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Ive noticed alot in the two courses ive done so far that when we are tuning ignition timing we either find the torque limit or knock limit of the engine. This makes sense to find this limit pull timing back say 2 degrees to give a nice safety margin for knock, but what about other factors that go along with peak cylinder pressure like lifting heads and such. The reason i ask ill be tuning a 2.0l 3sgte with a gtx2860 running E85 and shooting for around a responsive 200awkw. With this setup knock shouldnt be an issue (gotta love ethanol) The engine is freshly rebuilt but not anything crazy. Its really just a fresh standard engine. Essentially what im getting at is ill be trying to make this power as safely as possible and with that in mind would it safer to run higher boost with less timing to get the same amount of power but with lower peak cylinder pressure but a wider average cylinder pressure? Or am i totally off base here and 200awkw with 15psi and 18 degrees of advance the same amount of stress on the engine as 20psi with say 12 degrees of advance. (Figures are just an example)
I tune alot of Ethanol stuff and generally approach it this way when playing with new setups.
- Start with the timing 4-5 degree's from where I 'know' it'll be getting close to MBT (16-20* on most 4cyls at moderate boost levels).
- Use boost first to get the turbo up around its efficiency range, running boost pressure relative to what the usage of the car is. (You can have a pretty good idea to start with by modeling it all with the compressor map anyhow.)
- Once you are happy with the boost curve, AFR's are in the ball park, start feeding some timing back into the motor to see how it reacts.
If you are way off the mark timing wise, you'll see boost drop as the power and torque increase. Keep going til the gains start to drop off and leave it a degree or so from there.
- If the motor is a standard refreshed job, just keep an eye on the torque levels down low, as loading things up a little to much can have some ill effects on rods. You want a nice steady / smooth torque curve.
Cylinder pressures from poor / incorrect tuning will do way more damage than boost pressure alone will, especially on a forgiving fuel such as Ethanol.
I've run 4G63's to ~440wkw at 43psi on a 62mm turbo using the stock headgasket and 2000 (entry level) head studs when everyone has stated you need o-rings etc. If you are gentle on the tune, approach it methodically and things like mis-fires, etc under control, you'll be fine.
Thats what I thought
Essentially You can get 200awkw in different ways but its better to use more boost than timing and feed it in progressively
Wow id love to see that 4G with 41psi. Those engines can seriously handle power well.
I know the 3S can handle decent power but im still fairly terrified of the timing table
Within reason it's cylinder pressure that generates torque so regardless whether you're using more boost and less timing or vice versa, your peak cylinder pressures are likely to be very similar assuming engine torque is the same. If you're dealing with an engine that you expect to be the mechanical limitation on how much power you can make, the approach I'd suggest using is to artificially limit the peak torque the engine makes. You can do this by pulling timing, boost, or both, around the peak torque area. This reduces or limits the peak cylinder pressure but as you move up in the rpm you can then begin increasing the boost/timing again to maintain a flat(ish) torque curve.
That doesn't specifically answer your question and the preferred tuning approach will differ from one tuner to the next. Personally when tuning any high powered drag engine I always prefer to use a little more boost and a little less timing to get the numbers I need. As stated above, the net effect on cylinder pressure is likely to be identical to using less boost and tuning to MBT timing but this leaves a wider safety margin for the engine when it's being used at the track - Conditions that may perhaps differ from what I saw on the dyno and in extreme situations may promote knock.
Your tuning approach often comes down to having some experience or knowledge in the first place of what a particular engine is likely to be able to support power wise. Sometimes this can be picked up from trustworthy colleagues in the industry with experience on a particular engine and other times it has to be learnt the hard way. The hard way is also unfortunately the expensive way.
I've already learnt that hardway twice with this car
Once with the first tuner who "grenaded" then engine by adding way too much timing while running ludicurously rich and the second time by an engine builder doing a terrible job and charging me double the quote. Hence why i try to DIY now including tuning
Without a dyno this maybe difficult to find max torque. Ill try and get some dyno time soon hopefully