QOTW #92 – Dyno testing follow up, V8 ignition and knock control

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Welcome to Bamford Rose. And another question of the week. This week is picking up a question that comes off the back of the dyno testing video that I did with Steve over Aston 1936. And this question is specifically about the VA and dyno testing the VA, because the video that I shot with Steve talking about dyno testing and concerns relating to the validity of the results from dyno testing was all focused about the twelves. If you haven’t checked out that video and go watch it, if you just want the edited summary, then the summary is don’t bother dyno testing, go and buy something like a draggy and do your before measurements then do after measurements with the draggy. And that way you can prove that your upgrades have been worthwhile rather than a dyno, which comes with a whole heap of inaccuracies that are introduced by dyno testing.

So the question is, does the VA suffer from such inaccuracies on dyno testing? And the answer is yes, for two reasons. One is well it’s dyno testing and all of the input errors that we went through in ambient air temperature, pressure and temperatures affecting the wheel result and how you back calculate from wheel to flywheel. Well, they equally exist in the case of dyno testing of VA engine. But most VA models have something which V12 doesn’t, which is it’s not a control and spark strategy, which is designed to return as much ignition as possible, therefore as much power as possible. And depending on when you did your power curve and power test, you could actually have a different level of ignition advanced there for a different power figure. So we’re just going to talk about those softeners on the VA in this video. I did all of the performance development for the 380 and 420 BHP, 4.3 and both for 4.7 liter engines for the factory. So I know what I’m talking about here.

Reference conditions for the VA that the ignition has been mapped out, our 25 degree inlet, manifold temperature and something like a 97 99 octane fuel. Those inputs will dictate an ignition advance angle before the engine starts to detonate. And it’s that ignition angle, which will be in the base ignition map. So every time you run the car through the gears, if there is no detonation, then the engine will run the base spark value. And the performance will be the most optimum it can be. Perhaps if the ambient air temperature was a bit hot, fuel octane was a bit low. Then an engine might start to detonate. And if it donates, then not control, which is a system where a sensor feedbacks to the ECU that detonation is occurring. And then the ECU backs off a little bit to counter that detonation, so it doesn’t occur. And then it will learn that spark as an adaptive offset so that no detonation occurs.

That’s great because we don’t want that nation because that will lead to a hole in the piston, but it’s not so great because if the ignition is retarded, then the power is going to be a little bit less. For N 400 and the Aston, my empower upgrade kit, which was retrospectively sold to 4.3. I developed a little bit of a software algorithm that turns that traditional behavior on its head. This algorithm will actually advance the spark and seek out detonation. It then learns that positive adaptive offset as its basic mission value, which means that at all times, every single engine is running the most amount of spark that it possibly could. But at the same time, that is going on you’ve also got adjustments that will be made to certain outside conditions like ambient pressure temperature.

And whilst that strategy is trying to advance the spark to give the most amount of power, those normal reductions that I just spoke about are always going to try and reduce the spark. What that means is that the engine is always running the most amount of spark at all times that it possibly could. And it’s achieving the most amount of power at all times that it possibly could. But what that also means is where spark has to be adjusted. Then it’s going to have a reduction in power. So if you’ve got the VA on the dyno and you’re running say five back to back power runs, if that system is working, you could have five different spark curves across the rev range. Meaning you’ve got five different power figures. When I do dyno testing on a VA, I turn all of those features off. I run a set spark curve, that way I know that my result is not being compromised, not being adjusted by any spark offset.

If I didn’t do that, then my figures, my results could be skewed and my result is unreliable. So if you’re dyno testing your VA and you’re not measuring through the energy management system, these inputs, and you’re also not resetting your sparks, so it is fixed without any of those adaptive offsets taking control means the result isn’t really worth much and goes back to the example of the draggy, being the best tangible measurement of your pre and post modification results. We’re going to go out in a car now, and I’m going to show you their system working. And you’ll see that as we go through the rev range, then the spark is continually adjusting. At 7,000 RPM one degree spark is worth about 3.5 brake horsepower. You’ll see that this system has got authority to remove up to five degrees spark, which ultimately means power output can vary dyno test to dyno test by at least 15 brake horsepower.

So this first acceleration shows that the adaptive not control offset is doing absolutely nothing during this first acceleration, meaning that the spark value is the maximum from the base map, meaning that the power output is the maximum possible.

Now the second run, we’ve heat soaked some temperature into the engine. We’ve done a few accelerations and we’ve actually now detected some detonation through the onboard not control system. As you can see, that’s returning an adaptive offset, it’s called the slow correction. And as you can see, there is up to five degrees going in that slow correction adaptive offset, which means the power on that we just did is anything in the order of 15 BHP lower than the reference. Draggy is the answer. It’d be like that question of the week. As always, it really helps us if you can like, comment and subscribe and we’ll see on the next question of the week.

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