Well, it's been a year and I'd still like to know.
I logged last night and had 23degree's peak timing.

I heard anything over 20 is great. So I would say you are ok

There is some good information to be picked out of this one.


http://www.dsmtalk.com/forums/showthread.php?s=&threadid=115192&highlight=timing+optimum+fuel

PieEyedPiper said:

What is ideal?

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The exhaust temps start running hot on my car if I pull the timing down much below 15 degrees. So I would say as long as you're above that range, everything is fine. 23 degrees is a good amount of timing to be making. Just watch to make sure the timing is steadily increasing without dips in it due to knock.

ericbev said:

There is some good information to be picked out of this one.


http://www.dsmtalk.com/forums/showthread.php?s=&threadid=115192&highlight=timing+optimum+fuel

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Quick question: They talk as if there's one timing advance in that thread. This has to be RPM-dependent, as the burn speed of the fuel is fixed for a given condition, but the speed of the piston is not. At higher RPM, you need more timing advance to get peak pressure at the correct point ATDC, because the piston is moving faster. At lower RPM, you need less advance, because the motor is moving slower.

What am I missing? Those guys surely know what they're talking about, but they all talk in terms of one advance number. Is it an advance at a specific RPM that they're talkinga bout?

kenamond said:

Quick question: They talk as if there's one timing advance in that thread. This has to be RPM-dependent, as the burn speed of the fuel is fixed for a given condition, but the speed of the piston is not. At higher RPM, you need more timing advance to get peak pressure at the correct point ATDC, because the piston is moving faster. At lower RPM, you need less advance, because the motor is moving slower.

What am I missing? Those guys surely know what they're talking about, but they all talk in terms of one advance number. Is it an advance at a specific RPM that they're talkinga bout?

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They mean WOT when full boost is achieved. More importantly (for power potential/damage risk) in the upper RPM range where peak power/cylinder pressures usually occur.

So what is the expected timing pull when you first hit WOT? Mine will pull down to 4-5 degrees between 2800-3400 rpms then climb a nice smooth line to 18 degrees. Does this mean it is getting high counts of knock when full boost first comes on?

hottboost said:

So what is the expected timing pull when you first hit WOT? Mine will pull down to 4-5 degrees between 2800-3400 rpms then climb a nice smooth line to 18 degrees. Does this mean it is getting high counts of knock when full boost first comes on?

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As I understand it, the ECU bases its base timing curve on airflow rate and RPM. Lower rpm gets a more retarded timing value than higher rpm (because the piston is moving slower, and it takes longer for the piston to get to the proper ATDC crank angle for maximum torque, so the spark has to happen later). When you hit full boost (3200ish rpm), the flow rate goes through the roof which puts you in a more retarded point on the map (because the ECU is stock tuned to avoid knock at higher flowrates at one rpm value by retarding timing more than it does at a lower flowrate at that same rpm value). So when you do a 3rd gear pull, you start out on a normally aspirated looking timing curve until boost starts to come on. Up to that point, the timing will be advancing a bit due to the increasing rpm. When the turbo starts to boost, the airflowrate starts to increase more per 100rpm than it was when unboosted, so the timing starts to get pulled/retarded more. When you are first at full boost, you're at a very high flow rate and very low rpm, so the timing is most retarded at that point. After that, the rpms go up, but the boost does not, so the timing starts to advance all the way to redline (unless you get high enough knock counts for the ECU to pull more timing).

I'm not sure if 4* at first full boost is low, normal, high, or what, though.

PieEyedPiper said:

I've made several runs on the logger and have found my peak timing at WOT to be anywhere from 19-24 depending on ambient temperature and boost levels.

What is ideal? is higher always better?
Thanks.

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Higher isn't always better. If the engine wasn't detonation limited, then power would fall off at some point. The goal is to create the maximum amount of cylinder pressure at 16 degrees atdc, but in most cases that's not going to happen on pump gas, especially in a forced induction application. The only way to find out what works best is to get some dyno time on a load holding dyno.

First of all, great discussion guys. I've been waiting a year for this!!

kenamond said:

As I understand it, the ECU bases its base timing curve on airflow rate and RPM. Lower rpm gets a more retarded timing value than higher rpm (because the piston is moving slower, and it takes longer for the piston to get to the proper ATDC crank angle for maximum torque, so the spark has to happen later). When you hit full boost (3200ish rpm), the flow rate goes through the roof which puts you in a more retarded point on the map (because the ECU is stock tuned to avoid knock at higher flowrates at one rpm value by retarding timing more than it does at a lower flowrate at that same rpm value). So when you do a 3rd gear pull, you start out on a normally aspirated looking timing curve until boost starts to come on. Up to that point, the timing will be advancing a bit due to the increasing rpm. When the turbo starts to boost, the airflowrate starts to increase more per 100rpm than it was when unboosted, so the timing starts to get pulled/retarded more. When you are first at full boost, you're at a very high flow rate and very low rpm, so the timing is most retarded at that point. After that, the rpms go up, but the boost does not, so the timing starts to advance all the way to redline (unless you get high enough knock counts for the ECU to pull more timing).

I'm not sure if 4* at first full boost is low, normal, high, or what, though.

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Also very good information. I am curious too though what is a normal "dip" in timingwhen you first hit WOT. Personally I get down to a low of about 3-5* degreee's during the 2300-3200 rpms range. Similar to the poster above.

GVR4592 said:

Higher isn't always better. If the engine wasn't detonation limited, then power would fall off at some point. The goal is to create the maximum amount of cylinder pressure at 16 degrees atdc, but in most cases that's not going to happen on pump gas, especially in a forced induction application. The only way to find out what works best is to get some dyno time on a load holding dyno.

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So are you saying I am making my peak horsepower when I'm at 16*? And that anything past that is just due to decreased load/airflow from my T2small?
I've notice most of all the fast cars, run timing sooooo much lower than that. I've seen amazing output at 0 timing advance on one car, and up to about 15-16 on others. Never higher.

PieEyedPiper said:

First of all, great discussion guys. I've been waiting a year for this!!


Also very good information. I am curious too though what is a normal "dip" in timingwhen you first hit WOT. Personally I get down to a low of about 3-5* degreee's during the 2300-3200 rpms range. Similar to the poster above.

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If you're not seeing any knock, then the timing will be whatever the ECU timing map has for that flowrate and that rpm. The flowrate will depend on the compressor wheel, the level of boost, the IC efficiency, pressure losses in the intake, cams, etc. The ECU's timing map is basically a record of when you can safely spark given a certain amount of air/fuel in the CC when the motor is at a certain speed. A bigger turbo will cram more air in there, so the ECU will be looking at a different point on the map than for a smaller turbo cramming less air at the same rpm. However, if you're overheating that charge, then you'll get knock, and the ECU will pull timing to compensate (so you're not on the map at that point). So "normal" depends on your setup.

PieEyedPiper said:

So are you saying I am making my peak horsepower when I'm at 16*? And that anything past that is just due to decreased load/airflow from my T2small?
I've notice most of all the fast cars, run timing sooooo much lower than that. I've seen amazing output at 0 timing advance on one car, and up to about 15-16 on others. Never higher.

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No. But I'll give GVR4592 first dibs on answering why.

GVR4592 must be out to lunch, so I'll go ahead (sorry). He can correct me and add what I've left out.

The timing numbers you see in your log are the time when the spark goes off. These are measured before top dead center (BTDC).

The 16* is when you want peak cylinder pressure to occur. This is after top dead center (ATDC).

It takes time for the air/fuel charge to burn. As it burns, the pressure rises to some maximum level then drops back down - all pretty smoothly if you have no knock.

You want that peak pressure to occur when the piston has already gone through TDC and then 16 more degrees.

Remember that the time it takes for the crank to turn from 5* BTDC to 16* ATDC will get shorter and shorter as RPM increases. Therefore, at higher rpm, you need to spark sooner (advance the timing more) so that you have enough time for the peak cylinder pressure to build up to its peak at 16*ATDC.

The base timing map is kind of trying to do this, but it's not set up for peak torque. It's set up for good torque and good emmissions and good fuel economy - a balance of things like that. If you wanted to, you could keep everything stock except for a piggyback unit and tweak the timing curve and get more power out of the motor at the same T25 stock boost...but that's not as fun as tuning with a huge turbo, 25psi boost, etc.

Well that makes me feel alot better about my logs then. Thats kinda what I had gathered through other post and just base mech. knowledge but the more input the better as Ill be doing my 550's and safc this weekend and will want to start running higher boost.

I think you guys are thinking too much about this. Ask the best tuners around and they will say:

a- depends on the application
b- test and tune

You can come from the timing school of thought or the boost school of thought. Being pick your timing and raise the boost until there is knock and then back off a little, or pick your boost and raise the timing until there is knock and then back off.

Basically I don't care if I'm running 25* and 15psi at WOT, or 15* and 25psi, whichever gets the most HP is what I'm going with. Make sure you have no knock, set your boost where your turbo functions best and then start messing with the timing.

I do know that running 30-40psi you most likely won't be running 20* of advance. Again, if one is high the other isn't, most likely, and most people see benefit from running more boost, so in turn timing goes down.

And for "normal" timing when boost hits, I'm around 10-12 I believe (I'll check some logs). 4 degrees is pretty darn low.

Alright Ive got a good question then. I pulled logs from 14PSi -18PSI and it still pulled to 4-5* as full boost came on. Would it be knock. Everything is in profile except I havent did the 550's or Safc yet.

hottboost said:

Alright Ive got a good question then. I pulled logs from 14PSi -18PSI and it still pulled to 4-5* as full boost came on. Would it be knock. Everything is in profile except I havent did the 550's or Safc yet.

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Your airflow is probably pretty decent. With stock injectors you are most likely lean and knocking. Well, at 18psi I can almost guarantee it.

You'd be much better off with either DSMlink or a wideband. Even after you do injectors and an AFC you will never know your airflow, knock counts, or AF ratio. If you are serious about getting a good tune, you'll have to pony up and be able to monitor at least one of these. Or you could just get a knock sensor I guess. Pain to keep an eye on or you will have to find something that will feed into the datalogger so you know what knock count is with what RPM.

If you are ok with being "close enough" put in the injectors and AFC, set to a base figure and then keep turning the AFC down until your timing stops getting better.

Im pretty sure my datalogger does airflow. IF I REMEMBER RIGHT IT WAS LIKE 27.98. Again If I remember right. I am going to tune it as much as I can and then I live near a dyno shop so Ill probally have them do some dyno work at that point. Or I might break down and buy a wideband o2. Also thats exactly what I was going to do when I tune.

GVR4592 must be out to lunch, so I'll go ahead (sorry). He can correct me and add what I've left out.

The timing numbers you see in your log are the time when the spark goes off. These are measured before top dead center (BTDC).

The 16* is when you want peak cylinder pressure to occur. This is after top dead center (ATDC).

It takes time for the air/fuel charge to burn. As it burns, the pressure rises to some maximum level then drops back down - all pretty smoothly if you have no knock.

You want that peak pressure to occur when the piston has already gone through TDC and then 16 more degrees.

Remember that the time it takes for the crank to turn from 5* BTDC to 16* ATDC will get shorter and shorter as RPM increases. Therefore, at higher rpm, you need to spark sooner (advance the timing more) so that you have enough time for the peak cylinder pressure to build up to its peak at 16*ATDC.

The base timing map is kind of trying to do this, but it's not set up for peak torque. It's set up for good torque and good emmissions and good fuel economy - a balance of things like that. If you wanted to, you could keep everything stock except for a piggyback unit and tweak the timing curve and get more power out of the motor at the same T25 stock boost...but that's not as fun as tuning with a huge turbo, 25psi boost, etc.

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That pretty much sums it up. In the end it doesn't really matter because without complete control of ignition timing and a load holding dyno, you won't get optimal results.

weith1111 said:

I think you guys are thinking too much about this.

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I find it helpful to know what's going on and why. Without this, you lack intuition into what might help and why. I was just explaining jargon and basic timing principles. Nothing wrong with folks understanding what timing advance means and why it gets larger when you go up in RPM at fixed boost. It also helps me solidify my understanding by explaining it to someone (and if I'm wrong, I find out about it pretty quick!).

weith1111 said:

Ask the best tuners around and they will say:

a- depends on the application
b- test and tune

You can come from the timing school of thought or the boost school of thought. Being pick your timing and raise the boost until there is knock and then back off a little, or pick your boost and raise the timing until there is knock and then back off.

Basically I don't care if I'm running 25* and 15psi at WOT, or 15* and 25psi, whichever gets the most HP is what I'm going with. Make sure you have no knock, set your boost where your turbo functions best and then start messing with the timing.

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Excellent description! Both airflow and timing can be tinkered with, and you just try to find the combo that gives peak performance but with a safety margin (unless you're one of those hard-core guys who rebuilds the motor for each weekend at the track).

weith1111 said:

And for "normal" timing when boost hits, I'm around 10-12 I believe (I'll check some logs). 4 degrees is pretty darn low.

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What boost are you running? I get 12* when boost hits, but I'm stock exhaust still and only 11psi. 4* sounded kinda low, but if his airflow is much higher, maybe that's just what's on the stock map. Anyone have the stock timing map data?

And hottboost, air flow (cubic feet per minute) from your logger doesn't tell you the density of the intake charge. The ECU has combined the airflow numbers with other information to get mass flowrate, I believe, and that's what it uses when referencing the timing map. If you had a pressure and temperature sensor in your mass that you could see and log, then you could compute mass flowrate from these values, the volume flowrate, and the physical properties of air.

If you run your own aftermarket ECU, you can measure these, see them in the logging tool that comes with the ECU and design your maps with temperature as an additional parameter (not just mass airflow and RPM). Then you can account for weather fluctuations, boost changes, etc. to get low-knock timing maps.

Got ya! I pulled runs from 14PSi-18Psi. I also reset the ecu and it sill pulled 4-5*! I have 3in dp and cat and 2.5in cat back. I would also like to know the stock timing map. The reason I am confused is because I have always thought if you have a nice timing curve with no dips as rpms rise then you were good.

kenamond said:

I find it helpful to know what's going on and why. Without this, you lack intuition into what might help and why. I was just explaining jargon and basic timing principles. Nothing wrong with folks understanding what timing advance means and why it gets larger when you go up in RPM at fixed boost. It also helps me solidify my understanding by explaining it to someone (and if I'm wrong, I find out about it pretty quick!).

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I didn't mean it in that way, like who cares, I mean it in the way of you can talk about this for hours on end "well 22* of timing with 19psi on an evoIII in a 2800lb awd dsm will blah blah", but really, like noobs always ask "how much boost can I run" there is no paper answer. There is no perfect timing number. What elevation are you at? How much abuse has your motor taken? How many boost leaks do you have? Is your fuel exactly the same as mine? The list goes on forever. T&T it, that's how you will find out the best timing for your motor.

kenamond said:

What boost are you running? I get 12* when boost hits, but I'm stock exhaust still and only 11psi. 4* sounded kinda low, but if his airflow is much higher, maybe that's just what's on the stock map. Anyone have the stock timing map data?

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I try to keep it under 20 because I still have a SMIC and it gets wrecked after 5 seconds of WOT. Well I don't drive it anymore because it's going under the knife again and will have a FMIC when it awakes, but I did run 18-20psi.

kenamond said:

And hottboost, air flow (cubic feet per minute) from your logger doesn't tell you the density of the intake charge. The ECU has combined the airflow numbers with other information to get mass flowrate, I believe, and that's what it uses when referencing the timing map. If you had a pressure and temperature sensor in your mass that you could see and log, then you could compute mass flowrate from these values, the volume flowrate, and the physical properties of air.

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Possibly depends on the logger, and I'm not sure of the details, but I'm pretty sure your aiflow numbers aren't actual. I have pocketlogger and it shows airflow but it's not reading the right info. A search on dsmlink/loggers and airflow would probably reveal why this info is bogus. Kenamond may have it right.

weith1111 said:

Possibly depends on the logger, and I'm not sure of the details, but I'm pretty sure your aiflow numbers aren't actual. I have pocketlogger and it shows airflow but it's not reading the right info. A search on dsmlink/loggers and airflow would probably reveal why this info is bogus. Kenamond may have it right.

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I'm thinking the logger flowrate is just the translated hertz value from the MAS, so it's the volume flow rate through the MAS, but since you don't know the density of the air passing through the MAS, you don't know the mass airflow rate through the motor. You need temperature, pressure, and volume flow rate at one location in the intake tract to deduce mass flowrate.

I fully understand what you mean. But in order to tune properly you have to understand all varaibles that effect it. Obviously Im still learning but you have to ask questions in order to understand. As I have been seeing, I am going to have to go with dsmlink to do it right. Just have to save the $! It realy doesnt matter what aspect of a car you are talking about, EACH CAR WILL BE DIFFERENT. THANKS ALOT FOR THE GOOD INPUT!!

So, after reading this thread, I'm wondering if there is an advantage in advancing my base timing a few degrees (3-5*?)

I have an E3 @ 15psi and stock injectors, 190LPH and rewire but no fuel tuning. I don't see any knock, and my idc's hit around 100% just barely at the top of 3rd...

When I bought the car it knocked all over the place at WOT, so I took it to mitsu to check it out and they found that the timing was all the way advanced so when it did knock, the ecu had no room to retard timing. So they put it back to stock and the knock dissapeared. It might be my imagination, but it felt much quicker while it was advanced, at least it did before I began adding boost and saw the high knock counts.....

If I that did advance it that amount to make more power, it sounds like I'd have to retard it later on when I get injectors and chip/dsmlink/afc. Am I understanding this correctly?