Timing - When to pull due to nock

[JacobVH]

So I've been data logging timing on my truck (05 LQ4) trying to see if I can't throw some timing at it. Seems like its happy with +2 advance below converter speed and low throttle (IE low load areas of the curve)

My question has to do with where do you stop with timing? For example, I know that really humid you can typically run 4 deg more timing than in dry weather. Even with the stock spark table I see it pulling up to 3deg of spark in spots. Obviously the average value is about 0.5 to 1deg. Would you guys say drop timing based on average (attempting to get the average spark retard to 0) or drop the timing based on that 3deg? Is it okay if it pulls a little timing every so often (i would sorta assume so based on the fact that the stock tune already pulls timing)

Another great example would be high load (hill in 4th), Lower RPM with the converter locked, and high throttle opening. When I first started tuning it I noticed it pulled a lot of timing but it was just on a few hills (stock timing curve) should I be pulling timing based off of this?

I guess that's to say, is 0 average nock okay, or are you guys focusing on getting absolutely no nock retard at all?

[kingtal0n]

Do not use knock sensors as tuning tools. They are wildly inaccurate and unreliable.

Time an engine based on variables such as volumetric efficiency, rate of rpm, temperature, fuel quality, rod length, and load. Slow rate of rpm, heavy load, high VE = minimal timing

Traditionally, use dynometer to determine max load timing at some temp and fuel quality. Dynojet is a 'medium' load of roughly 3000lbs vehicles. Some dynos can adjust load as desired.

Street vehicles and owner/personal craft, use minimum timing. Dynojet while reducing timing until torque falls out and EGT rises. Set the timing right at the edge where EGT is reasonable and torque is within 3 to 5% of max for that load cell.


temperature affect chemical reaction rate, so if you add timing for peak cylinder pressure, when temp rises later during other conditions it will cylinder pressure spike and blow headgasket or break pistons.
If using high quality fuels as alcohol it will tolerate some 'high' temperature but gasoline will not.

[JacobVH]

I'm not try trying to find max torque spark. The motor is still stock and the computer contains another spark table listing max torque spark values. I'm going to be below those even on 93 because it's a heavy truck.

The stock timing table suddenly drops timing off after stock shift rpm. I'm shifting now at 5300rpm and will be revving my built motor to 6.5k so I've been throwing timing in there seems happy with about 2? per 5300rpm @ WOT

Why not use the nock sensors? assuming I'm sure it's not false nock, isn't the entire point on a street car to add timing trying to reach MTB timing and then if you hit nock before then back off a safe distance?

I'm only wondering because I did some more tuning last night and in certain areas it pulled max 4? on one run, but it only did that once and avg was around 0.5?. Should I just pull timing to remove that 0.5? avg?

Also where I live fluctuating engine Temps aren't a huge concern

[kingtal0n]

max timing for 100% 'VE' (volumetric efficiency) LS style engines from 3,500rpm to around 6,500rpm is about 23 to 24* btdc.
If the engine has a stock cam the VE will drop from say 5,500rpm allowing a bit more timing couple degrees approaching redline as with any modern engine with VE dropping.
A 'cam'd' engine that expects to pull to 6k 7k should stay near 24 max btdc to redline on 93 octane gasoline

A sign of efficiency and dense charge is low timing.
The lower you can get the timing to produce healthy torque and reasonable EGT the better the reliability and longevity.
This is where a hot day and dynojet experiment can help you out.

"MBT" Is confusing even to professionals. I coined the term Minimum Best Timing around 2001 and since then there have been at least 3 variations 'mean brake torque' or 'mean best torque' or whatever else.
The way I Intended MBT to be used for forced induction is like this:
1. Remove as much timing as possible from each load cell until the torque falls out and EGT spikes. This is the edge of minimum timing, the piston is outpacing the expanding gas and the gas is burning while exhaust valve is opening.
2. Add a couple degrees back in to restore torque and drop the EGT. This is "minimum best timing" MBT the way I intended it to be used.
3. Advance a couple degrees from there to determine safety window of fuel. The engine should pick up 3 to 5% torque and power across the board if the fuel quality is sufficient for the compression ratio. The EGT should drop slightly maybe 50 to 75*F on a turbine outlet 1 foot from the turbo for example. I don't use EGT for natural aspirated engines because they don't output the kind of heat a forced induction engine does so I never measured it, you can just tell by the torque dropping on the dynojet it is sufficient knowledge.

If #3 does not pick up 3 to 5% then the fuel quality is barely sufficient for the compression and density, its a sign the engine is already on the edge at minimum timing, not good. This is generally only an issue for forced induction engines running unreasonable compression ratio or extremely high theoretical VE 300%+.

Street cars use #2 setting. Daily drivers, personal craft. When the temperature of fuel/air goes up, or when you get bad gas, or when there is some additional load (Weight the vehicle down one day), or tire size suddenly increases (new tires) etc... anything that interferes with the expanding gas in relationship to the pistons instantaneous velocity at any given point in the compression or power stroke, the #2 setting has some headroom to take care of that issue and the engine can survive. If you've left it with #3 tuning then the additional load or bad gas or whatever will damage the connecting rod bearings and possibly blow the headgasket or take a chunk of piston. Most likely it will simply start to scrape a layer from the upper rod bearings little by little as the compressive force of peak pressure rises and small OEM bearing clearance with thin lightweight engine oil.

Without knowing anything about your vehicle or combo I would still be able to guess how this would go on the dynojet 80*F ambient 90*F iat 93 octane fuel and here is my recommendation / guesstimate at 3,200lbs vehicle weight.
For every +500lbs of vehicle weight remove around 1* of timing.

Since your vehicle is not forced induction it is easier to guesstimate numbers and write the map before driving the vehicle.
from 3,500rpm time it prob like this with a stock camshaft
3500 22
4000 21 <---soft spot for peak cyl pressure (is higher with stock cam and ports)
4500 21.5
5000 22 <---soft spot ends
5500 23 <-advance for the dropping torque/VE
6000 24
6500 24 or 25 <-low torque

With a 'decent size' cam these are prob better
3500 22.5
4000 23
4500 23.5x`
5000 23 <- start pulling out timing for high cyl pressure
5500 22.5 <peak cyl pressure?
6000 22 <peak cyl pressure?
6500 23 <torque falling a little bit
7000 23 <torque falling but at 7k rpm we don't push timing anymore for other reasons, also this should be the richest a/f ratio of the run peak RPM ~11.9 natural aspirated

Carbon buildup, hot plugs, low octane fuel, or oil induction will require reduced timing from these values. Maintain your PCV system and wash the intake manifold and ensure the PCV tube is connected like factory from the air filter tract to the crankcase for WOT pcv to protect the intake from oil induction. Use a brand new pcv valve it is very important and cheap insurance. Never use a breather on the crankcase it will occlude oil to the piston rings over time and create an oil mess/push oil from gaskets. I also recommend a pressure test to ensure leak free crankcase and intake pathways.

notice keep the timing numbers moving. Never use the same number in any cell next to another cell. Even if its just .3 or .5 different up or down. Keep it a moving target. This will help smooth out natural vibrations and perturbations for reasons beyond the scope of this lesson.

Dyno tips:
When you dynojet always use smoothing = 0 for diagnostics. Its okay to post a pretty pic online with smoothing=5 but if you want to use the dynojet for its true purpose you need smoothing=0.
Always get an airfuel curve on the dynojet.
Shoot for 12.0 at wide open throttle peak cyl pressure and try 12.4 and 11.8 also if there is time.
You can subtract 2* from anywhere during testing and look for that drop of torque but do not add more than 1 degree to anything with 24 or more degrees already (never use 26+ degrees of timing in general on any LS style engine)

[kingtal0n]

For clarification,

For every +500lbs of vehicle weight remove around 1* of timing.

This applies only to the vehicle on the road, and it may be a little excessive on the safe side.

On the dynojet, use the numbers posted. On the road, subtract as needed for vehicle weight, anywhere from 0.4 to 0.9* per 500lbs depending on the compression and rpm. Low RPM subtract more than high rpm.
The dynojet simulates a roughly 3000lbs vehicle no matter what the true weight is, but the tire weight and drivetrain does matter. There is some experience needed to know when heavy tires and heavy internal rotating parts *cough 4l80e* require reduced timing. If you are heavy tire and 4l80e then it will take less timing than posted numbers even on the dynojet. This is why the dynojet is powerful, you can add and subtract timing which helps you dial in the vehicles drivetrain by itself then subtract for the real weight of the vehicle on the street a little extra if necessary.

[JacobVH]

For clarification,
If you are heavy tire and 4l80e then it will take less timing

Wow and thanks, that's a ton of information
I am putting ported 799 heads on so better burn and lower timing numbers while still making good power. I also bought TR6 plugs for the new motor, mighty mouse catch can, and I'm going to be tuning for 91 and 87. Flat top pistons for 10.7:1 compression. going to use a ceramic heat coating on the top of those. SUM-8720R1 cam, 6.125 Manley rods, TBSS intake and tb, 1 3/4 headers, late model GM injectors flow tested so I can put the richest ones further back on cylinders 7/8/5/6...
I know I should get better results with stuff set up correctly so that's my aim. Squish should be 0.0380 with current deck height and the gaskets in my kit, that's with a 0.048" fel pro, might have to get something closer to stock which would make it 0.043".

It's a heavy vehicle 6200lbs, 4L80e, and 33s. I've been street tuning doing runs up smaller hills in 1st and 2nd. I might eventually throw it on the dyno to get timing dialed in because it sounds like that's the only real way to do it. It's nice to see some numbers too.

Thanks again, I'm not going to do much more timing adjustments with the stock motor. Maybe a little a little more up top using what you've said where the stock table falls off without much reason.

[kingtal0n]

I'm going to recommend against catch cans and especially breathers for the crankcase. It will eventually lead to oil deposits around the engine, stuck piston rings, cylinder wear, failure. It will take 50k maybe 80k miles so its hard for people to relate these things. Use the OEM pcv instead. Pressure test the crankcase to ensure leak free, it is very important. Use a new PCV valve. I use Supra Twin Turbo PCV valve inline with Chevrolet PCV valve in forced induction applications, OEM Chevrolet pcv is kind of bad. Sometimes I will use dual supra PCV valves for improved PCV flow at idle/cruise. The more crankcase gas you can pull out of the engine while it runs, the longer the engine will last, the cleaner the oil will stay. The shorter the lines and warmer the PCV flow (short, small diameter hoses with hot fast moving fluid) the less crankcase gas will deposit near the intake valves and intake ports. The blowby gas should be inside the cylinder, that is where it came from, the faster you can get it back there the better. A vacuum pump would be ideal of course because then you don't need to recirculate the fluid, but vacuum pumps are extremely maintenance heavy and costly and annoying for street applications.

[JacobVH]

I'm going to recommend against catch cans and especially breathers for the crankcase. It will eventually lead to oil deposits around the engine, stuck piston rings, cylinder wear, failure.

I'm going to have to do some more research into that. I completely understand that the crankcase needs to be under vacuum. And of course with a breather system it will suck in air that's not really clean, won't expel oil, and won't be under vacuum ever

The mighty mouse system I bough has proper check valves though. One regular style pcv check valve that will allow the throttle to put the crankcase under vacuum, and the other is inside the breather system so that should the motor be creating vacuum then it will also close to suck air from the crankcase. the only time this one should be open (aka venting pressure to atmosphere) would be if the throttle is closed and engine is at high rpm with excess crankcase pressure. In this case any excess pressure would push open the first check valve, the 2nd breather check valve is open because there is no throttle vacuum, and the oil is then trapped in the can and excess pressure vented to atmosphere.

I haven't seen any other catch cans like it. Isn't the whole idea of the catch can (or pcv system baffles) to stop oil from being pulled into the intake and coating the throttle body, valves, and sensors?

In theory the system shouldn't do anything different than a normal pcv system, other than the fact that it catches the dirty oil.

I could see why breathers aren't ideal but why would a catch can cause any issues? are you saying that vacuum won't be acting on the end of the catch can tubing of its too long?

[kingtal0n]

It will breath out anytime the crankcase pressure goes over atmospheric which is what you should never have, therefore there should never be a breather on the crankcase.

I know how those cans work and I do not recommend it. The engine will gradually sludge up, eventual wear and failure.
At wide open throttle the blow-by is maximum. This is when the engine tries to rise crankcase pressure the most. This is when you need a powerful suction such as vacuum pump. The OEM use the OEM Air filter to provide the pressure drop for a 0.5" to 1.5" Hg of pressure drop in front of the throttle valve. If you want I can share published papers and other various literature to help explain, I just don't want to drop 10 pictures into this thread about PCV systems if you aren't interested.

[JacobVH]

The design is such that the only time it would vent to atmosphere is if the engine is not creating vacuum and the crankcase builds pressure over atmospheric (which should basically never happen). That being said, I can run the can sealed as well

And i would be interested in more information. Trying to learn as much as can right now.

[kingtal0n]

The design is such that the only time it would vent to atmosphere is if the engine is not creating vacuum and the crankcase builds pressure over atmospheric (which should basically never happen). That being said, I can run the can sealed as well

And i would be interested in more information. Trying to learn as much as can right now.

The engine is always producing pressure over atmospheric when it is running. Blow-by is always happening. While there is pressure over each piston, some leaks into the crankcase through the rings.

Thus we have in a running engine:
Atmospheric pressure + Blow by = More than atmospheric pressure anytime the engine is running if we do not apply a suction (a vent is not suction)


Once you can visualize that, the next thing is to understand a pressure scalar. The two primary components of gas molecular behavior which influence pressure is the kinetic energy (speed) of gas molecules and the number of gas molecules,
https://www.grc.nasa.gov/www/k-12/rocket/pressure.html
https://studymind.co.uk/notes/pressure-in-gases/

I copied the rest from the site to bring out key points:
******
"
→What is pressure in gases?

Pressure in gases refers to the force exerted by a gas on a surface per unit area. It is a measure of the amount of force exerted by the particles of a gas in a confined space.
→What are the units of pressure?

The unit of pressure is the pascal (Pa), which is a unit of force per unit area. Other units of pressure include atmospheres (atm), kilopascals (kPa), pounds per square inch (psi), and millimeters of mercury (mm Hg).
→How does the pressure of a gas change with temperature?

The pressure of a gas is directly proportional to its temperature, according to the gas law known as Gay-Lussac’s law. This means that as the temperature of a gas increases, so does its pressure. Conversely, as the temperature of a gas decreases, its pressure also decreases.
→How does the pressure of a gas change with volume?

The pressure of a gas is inversely proportional to its volume, according to the gas law known as Boyle’s law. This means that as the volume of a gas increases, its pressure decreases, and vice versa.
→What is atmospheric pressure and why is it important?

Atmospheric pressure is the pressure exerted by the weight of the Earth’s atmosphere on the surface. It is important because it affects weather patterns and the behavior of gases and liquids on the Earth’s surface. For example, changes in atmospheric pressure can cause changes in air and ocean currents, which can impact the formation of storms and weather patterns.
→How does pressure affect the behavior of gases in containers?

The pressure of gases in containers can affect their behavior in several ways. For example, if the pressure inside a container is increased, the gas particles will collide with the walls of the container more frequently, which can increase the temperature of the gas. On the other hand, if the pressure inside a container is decreased, the gas particles will collide with the walls less frequently, which can cause the temperature of the gas to decrease.
"
********

So we have the number of gas molecules per unit volume,
and
The speed of gas molecules

to give us a unit scalar pressure

[Fast4.7]

max timing for 100% 'VE' (volumetric efficiency) LS style engines from 3,500rpm to around 6,500rpm is about 23 to 24* btdc.
If the engine has a stock cam the VE will drop from say 5,500rpm allowing a bit more timing couple degrees approaching redline as with any modern engine with VE dropping.
A 'cam'd' engine that expects to pull to 6k 7k should stay near 24 max btdc to redline on 93 octane gasoline

A sign of efficiency and dense charge is low timing.
The lower you can get the timing to produce healthy torque and reasonable EGT the better the reliability and longevity.
This is where a hot day and dynojet experiment can help you out.

"MBT" Is confusing even to professionals. I coined the term Minimum Best Timing around 2001 and since then there have been at least 3 variations 'mean brake torque' or 'mean best torque' or whatever else.
The way I Intended MBT to be used for forced induction is like this:
1. Remove as much timing as possible from each load cell until the torque falls out and EGT spikes. This is the edge of minimum timing, the piston is outpacing the expanding gas and the gas is burning while exhaust valve is opening.
2. Add a couple degrees back in to restore torque and drop the EGT. This is "minimum best timing" MBT the way I intended it to be used.
3. Advance a couple degrees from there to determine safety window of fuel. The engine should pick up 3 to 5% torque and power across the board if the fuel quality is sufficient for the compression ratio. The EGT should drop slightly maybe 50 to 75*F on a turbine outlet 1 foot from the turbo for example. I don't use EGT for natural aspirated engines because they don't output the kind of heat a forced induction engine does so I never measured it, you can just tell by the torque dropping on the dynojet it is sufficient knowledge.

If #3 does not pick up 3 to 5% then the fuel quality is barely sufficient for the compression and density, its a sign the engine is already on the edge at minimum timing, not good. This is generally only an issue for forced induction engines running unreasonable compression ratio or extremely high theoretical VE 300%+.

Street cars use #2 setting. Daily drivers, personal craft. When the temperature of fuel/air goes up, or when you get bad gas, or when there is some additional load (Weight the vehicle down one day), or tire size suddenly increases (new tires) etc... anything that interferes with the expanding gas in relationship to the pistons instantaneous velocity at any given point in the compression or power stroke, the #2 setting has some headroom to take care of that issue and the engine can survive. If you've left it with #3 tuning then the additional load or bad gas or whatever will damage the connecting rod bearings and possibly blow the headgasket or take a chunk of piston. Most likely it will simply start to scrape a layer from the upper rod bearings little by little as the compressive force of peak pressure rises and small OEM bearing clearance with thin lightweight engine oil.

Without knowing anything about your vehicle or combo I would still be able to guess how this would go on the dynojet 80*F ambient 90*F iat 93 octane fuel and here is my recommendation / guesstimate at 3,200lbs vehicle weight.
For every +500lbs of vehicle weight remove around 1* of timing.

Since your vehicle is not forced induction it is easier to guesstimate numbers and write the map before driving the vehicle.
from 3,500rpm time it prob like this with a stock camshaft
3500 22
4000 21 <---soft spot for peak cyl pressure (is higher with stock cam and ports)
4500 21.5
5000 22 <---soft spot ends
5500 23 <-advance for the dropping torque/VE
6000 24
6500 24 or 25 <-low torque

With a 'decent size' cam these are prob better
3500 22.5
4000 23
4500 23.5x`
5000 23 <- start pulling out timing for high cyl pressure
5500 22.5 <peak cyl pressure?
6000 22 <peak cyl pressure?
6500 23 <torque falling a little bit
7000 23 <torque falling but at 7k rpm we don't push timing anymore for other reasons, also this should be the richest a/f ratio of the run peak RPM ~11.9 natural aspirated

Carbon buildup, hot plugs, low octane fuel, or oil induction will require reduced timing from these values. Maintain your PCV system and wash the intake manifold and ensure the PCV tube is connected like factory from the air filter tract to the crankcase for WOT pcv to protect the intake from oil induction. Use a brand new pcv valve it is very important and cheap insurance. Never use a breather on the crankcase it will occlude oil to the piston rings over time and create an oil mess/push oil from gaskets. I also recommend a pressure test to ensure leak free crankcase and intake pathways.

notice keep the timing numbers moving. Never use the same number in any cell next to another cell. Even if its just .3 or .5 different up or down. Keep it a moving target. This will help smooth out natural vibrations and perturbations for reasons beyond the scope of this lesson.

Dyno tips:
When you dynojet always use smoothing = 0 for diagnostics. Its okay to post a pretty pic online with smoothing=5 but if you want to use the dynojet for its true purpose you need smoothing=0.
Always get an airfuel curve on the dynojet.
Shoot for 12.0 at wide open throttle peak cyl pressure and try 12.4 and 11.8 also if there is time.
You can subtract 2* from anywhere during testing and look for that drop of torque but do not add more than 1 degree to anything with 24 or more degrees already (never use 26+ degrees of timing in general on any LS style engine)

More BS from kingtalon at its finest. Vehicle weight has very little to do with timing advance, not some ball park guideline. On the L31s for example a 1500 truck had the same exact timing advance table as a P30 box van roach coach that weighs 2-3x as much.

The knock sensors are also pretty effective at telling you when things are out of whack. While you can lose power in some cases and not reach the point of detonation it is extremely unlikely with an engine running pump gas under a load in a heavy truck. Notice his timing recommendation was for a 3,200 lbs car and he said pull 1 degree for every 500 lbs. His recommendation would quickly have a truck pulling a trailer with too little timing to even run.

Then for your 2 cells together with the same values BS, GM has millions of vehicles running down the road with that exact setup in the stock tuning and they run fine. I have a 3 whole rows of the timing table reach a specific value on my 383 and it runs great. Mine are at the same value because that happens to be the maximum timing advance allowed by a V8 distributor setup. Every tune I have ever done also has the idle area flat lined to prevent timing changes that would negatively affect the idle as well. I guess you believe that engines did not run for nearly 100 years before computers became mainstream on timing advance setups that had physical stops for both centrifugal and vacuum advance.

[kingtal0n]

Vehicle weight is everything to the rate of change of the piston velocity which is everything to the rate of chemical combustion reaction. This is high school chemistry concept combined with undergrad engineering concept.

Expanding gas with a slow accelerating piston = high pressure
Expanding gas with a fast accelerating piston = low pressure

Very simple and easy to understand if you can visualize the concept. Engine load changes piston rate of change.

No reputable tuner will tune using knock sensors. That is just a joke, now you comedian.

Timing cells is a control theory concept. You can't put the same number into two side by side cells for something like ignition timing which is based on a mechanical input converted to wave form interpretation in a computer which expects to control a mechanical device from frequency domain without expecting a + and - variation in the output of frequency driver and mechanical device.
By altering the values the linear interpolation guarantees a smooth transition without + and - variations. Instead, they will all be - or +, not both. It will smooth perturbations and oscillations in the driver AND mechanical device.


I know people do stuff all the time thats bad for them. Smoking for example, and drugs, lots of people smoke and do drugs. A long time ago people didn't know smoking was bad for health.
Just because 'people' do stuff and copy each other doesn't make it safe. There are many bad habits for health of body and engine which people do not realize yet.

If you follow my directions carefully it will result with ideal engine operation. Combustion engines are antiquated, this technology is really old and obsolete. I am like an archeologist at this point trying to help people preserve their precious antique installations, my teaching is for longevity, reliability, cleanliness, above all else, which matters for antiques. The tuning methodology I presented here isn't for racing and peak power; it is for minimum cylinder pressure and lowest engine stress while maintaining a reasonable approach for controlling EGT and energy throughput.

We let the forced induction make the power and keep the timing out of it for long engine life by determining the lowest rate of change (slowest gear ratio for max output condition) and using a timing profile which is acceptable for the worst possible conditions (for high temp we choose minimum timing) with the slowest rate of change (high engine load = heaviest weight with longest gear ratio)

[SiriusC1024]

Timing cells is a control theory concept. You can't put the same number into two side by side cells for something like ignition timing which is based on a mechanical input converted to wave form interpretation in a computer which expects to control a mechanical device from frequency domain without expecting a + and - variation in the output of frequency driver and mechanical device.
By altering the values the linear interpolation guarantees a smooth transition without + and - variations. Instead, they will all be - or +, not both. It will smooth perturbations and oscillations in the driver AND mechanical device.

This is true for controls, but the crank position sensor doesn't have the resolution of an encoder. There's a lot of deadband. If the CPS had encoder resolution, and you could measure torsional vibration through it, that'd be cool.

[Alvin]

Forgive me.. I have not read the entire thread as it is a bit wordy.

When I tune a car the timing table might have -2, 0, 2, 5, 12, + more or less timing all in different spots. If it is knocking on the freeway with the converter locked up trying to pass someone without a downshift, that doesn't mean it couldn't still use some timing at wide open.

In short.. Add timing where you can, take it away where it knocks. Stop adding timing when you stop noticing a difference. If the knock is consistent/repeatable than timing should be pulled. It isn't unusual to see a random blip of knock even on a modest timing table.

[kingtal0n]

This is true for controls, but the crank position sensor doesn't have the resolution of an encoder. There's a lot of deadband. If the CPS had encoder resolution, and you could measure torsional vibration through it, that'd be cool.

wow somebody with a brain


Your observation emphasizes my point about resolution. Spark cannot be perfect from ECU driver- 30 degrees is 30.005, 29.984, 30.0914, 30.0554, 30.0395, 30.1482 etc...
Heating increases chemical reaction rate but it does not adjust starting point.

Engine parts are an energy storage with a frequency, gas expanding during piston ascent is a spring-load on bottom end components, there is an frequency(rpm in this case) response between chemical rate of expanding gas and energy absorbed and released by the piston load/wristpin/rod/fluid film.
Some energy is absorbed and returned unrelated to combustion but this energy must be delivered in phase with combustion or it will negatively influence the energy provided by combustion. Like parasitic loss from an accessory. During compression after a spark some internal energy is lost and more will be lost if the spark started sooner.

If the engine's rate is increasing then the same chemical reaction as previously will result with a higher cylinder pressure prior to TDC and a lower pressure after TDC (it will stress rod bearings and reduce integral torque).

When we consider something like 40 events per second for a cylinder and all of them have random positive or negative start times while the engine rate is always positive, this is where the issue of phase and damping can create oscillations in torque and engine parts.
if the engine was steady state with no macroscopic rate of change, the issue resolves itself because + and - start times with + and - rate of change will self damp the system as the engine rapidly speeds up and decelerates to maintain some RPM and output figure at constant load.
When we attempt to increase mechanical frequency the rate of change becomes positive. In response our chemical reaction rate also becomes positive which is why combustion keeps up with RPM, but if the timing/starting rate does not choose to become consistently positive or negative the system will randomly gain and lose internal energy shortly after onset of chemical combustion causing oscillations.


I base partly on observations after dynojet tuning many vehicles, sometimes an torque oscillation can be fixed by simply adding timing difference between cells.
Many people intuitively add timing anyways as rpm rises, and remove in response to peak torque, but still many do not and probably should.

Here is an example of torque oscillation likely caused by cylinder pressure rising and falling in response to rotating assembly rate change
torqueoscilation.jpg

As evinced by the torque curve in the dynojet- the engine peaks out with some rate but then rapidly decelerates and regains rate, like a spring damping system that lost energy and regained slowly out of phase.
1200px-Forced_Vibration_Response.png

Notice power never actually falls, frequency rate only slows down. We see apparent boost pressure does not fall and combustion continues. There is no apparent drop of spark at similar torque values with higher frequency. I am not saying we have accounted for every possibility but, to me,

It looks to me like a lack of damping
Damped_Free_Vibration.png

We add damping by always changing the timing setting to vary between cell linear interpolation. It will guarantee that despite imprecise starting point for combustion per second, there will always be a forward or reverse momentum energy storage between cylinder events which damps the output.

[SiriusC1024]

wow somebody with a brain


Your observation emphasizes my point about resolution. Spark cannot be perfect from ECU driver- 30 degrees is 30.005, 29.984, 30.0914, 30.0554, 30.0395, 30.1482 etc...
Heating increases chemical reaction rate but it does not adjust starting point.

Engine parts are an energy storage with a frequency, gas expanding during piston ascent is a spring-load on bottom end components, there is an frequency(rpm in this case) response between chemical rate of expanding gas and energy absorbed and released by the piston load/wristpin/rod/fluid film.
Some energy is absorbed and returned unrelated to combustion but this energy must be delivered in phase with combustion or it will negatively influence the energy provided by combustion. Like parasitic loss from an accessory. During compression after a spark some internal energy is lost and more will be lost if the spark started sooner.

If the engine's rate is increasing then the same chemical reaction as previously will result with a higher cylinder pressure prior to TDC and a lower pressure after TDC (it will stress rod bearings and reduce integral torque).

When we consider something like 40 events per second for a cylinder and all of them have random positive or negative start times while the engine rate is always positive, this is where the issue of phase and damping can create oscillations in torque and engine parts.
if the engine was steady state with no macroscopic rate of change, the issue resolves itself because + and - start times with + and - rate of change will self damp the system as the engine rapidly speeds up and decelerates to maintain some RPM and output figure at constant load.
When we attempt to increase mechanical frequency the rate of change becomes positive. In response our chemical reaction rate also becomes positive which is why combustion keeps up with RPM, but if the timing/starting rate does not choose to become consistently positive or negative the system will randomly gain and lose internal energy shortly after onset of chemical combustion causing oscillations.


I base partly on observations after dynojet tuning many vehicles, sometimes an torque oscillation can be fixed by simply adding timing difference between cells.
Many people intuitively add timing anyways as rpm rises, and remove in response to peak torque, but still many do not and probably should.

Here is an example of torque oscillation likely caused by cylinder pressure rising and falling in response to rotating assembly rate change
torqueoscilation.jpg

As evinced by the torque curve in the dynojet- the engine peaks out with some rate but then rapidly decelerates and regains rate, like a spring damping system that lost energy and regained slowly out of phase.
1200px-Forced_Vibration_Response.png

Notice power never actually falls, frequency rate only slows down. We see apparent boost pressure does not fall and combustion continues. There is no apparent drop of spark at similar torque values with higher frequency. I am not saying we have accounted for every possibility but, to me,

It looks to me like a lack of damping
Damped_Free_Vibration.png

We add damping by always changing the timing setting to vary between cell linear interpolation. It will guarantee that despite imprecise starting point for combustion per second, there will always be a forward or reverse momentum energy storage between cylinder events which damps the output.

I mean you could've just said feedforward control

You gotta work on brevity.

The pinnacle of science, the LHC, is basically monkeys smacking rocks together to see what's inside.
Your cancer research is just running freezer burned bacon and tide pods through a food processor.

When you say it like that, people are automatically more curious and engaged because it can't be that simple.
https://www.inc.com/bill-murphy-jr/h...ersuasive.html

Remember: KISS