Knock Prevention!?

[gtstii]

Would I be right in thinking the following:

People who have an SAFC in their cars and are running more boost and so on.... but do not have any timing control (ie. power FC, emanage etc..), might be losing a bit of power in the midrange because they cant optimise their timing, but isnt this sort of set up a lot less prone to knocking?

Your A/F ratios are tuned with the SAFC but imagine you are driving on a really hot day on crap fuel with a load condition not experienced on your dyno runs, then your car may sense from the knock sensor that you might have a bit of knocking - the ecu will retard your timing to prevent this and yes, you may lose a bit of power but you will be SAFE!

If you are running your car and there is no knocking, then your ecu wont retard your timing and you wont lose any power

It may not be 100% optimised, but isn't this a lot safer?

Does the fact that your ECU senses knocking and deals with it mean that it is very unlikely to happen?

[Steve]

Unfortuneately no. The higher the boost, the higher the revs, the more severe the knock - the more damage that can be done in a smaller amount of time.

Yes the stock management retards timing, and that isnt bad - it wouldnt be a bad idea to set up an ECU reset switch in the cabin, so you can 'retune' when conditions change, or do it the old way by disconnecting the battery.

I have knock detection with my power fc, it also keeps a track of the knock volume, so I can see if its starting to get a bit high, and take appropriate action, such as backing off, turning the boost down, pull a couple of degrees of timing or get some tolulene for the tank - so its not as scary as you may think with no automatic knock retard in the ECU

Bottom line, if you want safest, keep your car stock. If you want performance, just be careful, dont cut corners or try and push limits too far and all should be good:)

[gtstii]

SAFCII's also have a knock sensor.

Lately on hot days my readings sit on around 30 and reduce when I accelerate to close to b/w 0-10.

On cool days and at night, reading sit under 10 and will go to 0 under WOT!

[Steve]

All sounds good then:)

[gtstii]

I just dont know what the "scale" is - what level signifies a knock???

would it be the same as a power fc's output seeing as they are both apexi?

[Steve]

Dont have the manual? there is an e copy on the apex usa site http://www.apexi-usa.com/documentation.asp but I cant access it for some reason?

[gtstii]

I've got a copy of the manual but it just tells you how to set up the knock sensor settings but does not mention the knock levels at all!

What is considered a knock on a power fc's output!

[Steve]

60+

[Busky2k]

Yeah just make sure you do a peak hold after your WOT run. Sometimes pinging might be too quick to show up. So just flick the joystick up after to make sure.

Ive remembered plenty of times the peak hold showing like 100 but i never actually saw it just by watching. I believe its beceause as soon as the ECU saw the crazy pinging, it backed the timing right off, before I could see it on the display.

[Amaru]

Just as a point of note, in the Power FC manual there is a large section that contains "Caution: The Power FC does not retard ignition timing if the engine is knocking. If you notice the engine knocking, back off the throttle immediately" or something along those lines, ill post the exact quote from the book up when I get home.

[Steve]

Absolutely correct, as per my previous post, you do need to take action if knock is detected.

[JimX]

Gtstii, I gather you are trying to decide whether you should go with the S-AFC or full engine management like a PowerFC? If so, don't use the engine knocking prevention as a reason to get the S-AFC. As long as you have some sort of knock warning, whether the inbuilt function of the PowerFC, or some third party item like the one from Jaycar, you should be ok in that regard.

Have a look at my 2 attached dyno readouts. Both are S-AFC tunes done several months apart with different mods. The car had a T04 turbo (I think T3/4 hybrid, it has an internal wastegate) for both. With the first run it had a small front-mount intercooler. For the second run I had upgraded this to a better flowing fmic, and also changed to a front-facing plenum and installed a bigger fuel pump.

For the first pre-mod run everything was fine. It's got a uniform 15rwkw or so extra across the board. The post-mod run however things went haywire. From about 5000rpm and up the power just died. It had a decent peak power but it really felt totally flat above 5000rpm which you can see in the readout. I had a few theories thrown around by different people, including compressor surge, bad AFM, bad plugs, and one or 2 other things.

However I didn't think it was any of those, and after I installed my PowerFC I found that I was right. The flat spot is totally gone just by running the default PowerFC map. I haven't dyno'd it yet (hoping to get a tune done in February) but you can just feel that it's not there anymore. Power just builds and builds all the way to redline.

This is not to say that the S-AFC is useless! Like my first dyno readout shows, with the mods I had previously it did a very good job. It's just that if the mods get a little radical, the stock ECU does not cope and no adjusting of the mixtures will help. It was probably retarding timing all over the place for reasons unknown to produce that power dip. With the PowerFC it just does what it's told and there are no problems.

If you have the bucks I would definitely get the PowerFC or similar. If you go the S-AFC then you *may* be disappointed by the results. Not definitely, but maybe. It's just more of a risk performance-wise. (note: I am sure there are plenty of people running S-AFC's with more mods than mine with no problems! I am only speaking of my own experiences here).

Of course if you are poor then the S-AFC is always going to be better than nothing. You can always sell it when you can afford the upgrade to a full ECU replacement.

[Steve]

Or buy an ITC (ignition timing controller) if you can get one, have seen them for 200-250 in the forsale section.

[Busky2k]

Yeah the ITC is a great lil device. So i have the poor mans adjustable ECU. SAFC and SITC. Does the job I guess, but I cant really fork out another 2k to get a PFC + Handset + Dyno Tune.

[GTB055]

What "KNOCKING" mean??? can someone explain it's in a simple term. Should i be worry if i have POWER FC???. How can i detect knocking or gather information about it??

[edgasket]

a.k.a. detonation, put simply, knocking is when the airfuel mixture in the cylinder explodes before it's supposed to and if it's bad or left long enough it can put a hole in your pistons. It depends on many factors and so there are many ways to combat it, grade of fuel, charge temperature and most importantly, your timing. There's loads of sites that explain it with diagrams and animations and everything - just do a search in google

[Steve]

To add to edgaskets comments, the combustion process is a controlled burn, with a flame front being started by the spark plug.

Detonation, or knock is when the air/fuel mixture spontaneously ignites in the cylinder BEFORE the flame font - it is acutally an explosion, not a controlled burn.

This causes massive pressure to be generated in the cylinder, and can blow holes in pistons or smash ringlands (they are between the rings on the side of the piston).

Even forged pistons can be destroyed by detonation, as the force generated by detonation is that powerful, it is an explosion:). Infact argueably forged pistons can be more easily damaged by knock as they are more brittle than standard (cast) pistons, they tend to be better designed though - their main benefit being that they dont retain heat, and therefore the cylinder will run cooler, meaning less likely to knock.

As mentioned, their are many different causes of knock, some things that will cause an engine to knock:

high load - eg, going up a steep hill in too high a gear,

a hot day or high engine bay temps - raises the intake charge air temp (different causes here too),

adding boost - as the more air is compressed the hotter it gets

poor intercooling - heat thing again:) also remeber an intercooler may become heat soaked, such as when you are sitting at the lights on a hot day for a period of time.

poor fuel - octane rating is a measure of the fuels resistance to knock or detonation, some people like to add a few litres of tolulene to increase its resistance to knock and there fore allow more timing more boost and ultimately more power. It can also be good protection on hot days.

lack of fuel - mixtures lean out due to insufficient fuel supply or a dirty injector etc

too much timing - fuel mixture gets ignited too early, this is the most common adjustment made to combat knock, when a car is on a dyno and detonation is detected, assuming the AF ratios are correct, the next thing a dyno operator will do is pull some timing - well the ones that have tuned my car anyways:)

There are more, but as mentioned the main ones to keep an eye on are heat, timing, fuel and load.

Should you be worried about knock with a power fc? You should always be mindful of knock, as it will destroy an engine quite quickly and easily. Dont be worried about knock as long as you are mindful of it, and take necessary measures if it is ever seen/heard.

Power fc is good for this, as it gives a scaled reading, and warns throught the flashing of the check engine light if a reading above 60 is detected, enabling the driver to back off and take preventative action.

An aftermarket knock detector can be purchased if you are using another type of management too.

There are other ways to keep an eye on potential problems arising, such as an exhaust gas temp gauage, it will tell the driver if exhaust temps start to rise beyond their normal operating range that the engine may be running a bit lean - and lean mixtures may cause knock:)

Starting to rave on a bit here, sorry if I am confusing you.

Bottom line: be mindful of knock, be aware of the different situations that may cause knock, and make sure to back off immediately if you hear or detect it, and you wont have anything to be worried about.

[Guilt-Toy]

WATER INJECTION!!!! CHUCK SOME WATER INTO YOUR TURBO blades and watch the knock go down.

I got my GF to drive the car while i started playing around with water nozzles etc...

I noticed that with the water off it would knock up and over 100 but with the water down it hovers around 0 - 40

Water is the answer

[Steve]

so you reckon you should drive around with water constantly pouring into the turbo??? Wouldnt it be alot easier to just get it tuned properly? then if it starts knocking pull a couple of lbs boost, or a couple degrees of timing? Maybe add a couple of litres of tolulene?

Pretty bodgey form of knock reduction IMHO. I know that people use water injection for extra power, I can understand it for a trip down the 1/4, but on the street? No thanks.

[Busky2k]

Water Injection is one of the best ways to help prevent detonation. But dont just spray it into your turbo. You'll erode your compressor blades before you know it. You need to use a high pressure pump/atomiser sprayed after the intercooler.

Go to www.aquamist.co.uk for more info. FYI, i have waterinjection, and its bloody excellent.