BIG CAM TUNING ON LT1. Let's talk idle tuning

So like the title says. I have a big cam in an LT1 Camaro. I set the minimum spark to 5 degrees and it pretty much just stays there (did this to prevent negative timing) The car chops okay now but should chop harder for a cam of this size. Looking to get the spark to swing a bit. I noticed on a few other 1le Camaros they don't make much spark at idle for whatever reason even before the cam. So I'm a little worried it might not be possible for some reason.
I know you really need the torque numbers at idle to be perfect. What are your target numbers for a big cam?

What is the cam? I have a fairly large cam in my LT1 231/246, .635/.635, 114 LSA 111 ICl. Timing swings from 4-16 degrees.

Idle tab > adaptive and predicted; add 10% - 20% to get more chop. There is a point where drivability suffers. I found adding 20% made my car chop pretty good.

240/252 112lsa I need more work on the VTT tables. They can't be to far off because the car is holding the idle I'm requesting. It's just not getting any timing. It idle what are your torque read outs looking like?

Your torque on the left hand side of the log is ideal, but the right side after it starts fluctuating is quite a bit different. Your idle is stabil because of how you have your airmass side dipped. This focus's the torque to a specific area. I'm honestly surprised you don't have hot start slow rev to idle problems with the way you have it shaped. If you have a stock log for your car that's best to go by for how to shift the tm to best suite the new cam. Usually works, but not always. I've got some 2ss's where they're idling with -5 or -6 lbft if that'll help you. Personally I like to target something around 0 to 10 with hot idle and no load and something around 20 with load in idle.

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Originally Posted by JASON11WS6

240/252 112lsa I need more work on the VTT tables. They can't be to far off because the car is holding the idle I'm requesting. It's just not getting any timing. It idle what are your torque read outs looking like?

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Iron out your VVE and timing should come back in line.

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Originally Posted by STAGEUP

Iron out your VVE and timing should come back in line.

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I didn't even look at that. Yes, this will change everything so best to do that first then work on the torque model.

Tuned the ve in and I'm still dealing with negative timing. If I force the timing to a positive number it swings a bit.

Post the current tune and a log

Attachment 129715Attachment 129716

Even with the negative timing it still sounds decent. Not sure if I can deal with the glowing red headers though.

Where do you guys usually want your torque numbers at during idle? 0-20 ft/lbs I was always told.

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Originally Posted by JASON11WS6

Tuned the ve in and I'm still dealing with negative timing. If I force the timing to a positive number it swings a bit.

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The last cammed LT1 I did I purposely didn't touch any torque stuff till the end. I still think Qsubc x fuel flow is the driving thing on torque calculations


Anyway.. With no virtual torque edits at all but with a MAF failed and VVE tuned, and re enabled MAF the idle timing was a normal 12-18 degrees at an idle.


I disagree with the consensus on this board with the idea that VVE can be backed out from MAF. I've written my own equation, I've used the ones posted here. The signal is just too noisy to be accurate with it in most cases. That is just my experience.. use it how you want. I do this every day M-F 9-5 and I can say that yeah I've had cars I've gotten OK results with but I get great results each time failing MAF.

While I do agree with a large majority of what Alvin said, that doesn't necessarily apply to big cams. Even smallish cams after they get to a certain point require remapping the torque model to a degree and yes as I've personally always stated EVERYTHING that effects fueling will affect the torque calcs. I personally have had my customers fail the MAF to double check maths. At least the maths I use are nearly always within a couple of percent, but I do try to make them log with slow pedal movements - seems to make a big difference on the calcs.

I use two different ones on the calcs. The first uses airmass and should get you within 10% or less the first pass. I then switch over to the VE error calc which solely uses MAF and fueling errors to get it within a couple of percent. It does take a few passes and if anything is off causing fuel to shift then so will these. Just using the VE error calc, it's saying your VE is off about 1%, but again this will change slightly with the timing causing fuel to change.

(([50041.223]*(273.15+[50011.241]) * (1000/[50030.91]))
100 * ((([50040.71] * ([50114.156] + [50116.156])) - [2311.71]) / [50040.71]

Get another idle log only with this one. Don't drive with it. Just checking the changes and it still needs a lot of work. As long as you have positive timing now get a 10 min idle log so it'll learn the new settings.

Timing was still negative. I let it run for a minute or two but the headers are gonna start glowing red and burning up wires soon so I shut it down.

Idle torque wasn't that far off. Good chance you need to reset everything. Unhook the battery and do a global power down. Load this one after hooking the battery back up then let me know. Also did you tune the VVE with maf failed or with a math? It shouldn't be that far off, but nonetheless.

I did a failed maf for the vve tuning. I held my food on the pedal during this scan just to keep the timing positive for a little while. Otherwise it stayed negative.

Had to look at some other stock logs. Doesn't look like I shifted the airmass side enough. This one should be closer to stock.

AND you did do a global power down - unhooked and touched pos cable to neg post? Then did a throttle reset with the scanner and other usual resets?

Again this torque model is only for idle testing - don't drive on it.

I know I'm late to the party but ill give some feedback even though I see Ghuggins is helping you get on track.

I have had to make crazy looking Virtual Torque tables just to get a car to pass the throttle learn test. Then I was able to resort back to a more reasonable VT table. It was very strange but that was the only way I could get one car to idle in the positive. In hindsight I think I could have just skipped to my method below as I haven't had this issue again since.

But in general, if you're having low idle timing issues, you want the car to close the throttle blade more. To get the car to close the throttle blade more you have to tell it that its making MORE torque at idle. But WAIT, weren't we taught we need to reduce the VT to fix this? Yup and that works in some cases lol. This is why its confusing.

What I have done is lower the VT a bit, lower the VVE a bit(your VVE needs to be reset and start over), but increase the MAF in the idle area until the timing starts to come up. It's basically like you have to rescale the amount of torque(airflow) that counts towards combustion without having the controls to do so. So by telling it its making less torque via VT & VVE, but then telling the MAF its seeing more air(more torque) it sort of rescales the range in the throttle for idle. Also, you can't have any sort of crazy Throttle Area values. Maybe increase this by 10% at most. I have stage 2 heads cam cars running around with the stock throttle area scalar.

As for chop, this is two part. First you need it to idle with the correct timing and airflow. Second you set the chop in the adaptive idle area in the immediate(spark) table.


How big a cam is this?

It shows to be idling in the 80kpa range, but throttle and timing will change all of that and the resulting torque model.

I've never tried raising the MAF to force it to learn. Is there a percentage you overshoot it Jason? I have used a "general" torque model that I throw into them making the idle torque REALLY negative that seems to force them to shift. I like the MAF idea better......

I should have his torque model somewhat close in the idle region for a big cam - at least to match where his "stock" settings were - it still needs blending back to stockish for driving and curving for cranking, but other than that it should be somewhat close for idle. His map changes do favor his VVE, so it's possible his VVE is close. I've never seen one like that even with big cams, but...

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Originally Posted by GHuggins

It shows to be idling in the 80kpa range, but throttle and timing will change all of that and the resulting torque model.

I've never tried raising the MAF to force it to learn. Is there a percentage you overshoot it Jason? I have used a "general" torque model that I throw into them making the idle torque REALLY negative that seems to force them to shift. I like the MAF idea better......

I should have his torque model somewhat close in the idle region for a big cam - at least to match where his "stock" settings were - it still needs blending back to stockish for driving and curving for cranking, but other than that it should be somewhat close for idle. His map changes do favor his VVE, so it's possible his VVE is close. I've never seen one like that even with big cams, but...

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I usually aim for 8-12% negative fuel trims at idle. Then I pull the VT down by a fixed number on the first three columns, like say 20-70 by adding a negative value and then interpolating to the right. I apply the same to the MAF and MAP VT and I look and see where I am at. Sometimes this works great but sometimes you have to jump into the VVE table. What's strange is when you lower the Virtual Torque values the MAF values and MAP values hold a different weight when changing. I mean I guess it makes sense as its part of a calculation. And if you lower the Virtua Torque, that tells the equation that each gram of air makes less power. But then you add to your MAF and VVE and that tells the ECU that more air is coming in. I've had to mess with this ratio to get idle to play nice on some cams.

If you want the throttle to close more at idle to gain some timing back, you tell the ECU that you're making less torque at idle in the VT tables. But then you tell it your ingesting more air via the MAF table. Then the throttle starts to behave better and close and put some timing back in. I've also reduced Virtual Torque in the MAP tables and increased VVE to get the initial off idle throttle to not stumble. I'm probably doing a poor job of explaining this. I think about it like this which is actually old school thinking. The Virtual Torque is essentially saying how much of the incoming air is being used for combustion which then equals X power. The MAF and MAP are saying what the measured airmass coming in is. In the old days tuning VE was basically saying X amount means X percent of the incoming air measured is used for effective combustion resulting in created power. So compared to Gen 3 days, lowering VT and increasing the MAF/MAP would be the same as going into the VE table of a Gen 3 and lowering it to tell it that it is less efficient, yet the ECU was seeing more air through the MAF sensor.

lol....I hope I made sense of what I'm trying to say. I don't have it all figured out here, just sharing my experiences and thought process.

OK, so basically - at least as far as the making the ecm recalibrate itself - add 10ish percent to the MAF curve and force it to relearn things? Is there a given time period you let it idle like this to force the throttle recalibration process?

I have also found that by lowering DD idle cell (only to a point) and raising reserve will help bring timing up, but you have to find the balance to where everything is happy. On the ones where it's adjustable - if the DD idle cell torque is too high, such as the stock value on trucks - it can force negative timing to try and get torque up - if that makes sense? Usually cars have this set about right for cams, so not a big necessity to adjust.

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Originally Posted by GHuggins

OK, so basically - at least as far as the making the ecm recalibrate itself - add 10ish percent to the MAF curve and force it to relearn things? Is there a given time period you let it idle like this to force the throttle recalibration process?

I have also found that by lowering DD idle cell (only to a point) and raising reserve will help bring timing up, but you have to find the balance to where everything is happy. On the ones where it's adjustable - if the DD idle cell torque is too high, such as the stock value on trucks - it can force negative timing to try and get torque up - if that makes sense? Usually cars have this set about right for cams, so not a big necessity to adjust.

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I had to drop the Virtual Torque below where I would normally have set it, then ramped up the MAF. Then I did a cold start idle for 3 minutes, drove the car and it seemed to be better. Then let the car sit, did another mostly cold start and short drive. By the third cold start the car passed the throttle learn as the code(which doesn't set a CEL) was no longer listed when I pulled the codes. The car idled with positive timing. I flashed the Virtual Torque back but only pulled the MAF down just a little bit and the car has been fine since. This particular car has the LTFT enabled and they range from -8%-13% or so depending on weather. It isn't where I would normally leave the MAF, but its working for this car.

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Originally Posted by TriPinTaZ

I had to drop the Virtual Torque below where I would normally have set it, then ramped up the MAF. Then I did a cold start idle for 3 minutes, drove the car and it seemed to be better. Then let the car sit, did another mostly cold start and short drive. By the third cold start the car passed the throttle learn as the code(which doesn't set a CEL) was no longer listed when I pulled the codes. The car idled with positive timing. I flashed the Virtual Torque back but only pulled the MAF down just a little bit and the car has been fine since. This particular car has the LTFT enabled and they range from -8%-13% or so depending on weather. It isn't where I would normally leave the MAF, but its working for this car.

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So the same thing I do minus the MAF adjustment.

Other things for what they're worth - I've found the airmass and map side of the torque models need to match as closely as possible - at least for a very good controlled idle and drivability. I find shifting the models off of current airmass and map readings works really good to keep the model around stock then tweaking it from there for startup and control. If you're dealing with an auto and idling at negative torque you can wind up with clutch slippage going off idle, especially for reverse so it's key to adjust idle torque to where it's slightly above or around 0 if that low of a torque is necessary. Density table dial in is a must to keep torque and fueling balanced or rather the same at all times. I've had some interesting looking density tables, but they fixed a lot of problems - even with stock injectors being involved. Still don't have it to 100%, but I have the best resulting method pretty much figured out as I've got logs where the averaged fuel correction for PE or regular fuel trims don't change more than 1% from 0 error no matter the outside or engine temp - pretty happy with that...

So use the really negative torque model and a skewed maf setting to get timing back then readjust from there.

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Originally Posted by GHuggins

So the same thing I do minus the MAF adjustment.

Other things for what they're worth - I've found the airmass and map side of the torque models need to match as closely as possible - at least for a very good controlled idle and drivability. I find shifting the models off of current airmass and map readings works really good to keep the model around stock then tweaking it from there for startup and control. If you're dealing with an auto and idling at negative torque you can wind up with clutch slippage going off idle, especially for reverse so it's key to adjust idle torque to where it's slightly above or around 0 if that low of a torque is necessary. Density table dial in is a must to keep torque and fueling balanced or rather the same at all times. I've had some interesting looking density tables, but they fixed a lot of problems - even with stock injectors being involved. Still don't have it to 100%, but I have the best resulting method pretty much figured out as I've got logs where the averaged fuel correction for PE or regular fuel trims don't change more than 1% from 0 error no matter the outside or engine temp - pretty happy with that...

So use the really negative torque model and a skewed maf setting to get timing back then readjust from there.

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Yup, I always apply my Virtual Torque adjustments to the MAP tables as well. When forcing the idle learn, I just do a standard number like minus 100 in the first 2-3 columns and then interpolate to the right 1-2 columns. This usually shifts things enough for the learn to complete.

Force the learn/reset then tune. I like it. Will try on the next one ;)

Problem is - this will work for the first, but then tweaks always seem to require more driving to know for sure it will stay there. Be nice if there was a setting we could change for this?

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Originally Posted by GHuggins

Force the learn/reset then tune. I like it. Will try on the next one ;)

Problem is - this will work for the first, but then tweaks always seem to require more driving to know for sure it will stay there. Be nice if there was a setting we could change for this?

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I agree, there are definitely tables we don't have access to that could help too. And if the car ever loses power, IE battery disconnect, you have to flash the throttle learn file again to make it learn and then flash it back to your normal file.


I know we can search and find tables in HPTuners with some legwork, but I'm not motivated to find it. Well more like I don't have the time to.

Some good reading here. I'm gonna need to read it a couple of times to let it all soak in. This last tune seemed to jump around a bit more. Do you think from here we raise the maf around 10% and see if that brings the torque numbers back up?

Also, to be clear on what I'm considering a big cam. The cam specs are 240/252 on a 112lsa It chops even through the negative timing, so all we need is positive timing and it'll sound just fine.

I say lets try it. This one has a torque model that should idle somewhere around -40ish. Your maf was already adding 5 in that last log, so I added 15% to it. Since you have a manual, if you like it - you can continue to run this torque model or put the previous torque models idle regions back in - either/or...