Spark timing for optimum fuel economy

[Extinct]

Has anyone ever taken a look/tested the "optimal timing table" values versus the stock high octane tables (my ride is an '02 LS1, but I assume other gas burners have similar tables) ?

I see some very light load cells have very high timing values, about what I have read elsewhere optimal timing would be.

Anyone up for a testing session, or have the low gas prices got everyone disinterested ?

Also, while you are thinking about it, I am thinking with lean cruise these numbers might even need to go a little higher ?

[harascho]

I am also working on my spark tables. Got a '07 5.3 LMG

I will post the original and my modified tables later.

I am still running, logging and changing the values. I started with +5 additional degrees throughout the whole table. I had to reduce some, others were increased by another +2,3,4 deg

Harald

[harascho]

here is my original and the modified high octan spark table.
If you do some logs don't forget the octan scaler in addition to the KR PID.

The scaler will tell you whether the ECM is still 100% using the high octan table or not.

Harald

My table is still under construction after every testdrive I adjust some areas..

[Tre-Cool]

jesus 50+ degrees of timing!!!

yikes. you probably be better off with keeping timing to around 38~42 degrees and lean off the fuel to about 16:1.

[harascho]

...I thought timing is ok as long as there is no knock activity? And just in case the load is too big the ECM starts using the low octan table..which I left untouched..

The engine loves it and I get better mileage.

Harald

[Highlander]

The only way to really tune this is on a load dyno.

[macca_779]

The only way to really tune this is on a load dyno.

I use a technique where with the DVT control move timing around until you find the most vacuum. Obviously this doesn't work for WOT. But part throttle fuel economy tuning, it works great.

[harascho]

Nice ideas, but what if a dyno is out of reach and the only way to adjust the timing is by driving - logging -- adjusting --- driving----

Imagine this with the narrow German roads, a lifted Tahoe and the Laptop on the center console..... fun stuff..

Harald

[Highlander]

Max vacuum has always been an option, but you would have to log a SPECIFIC route that you can take with pretty much a lot of accuracy in order to find those max vacuum differences. Otherwise there is no better way than a loaded dyno. I have a dyno and its only inertial and I can apply a "brake" load and its still a pain in the butt doing it via the vacuum way.

You can also do it by logging the average TPS with the cruise control engaged. There are many different ways. But the best way is just that one.

[MSURacing]

...I thought timing is ok as long as there is no knock activity? And just in case the load is too big the ECM starts using the low octan table..which I left untouched..

The engine loves it and I get better mileage.

Harald

How much has it changed your fuel economy? You are running about 10 degrees more spark than I do. What type of fuel are you running?

[Supercharged111]

I'm wondering how to determine what the point of diminishing returns (without a dyno) is with regards to low MAP. I have my table maxxed out at 40 degrees right now, I fear going any farther will be less efficient and make the truck less responsive.

[Extinct]

Unless the dyno has regenerative loading, it won't be the best method as inertial dyno's are only meant for WOT burst.

Your best bet is a long, flat road in an area with little wind, tune/adjust AFR and spark for lowest fuel use.

Does that answer your question, or were you looking for something more explicit ?

My problem is there isn't a straight or flat road in this area for 150 miles. :(

[Highlander]

What people need to understand is that NOT always the peak Tq generated by an engine is just before detonation....

You can have gone WAY past your peak torque and not be near detonation... Same goes with max vacuum. There are so many variables that will affect max vacuum while driving that HONESTLY... it is very difficult...

What I do is... lick my thumb... put it in the air... and say... hmm.. it feels like i should put xx amount of timing there for max economy... LOL. In other words... experience, bucking, no bucking and a bunch of other factors that will account to what I feel is right... If i had a loaded dyno, it would be DEAD on for that AFR.

[Supercharged111]

It is for this reason that I am hesitant to advance my timing more than 40 degrees in the low load areas.

[Extinct]

The original question was related to the GM optimal timing table.

[Supercharged111]

The original question was related to the GM optimal timing table.

And their values exceed 40 degrees, so now you see why I'm so torn.

[hymey]

All depends how it feels whilst driving. Better off doing this stuff on the road, not dyno, only a dyno shop will inform you otherwise.

Watch your knock sensors, ensure your ve is spot on, also air temp changes. I only tune at night normally when IATs are more stable then pull timing with the iat table during the day if any knock occurs. Around 4 degrees from knock is optimum.

The biggest thing most tuners don't understand is if the engine is tuned correctly peak cylinder pressure occurs ATDC at the same time regardless of rpm and load. Hence if peak pressure occur at 5*ATDC with 22* timing at 5000 rpm then at 2000rpm with high MAP and timing is 40* then peak pressure will occur at the same 5*ATDC. So in this instance if the peak pressure occurs at TDC knock will result and you lose power, retard to far your at 10* ATDC peak pressure and you lose torque. So adjusting your timing up or down at low rpm and watching real knock and pulling away 5 deg timing will get you in the ball park, then if you retard more and g/cyl falls off you have gone to far, but 5 deg away from knock in cool air gets you right in the ball park.

[Highlander]

I am sorry hymey...

What you are trying to accomplish is correct, but your logic is flawed. There is no way of knowing exactly when peak cylinder pressure will occur for a given rpm/map combination without a dyno (unless some other special equipment is used)... I am not saying it because I have one, because my dyno has NO load control and there is no way I can actually tune part throttle like this correctly...

5º from knock can still be TOO far advanced for a given RPM/MAP combo, specially on the lower cylinder pressure areas... Just as an example.. I have maxed out the idle tables and I have never seen knock at idle, yet... Car was way past it's peak cylinder pressure at those points...

Often times you do see knock on the onset of peak cylinder pressure, but it's not always the case. That is why you need a dyno to see actual torque output to determine the result...

By using your logic.. if i see knock at 29º total advance and pull back 5 degrees I have just lost around 9rwhp on an LSx at WOT. Is that good?

There are only 2 ways of knowing peak cylinder pressures... A special spark plug that WILL measure it or a load dyno. The road is to imperfect (at least here) to actually have a nice reading that will reflect the various scenarios needed to accomplish certain things that can be easily measured on a Dyno, inertial dyno and that is aside from the risk of Pedal to the Metal...

[Highlander]

And their values exceed 40 degrees, so now you see why I'm so torn.

The lower the map usually means there is less cylinder pressure and less torque output as a result. The less cylinder pressure means a slower burn and then you need to advance the timing for it to occur at the point hymey described 5-15º ATDC.

[hymey]

I am very sorry Highlander but you have been mislead

No you don't advance that far at idle. Idle is combination of airflow and timing. I am not talking idle tuning. I am talking driving conditions. You tune for maximum torque at any given rpm and map for best economy and performance. Tuning LS1s I have always been able to get fueling better on the road then dyno 100% of the time you cant get road conditions on the dyno and if you can you have to compensate for it, and trust me I have 1000s of hours of logging. Ramp rates drastically change and alter fueling to the road by a hole 1 afr point at WOT generally. Best to use both dyno and road. Of course you need time to do this and usually at your own expense as it is faster to do it on the dyno then the road, Hence why so may self tuners can tune there car better then any shop, takes time and logging and temp variation to get it right. Many cars I have done have exceeded over 800km per tank by doing so.

Also ur statement there is no way knowing peak VE is far beyond the truth. We have efilive and good PCMs, you can log peak g/cyl in the log and it will show you right there and then. This is also backed up on the dyno. A load dyno at that. If to much timing is put in peak VE drops off dramatically. Its about using the tools at hand and having the knowledge and experience to carry it out. Hence why my peak dyno number tune and best ET track tune vary by a long shot.

I am stating a fact, its correct from a physics and chemistry point of view. And its proven. A dyno can't see this you and I can't. But a well tuned engine will have peak cylinder pressure occuring at the same time. If its to late you lose torque to early you lose torque. When you spark an engine changes as MAP and rpm varies. Maybe the average mechanic cannot comprehend this but its science and we can go much deeper if you like.

You can argue with me all day, but I listen to doctors in physics. I listen and learn.

Again argue the point with me. But there are to many variations to look at. Simply my point is peak pressure always occurs at the same time hence at 100kpa at low rpm your engine requires x deg timing at 5000rpm it needs more advance to fire earlier to ensure that peak cylinder pressure is occuring at the correct moment.

[Highlander]

I am very sorry Highlander but you have been mislead

No you don't advance that far at idle. Idle is combination of airflow and timing. I am not talking idle tuning. I am talking driving conditions. You tune for maximum torque at any given rpm and map for best economy and performance. Tuning LS1s I have always been able to get fueling better on the road then dyno 100% of the time you cant get road conditions on the dyno and if you can you have to compensate for it, and trust me I have 1000s of hours of logging. Ramp rates drastically change and alter fueling to the road by a hole 1 afr point at WOT generally. Best to use both dyno and road. Of course you need time to do this and usually at your own expense as it is faster to do it on the dyno then the road, Hence why so may self tuners can tune there car better then any shop, takes time and logging and temp variation to get it right. Many cars I have done have exceeded over 800km per tank by doing so.

Also ur statement there is no way knowing peak VE is far beyond the truth. We have efilive and good PCMs, you can log peak g/cyl in the log and it will show you right there and then. This is also backed up on the dyno. A load dyno at that. If to much timing is put in peak VE drops off dramatically. Its about using the tools at hand and having the knowledge and experience to carry it out. Hence why my peak dyno number tune and best ET track tune vary by a long shot.

I am stating a fact, its correct from a physics and chemistry point of view. And its proven. A dyno can't see this you and I can't. But a well tuned engine will have peak cylinder pressure occuring at the same time. If its to late you lose torque to early you lose torque. When you spark an engine changes as MAP and rpm varies. Maybe the average mechanic cannot comprehend this but its science and we can go much deeper if you like.

You can argue with me all day, but I listen to doctors in physics. I listen and learn.

Again argue the point with me. But there are to many variations to look at. Simply my point is peak pressure always occurs at the same time hence at 100kpa at low rpm your engine requires x deg timing at 5000rpm it needs more advance to fire earlier to ensure that peak cylinder pressure is occuring at the correct moment.

Hymey... everything you say in this thread is correct... My arguing point is. if you get max cylinder pressure you get max torque and the only true way to find this out is in a dyno...

Using efilive, i haven't had a car have a different A/F on the dyno than on the street and I test them ALWAYS.. they are pretty much DEAD ON.

On Fords, they usually get a tad richer on the street.

My point about advancing timing @idle was to show you that you could advance timing way beyond your max torque output and NOT get any knock.

One thing would be: could you post your HP curves for your best ET vs your best dyno graph?

Maybe the climate on the dyno changes a lot. It has always been my purpose to put the car as far close to street conditions in the dyno to get an accurate tune. Hence why I don't get much issues with it.

[ringram]

Simply my point is peak pressure always occurs at the same time hence at 100kpa at low rpm your engine requires x deg timing at 5000rpm it needs more advance to fire earlier to ensure that peak cylinder pressure is occuring at the correct moment.

Yeah, my understanding is that you want this point to be around 14* ATDC (engine dependant)