[David Gordon]

I read where adding the bigger GM throttlebody does not need tuning. Can someone confirm before I put it on my new ZL1?

[arpad_m]

Technically it may not require tuning, but not adjusting the tune to at the very least be aware of the throttle body surface difference will affect drivability—not a whole lot, though, and it may actually be [the pedal twitchiness] that someone wants, so I'm afraid these kinds of questions are hard to answer generically.

[Crusher Camaro]

stock LT4 supercharger isnt setup for a 95MM.
first pictures is the 95MM on the stock blower. Red marker is the standard snout.
2nd pictures is after a little love with the die grinder.

[Stephen12ZL1]

I tried one on my '21 on track and the car seemed a "little soft" which to me means the car was seeing more airflow than anticipated and had trouble adjusting appropriately. obviously with a tune this would work fine

[David Gordon]

Thanks guys, I'll wait till I tune it. I have seen a few videos where the guys added the LT5 throttle body and said they felt it responded a tad better.

[turbo_jimbo]

Originally Posted by Stephen12ZL1

I tried one on my '21 on track and the car seemed a "little soft" which to me means the car was seeing more airflow than anticipated and had trouble adjusting appropriately. obviously with a tune this would work fine

That doesn't make too much sense..

Granted I have only opened my hood once to change the oil, but most GM engines use a MAF and a MAP, meaning it measures the amount of air incoming and pressure of the air after it arrives.

[Joshinator99]

Originally Posted by turbo_jimbo

That doesn't make too much sense..

Granted I have only opened my hood once to change the oil, but most GM engines use a MAF and a MAP, meaning it measures the amount of air incoming and pressure of the air after it arrives.

It makes plenty of sense, the ECM is expecting to move a certain amount of airflow at a certain throttle body blade open position. At low RPM the car is referencing a VVE table that is preset by GM and the OEM TB blade size is programmed in (as referenced by Arpad above). Making changes to the inlet tract will have an impact on the tune. A 95mm TB will not be a drastic change, but it’s a change GM didn’t calibrate around. And TB changes can have a significant effect on part throttle response, especially if you do not tune for them.

[turbo_jimbo]

Yes, it will alter the effects of the VE table, but it shouldn't be significant enough that the o2 reference can't accommodate for it. Or, maybe I'm off base here, I haven't played with any reflash software for this engine.

[Joshinator99]

Originally Posted by turbo_jimbo

Yes, it will alter the effects of the VE table, but it shouldn't be significant enough that the o2 reference can't accommodate for it. Or, maybe I'm off base here, I haven't played with any reflash software for this engine.

There is no VE on the Gen5 LT engines, only VVE. Nothing to do with O2 trim since the previous poster referred to “feeling soft” which is typically a throttle response issue. No surprise since the TB is different and not tuned for.

[radz28]

Generically adding to Josh', these cars operate off torque modeling (and have for a while, and if you know this - sorry - just trying to justify my statements, however a beginner I am). The ECM is calculating torque, during all operation, based off fueling, because that's a constant (I thought it was airflow, but I read one of the Big Dogs on HPTuners [like GHuggins/Higgs Boson/Howard Tanner/etc.] said otherwise, if I recall [I just found the post by Tanner stating IT IS airflow, but I've read elsewhere it is fueling; I'm not sure how much it matters either way, necessarily, as the point is to calibrate correctly), so you're actually adding airflow to the fuel. But there is a direct correlation with fuel and torque, so you're adjusting airflow, through the throttle body, to match the fuel you want, because you're making a torque request through the accelerator pedal (it's even more complicated, to me, for turbo cars, which I'm playing with).

So - for all these systems to balance (ECM playing with the TCM, playing with the CCM for fuel pump, Traction Control/Stability Control/ediff'/Drive Modes/sub-modes, etc), they have to speak the same language: torque. So - when you push the accelerator pedal down 25%, the ECM might think you're requesting 400-lb.ft. of torque, and it will open the throttle (throttle body blade) to, say, 50%, because that's the torque the ECM is calibrated, by GM, to correspond with for that speed, at that RPM, in that gear (Driver Demand table), for 400. So the ECM will open the blade to the calibrated opening to achieve the airflow rate that it's calculating you are requesting. These sensors are not measuring the actual air particles that enter the throttle body. There are correlations that they have made by GM during development, and can be calculated, so long as there are constants they can go by. So...

... If you change the airflow enough, the torque model is no longer accurate, which means a lot of the other modeling is off. If it's off far enough, for example, at idle, the car could start trying to retard so much ignition timing, you'll melt your cats', because the change in airflow you made with the bigger TB is telling the ECM that to much torque is being made. If that torque exceeds the stock torque modeling (in the VTT), it's going to try to reduce torque. And the easiest way to do that, at idle, is retard timing (because you can only close the blade so much, and the ECM can adjust the timing so much faster than with the blade) - which can get low enough, perhaps, that you start melting things because the combustion process is now happening later enough in the cycle that a lot of the heat has moved from the combustion chamber toward the exhaust port, and that pushes too much heat into the cats'. So - changing airflow too much might push the ECM out of it's calibrated range to calculate torque accurately.

Were it me: I would do what it takes to monitor timing advance at idle (preferably more, but I'm staying with idle to keep from making this post longer) and make sure it's enough that you're not getting too low. Some people say keep it not too much lower than 10*, for example, but definitely not close to 0*, or you're into trouble.

Too much. Sorry... I'm rushing the response, so, please, don't roast me much, experts, lol.

[KingLT1]

What tends to happens with larger throttle bodies and especially on some aftermarket stuff is the timing will drop down at idle because the throttle blade angle is off. So the ECU pulls timing in order to hit target idle. Since we don't have access to all the throttle body tables like gen 4 stuff, you have to go into the Virtual torque editor and remove torque from the idle range area to get the ECU to add spark back. On a stock cam car the lower timing will likely go undetected to the average person. On a cam car it will run like crap because the cam needs more timing due to the lack of efficiency down low.

There is a popular brand throttle body that I won't name that is notorious for this...(Hint: they claim 107mm effective.)

[radz28]

Originally Posted by KingLT1

What tends to happens with larger throttle bodies and especially on some aftermarket stuff is the timing will drop down at idle because the throttle blade angle is off. So the ECU pulls timing in order to hit target idle. Since we don't have access to all the throttle body tables like gen 4 stuff, you have to go into the Virtual torque editor and remove torque from the idle range area to get the ECU to add spark back. On a stock cam car the lower timing will likely go undetected to the average person. On a cam car it will run like crap because the cam needs more timing due to the lack of efficiency down low.

There is a popular brand throttle body that I won't name that is notorious for this...(Hint: they claim 107mm effective.)

I know this brand, LOL. However - I'll say, that because I over-ported an LT5 in the past, the tune was already modified with the torque modification you're talking about, so when we installed the "107", when we went through the relearn procedure, it was totally fine. I couldn't say if I didn't already deal with the over-ported LT5 that the 107 wouldn't have been as easy, but all I know is we have 10* at idle, and could command more if we wanted, and it's just fine. I read about some of the stuff I think you're talking about though. Oof. No problems for me though (not because I'm a good tooner or something - just ?probably? because of that LT5-experience).

That TB was worth it for that car's combination though. It lowered inlet vacuum 4-5 kPa at WOT, surprisingly. And that was coming from a less-over-ported LT5.

[turbo_jimbo]

Originally Posted by Joshinator99

There is no VE on the Gen5 LT engines, only VVE. Nothing to do with O2 trim since the previous poster referred to “feeling soft” which is typically a throttle response issue. No surprise since the TB is different and not tuned for.

My apologies, like I said, I haven't played with a flash program for this engine yet.

I had to look up what a VVE table is, and from what I understand of it; it's a Virtual Volumetric Efficiency table, or rather more like a Speed Density table.

Nothing too ground breaking really. ITB's need to be set up like this when not using a MAF and air box.

So in a round about way, it calculates how much air it should be seeing and supplies fuel and timing to correspond with that. There is a benefit to altering the table to get more efficiency, translated as more power.

I am trying to wrap my head around one small point here though.

It's widely accepted the LT4 runs in knock retard due to the undersized SC. Sooo, why wouldn't the ecu be able to adapt around this? Timing tables and fuel tables are all adaptable tables relative to information from the o2 and knock sensors. Speed density is calculated from throttle position and MAP and IAT, so a change in throttle body size outside of adjustable range will cause more issues for sure, like throttle response and overall timing tables, but feedback from the other sensors should alleviate some of the downsides.

At least the way I understand it. I'm happy to be wrong here. Yall know way more about the flash tools for this than me.

[radz28]

Originally Posted by turbo_jimbo

My apologies, like I said, I haven't played with a flash program for this engine yet.

I had to look up what a VVE table is, and from what I understand of it; it's a Virtual Volumetric Efficiency table, or rather more like a Speed Density table.

Nothing too ground breaking really. ITB's need to be set up like this when not using a MAF and air box.

So in a round about way, it calculates how much air it should be seeing and supplies fuel and timing to correspond with that. There is a benefit to altering the table to get more efficiency, translated as more power.

I am trying to wrap my head around one small point here though.

It's widely accepted the LT4 runs in knock retard due to the undersized SC. Sooo, why wouldn't the ecu be able to adapt around this? Timing tables and fuel tables are all adaptable tables relative to information from the o2 and knock sensors. Speed density is calculated from throttle position and MAP and IAT, so a change in throttle body size outside of adjustable range will cause more issues for sure, like throttle response and overall timing tables, but feedback from the other sensors should alleviate some of the downsides.

At least the way I understand it. I'm happy to be wrong here. Yall know way more about the flash tools for this than me.

No expert, or even close, but from what I've gathered:

LT4s (and LT1s, among others) run in retard because they're tuned from the factory to run on 93 (states that right in the manual). So - any octane less is probably going to trigger them to retard timing a fair amount (and probably one of the reasons the knock sensors are pretty aggressive, along with Burst Knock, and a lot of those kinds of parameters). The SC is undersized (to fit under Z06's hood, to my understanding), so I'm not arguing that, but I think the retard is more due to octane and OEM timing than the blower. I could see an argument for heat from the blower, but there are MAT tables that account for blower heat, so I don't know the size is a big factor.

Timing can adapt some to a lower table if the ECM thinks the car's got a crap tank of gas.

I think the point that's missing is there is no real SD anymore, if I understand correctly. VVE handles that chore now, and is a redundancy of the coefficient table than anything. I think it's more there to be a visual representation of the coefficients than represent SD - at least in the usual ways in the past with Gen III stuff. So - as a result of this - the language I was talking about is torque (TQ), and if the coefficients are off enough, things like tranny shifting, traction control, and maybe even how smoothly the ECM adjusts for when the AC compressor engaging can be affected. If the model is off enough, the TCM may not, for example, command enough line pressure for a shift, and the result could be a flare or worse. VVE is now GMVE, and kinda' like SD, but GMVE isn't a percentage of efficiency, like it was (if I recall) in the Gen III days. The numbers in the VVE table seem to really only be numbers, but not units or anything. At least I believe that is what the current convention is. The ECM is collecting MAT, MAP, MAF, and all that, but it's not counting each particle of air or moisture the engine's ingesting. Rather - it's extrapolating values and calculating and back-calculating airflow so it opens the throttle to the TQ it thinks the driver is commanding.

More than ever - it's garbage in - garbage out. The VVE and coefficients are there for start-up and airflow transients (when the MAF is not accurate enough to measure the air), so one convention is making sure the airflow models are accurate (I've seen GM engineers state they want 5-10% accuracy for these systems) so it'll be up to everyone else to determine what that means to them and their combination.

Hopefully I got all that right.