Ignition Spark Timing and You!

I didn't see a thread like this so I figured I would type this up.

 

This write up will be based on ignition timing. Its goal will be to be as simple as possible while explaining a pretty in depth subject. At no point is this offering tuning advice but just basing one opinion. Use at your own risk;)

 

The goal will be for people to understand what influence ignition timing has on the engines ability to USE all the air and fuel in the cylinder without creating un-needed stress on the rotating assembly.

 

First thing to mention is the "explosion" inside the cylinder is anything but an explosion. It is a controlled burn designed to ignite the air and fuel at the optimum "Time" before top dead center (BTDC) to push the piston back down after top dead center in the power stroke *in degrees*. This also makes the controlled burn work its best at the ideal time and rod angle to seamlessly push the crank around.

 

The amount of acceptable Timing is directly effected by the octane of fuel being used, cylinder size, compression ratio etc but we will limit it to fuel type for this conversation. Fuel can be considered as*91,93*,100,C16,Meth,E85 etc* for this writeup. The reason for this is the amount of resistance the fuel being used can help to curb knock because of thier properties.

 

The purpose is to build up as much pressure as possible safely and then ignite it at the ideal time keeping in mind it takes a very small amount of time for the spark plug to fire, ignite the mixture and create the flame front across the cylinder before combustion. All of that takes time so you must anticipate it BTDC to have everything happening by the needed angle after top dead center.

 

The Main benefit to higher octane fuels is their ability to cool the cylinder and slow the flame front which allows more time to safely build pressure in the cylinder. This in turn allows you to make more power safely with timing advance as long as hard parts and supporting modifications are present. *obviously given a proper afr as well*

 

Detonation is the killer of engines. Detonation is also referred to as knock, pre ignition, pinging, etc. The audible sound of knock is like bb's in a can but if your hearing this sound the damage may already be done. Its not a good method to tune newer modern cars till you "hear" knock. Detonation can be caused by too much timing advance or too little fuel or both. A pre ignition event can be caused by a few things but the end result is a uncontrolled combustion which reaches much higher pressures and can put quite a bit of stress on the crankshaft and rotating assembly. The worst part is this event is not at the optimum rod angle. Imagine trying to press down the pedal of a bike with all your might when its strait up and down rather then at a slight angle, much harder and rougher on the bearings. A controlled burn creates standard operating pressures in the cylinder where as a pre ignition event caused by pressure or a glowing ember on a plug can ignite the mixture at the wrong time without spark creating a huge pressure spike and shock that will easily tear up a motor.

 

Alternate fuel sources like discussed above can help in this fight by pushing the knock limit a little further or a lot further depending on what it is and what the setup is. At that point you are no longer knock limited and must take caution because the efficiency of the engine/turbo etc will normally fall off before you see any signs of detonation. The goal is to keep timing in line to react to engine load. Timing will normally reduce as load increases and increase with rpm. The reason for this is engine efficiency and the rapid pace of which things are happening as rpms increase. Ideal timing for each car is different even with the same modifications.

 

The goal is to run the least amount of timing to make the most amount of power consistently and safely.

 

I hope this has been helpful to some and please provide any comments, opinions if you would like etc.

 

Dave

Bump for some recent questions my customer have asked.

 

Thanks

 

Dave

Hey Dave,

have you experimented with any of the decel overrun tables for the Legacy?

Thanks for all your write ups on what different things mean with tuning. I have certainly learned a lot from them. I still have one question though, or maybe you will answer it when you respond to my e mail, is the only thing that can cause timing to be pulled detonation? Or is there other factors? Is there that big of a difference between single octane rating points? In Oregon we have 92, not 93 for example.

Thanks for the write up, as technical person in the Sciences world I can appreciate explaining complex matters in common terms. I like the bike crank analogy! Nice briefing. Ill be directing some F/I EJ251/3 folks to this thread from various sites, I get dozen of questions on this topic weekly.

Thanks Dave I always enjoy these threads.

Hey Dave,

have you experimented with any of the decel overrun tables for the Legacy?

 

To achieve what specific goal? didn't want to assume.

 

Brian-

 

Timing will be "pulled" any time the specific knock control system is triggered and trips the limits. Subaru ecu's and knock control system in particular is very sensitive and will pick up low end drive train noise as knock and pull timing. Subarus newer ecu's have actually increased the range in which the ecu "learns" this reduced timing as well.

 

I have seen base timing reduced 4-6 degree's and still have no impact which shows its not benefitting from reducing the timing and just creating more stress due to lack of efficiency.

 

GEE-OTTO

 

I always like physical analogies to rather complicated terms. I'm a visual person and it makes things make more sense.

 

Don't get me started on PID systems and how they are easily explained with a talk about modern day cruise control

 

Dave

To achieve what specific goal? didn't want to assume.

 

 

To reduce the effect of engine braking and adjust when the fuel is cutoff. On some other cars, I've seen ignition timing adjustments available as well, but it appears for the Subaru ECU we don't have that option for overrun.

 

With my lightweight flywheel and cams, when I let off the throttle in 1st or 2nd gear, the car abruptly starts engine braking hard if I am below 3000 RPM.

I had a recent experience where my car wouldn't take timing because I had a boost leak!

Boost leak = turbo spinning faster to produce same PSI = more compression = hotter air

 

As soon as I fixed the leak I was overboosting to 20PSI from my 17 target. WGDC adjusted accordingly.

 

I have a Question for Cryo,

Where I live we only have 90 octane and Race gas and methanol setups. In your experience, how many degrees in timing at peak torque would a tune for a 90 vs 93 be? how many degrees on avg? Coming from the stock JDM map with their lower boost, I'm down by around 8 degrees on my setup.

To reduce the effect of engine braking and adjust when the fuel is cutoff. On some other cars, I've seen ignition timing adjustments available as well, but it appears for the Subaru ECU we don't have that option for overrun.

 

With my lightweight flywheel and cams, when I let off the throttle in 1st or 2nd gear, the car abruptly starts engine braking hard if I am below 3000 RPM.

 

Not sure how I missed this. It may be related to the lower vac caused by the cams but the flywheel isn't helping. What kind of in/hg do you see at idle? Unfortunately there are no timing adjustments in the Subaru ecu related to overrun like you mentioned per say, only based on coolant temp but sometimes trial and error testing is the only way to approach a situation like that. You can adjust the overrun fuel cut counter to test but its full logic is not available for testing.

 

JMLegacy- There is no average timing when it comes to octane points as there are a lot of other variables when it comes to how much timing can be ran safely *ie intake charge temp, flow designs, etc*

 

That's the biggest thing to tuning and testing is finding out where each individual car wants to be based on its particular setup. Your tuner must have decided that 8 was the safest,strongest peak timing he could get away with.

 

Dave

Where I live we only have 90 octane and Race gas and methanol setups. In your experience, how many degrees in timing at peak torque would a tune for a 90 vs 93 be? how many degrees on avg? Coming from the stock JDM map with their lower boost, I'm down by around 8 degrees on my setup.

 

Is it possible to get methanol to a decent price? I was mostly thinking of adding a water/methanol injection to the engine at boost to lower the knock risk and get more power. (this was used already on aircraft during WWII, so it's nothing new)

Not sure how I missed this. It may be related to the lower vac caused by the cams but the flywheel isn't helping. What kind of in/hg do you see at idle? Unfortunately there are no timing adjustments in the Subaru ecu related to overrun like you mentioned per say, only based on coolant temp but sometimes trial and error testing is the only way to approach a situation like that. You can adjust the overrun fuel cut counter to test but its full logic is not available for testing.

 

No worries. The initial enrichment was set to 0 ms on the LGT. I bumped it up to 1.2 ms and it helped a lot. Now, I'm still trying to tackle an issue I've encountered for a long time. When driving slightly downhill at very light throttle, the ECU commands and runs really rich AFRs with my larger injectors while the car is under vacuum. Have you seen any tables that help remedy this? Thanks Dave

JMLegacy- There is no average timing when it comes to octane points as there are a lot of other variables when it comes to how much timing can be ran safely *ie intake charge temp, flow designs, etc*

 

That's the biggest thing to tuning and testing is finding out where each individual car wants to be based on its particular setup. Your tuner must have decided that 8 was the safest,strongest peak timing he could get away with.

 

Dave

Yes, i was aware of this. I was asking in terms of similar setups but different gas. Just to get an idea of how much fuel octane affects timing. But still as you said, there are always more variables.

Is it possible to get methanol to a decent price? I was mostly thinking of adding a water/methanol injection to the engine at boost to lower the knock risk and get more power. (this was used already on aircraft during WWII, so it's nothing new)

 

All the fast subarus our here run water meth injection with some running pure meth. That will be my next move. I plan to first run meth with same boost level to increase power from timing and afr. Then maybe from boost.

 

One popular tuner has a stock legacy block at 400whp at 30 psi. Not sure what turbo. Not sure how long it will last. But I don't got the time nor money for them kinds of experiment

A water/meth injection is relatively easy to create. The crudest variant uses a closed canister that just takes the boost pressure from the manifold to push the water/meth mix into the intake before the turbo and a manual valve to control the mix. Cheap, pretty reliable but not very consistent in behavior.

 

A step up is to use a washer fluid pump and a pressure contact triggered by the manifold pressure - over a certain level of boost the injection comes on. Add valves to adjust the amount injected - and some overpressure bleed solution to avoid popping a hose with water/meth and instead return it to the canister. This will be more consistent in behavior. It may be a good idea to have the pump powered with double safety to make sure that it doesn't get stuck running and fills the engine with water/meth in case something goes wrong.

 

Just be careful with the amount sprayed into the intake, start small and log data to see when you reach the target you need. Added meth means that the engine will be a bit more rich while under boost.

Is it possible to get methanol to a decent price? I was mostly thinking of adding a water/methanol injection to the engine at boost to lower the knock risk and get more power. (this was used already on aircraft during WWII, so it's nothing new)

 

A water/meth injection is relatively easy to create. The crudest variant uses a closed canister that just takes the boost pressure from the manifold to push the water/meth mix into the intake before the turbo and a manual valve to control the mix. Cheap, pretty reliable but not very consistent in behavior.

 

A step up is to use a washer fluid pump and a pressure contact triggered by the manifold pressure - over a certain level of boost the injection comes on. Add valves to adjust the amount injected - and some overpressure bleed solution to avoid popping a hose with water/meth and instead return it to the canister. This will be more consistent in behavior. It may be a good idea to have the pump powered with double safety to make sure that it doesn't get stuck running and fills the engine with water/meth in case something goes wrong.

 

Just be careful with the amount sprayed into the intake, start small and log data to see when you reach the target you need. Added meth means that the engine will be a bit more rich while under boost.

 

Water+meth injection is a wonderful thing.... implemented correctly. What you've mentioned above is NOT the "correct" implementation.

 

Spend the money and do it right. Research Aquamist, and others. Research a LOT before turning any water/meth wrenches. Tuning alone is paramount, and as important as the mechanical setup.

 

People who run a mixture with meth a greater percentage than 50, simply do not understand the process. Really. No matter how "successful" or smart they appear. Water is what does the detonation protection, meth is just to make up for the water's displacement of fuel. Running high percentages of meth is a crutch to increase octane and add fuel above the fuel injector's capacity. But it's the water, not the meth, that's responsible for the reasoning behind water(meth) injection.

 

Injecting a mixture pre-turbo will erode the turbo's impeller. It is not a long-term solution. Some have done it knowing the consequences, for a purpose and a willingness to sacrifice the turbo for racing purposes. But it is not a viable solution for a street solution where reliability is a concern.

You hit all the nails on their heads.

I've done some research and fnd the hfs6 and aem kits to be sufficient. But the more I research the less I want to do it. Too much modifications.

I had hit all the nails on their heads.

I've done some research and fnd the hfs6 and aem kits to be sufficient. But the more I research the less I want to do it. Too much modifications.

 

The modifications aren't bad at all. It's the absolute dedication and awareness of consequences should you fail to be, that are hardest to shoulder.

 

The rewards, the next-level of performance, however, are worth the effort once fully accepted.

I'm hoping someone here might be able to help me with some issues with my timing. I have been getting some FLKC at high loads. I don't think my timing is too high in these regions either. I don't want to pull too much timing at this point. I have attached a learning view, a log where the timing was pulled and my base timing/ advance maps. Thank you for looking.

Learning View_A2WC522N_2014-06-15 20 36 50.csv

Timing.csv

log.csv

If you are custom tuning the vehicle yourself you need to make sure your knock is not being caused by lean air fuel ratio's rather than low timing. If you feel the timing is where it should be *obviously testing will conclude that* you might want to look at fuel and make sure boost is not to high for the setup and rpm

 

Hope that helps.

 

Dave

Thanks for the reply. The fueling doesn't seem to be too high (11.4 afr). I am tuned at 18 psi on my VF52 with a rewired DW65 and stock injectors. It may be that my injectors can't keep up that high though. I have injectors to install but was finishing up my maf scaling for a ks tech intake before installing them. At this point, my maf is within about 3% all around so I might install the injectors and tune them before lowering my timing more. From all of my searching and reading, my timing isn't too aggressive so like you stated, sources point to fueling.

Newbie question here...

 

What exactly happens when the ECU "adds" or "pulls" timing?

 

I'm assuming adding timing is firing the spark later in the compression stroke and pulling is firing it earlier? Or is that backwards?

Increasing Mean Cylinder pressure usually gives more power at the risk of detonation. Increasing or adding timing usually leads to this because the spark fires earlier in the compression stroke.

 

Adding timing =firing earlier

bump to make more available for those looking for a good read.

 

Dave

Any tips or hints on monitoring for knock with Romraider? I finally added the knock sum gauge to Romraider, it would pile up knock sum when I was just free revving. Having knock that low seems unlikely, but having engine noise/vibrations tripping the knock sensor does seem more plausible. Which makes me question the accuracy of it.

Most Subaru's will increment knock sum by free reving and that's normal. Subaru's knock system is pretty complex and there are a couple really good write-ups from cobb on the matter *as well as on the romraider forums*

 

Its pretty accurate at mid to high loads but there are a lot more variables in low load conditions.

 

Hope this helps.

 

Dave