4G63 4/2 inverted, 18-1, 12-1 etc.Opinions

Hi all

I have an Evo 8 that i converted to Maxxecu over a year ago as i had many changes in mind, you all know how it goes lol

Anyway, for a 450 ish road car, has anyone actually witnessed first hand experience of worthwhile improvements from stock to say 18-1 setup?

When i switched to stand alone, i fitted an 18 tooth trigger disc, removed one of the teeth and also removed 1 from the cam trigger to give me an 18-1 plus the one on the cam, biggest reason i went 18-1 was if i ever lost the cam sensor whilst out on a drive, i would have the ability to limp home in batch fire & waste spark mode, off course this is all when and good IF i carry my laptop....which i normally do! I also did Coil on plug, was a basic home made setup using some Aluminium plate and a set of Denso Toyota Yaris coils, along with other fuel system changes i fitted a set of Bosch 980cc injectors, i felt that was more than enough of ''Modern'ising'' the fuel, ignition and ECU systems, well actually i also switch to E throttle and what an improvement that was! Idle tuning has never been simpler!

What i would like to know is, are there any tangible differences between stock and likes of 18 tooth setups? People say that the extra resolution drastically improves drivability but also reduces the risk of ignition drift. I didn't notice any changes to the way the car drove at low rpm/load and also flat out. Is the timing drift really a big issue on the stock triggering system when moving over to stand alone?? I know this seems a strange question to ask AFTER switching ECUs but its always been a question i wanted to ask. Are there any noticable improvements to Knock control strategies going from stock to 18 tooth and so on?

Any feedback would be appreciated.

Thanks

On a 4G63 It's the difference of the ECU getting an update of the crankshaft cycle position twice per rotation vs 17 times.

Most modern engines have either 36-2 or 60-2 on the crank because it gives much better accuracy or resolution of crankshaft position.

This improves timing accuracy for any system that is performed relative to cycle angle and it also improves pattern detection during startup.

The most noticeable difference is timing drift under maximum crankshaft acceleration. With a low tooth count wheel your timing will advance significantly under heavy acceleration so you either need to run less than ideal ignition advance, or use a transient retard type function if you have one in your ecu. You can easily visually see it with a timing light (set to 0) if you lock the timing in the ecu and give the throttle a hard stab while watching the timing mark. On my evo 7 with a Link ECU I would say you can see around 3degs drift when you do this test. Note however Link has a special trigger mode for the Evo, it uses both the rising and falling edges on the stock crank trigger wheel, effectively giving you "4 updates" per rev, so this drift effect would be twice as large with most other ECU's.

Doing similar tests comparing with other tooth counts over the years, you see much less transient drift with 12T (say 1-2deg max visible with a good timing light), a further small improvement with 24T, then above 24T I have found it hard to tell any difference with this type of test - I suspect the timing light then has more drift than the trigger system. Obviously an engine/drivetrain with lower rotational inertia that can accelerate at a higher rate will exhibit more drift from this effect than a heavy/slow engine too.

Perhaps a little contrary to Scott's comment, I believe the main reason many Modern engines use a 36 or 60 based tooth count nowadays is mostly because they use crank acceleration per cylinder for the misfire detection strategy which is part of the emissions legislation in most regions now. It works well with 60 teeth but at 36 teeth it needs a lot of other qualifiers factored in and is more susceptible to false trips.

Thanks, all makes sense and generally as i suspected and i'm glad i made the decision! Am i correct in thinking that ignition system delay settings within the software can help to reduce this problem or am i completely off?

This would explain why i've seen a substantial variation in timing between a Stock ECU and stand alone ignition maps when running the same setup (same turbo, compression, cams etc etc) When i was prepping a base tune , i will quickly just add here that i am not a professional tuner by any means but however i have been tuning various systems on the road for around 10 years, whilst prepping a base calibration there was so many results for stock setups, as much as 2 to 4 degrees @ say 200 kpa on pump fuel!

Could this also explain why Evo engines visually appear to have such little timing? I know the rod angle etc etc has alot to do with it also, I remember thinking to myself 'this cannot be correct' as i was so used to seeing much more on various other engines.

When we say the timing can drift 3 or so degrees, is this likely to happen under normal driving as opposed to giving it a good throttle stab whilst stationary? 3 degrees is a hell of a lot and i can only imagine that many engines have been destroyed because of this! The Evo platform i wouldnt say 'that' particularly old it makes you wonder just why it had such a poor triggering system? specially when other makes had 60-2, 36-1 etc years before the Evo was launched!

Evo engines really MUST have knock control well setup when switching over to solenoid, and Adam I will go and read up on the feature you mention on Link ecus, seems a wise idea.

I appreciate the input guys, I would be keen to see what Andre's opinion is on the subject.

Another thing, could or would this be the cause of decel or shift knock?

Evo engines just have very efficient heads that allow to get very high BMEP values in conjunction with short block geometry. That's why they have such a small ignition timing.

Attached is Brake Mean Effective Pressure (BMEP) of various modern engines.

Normalizing the engines’ torque output against displacement allows for easy comparison of the efficiency of many different engine designs.

"Am i correct in thinking that ignition system delay settings within the software can help to reduce this problem"

No, the delay is to compensate for the fixed time delay that occurs in the ECU's output circuit and the ignition system. This delay causes a timing variation related to engine speed (since cycle time reduces with rpm but the delay is fixed), not engine acceleration. Timing variation due to a low tooth count trigger is the opposite, it occurs due to acceleration rather than speed.

The only "fix" for the drift caused by a low tooth count trigger is some form of ignition advance compensation referencing crank acceleration. In Link this is called "Transient Retard". It doesnt actually fix the problem that the crank shaft speed and position can change a lot between updates, but it can help reduce the exaggerated advance that occurs during acceleration.

"Another thing, could or would this be the cause of decel or shift knock?"

No, the timing drifts in the retard direction on decel, so again the opposite of what the engine actually needs. Phantom knock on high speed decel is pretty common, I suspect it is probably the clutch pressure plate hitting the cover in a lot of cases, possibly some other backlash in drive splines etc, or perhaps piston slap from the sudden loss of combustion pressure.

Adam - thank you for the detailed reply!

So in a nutshell, the stock triggering setup is bad!

id love to have the Kiggly kit, but i haven’t done the balance shaft delete and probably won’t, the engine is definitely smoother with it in place