I am getting a new chip and have been told I need to buy a boost guage and a knocklink.

What are they are why are they necessary.

Keep it simple guys - Im not questioning their need, just want to learn about them

Also, which ones would you recommend.

I have a 96 STi2 for those who don't know.

 

You need a Knock Link, Boost Guage and AFR meter of some sort.
The Knock Link is a microphone that is placed on top of the engine block and listens for a particular noise frequency. It detects, knock, also known as DET or detonation or pinking. This is a BAD thing for most engines and particularly for Subarus as it can wreck an engine in seconds.
When the microphone detects KNOCK a series of lights are illuminated on a small display pannel which is fitted on the dashboard somewhere. The microphone is listening to engine noise and two greens is normal, a couple of orange (or whatever colour comes next) means there is more engine noise and the fifth light in the sequence, either a bright white or red is a big no no. Lift off immediately.
Link are a New Zealand manufacturer who also make the Link ECU.
There may be a Group Buy active on these in the apprpriate section. If not Jap Innovations or Bob Rawle Developments (BRD) amongst other can sort you out. A bit over £100 I think.
Relatively simple to install, especially by someone who has done one before.
You can get a good boost guage for around £50. Very simple to install.
An Autometer AFR guage from Scoobymania or Apex is around £50 by post. This will indicate your air fuel mixture. Too weak and you run the risk of melting a piston. Too rich and there is the risk of bore wash.

 

All Impreza's have a standard knock sensor which is basically a microphone.
This listens for detonation/pinking/knock within the engine and retards timing.
The easiest way to describe this is that the fuel/air mixture is ignited to early causing the flame front to smash into the piston at the wrong time.
(somebody's bound to correct me)

Link produce a separate monitor which produces a visual indication of det via a series of LEDS, 2 green=normal, 2 amber=warning and a big old red=det/knock.
This is usually accompanied by a separate Bosch sensor mounted on the engine block all wired together.

http://www.brdevelopments.com/link.html

 

So am I venturing into a mod that could potentially harm my engine? And if all Imprezas already have a knocklink why do I need to purchase another one?

I particularly didn't warm to the words melting piston and bore wash

 

If the chip that you are getting is well mapped it shouldn't really increase the chances of you engine failing, but anything that modifies the car away from the standard spec is likely to increase the risks somewhat.

Scoobies don't actually have a knocklink, as standard, but they do have a knock sensor. The engine management uses the input from the knock sensor to adjust the ignition timing when it detects knock, in order to try and keep the engine in one piece. The reason that you need a Knocklink is that some of you extra performance when you chip the car or run higher boost is gained by using up some of the built in safety margin in the standard set-up. The Subaru knock detection system isn't the best even when running with the standard set-up, and when the car is modified it can get to a situation where the standard knock correction system is unable to adjust the timing far enough to eliminate knock. This is where the Knocklink comes in, it allows you to see that knock is happening, so that you know there is a problem.

Usually seeing knock when there was none before is an indication of a bad tank of fuel, but it can also help to give you vital early warning that one of the engines sensors, or the petrol pump, or any number of other things are on there way out, and give you a chance to fix the problem cheaply, before it takes the whole engine with it in one big pop.

 

Thanks for that AvalancheS8 Especially for taking the time to type all that information. It is very helpful.

Same goes for the rest of you. Many thanks,

Karen x

 

Also, I've heard that the Scooby's std knock sensor doesn't even detect knock over 5500rpm, which I can't help but suspect is exactly when you'd most want to know if anything bad was happening!!

 

Meaning I should ignore the fact I already have a sensor because it's pants

 

New Scooby 04 is about right there - the ECU ignores the factory fit knock sensor after 5500 RPM - and this is exactly when you need to know about it.

any chip getting more power and torque out of the engine will be eating into some of the safety margin that Subaru engineered into the design. You therefore need to keep an eye on a few things to keep up the reliability. As Harvey says, boot gauge, knocklink and AFR meter.

I'd argue that the cheaper AFR gauges are the least useful of the 3, as they aren't all that accurate (unless you get an expensive wideband one - I will show you one of these shortly ) Generally, any lean-ness will be shown by the knocklink, and a cheap AFR gauge won't ever show you the difference between "healthily rich" and "borewash rich".

 

I run an Autometer AFR guage (about £50 Scoobymania) and also have fitted, permanently in the car, a WBO2 with digital read out. Comparing the two, I am very impressed with the performance of the Autometer.
On Saturday I got someone else to check out the map using their WBO2 with digital read out and their probe up the tail pipe. Because my own WBO2 had been sent for overhaul I had already re-mapped the car after changing from an FSE FPR to an SX regulator, along with a fuel pressure reduction. The changes to fuel and ignition totalled 8 minor adjustments and that proves to me how useful the Autometer guageis. I have used another AFR guage that did not install confidence but the Autometer is in a different league for a narrow band.