Road Rager

Now if im a mile off here please tell me.

Its my understanding that an engine dets/knocks for 1 of 2 reasons
1. Running Lean
2. Running Rich

On this basis, would an Air Fuel ratio Guage be as good if not better then a knockling, i say better because you would see the issues before any chance of detting, wouldnt you?

I ask because im struggling to get my 93 wrx to be happy so was considering getting 1 or the other to see what going on. It is ok on optimax, but ive heard you can get bad tanks, ultimate makes it hesitate really badly, so im thinking of Esso SUL and some millers, but to be safe i want to run something to set my mind at rest.

All opinions welcome, if im talking **** please tell me

zhastaph

Amongst other reasons, Running Lean. Rich will inhibit Det.

I think you'll get varying opinions on this one. IMO a knock link is the preferred method. Although it is a bit like testing for a gas leak with a lighter, the car either is detting or it is not, there is no grey area.

An AFR will tell you whether the car is running rich or lean. But as to how rich or how lean, whether it is lean enough to det or not etc, your gonna struggle a bit.

As a general rule, when cars are detting they seem more powerful. So I think that this is unlikely to be det.

If you're finding the car is running poor, look at things like Sparks, coil packs, lambda sensor, leaking pipe work, blocked fuel filters.

When is it running bad, there is normally a distinction between on and off boost. What does it feel like?

zhastaph

Just wanted to add, a Knock Link is definately an Engine Saving buy, so whether it will or will not help your problem it is a highly advised upgrade.

Road Rager

its basically running bad when ive been using bp ultimate, but not all the time, goes fine on optimax, but as you have said, cars seem faster when detting, so it could be!!!

its nothing to do with any issues with the car, its purely working out which fuel it like s best.

so are you saying if i buy a knocklink there woudl be no need for the air fuel ratio guage.

are you running a JDM car, if so what are you putting in the tank

Road Rager

also if the afr guage was showing no lean running at all, is it safe to say it isnt detting?

AvalancheS8

No, there are other reasons it could det. In the case of JDM cars, running it on anything other than SUL and octane booster could cause it even though the actual air to fuel ratio is O.K. Some of the reasons that I am aware of that a car could det are: too lean, low octane fuel, high cylinder temps / hot spots (poss caused by being lean), wrong plugs, too much igntion advance... there are others. Knowing if it's running lean is a help, but you also need to know if it's knocking. If you are running your cars factory set up, no raised boost, no major changes to inlet or exhaust then a knocklink is likely to be more useful as it should be fueling correctly, assuming your MAF and lambda sensors are O.k. If you want to start turning up the boost, decatting etc then a lambda link will help you to make sure you are still running rich enough at WOT to stop you engine going pop.

The_Judge

One slight amendment to the above info. The leaner mixture will make your car faster. However, if your car's detting, it won't be as fast. Don't forget what det is - a part of the mixture combusting before the flame front induced by the spark plug reaches it. As its burn is "out of synch" with the normal combustion flame front, its energy does not create as much force on the piston. This results in a "bog down" during acceleration...

Road Rager

well ive been and bought some millers this morning, i just need to decide if im gonna run something along the lines of esso SUL or optimax, im a little dubious about optimax as its basicallt NUL full of additives, and there are reports of the additives dying off, leaving 95 ron fuel

The_Judge

That's precisely where the knocklink becomes worth its weight in gold. You could fill up with a tank of Optimax + Millers, reset the ECU, and whilst using up the tank, make a note of the knocklink activity. Then when you're nearly empty, fill up with Esso SUL + Millers, reset the ECU, and monitor the knocklink activity for that tank.

It won't be an exact science, as you may get a good tank of one, and a crap tank of the other. Also, it may take a while for the one tank to drain through before you can monitor the second tank. But it's better than nothing. Plus, you wouldn't be able to do this with an AFR gauge...

RICH WILD

Not strictly true. If the fuel air mix is on the rich side then yes, it will have better heat absorption characteristics and will therefore supress det but running far too rich can sometimes cause det also.

One of the main causes of det even more than underfuelling is too much heat in the inlet charge. If the air fuel mix is hot enough when it enters the cylinder it can spontaneously ignite, either wholly or in part either before combustion starts or during combustion.

That is why intercooling is important. To lower the inlet charge temp. that's why car's have waterspray.

Another main cause of det is insufficient fuel octane. Run an import on 95 RON and it may be running as rich as hell but it could be detting its nuts off.

Selecting insufficiently "cold" plugs can also contribute to det as can running too much ignition advance.

So it ain't just plain and simple AFRs you have to worry about.

Ideally get both displays but if you have to pick one, I'd go for the knocklink.

Rich

Road Rager

does anyone have some pics of a knockink then, where its best mounted in a classic and how much they are

The_Judge

More royalties for Ozzy...

Plus you can get them from BR Developments or from Jap Innovations...