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Old 08-14-2007, 12:14 AM   #1
Kastley85891
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Default Advancing timing to aid turbo spool up

Any one tried it? , any recommends to this method?
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Old 08-14-2007, 12:25 AM   #2
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Lean it out, advancing timing will lower EGTs in most cases and that'll slow spool but increase torque. Try to make as much torque at the leanest AFR that you can, spool up will greatly increase.
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Old 08-14-2007, 02:36 AM   #3
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Quote:
Originally Posted by Master2192 View Post
Lean it out, advancing timing will lower EGTs in most cases and that'll slow spool but increase torque. Try to make as much torque at the leanest AFR that you can, spool up will greatly increase.

Thanks for input, its all very interesting
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Old 08-14-2007, 07:44 AM   #4
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Pulling timing pre-spoolup and adding it back in right as the turbo comes on made a significant difference for me.
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Old 06-13-2008, 05:33 AM   #5
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just to be clear - when you say lean out and advance timing as much as possible during 'spool-up' means 'time the turbo starts spinning until it reaches peak boost/torque' right?
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Old 06-13-2008, 08:26 AM   #6
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correct.

There are many, MANY thoughts on how to make the turbo spool faster. The net result of all of them is that your EGT increases, because EGT+exhuast mass is what spools turbos.

However, all of these things generally speaking will reduce power pre-spool, because if the EGT is higher than it was when the engine was making max power (at MBT and correct AFR), then your engine is running less efficiently (heat in the exhaust is heat that didn't go into pushing down the piston).

The debate about which is more important is endless. Really, it comes down to which feels better to you driving.

Keep in mind that at low load/RPM it's very, VERY possible to advance timing past MBT without knocking. This is bad. Very bad. Remember also that MBT changes with AFR, because the speed at which fuel burns changes based on AFR. This isn't a liner relationship, but as you move away from 12:1 (leaner or richer) you must advance timing, and as you move towards it you must retard timing, assuming of course you started at MBT for the AFR you started at.

There are also other ways to increase spool. Changing the WGDC, changing the turbo dynamics tables, etc can also greatly effect spool, but you have to be careful as they can also cause boost spikes/overboosting.

Last edited by AruisDante; 06-13-2008 at 08:31 AM.
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Old 06-16-2008, 02:38 AM   #7
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Quote:
Originally Posted by AruisDante View Post
correct.

There are many, MANY thoughts on how to make the turbo spool faster. The net result of all of them is that your EGT increases, because EGT+exhuast mass is what spools turbos.
So in terms fuel, which are the most common and proven ways to increase spool-up faster ? In terms of fuel, do you run richest AFRs levels during peak torque/boost and bring it back up leaner towards target AFR levels, all the way across to redline? or do you lean out during peak torque/load and continue towards redline within target AFRs? Understand that as far as timing is concerned you will probably have to run the least amount at peak torque/boost.

Quote:
Originally Posted by AruisDante View Post
Keep in mind that at low load/RPM it's very, VERY possible to advance timing past MBT without knocking. This is bad. Very bad. Remember also that MBT changes with AFR, because the speed at which fuel burns changes based on AFR. This isn't a liner relationship, but as you move away from 12:1 (leaner or richer) you must advance timing, and as you move towards it you must retard timing, assuming of course you started at MBT for the AFR you started at.
I know you can actually log to see timing being pulled at high load/rpm on WOT pulls. But how do you know when you have achieved MBT and when you are starting to pass it at low load/RPM?

Am i right in saying that 'MBT' is maximum allowable timing right just before the onset of knock (or timing being pulled by ECU as a result) across the entire rpm/load range?

Thanks.
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Old 06-16-2008, 07:32 AM   #8
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No. MBT is "Maxium Best Timing" (or sometimes Maximum Best Torque). It is the timing at which the entier flamefront will have propogated at ~15* ADC. This is the "ideal timing", I.E. the timing which will give you the maximum torque/power for a given AFR/RPM. At low RPMs/load it is very possible to advance past this number before knock occors. At high RPM/load, it's most likely that you'll be slightly below this number before knock occors.

Here is a very good website which will explain it better: http://www.max-boost.co.uk/max-boost...ion_deeper.htm

Generally speaking, MBT will give you the lowest EGT for a given AFR.
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Old 06-17-2008, 07:36 AM   #9
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Quote:
I know you can actually log to see timing being pulled at high load/rpm on WOT pulls. But how do you know when you have achieved MBT and when you are starting to pass it at low load/RPM?
MBT is one of those terms that has multiple definitions, its correct definition as used by SAE and in NACA is "minimum best torque timing". It defines a safe repeatable tune. Torque and hp near ideal timing is a very flat hump if you were to graph it. Minimum timing that gets you within 1% of maximum torque is one common definition used by professionals. Basically you tweak the timing at a given rpm/load until you maximize torque then back off the timing until you can just detect a slight reduction in torque.

http://www.ecutek.com/tuning/ignition/
http://ieeexplore.ieee.org/xpl/freea...number=4162499
http://www.visteon.com/utils/whitepa...03_01_3266.pdf


That gives you a tune that is inherently safe as you are on the safe side of the hump. As mentioned above, it is very easy to over advance the timing at low load and rpm, then you put 4 big friends in the car and blow up the engine because now you are knocking heavily due to the increased load.

The same goes for AFR on your mixture. You gain very little by leaning it out to max out power, all you are doing is intentionally putting the tune in the most dangerous part of the mixture curve.

An old rule of thumb used in the muscle car days is that max power is typically 2-3 degrees of ignition advance retarded from detectable knock. Before testing instruments were affordable and easy to find folks would jack up the timing until they could just hear the engine rattle a bit (light knock) under high load, check the timing and then back off 2-3 degrees.


To answer your original question, retard the timing slightly just prior to the point you want the turbo to spool. This results in the exhaust valve opening when the burn process is still in progress because you don't have enough ignition advance, increasing exhaust pressure/energy and heat due to afterburning in the exhaust manifold.
Larry
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Old 06-17-2008, 08:34 AM   #10
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Don't tune for spool.
Tune for torque.

Who cares how much boost you are making if you are making power, you are making power. Boost is just a restriction.
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Old 06-17-2008, 09:38 AM   #11
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Quote:
Originally Posted by AruisDante View Post
Keep in mind that at low load/RPM it's very, VERY possible to advance timing past MBT without knocking. This is bad. Very bad. Remember also that MBT changes with AFR, because the speed at which fuel burns changes based on AFR. This isn't a liner relationship, but as you move away from 12:1 (leaner or richer) you must advance timing, and as you move towards it you must retard timing, assuming of course you started at MBT for the AFR you started at.
So how do you know if you are at 'MBT' at low rpm/load? Since it's bad to have too much or too little timing beyond MBT.

Also could you explain more on the moving away/advance timing and moving towards/retard timing and is 12:1 the magical AFR value this is based on?

And if i get you right, generally if you run leaner AFRs you don't need that much timing advance right? and a clear indication of this would be when ECU would start to pull timing on certain rpm/load points when it previously did not right?
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Old 06-17-2008, 12:08 PM   #12
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read the article I linked to. It will explain the answers to your questions far better than I can.

As for the spool vs. tq debate, I'm somewhat on the fence. However, for a street car I completely agree, as there's no question that trying to tune for spool will reduce initial response, and thus streetability. However, I can see some applications in race cars where scarificing tip-in power for spool would be adventagious if the net average power (area under the curve) is larger.

Since I've never seen dynos comparing the same car 'tuned for spool' vs. 'tuned for low end power', I can't make a judgement in that respect.

However, your statement about boost being a restriction in this context is false. Boost increasing due to a restriction would have to do entierly with the volumetric efficientcy of the engine, which is entierly mechanically dependant and thus wouldn't change based on the tuning of the car (except for variable valve/timing of course).
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Old 06-17-2008, 12:16 PM   #13
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To me tuning for boost means you will have to retard timing. In the spool up area of the curve timing is what will net you torque. If you reduce timing to gain a few hundred rpm of boost onset you loose out in the area under the curve. Just IMO.
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Old 06-17-2008, 05:12 PM   #14
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Quote:
So how do you know if you are at 'MBT' at low rpm/load? Since it's bad to have too much or too little timing beyond MBT.

Also could you explain more on the moving away/advance timing and moving towards/retard timing and is 12:1 the magical AFR value this is based on?
There are several things you can watch to determine that. If your timing is retarded, you EGT's generally go up as the fuel is still burning when the exhaust valve opens. If your timing is too advanced you start to see it in the spark plugs and engine heating (coolant temps spike under load for example). On a dyno or road tuning your looking for the minimum timing that gives you near maximum power. At highway cruise that would show up as being able to run at highway cruise speed with minimum throttle (ie highest manifold vacuum). If one timing setting at 65 mph cruise gives you MAF air flow of say 20 grams per second and another timing setting gets that same speed at 18 grams per second you are obviously using less fuel to reach your mixture if you drop your air demand by 10%.

The thing many people do not realize is that as you change AFR you are also in effect changing your timing because the burn speed of the mixture changes with fuel air mixture. On gasoline your fastest burn speeds are near11.5-12.5 AFR's as you go leaner or richer than that range your burn speed slows down. You have to think of the combined effects and realize that as you tune one you are also effecting the other and occasionally you need to go back and confirm you are still at ideal AFR or ideal timing.

On NA cars a good safe assumption is that 12.5:1 AFR will be near max power mixture under high load. In turbocharged cars that number tends to move to richer mixtures to control combustion temperatures and detonation with 11.5 or so being a good starting point. After that it is a matter of letting the engine tell you what it wants as you make small changes in both fuel air mixture and timing and see what the engine does with those changes. As you get closer and closer to the ideal timing/fuel air mixture the width of your sweet spot gets smaller and smaller as detonation happens earlier on the over ignition advance and lean mixture side, and high EGTs happen later (closer to the sweet spot) as you go rich and retarded in the timing. At some point you are dancing on the head of a pin where if you advance the timing or lean the mixture just a bit it goes into detonation, and if you retard timing or richen the mixture just a little you start to see high EGTs. At that point you have the best possible tune for those specific conditions -- but you have tuned away all your safety cushion At that point on a turbo charged car you need to back off the boost a bit to get your safety cushion back and retard the timing just a tad to put you on the safe side of the curve and call it a day. Engine tuning is as much an art as science as a skilled tuner knows from experience when to back off and say he is done. The inexperienced tuner keeps tuning to get that last hp and in the process ends up with a knife edge tune that is impressive on the dyno but will kill the engine on the street if conditions are outside his tuning conditions (too hot, lower humidity, stuck in a traffic jam and heat soaked, poor fuel etc.)

Larry

Last edited by hotrod; 06-17-2008 at 05:24 PM.
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Old 06-17-2008, 09:10 PM   #15
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Quote:
Originally Posted by hotrod View Post
There are several things you can watch to determine that. If your timing is retarded, you EGT's generally go up as the fuel is still burning when the exhaust valve opens. If your timing is too advanced you start to see it in the spark plugs and engine heating (coolant temps spike under load for example). On a dyno or road tuning your looking for the minimum timing that gives you near maximum power. At highway cruise that would show up as being able to run at highway cruise speed with minimum throttle (ie highest manifold vacuum). If one timing setting at 65 mph cruise gives you MAF air flow of say 20 grams per second and another timing setting gets that same speed at 18 grams per second you are obviously using less fuel to reach your mixture if you drop your air demand by 10%.

The thing many people do not realize is that as you change AFR you are also in effect changing your timing because the burn speed of the mixture changes with fuel air mixture. On gasoline your fastest burn speeds are near11.5-12.5 AFR's as you go leaner or richer than that range your burn speed slows down. You have to think of the combined effects and realize that as you tune one you are also effecting the other and occasionally you need to go back and confirm you are still at ideal AFR or ideal timing.

On NA cars a good safe assumption is that 12.5:1 AFR will be near max power mixture under high load. In turbocharged cars that number tends to move to richer mixtures to control combustion temperatures and detonation with 11.5 or so being a good starting point. After that it is a matter of letting the engine tell you what it wants as you make small changes in both fuel air mixture and timing and see what the engine does with those changes. As you get closer and closer to the ideal timing/fuel air mixture the width of your sweet spot gets smaller and smaller as detonation happens earlier on the over ignition advance and lean mixture side, and high EGTs happen later (closer to the sweet spot) as you go rich and retarded in the timing. At some point you are dancing on the head of a pin where if you advance the timing or lean the mixture just a bit it goes into detonation, and if you retard timing or richen the mixture just a little you start to see high EGTs. At that point you have the best possible tune for those specific conditions -- but you have tuned away all your safety cushion At that point on a turbo charged car you need to back off the boost a bit to get your safety cushion back and retard the timing just a tad to put you on the safe side of the curve and call it a day. Engine tuning is as much an art as science as a skilled tuner knows from experience when to back off and say he is done. The inexperienced tuner keeps tuning to get that last hp and in the process ends up with a knife edge tune that is impressive on the dyno but will kill the engine on the street if conditions are outside his tuning conditions (too hot, lower humidity, stuck in a traffic jam and heat soaked, poor fuel etc.)

Larry
Yep. This is why I told him to read that article I linked, it explains all of this in more detail and even gives numbers for flame speeds depending on AFR's.

I don't know if I'd go so far as calling tuning more of an art than a science. But that's a totally different debate for another time.
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Old 01-18-2018, 03:43 PM   #16
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Subscribed
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Old 01-18-2018, 07:37 PM   #17
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To a dead thread from a decade ago?
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Old 01-18-2018, 07:44 PM   #18
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Lol. yes. I was mobile and this is a good read I had to tag quickly without much attention to what I was doing.
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Old 03-22-2019, 04:21 PM   #19
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Yeah that one guy at the beginning is dead even. Bummer. The no knock at low load idea is new tho. I thought i was maybe going a bit high. Thanks guys
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