Why do blown engines require less timing advance at WOT? Does the mixture burn faster in a blown application?

 

They don't always require less timing. I run full timing on my car with 5lbs of boost, stock compression, no knock retard, no knock sensor counts, no pinging, no codes.

The most retard I have recorded (before disconnecting knock sensor) has been between 4200 and 5400rpms. Intercooled setups are less likely to detonate due to the lower combustion chamber temperatures..

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91 Formula 1LE 1 of 46
305 TPI 5speed
1LE/G92/WS6

Paxton SN92 supercharger, Ford SVO 24#injectors, Crane AFPR,SLP airfoil, ported/polished plenum, March alt. pulley,Crane Gold 1.6rrs,MSD coil,MSD6AL (5400rpm limit),Holley 9mm wires,Ac delco R43ts plugs,custom chip,Bosch O2sensor,SLP 1 5/8" headers,SLP catback,shortened shifter,3:73s w/Auburn posi,180* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.

[This message has been edited by theformula (edited April 17, 2001).]

 

well what happens is....is that you are cramming in all that extra air into the combustion chamber (boost/compressed air) and if the timing comes on too soon (before enough fuel can enter the combustion chamber) you wont have enough fuel and you will have too much air and it wont all atomize and then the timing comes, ignites the spark plug and BOOM detonation. that is why sometimes the ignition has to be retarded...so that the spark event will happen later when enough fuel can arrive

 

Main reason is that running more timing will cause detonation and broken parts. Since the air/fuel mixture has been heated from the compressor, it will detonate earlier and as much timing can not be run. Another consideration is that the more air that is crammed into the cylinder, the more turbulent the motion is, and it burns faster.

A.

PS-The intake valve has been closed for quite some time before the timing sparks the plug.

[This message has been edited by askulte (edited April 18, 2001).]