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MBT without knock sensor. What's "better" ignition timing? What to do?

EFI Tuning Fundamentals

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I'm from Brazil and I run with E100 (AKI 99,5) and about 12 psi in my Honda D16z6 without knock sensor. In this conditions, is secure to set ignition timing until the MBT, or in this case is more suitable to retard some degrees? What is the better strategy in this case?



A little more info about your setup would help alot. As well as what conditions the engine will see.

What tuning tools do you have at your disposal? Dyno, dragstrip, gps data?

Hi Rafael,

Are you meaning running the vehicle without the knock sensor at all times or for actual tuning?

Hi William and Chris!

Follow a little bit specs:

- 10,5:1 compression ratio

- stock head

- turbo 49 x 49,5 mm - AR .50/.63

- intercooled

- 1000 cc Ev14 injectors

- stock ignition system

- full forged

William, my honda is a street car and I will to tune on dyno, however, without torque optmization.

Chris, yes, all time. The only and current tuning was made analysing many other maps for similar setups, and of course, keeping the most "conservative" as possible.

Although I don't agree with your current tuning approach due to too many variables in most circumstances, your unlikely to overtime the motor on 100 oct unless your pretty far out in left field.

My approach to knock and the use of knock sensors as well as strategies is most likely frowned upon. After 17 years of doing this at very high power on very small motors and large, I am comfortable sharing my preferred method.

If I am using a accurate ECU, I never use a knock sensor or implement knock strategies. Once you have rattled a piston making enough power per cylinder, and it reacts, the damage has already begun. There is only one way to ensure you never hurt a motor from over timing it which is a proper tune. Knock strategies are reactive, and proper tuning is your only proactive possibility.

Be sure to use all your coolant and IAT multipliers. EGT failsafes are great safety added as well if your ecu can monitor and react.

Using ears while tuning and becoming familiar with a engine is never a bad idea. On 100 oct, at 12psi intercooled, you would have to try pretty hard to detonate that motor. I would be far more concerned with the belt driven distributor and its inability to accurately time a engine then overtiming on a dyno while tuning. Thats plenty of octane in your current situation.

Being sure to properly read your plugs at appropriate intervals is important as well.

In that situation where you don't have a knock sensor and you can't do steady state torque optimization, typically you have to do a series of WOT pulls. Start with a safe basemap, do a WOT pull for baseline. Advance spark 1 or 2 degrees, see if you pick up power, and repeat. Once you get to the point of only picking up a small amount of horsepower (or 0 horsepower/torque) for adding spark, you stop.

So in a simple example where we add 1 degree of spark to the whole WOT area of the map:

Baseline run: 200 Nm peak torque.

Add 1 deg: 210 Nm peak torque (+10)

Add 1 deg: 218 Nm peak torque (+8)

Add 1 deg: 223 Nm peak torque (+5)

Add 1 deg: 224 Nm peak torque (+1) . Stop here (total: adding 4 degrees).

Of course you may end up only adjusting it 4 degrees in a certain rpm range, but the principle is the same.

William, thank you for share a bit of your knowledge. I will consider all these tricks when tune. My approach really is not the best, but unfortunately my current situation forces me to follow with the tune this way.

Raymond, thank you for your response. This is the method as I was planning. I've seen a lot of people using this method on dyno that do not have a torque optimization, however, I never saw them being critical if their setups favors reaching the MBT before knock, which has motivated me to start this thread.

As it seems to me, do not to have any other options, and considering the fact that my setup, in theory, favors MBT before knock, makes me safer.

We usually reply within 12hrs (often sooner)

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