How much timing you guys run with stock l98 heads before you get knock?


I installed a set of vortec heads and I get a lot of audible knock with 30 degrees total(knock retard disabled). It's weird because this is on 94 octane and the fastburn combustion chambers.

My base timing may be off, I will check it as soon as I get my hands on a timing light(I know I should just own one...actually I think I will go buy 1 today). The reason I think it may be off is because the guy how installed my heads was using a dial-back timing light. I pointed out to him as he was looking for the 6degree mark on the crank pulley that he can set his timing light to 6 and just line up the 0 degree mark...I think he might have set his timing light to 6 and still set to the 6 mark...making 12 initial..I'll check tonight.

 

When my car was bone stock and I had the original heads around 28* (at sea level) and a little more at higher elevation. A guy who also has a bone stock L98 in Manitoba that I've been helping tuning can't run more than 23* without audible knock occurring. (This is with the KS set to only 1* retard which effectively disables it but still lets you see that it's occurring).

I now have a set of ZZ3 aluminum heads that have been ported and I polished the combustion chambers. My initial testing showed that it could easily handle 32* of spark advance without showing any signs of detonation. But I have yet to see 1) how far it will go and 2) what spark advance yields the best performance. I've been busy with our new house so I have only limited time to play with the GTA these days.

 

Unless you changed other things besides the heads, you should be able to run more adv than before. The vortecs have a better chamber and it's around 62cc. Not the 58-60 of F bodies. Probably not 6* though.

 

The iron head L98s used in F-bodies had 64cc combustion chambers. Only the aluminum head L98s used on the Vettes (and ZZ motors) as well as the 305s had 58cc chambers. And many of the vette guys with bone stock aluminum heads also find they cannot tolerate much timing without some cleanup of the combustion chamber.

Most of the newer GM heads tend to use less timing.

 

Is it possible that a lean condition by cause audible knock? I am think I might be running a little lean on the higher rpms/loads....I will try richening out my fuel map and see if it helps.

My brother is getting away with 31 total timing on his vortec heads, with 10:1 compression and a carb. I really thought I would have been ok with 29-30 total....

 

Using Craig Moates software it shows the amount of Spark Advance w/r/t TDC degrees.....does this include the intitial or is it what ESC is doing? (165 ECM)

Also in the 6E code there is a table named:

Spark Correction - LV8 vs. Coolant. What is this? and what happens over 160 LV8?

 

As I said in my earler post, for whatever reason, a friend in Manitoba at a higher elevation than me could not run as much spark advance as my original L98 could run (his was identical to my original setup).

I did a lot of testing of timing on my car a few years ago. Adding fuel would help a bit, but it wouldn't allow me to run any significant amount of timing. It definitely wouldn't allow me to go from 28* to 32* (let alone 36*). And the extra fuel made me run to rich and actually slowed me down.

Besides your brother running a carb (which people tend to run richer) vs. your EFI, I suspect he is running a bigger cam than you. Cams bleed off a lot of cylinder pressure and can allow you to run a little more timing. But I bet your brother still can't run the "old school" 36* at sea level.

Don't get too hung up on the actual timing you are running. As I said, the mythical 36* that car magazines use is old school. What is important is to find the timing your engine likes the best and makes max power. And the newer GM heads tend to work this way.

The one thing you can do (if you didn't) is clean up the combustion chambers. You'd be surprise how many sharp edges their are. Remove the sharp edges and smoothen out the combusiton chamber. I found that resulted in allowiing me to run more timing and DID yield more power.

 

Its really something that you have to figure out on your own. Two engines made exactly the same still might want two different timing settings.

There are soooo many variable that can effect the total timing an engine wants.

I would start out low and then keep increasing it 2* till you notice the performance drop off. You really need a good way to gauge the performance. I like to use MPH at the strip. Don't go by ETs, since they are greatly influenced by traction and other outside influences.

Many people do not understand that even if they spin, they will still turn the same MPH in the 1/4. The ET will just be slower. My car runs 120+ MPH no matter what my 60' times are.

So I would not look to hit a certain number, just use your performance to lead the way.

 

Glenn...yes my brother is running a slightly bigger cam...slightly though.

I am not shooting for a magic number, i.e. 36...I was trying to setup up my timing at 29 degrees total thinking that this should be fine for Vortec heads and start fine tuning from there. I didn't clean up the combustion chamber because these are fastburn heads, hence I assumed that it wouldn't really be an issue, there supposed to be very efficient combustions.

Looking back at my old scans I was getting a lot of knock even with my L98 heads and stock timing(more than now actually). My other brother mentioned that I should verify my crank pully is true at TDC...he says it can be off...is that possible? Even a 4 degree difference here would make all the difference in the world

I will definately pull back timing and start testing from there...and I do use MPH in the 1/4 mile for judging gains or losses.

I also notice that my O2(narrow band) goes leaner on the top end so I will add some fuel there as well...

Still what does the Spark Correction - LV8 vs. Coolant do?

 

Your brother is SOOOO true about the Crank Pulley. Mine was off by 2 degrees. I now have an adjustable timing pointer and I verify TDC everytime I do a cam swap. This is extremely important ... because if it is off then you won't be running what you think you are

Tim

 

How very true.......

But at the end of the day, the number is just for conversation purposes. If you use the methods to find your best timing, it is what it is. The actual numeric value is really irrelavant.

My timing mark says I am getting over 40* of advance, which I know its truely not. If I would have been trying to stay within a certain guidlines someone else laid you for me, I would have never gone that far with my timing to find the "sweet" spot.

As I said I gained ~40hp and an equal amount of Torque by increasing the advance to where it is now.

I believe there are many people here that would be running much better if they forgot the "numberic" constraints and ran the timing their engine performed best at.

So many thing can effect total timing. Octanes, temperature, head efficiency, A/F mixtures, RPMs, sensors, altitudes, etc. etc.

If you go at it without trying to achieve or run a specific number and have a well thought out game plan, then you can easily find what you should be running. Irregardless of the numeric number, and what others think you should be running.

Good luck.

 

I agree with you Ski...I wasn't really looking for a specific number...I was just starting from there....just made me curious as to why I would get knock at only 29 total...but I think I might be my own worst enemy....after analyzing the timing table I am running a little more carefully I have noticed that I add as much as 4 degrees more than the stock L98 table at the heavy loads between 2800 and 4400 rpm....where I am getting my knock.

I will be reverting back to the stock L98 tables and starting over from there....but I will check my crank...if that's off then my initial is off and the ESC is adding too much timing everywhere.....

Still no answer on what Spark Correction - LV8 vs. coolant!!!???

Man I really should get some actual work done instead of going through all this stuff....TGIF

 

Ahh, the '165? When scanning in 8192 baud mode (w/the 10K resistor) the code adds a particular amount of timing (6° SA out of the blue). You mentioned mask $6E (possibly ARAP), if so then zero out location $23 in the bin. That is the ALDL adder SA.

The coolant vs LV8 table makes timing corrections based on coolant temperature and load. _typically_ at normal coolant temperatures (195° stat) the timing corrections are/should be zero. But they aren't always that way.

RBob.

 

Here is what the stock L98 for 89 165 ECM has in this table:

 

Yeah I started with the ARAP....how do I do that with GMECMEdit? And is it really necessary? Is it just adding the 6 into what I see or what the ECU sees? I want to stay with the ARAP based bin, it seems to have the best MAF tables and scalers...

 

I would imagine that you need to add that location to the .ecu (or whatever GMECMEdit uses for a definition file). The other way is to use a hex editor on the bin and zero it out.

As for being necessary. . . To zero it out? If not zero'd then your timing will be different when scanning and not scanning.

The ALDL SA adder is added in such a way that it ends up at the crank. Don't know if the scan tool shows it or not.

RBob.

 

So you're telling me that when I am connected to the ALDL, the ALDL SA is adding 6 degrees?

Is the added to the field that moates shows as total spark advance?

When not connected my timing goes back to it's normal timing tables + 6 initial?

This may be my problem all along...an extra 6 degrees is alot.

 

I don't know if the vortec's are fast burn or not, but Fast burn heads[/I] shouldn't need as much spark advance because they are burn fast. Engines run better with spark advance because it takes time for the combustion to really take off. If it burns faster it shouldn't require as much timing.

 

Yeah I understand that...and yeah the Vortec are indeed a fastburn combustion chamber....


But that also means that they should be able to handle more timing, no? I don't want to run more timing...I was just wondering why I would ping with 30 degrees...I want to make sure everything is proper...

 

Whenever the 10K resistor is across ALDL terminals A & B the code adds the ALDL SA adder. No 10K resistor, no ALDL SA adder. As I mentioned I don't know if it shows up in the ALDL data stream. (This is all for the $6E mask, $8D does not require the 10K resistor for 8192 baud ALDL).

As an aside I checked ARAP and the ALDL SA adder value is 8.1 deg.

RBob.

 

I currently have a switch between A&B with a 10k resistor on it. Will turning off the switch after the datastream starts flowing to the scanner disable the ALDL SA....

The reason I ask is because Craigs software seems to make the ECM exit ALDL mode once receiving data, i.e. the idle drops to normal operation instead of the fast idle before communications occur.

I am heading to the track tomorrow and will do some testing but would love to have these answers before that.

Where is CRAIG???

 

NO,
They will not be able to handle more timing.

If your motor pings at 30, and if the AFR is correct, then you've exceeded the timing demand of the engine. You tune to what the engine wants, and likes, not what you think it should need.

The whole idea is get the peak pressure on the piston at 8-12 AFTER top dead center, so as to exert as much energy in moving the crank. The less timing you need to acheive that means the less energy is wasted by the piston having to work against expanding gases.

There's a few things going on that are often ignored.
The combustion process doesn't need a spark, as evidenced by there being diesel engines. The spark just avalances a work already in progress. There is also what's called a flame kernel. It's not until the flame front from the sark get to about a .1" flame fron that it moves quickly thru the chamber.

Goggling for NACA will give a whole series of documents about internal combustion engines, if you really want to get in on the details of what happens.

 

Thanks Grumpy...good info....I do understand that's how Spark Advance works....

now I just want to make sure that when I am datalogging and when I am not I have the same spark advance...

I am using the values I see in the scanner to adjust my timing accordingly...If there is 6 or 8 degrees more advance when I am scanning and I tune for no knock that way and maximum performance, when I am not scanning I still have room for more Spark Advance(if needed for more performance) but I will not be able to accurately use it because I would need to scan to determine whether I am getting any knock!!??!?

 

ttt

 

Interesting, a Moderator brings this back ttt. I already explained to Poncho@home (in this thread) how to eliminate the problem. Zero out the ALDL SA adder, location $23 in the bin. It is a calibration term.

RBob.

 

So to question your 10K ADDER..
You say Hex $23 for the location and the value or Real world factors should be what ?

I just read mine and it reads 23 for a value .. not 6degree or anything close // Decimal direct would be 30 deg..

Maybe I done something wrong here

 

It is hex address 23, and yes, the decimal value at that location is 23. To convert that to SA multiply the data value by 0.352: 23 * 0.352 = 8.1, or 8.1 degrees of SA added whenever the 10K resistor is across ALDL terminals A & B.

RBob.

 

Thanks .. Thats got it.. I figure, if im not assuming too much, the Real world value can be calculated automaticly by adding the conversion to the FACTOR table in hte ECU edit of Tuner Cat ?

This stiff is just getting kewl.. I have made my 12 chip.. and am adjusting spark tables as much as 2 deg at a time..Somethings in the tuning guides are very informative and other areas are not really covered...

Im new, but I added a Flag for the engine type, just to play around. Instead of knowing hte HEx value.. You just select if there is no V8 or its a V6 model.. and it converts for you..