Lower VE with newer/better engine?

[edcmat-l1]

can you predict where (in terms of RPM and/or MAP) it would start to show an advantage over the stock '02 LS1? It would be nice to have some intuitive sense of whether the changes I find myself making are reasonable.

Only way to know that is to post the tune file so I can see it.

[ns158sl]

At the top of the forum. Well you don't need to attach the .cfg anymore.

[JakeRobb]

Don't have to do VE before MAF, but yes that's typical.

If VE isn't right when you do MAF, wouldn't that lead to a tune where the MAF calibration was wrong, and the VE was also wrong in an equivalent/opposite direction? And wouldn't that lead to an incorrect tune in situations where the MAF isn't being used, since the MAF cal wouldn't be compensating for the incorrect VE?

Only way to know that is to post the tune file so I can see it.

Happy to; will do next time I'm at my tuning computer.

That said, I'm curious what the tune file can tell you that would help you answer this question. At this point all of the tables are still OEM LS1 data -- it just has updated displacement, tire/gearing, fuel injector, and MAF settings.

[ns158sl]

If VE isn't right when you do MAF, wouldn't that lead to a tune where the MAF calibration was wrong, and the VE was also wrong in an equivalent/opposite direction? And wouldn't that lead to an incorrect tune in situations where the MAF isn't being used, since the MAF cal wouldn't be compensating for the incorrect VE?

Kind of. You are thinking if you are in hybrid mode. Hence with Gen3's it seems easier to do it the old fashion way of disable MAF, dial in your VE, Then disable dyn air and tune the maf. Then put it back in hybrid(normal) and see how the car reacts. If you start messing with timing a bit after, you will have to go back and adjust VE or maf, or both.

Most important is correct injector data before you start adjusting fueling.

I also find searching the forum using google sometimes retrieves better results. There are a many decent writeups. I think they might even be in the Sticky on the top.

[edcmat-l1]

can you predict where (in terms of RPM and/or MAP) it would start to show an advantage over the stock '02 LS1? It would be nice to have some intuitive sense of whether the changes I find myself making are reasonable.

Only way to know that is to post the tune file so I can see it.

That said, I'm curious what the tune file can tell you that would help you answer this question. At this point all of the tables are still OEM LS1 data -- it just has updated displacement, tire/gearing, fuel injector, and MAF settings.

A stock tune file will not tell me if the changes you are making are reasonable. How can it?

[JakeRobb]

A stock tune file will not tell me if the changes you are making are reasonable. How can it?

That's what I wanted to know!

I am not asking for specific help with my tune; I've scarcely begun tuning. The very first changes I was making didn't make sense to me, so I didn't save them. Instead I came here and posted this thread to find out what was up.

Turns out my intuition was flawed; I didn't realize that a bigger cam would be less efficient at low RPM. That bit of my intuition is corrected, but only partially; what is "low RPM"? I am sure it varies by engine and cam, which is why I shared those details when asking if anyone here had an intuitive sense of the RPM range where I should start to see VE advantages over the stock LS1. If they could share that, even if it's just a guess based on experience, then I would could take that and have it in mind when proceeding with my tune changes, and could feel a little more confident moving forward.

Turns out I also have some other issues I need to iron out before I go back to VE tuning.

[edcmat-l1]

There are multiple factors in play. It's far easier for an experienced eye to look at it and tell you yay or nay than to try and explain it to you. The more radical the cam, the lower the efficiency at idle and part throttle. Use your trims to dial it in. They will tell you where to pull fuel and where it wants more. Need to make sure your injector data is right and you need to put a fuel pressure gauge on it you can monitor constantly for the entire tuning process.

[kingtal0n]

Bigger cam makes the engine less efficient at bringing in air and holding onto that air at low rpm, and it also creates large standard deviation in airmass between cylinders. This in turn leads to a drop in fuel economy and may characteristic lope.
Key point #1: Larger cams reduce economy at low speeds, they require more fuel. Otherwise, you know, the OEM would use larger cams to begin with to save fuel.

Again fuel is wasted by the variability in cylinder fill and lost fuel due to open valves during overlap and poor vaporization, poor use of fluid momentum, and reduced energy transfer between cylinders and timed events.

Next, VE
VE table numbers going down means inject less fuel, whereas larger VE values means more injected fuel. This is a hard fast rule but only applies to injector pulse not duty cycle.
Thus, The VE table is really a fuel table where larger VE values is more injector pulse.
Key point #2: The VE table controls injector pulse: The VE table is a fuel table


Lets put these together. Larger cams reduce economy and require more fuel. VE tables control fuel pulse. Therefore _____ The VE numbers would need to increase to support the additional fuel requirements.


Then why do people say the VE number gets smaller and erroneously attribute that to the breathing efficiency of an engine?

Answer: People sometimes seem to become confused by the difference in duty cycle and injector pulse. The VE table is an injector pulse table, not a duty cycle table. When you install a larger cam the engine RPM is also increased. This in turn fires the injectors more often. Energy is supplied by fuel so as long as the fuel flow is increased en total the fuel requirements of the cam will be met. For examples

Stock cam example
Idle injector pulse: 2.5ms
Idle RPM: 550rpm
Idle Duty Cycle: 1.1%

Aftermarket mild cam example
Idle injector pulse: 2.6ms
Idle RPM: 625rpm
Idle Duty Cycle: 1.7%

Notice the injector pulse only changed a small increment but the overall duty cycle increased significantly, flowing more fuel en total (energy rate) to make up for the reduced efficiency of the camshaft influence.
It can go either way, same pulse more duty, or more pulse more duty, or even less pulse (high rpm) more duty. But the overall fuel flow must increase due to the larger camshaft somehow.


That was a made up example. Here is a real world example.

I have LM7 5.3L did camswap around 200,000 miles





Here is the before and after VE tables and scanner logs showing a/f ratio idle speed injection pulse etc... I matched the log to the tune file as well as operating conditions as close as possible. Same injectors obviously.


Here is the final difference in the VE tables from before cam swap to current file


As you can see the mild cam uses more fuel everywhere. At idle, at cruise, at wide open throttle, it doesn't make the engine any more fuel efficient, the VE table values did not go down.

We can make the VE values go down by adjusting other aspects of the airflow model and the fuel system, however. For example increasing fuel pressure, or decreasing the injector size in the injector size table. There may be many ways to offset or change the injection pulse outside of the VE table, things like Fooling with engine displacement or accessory torque perhaps. I have not tried to screw it up on purpose. It is simply worth mentioning if you notice some changes not to immediately assume it came from the VE and realize many outside influencing tables control the fuel not just VE.

[JakeRobb]

Haven't had time to digest your whole post yet, but:

VE table numbers going down means inject less fuel, whereas larger VE values means more injected fuel. This is a hard fast rule but only applies to injector pulse not duty cycle.

The VE table has RPM as one of its axes. At a given RPM, are pulse and duty cycle not equivalent measurements?

At 3000rpm, each revolution takes 20ms. Each injector fires once every two revolutions, so there's a 40ms window in which each pulse must occur (of course, the actual time within that window in which a pulse would be appropriate is much smaller -- but still, the injector gets to remain closed during the rest of that 40ms). So, at 3000rpm, a 2.5ms pulse would be semantically identical to a 6.25% duty cycle, would it not?

[kingtal0n]

Haven't had time to digest your whole post yet, but:


The VE table has RPM as one of its axes. At a given RPM, are pulse and duty cycle not equivalent measurements?

At 3000rpm, each revolution takes 20ms. Each injector fires once every two revolutions, so there's a 40ms window in which each pulse must occur (of course, the actual time within that window in which a pulse would be appropriate is much smaller -- but still, the injector gets to remain closed during the rest of that 40ms). So, at 3000rpm, a 2.5ms pulse would be semantically identical to a 6.25% duty cycle, would it not?

As much as I love math. We don't need math. Duty cycle is just how often the injector is open. For example 100% is open all the time.

So lets say we set the injector to be open 100% of the time, just flowing fuel.

You will see that as the rpm is increasing, the amount of fuel or mass of fuel each cylinder gets is gradually being reduced.
This is because the length of time or pulse width of the injector with respect to the frequency of the engine is getting shorter because each clock cycle is occurring sooner and sooner.

To put it another way if we set the injector to pulse 1ms every revolution, then at 1rpm our we will have 1 pulse per minute. At 2rpm 2 pulses per minute. 3rpm is 3 pulses per minute. And so forth. Gradually our duty cycle will rise with RPM despite the pulse width for each combustion event being the same.

This is why we could have a situation where duty cycle rises while pulse width drops. But that happens naturally for engines with good vacuum and factory valvetrain components anyways, usually. It just so happens when doing a cam swap the native or idle rpm of the engine is also increased, kind of like stepping on the throttle a little bit, which increases airflow, friction, all of that, whether the cam is installed or not we get the same affect, but now its all the time with the cams new idle rpm.

Good question though thanks for working it out

[kingtal0n]

I Wasn't sure if everybody knows how much I love math. You see, real math isn't numbers at all. I feel sorry for the 'numbers' guys as I used to be one of them.

I kept all my homework , these equations used to quite run off the page, pages of them. Mathematical methods course I'll never forget my professor says "You believe this?" I couldn't.

[kingtal0n]

Oh here I found this real quick

https://www.stealth316.com/2-calc-idc.htm

[JakeRobb]

As much as I love math. We don't need math. Duty cycle is just how often the injector is open. For example 100% is open all the time.

So lets say we set the injector to be open 100% of the time, just flowing fuel.

You will see that as the rpm is increasing, the amount of fuel or mass of fuel each cylinder gets is gradually being reduced.
This is because the length of time or pulse width of the injector with respect to the frequency of the engine is getting shorter because each clock cycle is occurring sooner and sooner.

To put it another way if we set the injector to pulse 1ms every revolution, then at 1rpm our we will have 1 pulse per minute. At 2rpm 2 pulses per minute. 3rpm is 3 pulses per minute. And so forth. Gradually our duty cycle will rise with RPM despite the pulse width for each combustion event being the same.

This is why we could have a situation where duty cycle rises while pulse width drops. But that happens naturally for engines with good vacuum and factory valvetrain components anyways, usually. It just so happens when doing a cam swap the native or idle rpm of the engine is also increased, kind of like stepping on the throttle a little bit, which increases airflow, friction, all of that, whether the cam is installed or not we get the same affect, but now its all the time with the cams new idle rpm.

Good question though thanks for working it out

That was an incredibly verbose and indirect way to say "yes, you're right!" without actually saying it. I'm seriously impressed. That's almost at the level of Pinocchio trying not to tell Lord Farquaad where Shrek is. Bonus points for explaining something I clearly already understand, and also for using a nonsensical example (one revolution per minute? What is this, a waterwheel?!).

The directly proportional relationship at a fixed RPM paired with the inverse relationship as RPM changes is certainly interesting, and that's a valuable thing to keep in mind when reasoning about this stuff. But, much like miles/gallon and liters/100km, or horsepower and torque, there is a straightforward mathematical conversion from one to the other for any given data point. Likewise, depending on context, it may be easier to reason about a given scenario by focusing on one vs the other.

I Wasn't sure if everybody knows how much I love math. You see, real math isn't numbers at all. I feel sorry for the 'numbers' guys as I used to be one of them.

I'm a math lover too. I'm not sure how anyone's love of math, nor your unexplained bias against "numbers guys," is relevant to the conversation.

I kept all my homework , these equations used to quite run off the page, pages of them. Mathematical methods course I'll never forget my professor says "You believe this?" I couldn't.

Again, I can't figure out how this is relevant. We're bragging now? It's been a couple decades, and I don't often have a need to exercise the skills anymore, but I minored in applied computational mathematics. I can't say I kept my notes, but mine looked similar. I studied matrix algebra, multivariate calculus (which, at a glance, seems to be what I'm seeing in your notes), ordinary and partial differential equations, Laplace and Fourier transforms, boundary value problems, and lots of other fun stuff that rarely if ever involves actual numbers.

[Alvin]

Disable the MAF, Dial in SD with good proper injector data, once that is settled turn the MAF back on and tune that.

Do not try to back out VE in GEN 3. Notice how the GEN 4 VVE from MAF threads are still deciding on best approach? It's not a great way to do things.

[JakeRobb]

Okay, I've had time now to digest.

Bigger cam makes the engine less efficient at bringing in air and holding onto that air at low rpm

Yep, we've covered that.

Although I'll quibble with your choice of words -- "bigger" and "larger" to describe more aggressive cams. The only real thing you could be referring to is valve lift, as higher lift literally translates to the camshaft being physically larger. But you can actually make an engine more efficient by employing lobes with more lift, and/or more aggressive ramp rates, so long as the timing of the open/close events remain unchanged.

The thing is that it's pretty uncommon for people to replace OEM cams with aftermarket ones that have identical-to-OEM timing characteristics and simply use a different lobe profile. Aftermarket cams also vary the lobe separation and the exact timing of the various open/close events, and it's these changes which lead to pumping losses at low RPM.

The reasons OEMs don't do this are primarily related to cost and parts longevity. Those larger lobes would demand a better (more expensive) spring in order to meet durability targets, and that might not be the only part of the valvetrain which might be compromised. Although as CAFE targets become more and more aggressive, I suspect the balance is changing here, with OEMs willing to employ more expensive valvetrain components in order to achieve higher efficiency. Of course, most of the vehicles in any given manufacturer's lineup use VVTL (and usually DOHC) to greatly increase the RPM range during which they can operate efficiently while still meeting performance targets.

So yeah, let's maybe say "higher performance" or "more aggressive" or "hotter" (figurative, of course) instead of "larger"?

and it also creates large standard deviation in airmass between cylinders. This in turn leads to a drop in fuel economy and may characteristic lope.

Increase in SD is not something I had considered. What is it about a more aggressive camshaft that causes this? It's not like the lobe profiles vary from one cylinder to the next....

I imagine that this is a super-complex scenario where things like reflected exhaust pulses are coming into play at some RPMs, and having a greater effect on airmass due to increased overlap. And probably a handful of other similarly complex dynamic interactions, all contributing to the situation together.

It makes sense that increased SD would be the cause of the characteristic lope, although it doesn't quite sit right with me that the variance could be so great as to cause the significant lope we've all seen with the most aggressive cam specs.

Again fuel is wasted by the variability in cylinder fill and lost fuel due to open valves during overlap and poor vaporization, poor use of fluid momentum, and reduced energy transfer between cylinders and timed events.

I'm assuming we're still referring primarily to low RPM? If these things were problematic at all RPMs, then we wouldn't see more power anywhere in the rev range.

Next, VE
VE table numbers going down means inject less fuel, whereas larger VE values means more injected fuel. This is a hard fast rule but only applies to injector pulse not duty cycle.

I have to argue with you here. As previously noted, the VE table has RPM as one of its axes. So when any one number goes up or down, it is doing so in the context of a specific RPM, and therefore an increasing number does correspond to an increase in both pulse and duty cycle at that RPM.

Key point #2: ... The VE table is a fuel table

Um, duh? Not sure why this is a point you feel you need to make at all. Of course it's a fuel table.

Lets put these together. Larger cams reduce economy and require more fuel. VE tables control fuel pulse. Therefore _____ The VE numbers would need to increase to support the additional fuel requirements.

Then why do people say the VE number gets smaller and erroneously attribute that to the breathing efficiency of an engine?

Answer: People sometimes seem to become confused by the difference in duty cycle and injector pulse. The VE table is an injector pulse table, not a duty cycle table. When you install a larger cam the engine RPM is also increased. This in turn fires the injectors more often. Energy is supplied by fuel so as long as the fuel flow is increased en total the fuel requirements of the cam will be met.[/QUOTE]

Again, no. I have to disagree with you here. At a given RPM, the values in the table correlate directly with both pulse and duty cycle.

I feel like you're on some kind of hobby horse about IPW vs IDC that has exactly nothing at all to do with my question. You're going to all this effort to explain stuff that has already been explained in a single sentence (post #11). That was all I needed to understand the problem with my expectations. (Plus the MAF calibration bit, which is probably amplifying the magnitude of the VE changes I needed to make.)

Before you argue, I'll say that yes, a more aggressive cam likely requires a higher target idle RPM, and that's going to introduce additional variability in terms of idle fuel requirements, but that's still not relevant to my question. All that means is that there's some small number of columns in the table which were relevant before because they were at or above the minimum factory idle RPM, but which are no longer relevant because they're below the new cam's minimum. My question was not about overall volumetric efficiency, nor about fuel economy -- just about when looking at a specific cell in the table, why would the number decrease if the engine supposedly flows more air? That question has been answered, and as far as I can tell, nothing you have said has contributed to that answer in the slightest. In particular, your focus on idle is irrelevant, since at the time my engine wasn't idling on its own at all, and so everything I was well clear of idle RPMs.

That said, I believe I've solved my idle issue (needed a TPS relearn), and I'm looking forward to seeing what my new idle RPM will be! Based on my first start (cold, OEM LS1 tune), it seems like it'll settle in no higher than 700 once it's warmed up.

[edcmat-l1]

I would completely ignore that guy. Few weeks ago he didn't even understand the definition of VE.

[SiriusC1024]

Well whenever you're ready to get down to business let us know. That build has a lot of potential. TPS sorted out yet? Ready to post the tune file?

[JakeRobb]

Do not try to back out VE in GEN 3.

I don't know which approach you're referring to with "back out VE."

Notice how the GEN 4 VVE from MAF threads are still deciding on best approach? It's not a great way to do things.

I can't say I've noticed. As a DIYer with only a gen3 to tune (for now), I've not been paying any attention to gen4 conversations.

[JakeRobb]

Well whenever you're ready to get down to business let us know. That build has a lot of potential. TPS sorted out yet? Ready to post the tune file?

I don't get a lot of time to work on it, especially during the week. Was really busy during the holiday weekend, too. That said, I confirmed the need for a TPS relearn last night (min % was 0.4%). Did that, and I am now seeing TPS 0.0% when not on the throttle, so I think it'll idle now. I also identified a throttle cable issue, wherein I can't open the throttle all the way via the pedal (it stops at about 50% with the pedal on the floor). That was all the time I had, and I haven't started it yet to test.

I still don't have anything customized in my tune tables beyond what I've already mentioned, so nothing to share on that front yet. With it running as rich as it has been so far, I can't start the engine for more than a minute or two without smelling like fuel. My wife is super sensitive to that, so I have to choose my opportunities wisely. Hopefully I can get past these next couple tuning hurdles and get it MUCH closer too stoich soon, and then I'll be able to work on it more often!

I also have a variety of things to finish unrelated to the tune -- hood won't close on the 104mm lid, interior isn't fully buttoned up, I need to make some camber and toe adjustments before I can even drive it to an alignment shop, etc. It's a multifaceted project!

[kingtal0n]

That was an incredibly verbose and indirect way to say "yes, you're right!" without actually saying it. I'm seriously impressed. That's almost at the level of Pinocchio trying not to tell Lord Farquaad where Shrek is. Bonus points for explaining something I clearly already understand, and also for using a nonsensical example (one revolution per minute? What is this, a waterwheel?!).

Oh I didn't really look at your math. I didn't assume it was right or wrong I just show the easy way to do these things without math if possible. I teach math and engineering at university its how I always do. We also build microcontroller based projects such as line tracking robots and obstacle avoidance and underwater rov and learn to code and I consistently go back to the fundamentals of engineering behind the components on the board and how they culminate to some grand scheme.

The directly proportional relationship at a fixed RPM paired with the inverse relationship as RPM changes is certainly interesting, and that's a valuable thing to keep in mind when reasoning about this stuff. But, much like miles/gallon and liters/100km, or horsepower and torque, there is a straightforward mathematical conversion from one to the other for any given data point. Likewise, depending on context, it may be easier to reason about a given scenario by focusing on one vs the other.

Right, we do pulse for torque and VE. And we do duty cycle for energy content per unit time. Energy from fuel may be turned into heat and lost (melting parts) Or it can be turned into torque (pressure over area). It also disperse as sounds vibration through materials and there is a restorative feature with respect to conservation of energy which comes into play further into this discussion.

Again, I can't figure out how this is relevant. We're bragging now? It's been a couple decades, and I don't often have a need to exercise the skills anymore, but I minored in applied computational mathematics. I can't say I kept my notes, but mine looked similar. I studied matrix algebra, multivariate calculus (which, at a glance, seems to be what I'm seeing in your notes), ordinary and partial differential equations, Laplace and Fourier transforms, boundary value problems, and lots of other fun stuff that rarely if ever involves actual numbers.

It is simple reminder that our analytic solutions rarely evolve appropriate approximations which are more akin to modelling and how we get these water down approaches by suggesting errors on the order of (to some degree) and assumptions which derive constants from variables.

I Like that you read, think, respond, Sorry if I came off a certain way I just get excited about math and these topic.