I'm using dash command for iPhone for data logging

The PCM advances timing **a lot** to boost gas mileage at cruise.

Do some browsing and searches on this site and learn more about the Riv.

Uh, no....

The PCM advances the spark for mileage under light cruise - retarding lowers economy. However 33 degrees of advance, depending on octane, would be right in the ballpark. This is just a case of a program using semantics that we don't recognize, as I believe Charlies' scanner-program was doing with +/- fuel trim.

While we might think of advance as being 'positive', that advance is before top-dead-center, thus a program could well display it as a negative number...

Ok I can't get it to display the pid for kr. But at wot it's reading -15*.

Eldo is correct. Our engines normally run increased spark advance (hotter timing) at cruise. More advance can actually improve fuel economy at lower RPM. The L67 can support some of the most advanced spark timing of any engine I've seen. I've tuned mine for +45 deg at cruise, some on DHP board have tried up to +50º.

I always think of spark advance as a positive number, because the term "advance" represents how many degrees BTDC (before top dead center) the spark is initiated, and so is expressed as a whole (+) number. A negative timing value would indicate negative advance, or ATDC, which is actually not advance, but rather "retard". Retard is also measured as a + number. So, +10º advance = -10º retard, and -10º advance = +10º retard.

Rarely should you encounter it, but negative advance (spark ATDC) is usually not good. I don't like seeing values below +11º at WOT. 0º means something is wrong. +15º seems just fine.

Here's how GM illustrates timing on the A-pillar gauge in the Cobalt SS. Note +40º means "40º advanced":

I have seen other 97s (Pontiac GTPs) where the scanner reads - for the timing, It's not actually -, it's correct - you have 33 degrees of advance, not -33. '98s and newer read normally. It's just a display issue.

I should have been even clearer with my nomenclature...
While I was explaining 'advance' I didn't use the same term as SuperRiv did: Timing

As AA and the Cobalt say, if you're calling it advance, then negative advance is of course retarded. The neutral term of timing is where the interpretation of + & - can be troublesome. That's what I was referring to when I said that before TDC could be considered negative, and after TDC (retarded) could be considered positive.

My own timing seems to be move a lot, so I've always assumed that it was the knock sensors letting it go as advanced as is practicable - I didn't think that the tables were limiting it. Also, like SuperRiv, I'm in 91-octane California at zero altitude, and these parameters should always be mentioned when discussing timing.

If you're using the term "ignition timing" rather than "spark advance", you could stipulate BTDC/ATDC with + numbers. For example, 40º BTDC, or 5º ATDC. No negative values needed. I think we're on the same channel. Here's a visual:



My timing moves around a lot, too. It varies widely in the good fuel spark table, which is arranged according to RPM and fuel injected (Mg/Cylinder). Values range from as low as 6º to about 33º advanced in a stock table (note no neg values), but there are also modifiers that push this higher or lower based on vehicle performance. TCC lock-up, intake air temp, and some other things we don't know can affect spark.

My spark tables are posted on the previous page.

will someone please post pics of a stock 98-99 Riv timing map and the 05 GTP's map? I am curious to see the difference. Is anyone else tuning their timing tables like AA did?

Anyone have that 05 GTP map? curious to see the differences.

Thank you!

Map of what

I think I do, but it's buried. If no one else can provide I'll do some digging.

Thanks, AA. Will you also post a copy of your current map so I can see what you're working with?

https://dl.dropboxusercontent.com/u/84264401/Tuning/GFS-05GTP.csv