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#3: 08-25-2012, 11:13 PM
cryo's Avatar
Title: Authorized Tuning Vendor
Location: Colorado - Cryotune Performance
Car: 08 Spec B now,06specB,2011 STi,2015 WRX
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~Continued from above- ran out of room~

Ignition Spark Timing and You!

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 *ideal gas law* 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.


Pre-Tune Checklist

The first thing to note is a tune will NOT fix any mechanical issues. Mechanical issues should be addressed before any tuning as it will result in extra time spent just to realize the tune cannot be completed without further work being done to the vehicle. If you have any reason to suspect a mechanical issue DO NOT GO FORWARD WITH TUNING before resolving the issue.

1. The quality and level of oil should be checked. If you are near your next oil change service interval you might consider changing it as The tuning process will push the engine harder than daily driving and its cheap insurance.

2. The quality and level of coolant should be checked and addressed as needed.

3. If any fuel components were replaced/upgraded a check should be made to make sure there are NO leaks and everything is seated correctly *ie fuel pump in basket tightly, injectors seated in rail etc*

4. No oil or coolant leaks present.

5. Tires in good condition and not showing cords

6. Depending on how many miles on the car you may think about replacing the spark plugs before the tuning process.

7. Clean your MAF sensor with MAF sensor cleaner.

8. The MOST common issue with these specific cars after any modifications seems to be intake/charge pipe leaks. A pressure test should be performed without question for any setup changed to a FMIC although a simple pressure test/smoke test can eliminate even simple leaks on a TMIC system as well. * a hint for pressure testing is to have a 2ft piece of hose to put up to your ear while the system is pressurized, This allows you to trace all vacuum lines and connections with the other end and actually use this as a stethascope of sorts since a small leak will be VERY LOUD when found this way. It also allows you to get to problem areas like the throttle body coupler. The other thing to have is a spray bottle with a small amount of soap and water to spray on all connections*

These are two diagrams of the basic vacuum system on the LGT/OBXT. I say basic because this follows the 05/06 model but is very similar on 07-09 as well. Thanks goes to Boostin for the diagrams. I may snap actual pics in the future and label EVERYTHING but this will work for now.

This is the Fuel and emission vac diagram

and this is the Turbo,BPV,etc diagram

These are just a start and hope they are helpful to some, again thanks go to Boostin for the diagrams. I have found the throttle body coupler seems to be the most common source of an overlooked leak. I normally suggest looking over every hose for condition *keep in mind 05/06 models now have vac hoses over 7 years old* and ziptie or hose clamp any vac line you have access to for added insurance.



Last edited by cryo; 09-29-2013 at 10:52 AM..
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