Headers vs. timing advance

[Redline Motorsports]

We install at least three sets of headers a week on LS1's. It seem to me that everyone of them actually wants timing taken away in the mid range, on WOT pull, from the stock timing table. Has anyone else seen these kinds of results?

[ringram]

Has the VE/power increased at these points?

If so there is your answer. Increased cylinder fill = more torque, more efficiency & faster burn due to denser charge.

[dc_justin]

Has the VE/power increased at these points?

If so there is your answer. Increased cylinder fill = more torque, more efficiency & faster burn due to denser charge.

Does it really work that way though? If the spark table was defined as RPM x Map, then I would totally agree with you, but since it is RPM x cylair, it stands to reason that the headers would just push you into a set of cells to the right of the previous set. Eg, 0.76x4400rpms instead of 0.72x4400...

Since the physical shape of the combustion chambers and thus, their burn characteristics haven't changed, only the mass of air that enters the cylinder at a given throttle point, it doesn't make sense that you'd need to modify the spark advance in previously adjusted cells. The only way I could see this happening would be if the scavenging ability of the headers manage to cause the DCR to change slightly, in which case I could see the spark change.

Am I off base here?

[joecar]

We install at least three sets of headers a week on LS1's. It seem to me that everyone of them actually wants timing taken away in the mid range, on WOT pull, from the stock timing table. Has anyone else seen these kinds of results?

TOL (thinking out loud)...
Would have thought stock timing would have been fine with headers...
What was the AFR there...?
Was it in PE mode...?
Would it like more PE fuel there...?

[Redline Motorsports]

TOL (thinking out loud)...
Would have thought stock timing would have been fine with headers...
What was the AFR there...?
Was it in PE mode...?
Would it like more PE fuel there...?

Joe,

This post has come after countless installs of headers and is not based on one particular car. I just keep seeing a consistent trend. From all the baselining we do prior to any install, most of cars have AFR;s in the 11.8-12.1 range. The headers alone without any adjustments will move the AFR's in the 12.1-12.4 range. I always play with timing first as long as its withing .5 points of where want to be. Unless its a boosted motor that could use up fuel fast. I guess whatever works...works. We are a dealer for Kooks headers and can't even begin to tell you the sucess we have with them. On an average we see 30 RWHP without a tune and another 10-12 with the tune. The cars are definately making power and it starts the minute you drop the hammer. I would agree to some extent that the VE has to be increasing if more power is being made at a given RPM....

Good discussion!

Howard

[joecar]

Howard,

When you reduce timing, does the TQ stay the same...?

When I installed my LT's on my otherwise stock TA, my dyncylair stayed mostly the same, maybe up by 0.1 g/cyl in the upper RPM/MAP regions, my VE table increased ever so slightly, but my SOTP can tell there's a good sized increase TQ thru-out the range; also, prior to the LT's, I would get low RPM chugging (say 1700 RPM) in 3rd (A4) and sometimes pinging (and other strange ignition noises), now I don't get any of that, it just pulls the car along with no drama;

I might try to reduce mid rpm timing to see what it does.
Yes, this is an interesting topic.

Joe

[minytrker]

I have never tuned a car with kooks but have done many other brands and have not seen this yet. I run LG's on my cars. Is it at the same rpm range on all the cars? Is it just from header installs or other bolt on plus headers?

[SSpdDmon]

I have Pacesetters and run up to 1.75 degrees more timing over stock. What I did in setting up the timing table was to remove the akward valley that appears around 4,000-5,000 rpm. If timing is 18 degrees at 4400 rpm & .80 g/cyl, why would it be 19.5 degrees at .84 g/cyl??? Basically, I took the values in the .80 column and carried them over to the columns to the right if the .80 column was lower. I don't know if I'll hit the cells in the .84 and greater columns anytime soon. But, since the PCM interpolates the nearby cells, I figured this was for the better. Once this was done, I then added timing as follows...

In the .72+ g/cyl columns, I added 1 degree from 400~4800 RPMs, 1.25 degrees to 5200, 1.5 degrees to 5600 and 1.75 degrees from 6000 up. I don't notice a whole lot of KR (other than the occasional degree or two) as long as the fueling is in line. I'm almost convinced it's false since it's not audible and the car is running strong almost all of the time (weather permitting).

[joecar]

SSpd,

Yes I also removed that "valley", why did GM put it there...?

Also, what is the valley under 1400 RPM 0.08 g all about...?


Stock 2001 F-body:



After I started messing with it:

[dc_justin]

Loosk like you've still got a lot left on the table there Joe.

Here's mine based on the Optimal Spark table. It's very similar to the 98 spark table, which many people have recommended using in 00+ pcms.