5.3 sloppy stage 1 needs tune/ help

[kingtal0n]

So, basically the VE table isn't normalized for atmospheric pressure at STP. VE is cylinder fill for a given manifold pressure.

VE has multiple definitions.
VE table depends on who programmed the ECU, and some have more options for enrichment interactions than others and some have more complex airflow characteric models than others.

I have written software applications to automatically tune VE tables in 2001 stand-alone ECU
https://www.thirdgen.org/forums/dfi-...der-950-a.html

My understanding of ECU to engine behavioral tuning and what a VE table is doing from over 20 years ago was better then than most people on this forum will ever achieve in a lifetime. You really need a programming background to understand microcontroller capabilities otherwise you can not grasp possibility boundaries. Many cannot fathom how a computer is 'thinking' and this is a hurdle between the reality of what a computer is capable of doing and what they perceive as 'correct' and 'typical' or 'original'. It is the major source of frustration for them when they read my words and cannot interpret or make the jump between something like VE and injector on-time in terms of code.


The definition in terms of VE for coding is not conceptual, it is idiopathic. We do not program the ECU therefore we are at the whim of the unknown programming, underlying conditions we could call it.

When we say something like VE Is ______. This can be true for some computers but not others. You must define the scope for which you pretend to evaluate the word VE.

For Haltech, I would say VE is merely injector on-time and that larger VE values result with larger injector on-times. It is that simple. If you want to globally reduce the perceived VE values you would simply adjust fuel injector size globally or engine displacement globally and walaa- a new VE table shape and form emerges for the same old engine.

In HPtuners it is a tiny bit more complex because the airflow modelling also influences other tables such as friction (calculations for torque) and transmission pressure (torque during a shift = pressure). However these limitations are merely perceived if you have not built and understood how a transmission works from the mechanical point of view. For example you can easily use a external transmission pressure gauge to dial in the force motor current table to desired real-world pressure no matter what the airflow model suggests. There is always some solution if you understand what the ECU is capable of and what is isn't. Another example I frequently see people complain about timing for boost, the g/cyl limitation in the timing map. They seem to think that because the table maxes out at 1.2g/cyl that you cannot adjust timing beyond that point. When in reality there are a couple other tables which allow us to continue to adjust timing into boost, AFR advance for example, some ECU have that table to change timing based on air fuel commanded ratio. Then by adjusting the commanded vs actual air fuel ratio we can achieve any desired timing at any boost despite the limitation of g/cyl timing table. It isn't so much thinking outside the box as it is just knowing what tools you have available I guess. But that means people are not looking at their software, they aren't delving into the possibilities offered to them, they don't check every table and read it and try to make sense of it. I could not imagine owning a piece of software that does anything and not understanding every single option contained within- but that is the difference some people don't care and suffer the consequences.

[SiriusC1024]

I think it just finally clicked.

55kPa, VE = 47. The cylinder was still in the process of filling, but the valves shut. If allowed to hold at max cylinder volume and stabilize the pressure in the cylinder would be 25.85kPa.

180kPa, VE = 110. Same situation would yield 198kPa. In this case the inertia of the charge stacked air into the cylinder. In the case of FI, more mass, as a result of higher manifold pressure, moving means more inertia to overcome the resistance of pressure. Ram effect.

Now for overlap increasing VE. The vacuum of the outgoing exhaust pulse induces flow at low lift. It starts the incoming charge in motion through both valves as they are open. Inertia again stacks extra air into the cylinder.

VE scales with pressure because of essentially pushing air through a small hole. Takes more time with less pressure differential.

VE scales with RPM because there is less time for the cylinder to fill as RPM and valve events increase. On the other hand, a sonic effect, dictated by valve timing and induction tuning, increases airflow with increasing RPM to offset this.

Right?

[kingtal0n]

I think it just finally clicked.

55kPa, VE = 47. The cylinder was still in the process of filling, but the valves shut. If allowed to hold at max cylinder volume and stabilize the pressure in the cylinder would be 25.85kPa.

180kPa, VE = 110. Same situation would yield 198kPa. In this case the inertia of the charge stacked air into the cylinder. In the case of FI, more mass, as a result of higher manifold pressure, moving means more inertia to overcome the resistance of pressure. Ram effect.

Now for overlap increasing VE. The vacuum of the outgoing exhaust pulse induces flow at low lift. It starts the incoming charge in motion through both valves as they are open. Inertia again stacks extra air into the cylinder.

VE scales with pressure because of essentially pushing air through a small hole. Takes more time with less pressure differential.

VE scales with RPM because there is less time for the cylinder to fill as RPM and valve events increase. On the other hand, a sonic effect, dictated by valve timing and induction tuning, increases airflow with increasing RPM to offset this.

Right?

I'm not sure I follow your numbers. But I explain some phenomena you seem to be interested in.

There are two types of 'ram air' major affects
1. momentum flow, or flow work
2. Harmonic or acoustic tuning

The acoustic tuning is a sound wave that travels away from the valve when it closes, this is called water hammer in the fluid mechanics book. It arrives to the plenum and returns to another cylinder at a specific time and if the valve there happens to be open it will reinforce the intake charge. This is how TPI got such high mid-range torque values in the 1992 camaro TPI engine, long runners with a acoustics that arrived to valves around 4400rpm give or take. The acoustic wave travels at the speed of sound and is separate from the physical bunching up of air molecules that occurs as they are forced to stop and rebound on the back of an intake valve.

Momentum flow is the energy fluids carry as they travel through a pipe, we could also say kinetic energy. Think of a straw you hold your finger over the top and hold the straw in liquid then release your finger from the top- the fluid travels up the straw and raises higher than the liquid because it carries momentum energy. Same thing with a heavy flywheel hard to slow down because internal energy. Momentum energy can inhibit performance when the fluid is bunching up and changing direction just as the intake valve is opening. It has a hard time reorganizing and reversing column of airflow if the velocity is inhibited by large ports volumes. In other words it is easier to reorganize and speed the flow a new direction when the ports are very small and capable of high velocity at low flow rates such as idle and mid-range flow which are lower than peak power.

Momentum flow and acoustic tuning are not the only forces at work though. But they are the main intake forces to consider.
We also have exhaust overlap scavenging which can pull on the cylinder harder than the intake stroke according to David Vizard. When I was 15 years old getting into cars I used to read those books about building small block chevy and david vizard reported that exhaust overlap and scavenging was far more effective at bringing fresh air in than the intake stroke was. And of course he is correct, if you can get the proper exhaust velocity to create a pressure drop behind the exhaust valve. Which may not be feasible in high exhaust gas pressure turbocharged situation...

Turbo engines seems to rely on differential pressure to drive flow, not so much scavenging. It depends on the engine, the 2jz and sr20 and rb26 for example with their 4-valve per cylinder seem to respond as well as any natural aspirated engine with respect to scavenging, long overlaps and tight LSA (they can have adjustable cam LSA). When exhaust gas pressure rises uncontrollably its time to stop, it will stop itself, stop the from flowing though. This is why we can use stock exhaust manifolds for 800rwhp if we can maintain a reasonable intake:exhaust pressure, or drive pressure sometimes it is called. Generally I think there is a 1:2 ratio acceptable for hobby applications. But I do not spent my time worrying about that in a sub 1200rwhp setup. Which brings me to my overall worldview, I guess,

We can treat turbo or forced induction engines just like naturally aspirated engines in hobby applications below 1300rwhp or so. This goes for 3L 2jzgte or 5L LS anything modern combustion chamber. Before tuning any engine I determine the combustion chamber tech. Old tech like sbc uses high timing and inefficient I avoid those engines are pre-computer modelling. Modern tech like 92-02 skyline/supra and 02+ chevrolet is lower timing more efficient design, and this lends to the block design and piston design it all happens at the same time the chamber gets better because of computer modelling. In those engines you can 2x or 3x sometimes 4x the factory output using mostly OEM components. Pushing 2 or 3 times the airflow through them than factory. I never worry about the engine VE or overall flow rate at first when setting up though; Instead, I focus on the compressor, and the natural aspirated aspects. I design the parts combination around a strong street (sub 1000rwhp is street stuff) mid-range profile for the cam/head/intake and luckily that means using OEM heads, OEM intake, and a mild cam, right? Minimal modifications needed to achieve this simple goal. Then, just look at the compressor. Use Matchbot. There is a theorem in fluid mechanics called continuity theorem or law of continuity which simply states that mass flow in must equal mass flow out. What that means to us is the engine's flow rate no longer determines power output. Instead the compressor is the king of power output and we just look at what is going into the engine at some compressor wheel speed to determine mass flow. 50lb/min on a 3L engine is 50lb/min on a 5L engine is both make 500bhp for example. Once we select a compressor to match the volumetric flow rate (cough* VE) of any particular engine the power will be known before we even buy the turbo or install the engine. the work is done before the car is built. That is the worldview.
The shape of the VE curve is the shape of the torque curve- the mild cam puts peak torque somewhere near 4500-5000rpm usually depending on the engine, small displacement engines will rev out 7k sometimes 8k unlike a LS engine where I would limit to 6k for street stuff. When doing the compressor (matchbot) you would take the rpm limitation into account for the application to avoid flowing off the compressor map of course. What you wouldn't want is a torque or VE curve that puts peak torque near redline 6k 7k rpm because the engine will suffer low torque in the mid-range where daily drivers live day to day.

When it comes back to VE there are two perspectives. Engine realistic VE and tuning VE. The realistic engine VE is the torque curve. You simply dyno the car and you can see peak torque, that is peak VE generally speaking.
The tuning VE is different because when we tune the engine there are a number of obstacles which may present a challenge and our only goal is to achieve some a/f ratio regardless of what the real VE is. Just change the numbers to make the desired a/f ratio and don't worry about what those numbers are. Leave the actual VE to your timing and cylinder pressure considerations based on real world dynojet output curve you calculated from power (dynojet calculates power, not torque).
In other words, tuning land is just a/f curve , don't worry about the VE.
VE on the other hand as a peak torque on the dyno tells you where to soften the timing, where cylinder pressure is high, where to be careful with fuel and timing, where to adjust boost if you want to flatten the curve, it is still tuning stuff but it isn't related at all to the actual VE number placed into a VE table for any computer- those are simply injection values to achieve desired a/f ratios.

[SiriusC1024]

Oh I understand the effect of intakes Used to own one of these.
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Talking with you I got some answers. Thanks for another productive discussion.