david

Not wanting to start another debate about how to improve performance, but after reading the 'cold start' thread, can anyone tell me what an AFR is and does and how much they cost, where to have fitted etc? Is it a good thing to have on an STi V with the reported problems at high revs, and how much fuel economy do you loose (if any).

Cheers

Dave

quattro

Some time ago I have been involved in a discussion about the HKS Air-Fuel Ratio module that I have had installed into my STi5 (in conjunction with the exhaust and the induction kit). If you wish you can search under HKS parts or my username for that discussion.

Now, some time and some miles later, I can confirm that AFR proved to be a very useful item, esepcially when some other devices were used which enabled me to monitor the data coming off the lambda sensor and actually 'see' what mixture of air and fuel I have been using on different throttle settings. As we all know, Phase II engine as served from STi is running very rich in order to prevent other well known problem (detonation) from occuring. When set up correctly, the mixture can be somewhat leaner which not only makes the engine run better, but also reduces consumption. The best person to speak on the subject is most certainly David Power who will say the same thing I will say and that is: do not tamper unless you know what you are about to do! AFR module is certainly good to have, costs around £100 and, once installed, Power Engineering can easily perform their diagnostic exercise and find out whatever the best mixture setting may be. So, based on my experience this is certainly useful to have, but ONLY IF CORRECTLY APPLIED AND COMPETENTLY ADJUSTED!!

Finally, (and I am NOT going to start the same discussion again!) the whole affair around STi 5 and 'problems at high revs' is no longer a mistery to me (and a few others), and while it is quite possible to generate detonation with the STi5 engine, there are some very good (and rationally possible to explain) reasons why this may have happened. As has been generally accepted, 98RON petrol and octane booster for added safety will keep it more than safe in any kind of everyday's use.

Hope this gives you a somewhat better insight into the subject. Perhaps some technically more competent members will like to add/correct to this.

q.

[This message has been edited by quattro (edited 27-10-1999).]

Trout

iTrader: (1)

Just out of interest - I also ran the same set up as quattro - HKS Induction, Exhaust, AFR, Plugs...

...until my neighbours complained about the tremendous din at 0530 as I rumbled off to work!

Anyway - when all was on song the car was quicker, less asthmatic over 6000 rpm, smoother acceleration - and in motorway cruising type stuff gave me an extra 2mpg.

So it all must have worked!

Now, back to quiet STi (mind you I would have been deaf by now - 10,000 miles barrier just passed yesterday in 6 months driving).

David

quattro

Rannoch

The main improvements aside from the effects of the AFR already mentioned are extremely sensitive throttle response and a MUCH improved performance above 4000rpm but, at the same time, due to the free flow exhaust and much less back pressure in it the 'pickup midrange point' has shifted itself at least 600rpm higher than it was with the standard 'silent' exhaust. I hope to make up (and more!) for this drawback with a new ecu very soon.

However, let us not digress from David's initial question too much, ok?

q.