2008 Z06: Head, Cam and Long Tubes: Bucking below 1900rpm

[MMGT1]

What I've done:

Car has a NW103 TB, Camshaft: 237/250 .646"/.632" 113LSA, Lingenfelter CNC Heads, MSD Atomic AirForce Intake, and a set of long tubes. 7.0L
*Previous LS7 with the MSD Intake responded perfectly with the plenum volume set to 1000cc, so same has been entered here.

FIC 60lb Injectors Ive checked the data sheet and it looks to me that the previous tuners, yes there have been a few before me on this one, have the scaling correct.

MAF is spot on, within 2% for the entire range of the car. Pulls great, no hick-ups at all, but bucks below 1900RPM.
I have tried locking timing below 2k RPM at 15-17*(Thinking Cam Surge) and only made the situation worse. Put timing back in, smoothed tables, still bucks.
Matched Idle Timing to High and Low Timing and still bucks.
Set RAF to around 13-14g/sec in the main, and then used modifier to add air, still does it.

Thought that tuning the VE Tables may help or rid the car of this issue. Have the fuel just roughed in for VE, only up to 2k RPM... the table is still ugly but the bucking hasn't really changed at all. What I am seeing is the Throttle Body seems to be jumping when this happens. If anybody is willing, have a look at the attached scan and tune. Let me know if something here sticks out to you. I've done many Gen4 modded engines, but this one just wont settle down so I'm here looking for a little help.

[Alvin]

What I've done:

Car has a NW103 TB, Camshaft: 237/250 .646"/.632" 113LSA, Lingenfelter CNC Heads, MSD Atomic AirForce Intake, and a set of long tubes. 7.0L
*Previous LS7 with the MSD Intake responded perfectly with the plenum volume set to 1000cc, so same has been entered here.

FIC 60lb Injectors Ive checked the data sheet and it looks to me that the previous tuners, yes there have been a few before me on this one, have the scaling correct.

MAF is spot on, within 2% for the entire range of the car. Pulls great, no hick-ups at all, but bucks below 1900RPM.
I have tried locking timing below 2k RPM at 15-17*(Thinking Cam Surge) and only made the situation worse. Put timing back in, smoothed tables, still bucks.
Matched Idle Timing to High and Low Timing and still bucks.
Set RAF to around 13-14g/sec in the main, and then used modifier to add air, still does it.

Thought that tuning the VE Tables may help or rid the car of this issue. Have the fuel just roughed in for VE, only up to 2k RPM... the table is still ugly but the bucking hasn't really changed at all. What I am seeing is the Throttle Body seems to be jumping when this happens. If anybody is willing, have a look at the attached scan and tune. Let me know if something here sticks out to you. I've done many Gen4 modded engines, but this one just wont settle down so I'm here looking for a little help.

Have you tried SD? A cam that big will have a hard time getting along smoothly with a MAF at low load/low RPM

[MMGT1]

Yes, the car is in SD mode now in the attached files in post #1. Trims are also off, using WB for adjustments.

[Alvin]

The VVE needs some work. But i doubt it's so far off it would cause this. It could only get better.

You might want to reach out to NW about the throttle body. I ran into a early "new" versions of one of his throttle bodies and the TPS had slop on the blade so the ETC position would kinda jump around at low load cruises. It made more of a surge rather than a buck.

[pannetron]

Enabling "Spark Smoothing" and reducing the allowed torque corrections helped me:

2022-09-16_09-14-42.jpg

[MMGT1]

Enabling "Spark Smoothing" and reducing the allowed torque corrections helped me:

2022-09-16_09-14-42.jpg

I actually disabled it myself going after the problem to try it out. I can try this though, I didn't try going after corrections.

[MMGT1]

The VVE needs some work. But i doubt it's so far off it would cause this. It could only get better.

You might want to reach out to NW about the throttle body. I ran into a early "new" versions of one of his throttle bodies and the TPS had slop on the blade so the ETC position would kinda jump around at low load cruises. It made more of a surge rather than a buck.

Thanks for that info; We can look into that issue with the TPS and if it applies at all to this one. Kinda sounds promising here. The VE is a lot better now than that file. Had another couple of rounds last night getting into it. It's still early into the VE stuff. Been really keeping it low to try and find the root of this bucking issue. But agree, the couple % it was out there I dont see causing this.
I did find out today it has some race plugs in it so I'm going to try a set of TR6s in there just to test this hunch out at .035".

[smokeshow]

Cam like that needs to be treated gently lol. Low RPM torque is erratic due to the poor motion of the mixture in the cylinder at low speed. The best tool you have to combat that is spark. You'll notice the bucking tends to happen at part load and almost always when spark is low or transitioning between tables. First step would be increasing main spark at low speed. Get the burn started sooner and avoid the partial misfires. Once you've done that I'd make coastdown idle spark look like the main spark table. The only thing that 25 degrees across the whole thing does to help you is make it easy to spot where its active and causing a problem lol. Every time spark bottoms out at 13?, it's because its in coastdown and the overspeed table is pulling out the other 12...spark is too low there. You also look to have base idle spark active when you're lightly on the pedal, locking you at the 20? idle spark value until enough of a pedal tip-in pushes it out of idle mode. That looks to be due to a combination of that ETC scalar and the throttle max idle effective area cal. You really have to give it some pedal to get it to leave idle mode and pick up some more spark. This car is just begging for more spark...

[hjtrbo]

Fuck. How's that for a response. Legend

[MMGT1]

Cam like that needs to be treated gently lol. Low RPM torque is erratic due to the poor motion of the mixture in the cylinder at low speed. The best tool you have to combat that is spark. You'll notice the bucking tends to happen at part load and almost always when spark is low or transitioning between tables. First step would be increasing main spark at low speed. Get the burn started sooner and avoid the partial misfires. Once you've done that I'd make coastdown idle spark look like the main spark table. The only thing that 25 degrees across the whole thing does to help you is make it easy to spot where its active and causing a problem lol. Every time spark bottoms out at 13?, it's because its in coastdown and the overspeed table is pulling out the other 12...spark is too low there. You also look to have base idle spark active when you're lightly on the pedal, locking you at the 20? idle spark value until enough of a pedal tip-in pushes it out of idle mode. That looks to be due to a combination of that ETC scalar and the throttle max idle effective area cal. You really have to give it some pedal to get it to leave idle mode and pick up some more spark. This car is just begging for more spark...

My next move was to go up with timing just as you've pointed out, but being 100% honest here, had no idea if it would help. Was going to be a total shot in the dark. The scaler you see in this is how I got it. I had returned the scaler to stock values, as per info I found on the NW103 being left stock for this body, and the car absolutely didn't like it(Again, the low timing makes sense as to the underlying problem here). I do think that with the increase of timing discussed I may be able to also set that dam scaler back to stock. I wasted an entire session with the car on that scaler and the values that were dumped into it. Your logic sure seems sound to me bud, and I thank you greatly for the info. Hopefully get into this today sometime if the car is available and Ill definitely post back on this one.

[turabo87]

My next move was to go up with timing just as you've pointed out, but being 100% honest here, had no idea if it would help. Was going to be a total shot in the dark. The scaler you see in this is how I got it. I had returned the scaler to stock values, as per info I found on the NW103 being left stock for this body, and the car absolutely didn't like it(Again, the low timing makes sense as to the underlying problem here). I do think that with the increase of timing discussed I may be able to also set that dam scaler back to stock. I wasted an entire session with the car on that scaler and the values that were dumped into it. Your logic sure seems sound to me bud, and I thank you greatly for the info. Hopefully get into this today sometime if the car is available and Ill definitely post back on this one.

I posted a Heads Cam FBO C6Z tune recently I did, feel free to use it for reference. I used stock scalar and works well with the NW102.

[07GTS]

just more info, with mine i found spark smoothing needed to be enabled and set to suit, if i disabled it then steady state driving was jerky, i lowered it as much as possible before it became an issue

[MMGT1]

just more info, with mine i found spark smoothing needed to be enabled and set to suit, if i disabled it then steady state driving was jerky, i lowered it as much as possible before it became an issue

If I get into this one today, I'll re-enable that because you just hit the nail on the head. Going on Smokeshow's input, I did increase the timing in the problem area and it seems to be having a positive effect.(Still there but absolutely moving in the right direction here) Just adding 1-2* at a time but have only gotten two scans so far since then. But...just like you have said, in steady state it is a little "jerky". Think you are on point with your info there. I'll adjust that now so the next one I send him will have this updated.

As far as the scaler goes, anything I've tried, even stock settings, makes this thing "wig-out". I don't have a clue where the previous tuners got that value from, I've tried to find any reference to that value and found nothing. I get this buck and jerking under control and I'll go after that scaler next and see if I cant get it to a more reasonable setting.

Thanks everybody for the help, very much appreciated!

[Alvin]

The later NW throttle bodies call for a stock ETC scaler.