Ok so I have a question, unless your timing is already advanced ahead of normal, how does retarding your timing help against PRE-ignigtion? I mean the DEFINITION of PRE-ignition is the fuel igniting BEFORE the spark takes place, am I wrong? Kind of the same effect as diesel engines that use no spark plugs(cant retard your timing more than NO timing). Or like older carbed cars that would continue to diesel over when they were shut off(had no spark), because they would still suck fuel? Im seeing all these ignition kits that retard your timing like 50 fucking degree's for every pound of boost you run, and all that is spelling to me is loss in HP. Ill stick to bigger intercoolers and lowering compressions if I want to run more boost. I got knock in my 240 and retarded the timing until the thing could barely idle, didnt do shit, put a bigger intercooler on and havent heard a ping since, even ran 3 more psi. So anyone tell me why paying $400 for one of these kits isnt wasting my money?
ggeiss240sx
From what I understand, if you set things up and aren't worried about knocking or pre-ignition then, sure, all pulling timing's going to do is make you lose power. I think retarding on boost is supposed to prevent knocking more than pre-ignition, really, though knocking over time can heat up the plug and cause pre-ignition. The chances of knocking become higher with boost because of the larger amount of combusted gas, higher cylinder pressures and temperatures.
Sparking later (within a reaosnable limit) can make knocking less likely by reducing the time window of opportunity for knocking, lowering the burn rate at the end of the burn, and lowering overall cylinder pressures and temperatures. Sure, you lose power, but it might allow you to run more boost, or offer a greater margin of safety for something like a forced 91 fill-up.
The cheapest boost retard units are like $150 from Summit Racing. Though its approach of pulling timing with a fixed rate starting at 0psi seems quite compromising (though there are decent ways of making the 'curve' more suitable), the unit seems like a good deal, especially if boosting a high compression motor.
Shiva
Sparking later (within a reaosnable limit) can make knocking less likely by reducing the time window of opportunity for knocking, lowering the burn rate at the end of the burn, and lowering overall cylinder pressures and temperatures. Sure, you lose power, but it might allow you to run more boost, or offer a greater margin of safety for something like a forced 91 fill-up.
The cheapest boost retard units are like $150 from Summit Racing. Though its approach of pulling timing with a fixed rate starting at 0psi seems quite compromising (though there are decent ways of making the 'curve' more suitable), the unit seems like a good deal, especially if boosting a high compression motor.
Shiva
Don't confuse pre ignition or "pinging" with auto ignition or "detonation."
Pinging is ignition started before the sparkplug fires. (for whatever reason) and can lead to detonation,.... But detonation usually occurs after the scheduled (timed) spark. It occurs when peak cylinder pressures generate enough pressure (pressure=heat) to overcome the fuel's octane rating and causes AUTO ignition, where ALL the fuel burns simultaneously,... Ie. explodes.
The earlier the spark timing (btdc) coupled with higher static compression and/or more boost, the higher peak cylinder pressure becomes and the greater the likelyhood of detonation without additional octane rating.
A few degrees of retard can drop the peak cylinder pressure enough to spread the burn out over a greater duration giving the desired controlled burn and the additional power you are expecting from more boost. There is little need for more than 12*-15* of retard in all but the most advanced timing event(s) or lousy fuel.
Remember we are talking about TOTAL advance here not initial. Racing engines may run as much as 48-52 degrees of total advance depending on chamber design, static compression ratio, fuel specs, cam specs etc.
More advance in the low-mid RPM ranges can increase off boost torque and help spool the turbo earlier, but would be catastrophic as the boost and RPMs climb, thus the need for some later (boost) retard.
Boost retarders are just one more tuning tool when you are pushing the envelope.
Ihth,
Jamie
Pinging is ignition started before the sparkplug fires. (for whatever reason) and can lead to detonation,.... But detonation usually occurs after the scheduled (timed) spark. It occurs when peak cylinder pressures generate enough pressure (pressure=heat) to overcome the fuel's octane rating and causes AUTO ignition, where ALL the fuel burns simultaneously,... Ie. explodes.
The earlier the spark timing (btdc) coupled with higher static compression and/or more boost, the higher peak cylinder pressure becomes and the greater the likelyhood of detonation without additional octane rating.
A few degrees of retard can drop the peak cylinder pressure enough to spread the burn out over a greater duration giving the desired controlled burn and the additional power you are expecting from more boost. There is little need for more than 12*-15* of retard in all but the most advanced timing event(s) or lousy fuel.
Remember we are talking about TOTAL advance here not initial. Racing engines may run as much as 48-52 degrees of total advance depending on chamber design, static compression ratio, fuel specs, cam specs etc.
More advance in the low-mid RPM ranges can increase off boost torque and help spool the turbo earlier, but would be catastrophic as the boost and RPMs climb, thus the need for some later (boost) retard.
Boost retarders are just one more tuning tool when you are pushing the envelope.
Ihth,
Jamie
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