Effects of 'knocking' or detonation in air/fuel mixture?

[Paul the 6th]

I meant I just dropped a whopping stinky brain fart lol - I already knew it was for the US emissions but went down 'lower RON rating lane' for some reason...

ah I'm not chasing big power for competition or anything, just a mate of mine had an S4 which was an ex-demo car for MRC Tuning (google them - they can do insane stuff with pretty much all of the top end VAG cars). His was around 500bhp... easily the fastest vehicle I've ever been in but you have to experience it to see what all the fuss is about. I'm not after the same thing but I fancy a re-map for mine since it's probably the least invasive of all the tuning procedures, and against my better judgement I do actually buy into the idea that it'll improve economy on motorway runs. (Peak torque being cracked up and moved further up the rev range, cruising at a constant speed on the motorway will still be at the same RPM but lower down the powerband in relation to the state of tune it's in - if any of that makes sense? lol)

I'd love one of the 4.2 v8's (b6 series) but it'd be thirstier than the 2.7 turbo (b5), the latest version (the b7) is a 3.0 v6 turbo and seems like the best compromise but they're prolly still hovering around the £30-40k mark lol..

Plus I like the fact mine looks like a common garden saloon car with nothing special to note... It's properly juvenile but there's a strange satisfaction to watching the chav'd up corsa behind you disappear when they thought you were 'just another a4'

[andrewsmith]

Lol the older ones are hidden with the rep-mobiles.

Its like any vehicle, 'how bigs yours wallet?'
I'd love a tuned Monaro but it'll never happen as the tune I want is £30k +

i want a tuned, mk2 escort around 650bhp full welded "cage" (no pun intended) blisteen dampers the lot

but keeping it low key with a chavvy exhaust so i look like a chav but go like a rocket

[Sid Squid]

Detonation is a spontaneous, uncontrolled burn, the greatest effects are, as Barwell has alluded to, the significant change in burn timing and speed, and thus timing of peak cylinder pressure. Essentially instead of a smooth flame front initiated by the plug and travelling predictably through the mixture*, the burn occurs uncontrollably and at multiple points in the gas.
Detonation is not the same as, but may be caused by the same problems as, pre-ignition, other descriptions are, (with varying degrees of accuracy), 'knocking', 'pinking' and 'pinging'.

The reason that it can vary in it's effects between being an innocuous process or serverly damaging is because there are so many variables in it's specific causes and circumstances. It's very diffiicult to predict the effect it may have on any given engine - you may have to wait until someone else finds out! The one thing that is predictable is that it's never a positive thing.

* Even though as is usual nowadays cylinder turbulence is promoted by inlet shaping and gas flow swirl intermingling between ports so that flame propogation is improved and thus burn time is reduced - but in a controlled and predictable way.

[maviczap]

I know you used to be able to buy octane boosters to bring the Ron up to a high level, which I think was to account for our unleaded petrol.

If not fill up at an aerodrome with avgas

Wont it have a knock sensor anyway? I was under the impression most modern cars did?