TUNERS: discussion of ignition timing and spool time
09-12-2012, 12:35 PM
#1
Staging Lane
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TUNERS: discussion of ignition timing and spool time I figured since a couple of us were clogging up someone's thread, that it would be beneficial to start a thread discussing the pro's/ con's and theories behind advancing or retarding ignition timing and the effects it has on spool time. Ill go first :
Advancing the ignition timing increases cylinder pressure, which in turn increases the velocity and volume of exhaust flow into the turbine. It also increases the power output of the engine (prior to boost onset) to increase rpm's 'quicker'.
I believe that retarding the ignition timing in an attempt to increase exhaust temperature doesn't compare as exhaust flow and 'non boost' power are sacrificed.
Heat can be increased in either theory with leaning out the afr's, and I see where, with retarding the timing, a leaner afr 'could' be safely reached for more heat and possible power......
Advancing the ignition timing increases cylinder pressure, which in turn increases the velocity and volume of exhaust flow into the turbine. It also increases the power output of the engine (prior to boost onset) to increase rpm's 'quicker'.
I believe that retarding the ignition timing in an attempt to increase exhaust temperature doesn't compare as exhaust flow and 'non boost' power are sacrificed.
Heat can be increased in either theory with leaning out the afr's, and I see where, with retarding the timing, a leaner afr 'could' be safely reached for more heat and possible power......
09-12-2012, 01:04 PM
#5
Staging Lane
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Yes... that is my whole core with it. We were having a dicussion with atomic in another thread and he is under the impression that retarding ignition timing spools turbos quicker than advancing the timing simply due to heat
09-12-2012, 01:37 PM
#7
I've found with automatics timing, timing, timing and leaner AFR's get the turbo to spool with heat, more cylinder pressure and exhaust velocity all at once.
With manuals dumping fuel and retarding timing in a no load application(clutch dis-engaged on the line) builds boost better from everything and everyone I've ever listened to talk about turbo's and spooling with manuals.
Will retarding timing and relying on heat spool a turbo? Probably, but the question is...how quickly? How long does it take for it to finally build enough heat just waiting on that one component to help it spool?
I dunno, but I know I'd rather use increased cylinder pressure, increased exhaust velocity, increased heat from leaning the mixture out all together at once to build my boost and get up and spooled quickly as in 3-5 seconds at the most from footbrake spooling to on the transbrake hitting the two step limiter waiting for the tree to drop not 3-5 seconds on the footbrake then bumping in to the beams, then grabbing the transbrake waiting for the tree to drop.
There are a million ways to skin a cat, but most cat skinners use timing timing timing and lean afr's, and some....once they have their spool limit boost met(footbrake) will retard the timing as a way to build more boost as sometimes once you get a certain amount of boost built at the rpm you have your spool limit set at(footbrake) it will flat line at that rpm and won't build anymore. To build more they retard it once they have 5-9psi built and good shaft speed to move the combustion process out of the cylinder and into the hot manifolds where the fuel then lights off closer to the turbine creating more boost.
Last edited by Sales@Tick; 09-12-2012 at 01:47 PM.
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09-12-2012, 02:37 PM
#10
I was just messing with you.
I've found with automatics timing, timing, timing and leaner AFR's get the turbo to spool with heat, more cylinder pressure and exhaust velocity all at once.
With manuals dumping fuel and retarding timing in a no load application(clutch dis-engaged on the line) builds boost better from everything and everyone I've ever listened to talk about turbo's and spooling with manuals.
Will retarding timing and relying on heat spool a turbo? Probably, but the question is...how quickly? How long does it take for it to finally build enough heat just waiting on that one component to help it spool?
I dunno, but I know I'd rather use increased cylinder pressure, increased exhaust velocity, increased heat from leaning the mixture out all together at once to build my boost and get up and spooled quickly as in 3-5 seconds at the most from footbrake spooling to on the transbrake hitting the two step limiter waiting for the tree to drop not 3-5 seconds on the footbrake then bumping in to the beams, then grabbing the transbrake waiting for the tree to drop.
There are a million ways to skin a cat, but most cat skinners use timing timing timing and lean afr's, and some....once they have their spool limit boost met(footbrake) will retard the timing as a way to build more boost as sometimes once you get a certain amount of boost built at the rpm you have your spool limit set at(footbrake) it will flat line at that rpm and won't build anymore. To build more they retard it once they have 5-9psi built and good shaft speed to move the combustion process out of the cylinder and into the hot manifolds where the fuel then lights off closer to the turbine creating more boost.
I've found with automatics timing, timing, timing and leaner AFR's get the turbo to spool with heat, more cylinder pressure and exhaust velocity all at once.
With manuals dumping fuel and retarding timing in a no load application(clutch dis-engaged on the line) builds boost better from everything and everyone I've ever listened to talk about turbo's and spooling with manuals.
Will retarding timing and relying on heat spool a turbo? Probably, but the question is...how quickly? How long does it take for it to finally build enough heat just waiting on that one component to help it spool?
I dunno, but I know I'd rather use increased cylinder pressure, increased exhaust velocity, increased heat from leaning the mixture out all together at once to build my boost and get up and spooled quickly as in 3-5 seconds at the most from footbrake spooling to on the transbrake hitting the two step limiter waiting for the tree to drop not 3-5 seconds on the footbrake then bumping in to the beams, then grabbing the transbrake waiting for the tree to drop.
There are a million ways to skin a cat, but most cat skinners use timing timing timing and lean afr's, and some....once they have their spool limit boost met(footbrake) will retard the timing as a way to build more boost as sometimes once you get a certain amount of boost built at the rpm you have your spool limit set at(footbrake) it will flat line at that rpm and won't build anymore. To build more they retard it once they have 5-9psi built and good shaft speed to move the combustion process out of the cylinder and into the hot manifolds where the fuel then lights off closer to the turbine creating more boost.
09-12-2012, 02:55 PM
#11
9 Second Club
Tuning and engine with abnormally low timing will just make it lethargic and slow whether n/a or boosted
the only time low timing assists spool is when the exhaust valve is still open. But that's a totally different scenario altogether.
09-12-2012, 04:16 PM
#12
LS1Tech Co-Founder
iTrader: (34)
Seems self evident that running overly rich will only make it harder for the engine to climb up through the rpms. And for racing-only applications it would seem to me that you'd want to get it light off good because in some cases you could be running some seriously cold spark plugs with barely any gap.
09-12-2012, 04:22 PM
#13
This is off the line, actually on a roll is easier at least for me...If a maf car you have to manipulate the scaling of the maf in the kpa range off the line, you also need to get into the PE tables because of % TPS that controls the fuel, % TPS that goes into the PE mode ect. I mean its just not plain and simple, it does take time to get it correct....
09-12-2012, 04:28 PM
#16
This is off the line, actually on a roll is easier at least for me...If a maf car you have to manipulate the scaling of the maf in the kpa range off the line, you also need to get into the PE tables because of % TPS that controls the fuel, % TPS that goes into the PE mode ect. I mean its just not plain and simple, it does take time to get it correct....
09-12-2012, 08:11 PM
#19
with out question the best way I have found with my clutch car is to pull all the timing out of it when I have the clutch pressed in. I have boost in an instant when I pull 20* of timing...