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LS3 Grandsport with Headers - tune & timing questions
Hey guys,
I added headers to my GS about 6 months ago and its been running fine, but I have some question about my tune and tuning in general. I've been curious if its worth getting HP Tunes to tweak a few parameters over time, but before making any decisions I wanted to post my questions here to see if I'm walking down a path that I'll eventually regret. So here goes....
Car Setup:
- 2013 C6 Grandsport Manual Coupe
- AFE 1-7/8 Tri-Y Headers with cats
- Attack Blue Filter
- Tuned on Dec 2017 @ 95K miles
- Currently July 2018 @ 115K miles
HPDE Session @ VIR Full during April 2018, Ambient high 50F
Big Question:
I don’t understand why my tuner set the minimal timing chart to 12* across the board for all RPMs and under all loads (g/cly). Can someone explain any potential pros vs cons to using this strategy? Right now I’m currently considering having the table reflashed to the stock values. Is this a bad idea with headers? Does anyone know why GM went with varying negative values in the stock table?
Smaller Questions, Thoughts:
At this summer's VIR event I noticed there is a higher fall-off in power and a greater increase in HPDE running temps as the ambient temp approached 90F. Historically when I ran in low-mid 90's ambient I would only see +235F coolant near the end of my session, but at this last event I saw almost 240F coolant after 3 laps.
I raised my redline to 6800, and asked my tuner to richen it up at bit over 6K due to the high ambient temps I see at HPDE’s in the summer. I welcome any thoughts one this one.
Looking over all the changes listed in the below post, are there any modifications that stand out or is anything missing that "could've/should've" been touched?
I’ve included what I feel is relevant timing charts, I have everything screen shot so just ask if there anything missing.
Tuning can be done many different ways, with that being said I would take your timing table from High Oct and copy it over to the Low and subtract 4 or 5 degrees, your Power enrichment table is commanding 12.0 up to 6k and then it goes to 11.5 (gas scale), for a N/A car I would consider that rich, I normally shoot for 12.5, keep in mind the MAF/VE table has to be dialed in 100% for PE to be accurate. So if he didnt tune those tables and just used the PE table to dial in A/F the actual A/F may be different. I would change the minimum final spark table back to stock but thats because on the boosted cars I tune i use spark as a rev limiter.
Tuning can be done many different ways, with that being said I would take your timing table from High Oct and copy it over to the Low and subtract 4 or 5 degrees, your Power enrichment table is commanding 12.0 up to 6k and then it goes to 11.5 (gas scale), for a N/A car I would consider that rich, I normally shoot for 12.5, keep in mind the MAF/VE table has to be dialed in 100% for PE to be accurate. So if he didnt tune those tables and just used the PE table to dial in A/F the actual A/F may be different. I would change the minimum final spark table back to stock but thats because on the boosted cars I tune i use spark as a rev limiter.
Thanks for the response. Can you elaborate on what it means to have the MAF/VE tables dialed in 100% for PE (assume Power enrichment) to be accurate. And do you think that process can be accomplished on the street by myself over time with a wideband installed and thousands of daily driven & HPDE miles? I know when the car was tuned he used a wideband sensor in one of the inner NPP bypass tail pipes to measure A/F ratio of the WOT pulls.
Yes it can be done, if you are not logging your wideband it would be just getting your STFT as close to 0 as possible (with LTFT disabled) and a way to "back door" the PE is set it to the A/F you want in the PE table (what ever stoich is... so 14.0 in this case 14.0/1.22 = 11.4.... 14.0/1.1 =12.7 and change the MAF or VE table (how ever the tune is setup) to achieve the corresponding PE number
My first thought when I looked at your dyno sheet, I thought that car must be knocking a lot and that's why the curve is so "saw bladeish". I though it must have to much timing. I see your first recorded pull is run 3 and your last is run 5. To me that says he did two or three tuning pulls and said here you go. Your RWHP should be about 10 RWHP higher with your set up, but more of a concern is your peak HP is where the saw blade peak is, so I don't think your making as much as the sheet says if you smooth out the curve.
When I tabbed down to your timing table picture and I saw 30 degrees and 25 degrees of timing during WOT, Id be VERY surprised if it wasn't knocking during WOT. I call that block tuning. the tuner just puts a number in a block across the board. There's a reason GM staggers timing. Some areas of efficiency may be able to handle 30 degrees of timing at certain RPM, but some areas of the power band might only handle 23 degrees. This is also dependent on how Rich he makes the car. The richer the rich the more timing it will take, but will also take longer to get through the RPM band because its richer. Leaning it out some is fine, but it wont tolerate as much timing. So what im saying is the tuner based on experience should know where in the RPM he can add timing, and know where maximum efficiency is and drop some timing so the table will carry additional timing after the timing dip.
So personally if I were you and I see you have HP Tuners, id scan how much timing is being retarded during some spirited driving to make changes to the octane tables. For me if I see 4 degrees of timing for instance at 4000 RPMs, I try and take out one degrees on the cell its knocking at, and one degrees on the cell before the knock comes on. You adjust that a couple times and if retarding in that range doesn't get lower, start looking at false knock.
I recently read on this forum someone on here saying there is no such thing as false knock. That's BS and someone that shouldn't plug into a car. You can get false knock reading if your exhaust is rattling. Your knock sensors are microphones. You fix the exhaust from hitting the heat shield in the tunnel and the knock goes away. If your catch can is loose and rattling, To me that's false knock.
Sorry I had to much coffee this morning.
Last edited by phils C5 vette; 07-11-2018 at 08:53 PM.
A lot of this seems to have been touched on, but some of my opinions:
-As I recall, the minimum final spark timing helps prevent torque management from kicking in so aggressively. So any event where the car deems a need to pull timing can go no lower than 12 degrees, vs the pretty dramatic negatives that are sometimes allowed. I'm sure this change also makes your traction control a lot softer-acting.
-Your PE table definitely is commanding richer than ideal. If you're running it WOT for long-ish periods on a road course maybe he was accounting for that. He also made changes to allow PE to come in sooner and more quickly that I generally agree with.
-The timing changes definitely look heavy-handed. I would expect to see timing being pulled if Knock Retard was logged.
Yeah, min timing can be used to prevent tq mgt from pulling too much
Agree, PE table looks a little rich. But that doesn't mean it actually is. Need a wideband to confirm. Also, you can typically lean out some after peak torque. May not be the best idea for long pulls/road course type driving though, may be better to leave it a little richer
The timing table has some pretty big jumps in it and looks high to me. At the very least it needs to be smoothed out.. check it out in the 3D graph view and you'll see what I mean. The crazy EKG looking stuff in the dyno pull could very well be from knock retard.
My first thought when I looked at your dyno sheet, I thought that car must be knocking a lot and that's why the curve is so "saw bladeish". I though it must have to much timing. I see your first recorded pull is run 3 and your last is run 5. To me that says he did two or three tuning pulls and said here you go. Your RWHP should be about 10 RWHP higher with your set up, but more of a concern is your peak HP is where the saw blade peak is, so I don't think your making as much as the sheet says if you smooth out the curve.
When I tabbed down to your timing table picture and I saw 30 degrees and 25 degrees of timing during WOT, Id be VERY surprised if it wasn't knocking during WOT. I call that block tuning. the tuner just puts a number in a block across the board. There's a reason GM staggers timing. Some areas of efficiency may be able to handle 30 degrees of timing at certain RPM, but some areas of the power band might only handle 23 degrees. This is also dependent on how Rich he makes the car. The richer the rich the more timing it will take, but will also take longer to get through the RPM band because its richer. Leaning it out some is fine, but it wont tolerate as much timing. So what im saying is the tuner based on experience should know where in the RPM he can add timing, and know where maximum efficiency is and drop some timing so the table will carry additional timing after the timing dip.
So personally if I were you and I see you have HP Tuners, id scan how much timing is being retarded during some spirited driving to make changes to the octane tables. For me if I see 4 degrees of timing for instance at 4000 RPMs, I try and take out one degrees on the cell its knocking at, and one degrees on the cell before the knock comes on. You adjust that a couple times and if retarding in that range doesn't get lower, start looking at false knock.
I recently read on this forum someone on here saying there is no such thing as false knock. That's BS and someone that shouldn't plug into a car. You can get false knock reading if your exhaust is rattling. Your knock sensors are microphones. You fix the exhaust from hitting the heat shield in the tunnel and the knock goes away. If your catch can is loose and rattling, To me that's false knock.
Sorry I had to much coffee this morning.
Thanks for the reply. I'm really interested in why it takes longer to get through the RPM band if the engine is tuned rich vs lean. New question how trust worthy is the Knock Retard PID coming over the OBDii plug? I ask this because I log timing,KR,fuel trims, etc during all my HPDE sessions and the car wasn't showing excessive knock or pulling alot of timing during the event. Also I wonder if the extra timing was okay due to the richer fuel mixture.
A lot of this seems to have been touched on, but some of my opinions:
-As I recall, the minimum final spark timing helps prevent torque management from kicking in so aggressively. So any event where the car deems a need to pull timing can go no lower than 12 degrees, vs the pretty dramatic negatives that are sometimes allowed. I'm sure this change also makes your traction control a lot softer-acting.
-Your PE table definitely is commanding richer than ideal. If you're running it WOT for long-ish periods on a road course maybe he was accounting for that. He also made changes to allow PE to come in sooner and more quickly that I generally agree with.
-The timing changes definitely look heavy-handed. I would expect to see timing being pulled if Knock Retard was logged.
Torque management was disabled therefore I assume he might have done this to soften traction control events. What AFR would you assume ideal given the car is driven mostly on the street with about 3-5 HPDE's a year? Specifically, I'm trying to determine how conservative I need to be, and what's the smart play? Right now I'm leaning towards less timing with slightly leaner mix and smoother transitions.
Yeah, min timing can be used to prevent tq mgt from pulling too much
Agree, PE table looks a little rich. But that doesn't mean it actually is. Need a wideband to confirm. Also, you can typically lean out some after peak torque. May not be the best idea for long pulls/road course type driving though, may be better to leave it a little richer
The timing table has some pretty big jumps in it and looks high to me. At the very least it needs to be smoothed out.. check it out in the 3D graph view and you'll see what I mean. The crazy EKG looking stuff in the dyno pull could very well be from knock retard.
I bought a wideband and installed it today and so far here are my take aways:
- idle AFR is bouncing from low 14.xx to high 15.xx before it roughly somewhat stabilizing @ 14.5ish
- a few half to full throttle stabs showed an AFR of 12.2
- with cruise set on a relatively flat road the AFR moved around alot
Torque management was disabled therefore I assume he might have done this to soften traction control events. What AFR would you assume ideal given the car is driven mostly on the street with about 3-5 HPDE's a year? Specifically, I'm trying to determine how conservative I need to be, and what's the smart play? Right now I'm leaning towards less timing with slightly leaner mix and smoother transitions.
Originally Posted by truth.b
I bought a wideband and installed it today and so far here are my take aways:
- idle AFR is bouncing from low 14.xx to high 15.xx before it roughly somewhat stabilizing @ 14.5ish
- a few half to full throttle stabs showed an AFR of 12.2
- with cruise set on a relatively flat road the AFR moved around alot
Even with torque management disabled, there are still times the computer will pull timing in a "torque management" type way, from my understanding. It's a little weird. As far as AFR I'd probably target more like 12.8. You probably will want to back a couple of degrees of timing out of it at WOT. It's normal for a car in closed loop operation to fluctuate afr. Nominal at idle and cruising would be 14.7, but from the factory that will swing from low 14s up in to the 15s. It's pretty normal because of how the computer interprets the signal from the narrowband sensor.
Regarding the tuning, for a relatively stock car (as yours is) getting the AFR dialed in with a wideband should be pretty quick. MAF calibration will be 95% of the job. VE tables can be changed if you want, but in my experience with a stock cam they won't need to be changed massively.
Last edited by nickalltogether; 07-12-2018 at 08:02 AM.
07-04-2018, 11:41 PM
LS3 Grandsport with Headers - tune & timing questions
