I don’t know if the following is possible, or if so, if anyone has done it, and if it would make a positive difference.
I have seen many recommendations for advancing the baseline ignition timing from between 14 and 18 degrees, the limitations being knock or pinking, so it occurred to me that it may be possible to do this actively in some way.
I’m only talking about base line timing here, since its well known that an increase produces more low and midband torque.
Would it be possible to produce some ECU, in conjuction with a knock detector, which could be inserted into the circuitry between the CAS and the main ECU to continually adjust the base line ignition timing for max advance?
Would this also enable an NA to take advantage of higher octane fuel?
Is it possible / desirable, or am I completely misunderstanding?
The base setting is just that. The ECU then adjusts the advance based on inputs from the various sensor inputs and the programmed map. By advancing the base line timing you move this map and if you advance to far you will get knock.
Knock or pinking is the sound exploding gas hitting the cylinder wall as the fuel does not deflagrate(rapid burn) evenly when pinking takes place but has small pockets of mixture exploding outside the flame front.
High Octane fuels contain no extra power, octane is used as a measure of the fuels resistance to knock (LPG is around 110 octane notoriously difficult to light hence the need for special plugs and even in the best systems only produces around 90% of the power that petrol would) the power comes from other factors usually a raised compression ratio or higher rev limit both of which induce knock
To answer your question it is possible to produce an ECU that uses a knock sensor to pull the timing , it would allow the timing to adance more if higher octane fuel was used.
At best you might gain a couple of horsepower but you might well lose a couple due to inefficient running.
If you were running forced induction then it would allow you to run more boost and that wold increas the power.
If you’re going beyond 14 deg BTDC then you should be using super unleaded (the highest octane you can get; some are a miserable 97). Admittedly, most of the time you won’t get pinking with 95 octane fuel, but on a hot day when climbing a hill you may start to hear it. Detonation becomes more likely as the intake air and/or coolant temperatures increase.
In general terms it is not true than more advance == more power. It just happens to work on the MX-5 Mk1 1.8. One theory of engine design says that the design that requires the least advance is usually the most powerful*. What’s really going on is that you’re moving the timing of peak cylinder pressure around; most engines develop maximum power and highest efficiency when this is about 15 deg ATDC**, so in the case of the Mk1 it’s taking around 29 degrees of crank rotation to get from ignition to maximum pressure.
*the classic example being a hemispherical head, which burns the fuel so fast that the ignition timing may be after top dead centre. They produce too much NOx for current regulations due to the very high flame speed and temperatures.
**you’d think it would be 90 deg ATDC because the crank throw is horizontal at that point, but it’s a lot more complicated than that because the power stroke is long and sustained.
Personally I’d set it to 12 deg BTDC and run on normal unleaded. I used to run mine at 14 deg BTDC but my father-in-law used 12 deg on his car and got slightly better mpg than me (up to 41mpg on long motorway trips), even though his car had power steering and he was far less inclined to observe speed limits*. The 14 deg mod is known to reduce maximum power (which is at very high revs) but you get a little more low-speed torque.
*I was once in the car with him doing 115mph with the roof down. Windy.
I’ve been running at 14 deg for the last year and noticed much bettter low end acceleration and average motorway fuel consumption down from 34mpg to 36mpg (when I can keep it legal) I can also confirm that 115mph is a bit drafty with the roof off.
“If you live at high rpm, 14 degress of base timing advance will make you sing. If you spend much of your time under 4,500rpm, 18 degrees of timing (and high octane fuel) will serve you better.”
So what this is suggesting is that to get the most out of an NA there is a case for an inline ECU, between the CAS and the PCM, to change the base timing from 18 to 14 at around 4,500rpm.
Its not going to pink at all loads and conditions at 18 degrees on regular octane fuel, so the addition of a knock detector to retard the the timing slightly when needed would take care of that. Otherwise one could use high octane and forget about it.
The above is just what the quote seems to be suggesting.
There was a Bipes ECU for sale or Nutz . It’s meant for FI but it will work NA . Pulls the timing based on temp ,air flow and revs and you can fita knock sensor.
That expains quite well, what the potential of the MX5 engines is.
I got my Bipes ACU for approx. 70$ from US and was one of the best mods ever done. After experimentig a lot with static timing and later with the dynamic setting of bipes I had my 1.8 set to retard to 22 degrees below 4000 revs with basic timing of 10 degrees, as this gave most high end power. It is very close to what those articles are stating actually. The fuel I was using is 95.