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Advice needed on Knock

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Hi Andre,

I'm tuning a 4 cylinder 1600cc Suzuki high compression (11:1) naturally aspirated engine with a haltech elite and I'm noticing very strange things with the behaviour of the engine.

Firstly, it goes to accessing wot map from about 50% throttle opening which means I had to use alpha n to tune the engine. Why it's doing this? I have no clue, and no there are no vacuum leaks I'm 100% sure. I'm also using the VE model.

The next strange thing is at peak torque 4500 rpm the engine is severely knock limited, I mean REALLY limited, I am at 16 degrees of ignition advance to get it to not knock on a ramp run. Below and above 4500-5000 the engine accepts timing you'd normally expect from a NA. This means I have a really huge hole in my timing map at 4500-5000. I'm also using a Plex knock montior so I know 100% it is knock. Fuel is 95 RON.

Any cues on what could be going on? Or is this not something that abnormal?

A high compression engine on a low octane fuel will be prone to being knock limited, is there any way you can dose the fuel with octane booster to see if it reduces your knock?

Hi Chris, yea maybe we can try that. I think it has something to do with a variable intake runner length feature this engine has on the intake manifold.

I'm seeing quite a lot of problems getting this to work through the haltech elite so right now it's just stuck in one position when it should be changing position twice through the rev range. It did work for a little until the motor failed though and I was still getting this problem.

Strange thing is, the engine is making the torque it ought to at 4000-4500 even with the severely retarded timing, end result is the cuvre looks smoothe and continuous, how it ought to look based on comparison of OEM engines on OEM ecus but my timing map has a huge sink around 4000-4500 from 40-100% tps.

If the engine is fitted with cams that offer more overlap than factory then this can result in low MAP values and you may get a better result swapping to Alpha-N. I do this quite regularly with N/A engines that use aggressive cams even if they are using a plenum and single throttle.

As Chris has mentioned, I wouldn't be surprised that the engine is heavily knock limited on pump gas with high compression. The area where peak cylinder pressure occurs will coincide with peak torque so this is the area you'll need to pull timing in order to stop knock. You may find that once you sort out the inlet runner control that this will affect the rest of your ignition table too.

Hi Andre, the engine is bone stock as it came from Suzuki but there's also another thing that points to it seemingly having "aggressive aftermarket cams.....I've conducted compression tests on several of these engines and they're all giving around 140psi across the board which again, points to the engine having a lot of overlap , it's quite strange because as I said this is how they behave bone stock.

Ok on the knock/timing, but would you ever leave a timing map looking like what I'm describing? The engine is taking around 32 degrees at peak rpm but around 4500 I'm all the way down to 15....there's a big jump at 5500 as it's taking 24 degrees there....it's quite ugly but the engine does not feel erratic or hesitant so I left it like that.

Just wondering because all the training I have from HPA says having a big dip like this is something you never want to see

It's not something you ever want to see but if you've got a knock limitation then it's unavoidable unless you make changes to the set up, i.e. octane boosting or mechanical changes

What you're describing is pretty unusual. The comp test suggests a lot of overlap as you have said, particularly with a high compression. I'd still like to see what the timing map wants once you have the inlet runner control sorted out. It's possible that you're reducing airflow at lower rpm and this is why the engine wants more timing there.

A smooth timing curve is typical but this shouldn't be at the expense of giving the engine what it wants. I do try and keep a relatively consistent change from one cell to the next and in some instances I may choose to 'detune' the surrounding cells to reduce the magnitude of change. Ultimately though if the engine is smooth to drive then there's really no harm.

Fully understood Andre, and yes it is very strange. It's the ZC32S swift sport 2011-2016 model in case you ever come across one. I've done the compression on a couple OEM ones and they're all 140ish across all 4 when the quoted compression ratio from Suzuki is 11:1. Very strange.

I am having lots of problem trying to get this variable intake to work with the haltech elite, maybe you can offer some insight here too? Zac has helped me loads but I'm a point now where I've done what he suggested and I damaged the actuator...no fault of his of course. Basically the flap is being controlled my a DC motor....it reverses polarity to turn the flap one way or the other. I have it all set up with changeover relays and repurposed the switched cam function on the elite 1500 to turn the motor both ways pending rpm.

Problem is I was keeping 12v and ground when it switched polarity which in essense was having the motor trying to spin against the hard stops in the intake manifold....the motor burned eventually. I need to figure a way to break the circuit once it switches in each direction...this is where I'm at....