Martin,

You're lucky this isn't the GTF BBS, as you would have been flamed, barred, hung, drawn and quartered for asking such a question

 

GTF BBS?

 

 

LOL!!!

 

..what is detting?

I was interested in one of the previous posts regarding fitting the down pipe to a P1 and related problems, but know only the basics about engines. Is detting the same as pinking?

Also what is a Knocklink?

Sorry to be really thick..

MS

 

i see that the scoobynet bbs suffers from topics that dont actually cover what the post is about.

Why dont you put

"what is detting????" in your post, then not everyone in the whole of scoobynet will have to look in here. And the people that know what detting is will be able to post an answer.

Anyhows Detting is when the flamewall meets the piston before the piston has reached top dead centre.

Basically the piston is coming up beinf forced by the crank and the rest of the engine upwards and the force of the explosion of combustion hits it pushing it down even tho the piston HAS to come up before it goes back down,

so imagine the piston is going up and then is hit by a hammer downwards even though the crank is pushing the piston up.

so it creates amazing heat and melts the pistons

rw

 

Check out this recent thread:

 

Rich R,

cheers, clear as a whistle now. That's what I needed.

MS

 

phew! glad i'm not alone here then, wondered what that meant myself, no i know

Thanks

Greg

 

Ah Cem, oh mighty Muppet leader - great minds think alike

 

Martin

Take a trip to the Muppet section and look at some of Blow Dog's recent threads

Chris

 

lol Dave,
once a muppet, always a muppet.

 

.....until, of course, you climb the hallowed steps and become a Muppet Moderator eh? - Just don't forget your roots mate

 

I am prepared for a flaming but my understanding of detting is slightly different:
Petrol air mix doesn't actually explode as commonly assumed but in fact "burns". This is a much smoother and progressive form of combustion than an explosion or detonation.
The action of burning causes the mix to expand and therefore push the piston down the cylinder creating power.
Many factors influence the way a petrol air mix combusts including location of spark, spread of the mix, temperature of the mix, ignition timing, compression ratio, boost and fuel RON rating.
Generally of most interest to Scooby owners is boost and RON rating.
A higher RON rating means that a fuel mixture can be compressed more before the induced heat of compression causes it to explode (this incidentally is the way a diesel engine works and why they sound like a bag of nails; they're always detting!).
And hence the widespread use of octane boosters.
Also, higher turbo boost causes higher effective compression causes likelyhood of detting etc etc.
What the engine management system tries to do is give you the highest boost and highest timing advance it can with the fuel mix quality available.
Retarding timing is one way of reducing det (many unleaded conversions were merely a timing retard to get around the loss of the anti det properties of lead in petrol although it doesn't stop your valve seats burning out) and retarding boost is another.
Which comes first I don't know.
The retarding of timing alows the piston to set off back down the bore before firing the mix so there is effectively less compression, hence less heat, hence less chance of detonation at the time of the spark.

I hope this is of some help and that I don't get flamed (or detted?) too much.

Neil.


[This message has been edited by Neil F (edited 27 March 2001).]

 

Cheers Neil,

all replies greatly appreciated. Although a performance car owner, I never professed to be an engineer..

MS