VVE tuning LS7 with big cam

[Pierrel]

Hi,

Ive got a big cam LS7 engine (BTR stage 4) thats been MAF only tuned. Im having some driveability issues, and wanted to try my hand at tuning the VE (or VVE) tables to run together with the MAF.
Ive put the car in SD mode, and have had 3 runs of scanning and modifying the VVE tables

Thing is, Im just unsure. Ive been removing ALOT of fuel from the table (Pretty much -20+ percent every time). Ive been using LTFTs to get close enough to start using the STFTs.
Is it normal to take out this much fuel with a big cam engine?

Ive attached images of the stock table, and after 2 corrections. Ive also attached both scans, and a separate scan showing how erratic my AFR error graph is. Normal?

Input is much appreciated!

AFR screenshot.PNGVVE table stock.jpgVE tuning stock 1 LTFT.hplVVE table 1.2.jpgVE tuning 1.2 LTFT.hpl

[Ben Charles]

At idle speeds and low speeds that cam is less efficient by a large margin over factory camshaft (hence the trade off for much more topend power)
So volumetric efficiency will be much lower... so pulling out 30% makes sense in low RPM ranges..

[Pierrel]

At idle speeds and low speeds that cam is less efficient by a large margin over factory camshaft (hence the trade off for much more topend power)
So volumetric efficiency will be much lower... so pulling out 30% makes sense in low RPM ranges..

Thanks alot! Just wanted to confirm.

I wanted to double check my MAF tune, and tried to use my AEM wideband in open loop. I forgot to put all the OL adders to 1, and had the car run around 13,6-14.1 AFR in cruise. AFR error was between 2-7 percent lean. Its been corrected and smoothed out. Is it really necessary to force 14.7AFR Open loop, the error is still the same between commanded and actual, or is my thinking wrong? Is it better to use Wideband during idle, part throttle with this big a cam?
I noticed in Open Loop my O2 sensors acted weird, bank 1 is always at 900 mV, but bank 2 sometimes drop to 100, or acts erratic. Could it be a faulty o2 sensor?
Maf 1.hpl

Then i switched to logging STFT to confirm my trims, and Bank 1 is still behaving erratic, with trims B1 -8% and B2 +7% at the same time (cruise 1400 rpm, 5th gear)
Maf OK Wideband, logging STFT higher timing.hpl

Feels like i cannot trust using the O2 sensors until i figure out the erratic movements. Maybe thats why my VVE tables never got any good.
Is there any way to "slow down" the STFTs?

Thanks!

[Ben Charles]

Sounds like you have bank to bank issues.. I would check o2 sensors, exhaust leaks, intake leaks, pull plugs and see if they all look the same..

I wouldn’t target 14.7 either

[Pierrel]

Sounds like you have bank to bank issues.. I would check o2 sensors, exhaust leaks, intake leaks, pull plugs and see if they all look the same..

I wouldn’t target 14.7 either

Will do, somethings not right. Thanks!!
Figured id ask you what you'd set target at, even though i think i know why you left that out in your last post? You mean stoich target?

[acammer]

Hi,

Ive got a big cam LS7 engine (BTR stage 4) thats been MAF only tuned. Im having some driveability issues, and wanted to try my hand at tuning the VE (or VVE) tables to run together with the MAF.
Ive put the car in SD mode, and have had 3 runs of scanning and modifying the VVE tables

Thing is, Im just unsure. Ive been removing ALOT of fuel from the table (Pretty much -20+ percent every time). Ive been using LTFTs to get close enough to start using the STFTs.
Is it normal to take out this much fuel with a big cam engine?

Ive attached images of the stock table, and after 2 corrections. Ive also attached both scans, and a separate scan showing how erratic my AFR error graph is. Normal?

Input is much appreciated!

I found that when dialing in the VVE on my LS3 with a good sized cam (233/253 on a 112) that at idle (~850rpm and 68kpa vac) I have to have the VVE cut in HALF. At light cruise (~1800rpm, 55kpa) it's still 25% lower. The VVE seems to meet around 3200rpm under moderate (72.5kpa), and then beyond that for load or RPM the big cam leaves the stocker in the dust.

I used LTFT+STFT math, and that seems to work pretty good. Just make sure you're getting quality data - ie. don't reflash a hot car, restart, and immediately start trying to log your idle ranges. I usually hit the road with a warmed up car, drive a mile or two, then pull over, clear LTFTs in the scanner, and then start recording. Rinse and repeat till dialed.

For what it's worth I did the same as you to improve driveability, and getting the VVE dialed in and running blended helped a bunch with transient throttle response, and it smoothed things out some. I also found that taking spark away from the trouble areas helps too - under low rpm real light (nearly coasting - think 1400-1800rpm and under 0.24g/s cyl airmass) load having sub 20* of timing settles down some of those bucks and kicks - the engine doesn't have the torque with the low timing to make them so pronounced. You have to take care to blend that back in nicely so you don't get any wild changes, and it won't totally remove it, but it helps.

Also, getting your injection timing dialed in can be valuable. For me, my EVC is something like 25* later than stock, so I have EOIT retarded 30* from stock from 0 to 1536rpm with a slow fade back to stock by 3584 rpm. Helped with the fuel smell and fuel consumption at idle.

[Pierrel]

I found that when dialing in the VVE on my LS3 with a good sized cam (233/253 on a 112) that at idle (~850rpm and 68kpa vac) I have to have the VVE cut in HALF. At light cruise (~1800rpm, 55kpa) it's still 25% lower. The VVE seems to meet around 3200rpm under moderate (72.5kpa), and then beyond that for load or RPM the big cam leaves the stocker in the dust.

I used LTFT+STFT math, and that seems to work pretty good. Just make sure you're getting quality data - ie. don't reflash a hot car, restart, and immediately start trying to log your idle ranges. I usually hit the road with a warmed up car, drive a mile or two, then pull over, clear LTFTs in the scanner, and then start recording. Rinse and repeat till dialed.

For what it's worth I did the same as you to improve driveability, and getting the VVE dialed in and running blended helped a bunch with transient throttle response, and it smoothed things out some. I also found that taking spark away from the trouble areas helps too - under low rpm real light (nearly coasting - think 1400-1800rpm and under 0.24g/s cyl airmass) load having sub 20* of timing settles down some of those bucks and kicks - the engine doesn't have the torque with the low timing to make them so pronounced. You have to take care to blend that back in nicely so you don't get any wild changes, and it won't totally remove it, but it helps.

Also, getting your injection timing dialed in can be valuable. For me, my EVC is something like 25* later than stock, so I have EOIT retarded 30* from stock from 0 to 1536rpm with a slow fade back to stock by 3584 rpm. Helped with the fuel smell and fuel consumption at idle.

Thanks, ill give that a try.
Ive been running pretty low timings, and the bucking is there about just as much with 14 degrees as with 25 degrees. Im cruising at about 0.36-0.40g/s cyl airmass, will try to remove some timing below and blend it in.

Did you adjust the EOIT with ECT or RPM? at RPM around 1000 rpm i have stock values of 4-10. Im running stock Boundary 520 and have decrease the ETC table at operating temp from 110 to 85. Am i thinking backwards, and should add to that table?

Id very much appreciate what TARGET AFR to aim for with this 247/258 112 LSA cam, with 28,5 deg overlap. Richer or leaner at cruise?

Thanks!

[Ben Charles]

Did an 09 z06 yesterday with a 243-254 cam 112lsa and in 6th gear at 1000rpms smooth as butter..

Get timing and fuel right and you’ll be amazed