So i was reading around on mazdaspeedforums found this interesting post
http://www.mazdaspeedforums.org/forum/f ... ost-48325/
I think we can get a good discussion going on here, would like your input steve, Me in just trying to learn. This is the first post.....
I've been thinking about this a LOT. I've had what I felt was a really good tune going with ATR, based on the appropriate Cobb OTS map, for a long time. I was running about 18psi peak tapering down, and it felt quick. Changes I had made to the OTS values were the load tables to make load less at lower rpm and peak at 3500 rpm, richened up part throttle fuel, but leaned out the high load, non WOT values to match the WOT tables, calibrated my MAF values, etc. Car ran good.
Then I swapped back to the stock map (not worth explaining why here). And really... I have to say, even though boost was a few psi less, and fuel is much more rich, load values are much lower, etc etc., to the butt dyno the car didn't really feel slower...
Then I ran some logs and noticed that one big thing that the stock map does WAY more agressively vs. the Cobb tunes is the timing advance. Well... that got me thinking... I know that more advance does make more power, to a point, through the whole power curve, on and off boost. I also know that our tiny stock turbo really isn't running at it's most efficient at 18psi, especially with the stock IC and exhaust (my only other mod is a CAI). At those boost levels, I think that the hp-gained-per-psi is very little. On the other hand, I have no idea how many HP you can pick up per degree of advance. I can say the stock map is running several more, like 5-6 more degrees more advance or more at WOT.
Has anyone ever considered that you can make just as much power running lower boost but going back to the stock-style, more agressive ignition timing? What I'm doing now, just for the hell of it, is running a new map which is based on the "installed stock v105" map, with the only changes being that I leaned out the WOT fuel and the high load areas of the other fuel tables to not run any richer than 11:1 in no-knock conditions. Boost, MAF values, load values, and ignition values are all stock.
The car feels plenty fast. Of course, the drop off after 6000 rpm is back, no big deal as I never shift past there anyways, and the throttle has that big jump at 35% or so where it feels like you suddenly floor it (easy enough to fix again, wasn't worried about it for this experiment). If I've lost any power at all, I can't tell.
But think of the benefits. The turbo is back down towards it's good efficiency range, meaning it's blowing less hot air. In the meantime, the more advanced timing hasn't caused any KR issues. And though I'm running an almost-stock map, I am running the fuel tables much closer to Cobb's values, so not retardedly rich, which should be resulting in a power increase over the stock map either way, no?
What are your oppinions? I mean... I know we are all of the mind that more boost = more power... man I wish I had endless cash to spend dyno testing this, but if the butt dyno can be at all trusted, I haven't lost any power by doing it this way!
Boost Vs Timing Power
Re: Boost Vs Timing Power
more boost = more trouble, not necessarily more power. You are pushing more air into your system, but can you compensate it with more fuel? Going back to spark advance, are you burning all that mixture efficiently? In time? There are a lot of things to consider here ... I am not all that knowledgeable in this stuff, but a lot of common sense applies ... The closer to stock I am, probably better I'm off. Anything is up for discussion though ... I'm curious to hear something from our tuning guys...
Re: Boost Vs Timing Power
The honest truth is that I wouldnt risk a stock motor testing out agressive timing changes. Having said that, alot of race motors run up to 37* of advance at wot at high rpm because you can technically run more advance as you go up rpm because the flame front does not speed up or slow down with rpm. Imagine this, if you want peak cyl pressure (max power) at say 10* into the power stroke at 3000rpm, and you get that peak with maybe 12* of advance, then you hold the timing steady and increase rpm to 6000rpm, because you have doubled the rpm you have, at least in theory, half the time to allow the flame front to build pressure. Because it took 22* of timing to build max cyl pressure at 3000rpm, it will take 44* of timing at 6000rpm, with that same 12* of advance, it will put the piston 30* into the bore before peak cyl pressure is reached vs 10* into the bore at 3000rpm.
Granted that everything I said is nearly complete bull shit because real life doesnt work that way because there are too many other variables to consider, but it does show that there is power to be made by advancing the timing as rpm increases.
I think the low rpm, low load timing on the stock tune can be fairly agressive, but as load and rpm increase, timing somehow gets stuck in a 4 to 12* range which is laughably safe. Ideally the way to go about setting timing is to run about 2* less than the maximum timing that you can run without knock, but few things about this motor are ideal.
Granted that everything I said is nearly complete bull shit because real life doesnt work that way because there are too many other variables to consider, but it does show that there is power to be made by advancing the timing as rpm increases.
I think the low rpm, low load timing on the stock tune can be fairly agressive, but as load and rpm increase, timing somehow gets stuck in a 4 to 12* range which is laughably safe. Ideally the way to go about setting timing is to run about 2* less than the maximum timing that you can run without knock, but few things about this motor are ideal.
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Steve @ VersaTune
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Re: Boost Vs Timing Power
This is a very complicated topic for sure.
I'll try to address the points separately
Stock turbo - The stock turbo is very efficient at 18psi, at lower mass flow rates. That's why 18psi at 3500 feels like a stump puller truck motor. As the RPMs increase and boost stays the same, the flow rate increases and the turbo starts to move out of it's peak efficiency range. Once you pass the peak efficiency, the more you flow at the same pressure ratio the less efficient it is. The air charge is heated more as efficiency drops. If the air charge gets too high and you exceed the ECU's high BAT threshold, the ecu begins to segue into the high BAT tables which have much lower load targets (see the implications of exceeding load targets below). Also, as you approach the flow limits of the turbine section, the exhaust back pressure increases significantly. This will show up as a boost increase with little or no mass flow increase. You have to raise the boost pressure to push against the exhaust back pressure. Pumping losses reduce the mechanical efficiency of the engine as well. This is why a 3" catless DP and 3" CBE make a huge difference in the performance of this engine. The stock turbo's turbine section is very small and restrictive. Opening up the exhaust after the turbine increases the pressure differential across the turbine and allows it to flow more. The side benefit is earlier/quicker spool. All of this is why a larger turbo can make more power at the same boost pressure. It's compressor is more efficient at higher mass flow rates and it's turbine is larger and has less back pressure. It will flow more air mass at a lower temperature making more power. The down side is possibly later/slower spool.
Timing - Peak torque is the point at which the least spark advance is required. As RPMs increase from there, more timing is required to get the peak cylinder pressure to occur at the desired crank angle. As stated above, this is because the flame front does not speed up significantly with increasing RPM. Typically in turbocharged engines on pump gas, max spark advance is knock limited. Direct injection engines tend to require less spark advance than port injected engines though. This is due to the better fuel atomization and cooler air/fuel charge resulting in faster combustion. Fine tuning spark timing usually requires a dyno to measure the subtle differences. More timing is not always better either. It is possible to have ignition start too early and build pressure too soon which pushes against the rising piston, but not cause knock.
Load Target Exceeded - It is important to know how the ECU uses spark timing to control excessive load. Specifically, when the ECU sees load output above the load target, it pulls timing - a lot. It can retard all the way to -14* with the stock tune. You won't see much cylinder pressure if you start combustion 14* ATDC!. If you are not closely watching load output, load targets, and spark timing, you might not get an accurate idea of whether tuning changes were beneficial or not. You might make a change that creates more load than the load target and the ECU is retarding timing.
Hopefully I answered some questions.
I'll try to address the points separately
Stock turbo - The stock turbo is very efficient at 18psi, at lower mass flow rates. That's why 18psi at 3500 feels like a stump puller truck motor. As the RPMs increase and boost stays the same, the flow rate increases and the turbo starts to move out of it's peak efficiency range. Once you pass the peak efficiency, the more you flow at the same pressure ratio the less efficient it is. The air charge is heated more as efficiency drops. If the air charge gets too high and you exceed the ECU's high BAT threshold, the ecu begins to segue into the high BAT tables which have much lower load targets (see the implications of exceeding load targets below). Also, as you approach the flow limits of the turbine section, the exhaust back pressure increases significantly. This will show up as a boost increase with little or no mass flow increase. You have to raise the boost pressure to push against the exhaust back pressure. Pumping losses reduce the mechanical efficiency of the engine as well. This is why a 3" catless DP and 3" CBE make a huge difference in the performance of this engine. The stock turbo's turbine section is very small and restrictive. Opening up the exhaust after the turbine increases the pressure differential across the turbine and allows it to flow more. The side benefit is earlier/quicker spool. All of this is why a larger turbo can make more power at the same boost pressure. It's compressor is more efficient at higher mass flow rates and it's turbine is larger and has less back pressure. It will flow more air mass at a lower temperature making more power. The down side is possibly later/slower spool.
Timing - Peak torque is the point at which the least spark advance is required. As RPMs increase from there, more timing is required to get the peak cylinder pressure to occur at the desired crank angle. As stated above, this is because the flame front does not speed up significantly with increasing RPM. Typically in turbocharged engines on pump gas, max spark advance is knock limited. Direct injection engines tend to require less spark advance than port injected engines though. This is due to the better fuel atomization and cooler air/fuel charge resulting in faster combustion. Fine tuning spark timing usually requires a dyno to measure the subtle differences. More timing is not always better either. It is possible to have ignition start too early and build pressure too soon which pushes against the rising piston, but not cause knock.
Load Target Exceeded - It is important to know how the ECU uses spark timing to control excessive load. Specifically, when the ECU sees load output above the load target, it pulls timing - a lot. It can retard all the way to -14* with the stock tune. You won't see much cylinder pressure if you start combustion 14* ATDC!. If you are not closely watching load output, load targets, and spark timing, you might not get an accurate idea of whether tuning changes were beneficial or not. You might make a change that creates more load than the load target and the ECU is retarding timing.
Hopefully I answered some questions.
Re: Boost Vs Timing Power
Here is what I got out of this:
"Fez, you know NOTHING about tuning. Stick to your desk job and leave your car to the professionals. plzktnx"
hahahaa!!
Thanks for the explanation, Steve. That actually makes sense.
"Fez, you know NOTHING about tuning. Stick to your desk job and leave your car to the professionals. plzktnx"
hahahaa!!
Thanks for the explanation, Steve. That actually makes sense.
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laxplayermjd
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Re: Boost Vs Timing Power
hmm interesting good information. althought its doesnt directly answer the question lol.
i believe it all depends on who you ask. they may be no way to tell
i supposed timing isnt as much important as big effiecient turbo vs small and the heat that they produce,
i was kind off confused as to how you can really change from low boost with extra timing that high boost with low timing. as either way they are both going to advance with rpms.
i believe it all depends on who you ask. they may be no way to tell
i supposed timing isnt as much important as big effiecient turbo vs small and the heat that they produce,
i was kind off confused as to how you can really change from low boost with extra timing that high boost with low timing. as either way they are both going to advance with rpms.
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Ugnius @ VersaTune
- Lead developer
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Re: Boost Vs Timing Power
Well, the way I understood is that for each specific engine configuration there is a single timing scheme that produces maximum torque while avoiding knock. Once you find that sweet spot, you won't add power by advancing timing further and will actually make things worse by creating peak pressure before the piston reaches TDC.
Stock timing scheme takes into account all kinds of situations the car might face, such as being able to operate all the way from Alaska to South California on the same tune. I think it definitely is possible to gain some power by fine tuning timing on a dyno and by making the scheme more aggressive and less safe.
What concerns boost, it directly relates to the amount of air pushed through the engine. It's like increasing displacement and as you know more air = more power. And you can keep raising boost as much as you want (provided you take care of fueling, charge air cooling and your block is strong enough). Theoretically it is possible to push out more than a 1000 HP out of our engine by raising boost sufficiently.
So in the long run, raising boost is the only way to make big torque and, consequently, power. If your question is what gives a bigger effect on a bone stock engine and stock turbo, I don't think we have that data. Moreover, I don't think you have to choose one or another, you can both raise boost and then fine tune timing on a dyno to get the best tune.
Steve, please correct me if I'm wrong.
Stock timing scheme takes into account all kinds of situations the car might face, such as being able to operate all the way from Alaska to South California on the same tune. I think it definitely is possible to gain some power by fine tuning timing on a dyno and by making the scheme more aggressive and less safe.
What concerns boost, it directly relates to the amount of air pushed through the engine. It's like increasing displacement and as you know more air = more power. And you can keep raising boost as much as you want (provided you take care of fueling, charge air cooling and your block is strong enough). Theoretically it is possible to push out more than a 1000 HP out of our engine by raising boost sufficiently.
So in the long run, raising boost is the only way to make big torque and, consequently, power. If your question is what gives a bigger effect on a bone stock engine and stock turbo, I don't think we have that data. Moreover, I don't think you have to choose one or another, you can both raise boost and then fine tune timing on a dyno to get the best tune.
Steve, please correct me if I'm wrong.
Re: Boost Vs Timing Power
Haha Steve made us all look like we dont have a clue, and somehow I like it.
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Steve @ VersaTune
- Lead tuner
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- Joined: March 29th, 2010, 12:58 pm
Re: Boost Vs Timing Power
Hopefully this will be more to the point
Boost - You need to look at MAF as much as you look at MAP. If you increase MAP (boost) and do not see an increase in MAF, you have an efficiency problem or flow limitation. The whole goal of tuning is to get as much air MASS, not necessarily pressure, into the engine, then ensure you have optimal fuel and timing. If you are increasing boost, but not seeing an increase in mass air flow, then you are most likely heating the air charge which will lead to knock and require you to back off timing. Remember the ideal gas law from high school chem class PV=nRT.
There certainly is a point of diminishing return with boost increase. The size of all of the engine components determines where exactly that point is. It is difficult to predict without doing a LOT of math, but you can tell by logging though. If a boost increase doesn't result in a mass air flow increase and especially if you see a rise in BAT, then you need to lower boost. That is how you determine whether a boost increase is useful.
Whether or not the engine is mechanically capable of handling the increased cylinder pressure is another discussion
Timing - When OEMs tune engines, they use incredibly expensive dyno cells with in-cylinder pressure transducers, gas analyzers, $10k microphones with DSP farms to listen for various noises, etc. I have toured the Ford dyno lab. It's serious stuff. There is a valid reason for each value in the table. But, as soon as you start changing engine components, that factory R&D becomes less relevant.
If timing is way off, you will feel the difference a few degrees makes. If you are within a degree or two of ideal, you might not feel much of a difference in the seat of the pants. There are too many other variables. The best we can affordably do is chassis dyno testing and monitoring the knock sensor. That and some common sense will get you a reliable, powerful tune.
Boost - You need to look at MAF as much as you look at MAP. If you increase MAP (boost) and do not see an increase in MAF, you have an efficiency problem or flow limitation. The whole goal of tuning is to get as much air MASS, not necessarily pressure, into the engine, then ensure you have optimal fuel and timing. If you are increasing boost, but not seeing an increase in mass air flow, then you are most likely heating the air charge which will lead to knock and require you to back off timing. Remember the ideal gas law from high school chem class PV=nRT.
There certainly is a point of diminishing return with boost increase. The size of all of the engine components determines where exactly that point is. It is difficult to predict without doing a LOT of math, but you can tell by logging though. If a boost increase doesn't result in a mass air flow increase and especially if you see a rise in BAT, then you need to lower boost. That is how you determine whether a boost increase is useful.
Whether or not the engine is mechanically capable of handling the increased cylinder pressure is another discussion
Timing - When OEMs tune engines, they use incredibly expensive dyno cells with in-cylinder pressure transducers, gas analyzers, $10k microphones with DSP farms to listen for various noises, etc. I have toured the Ford dyno lab. It's serious stuff. There is a valid reason for each value in the table. But, as soon as you start changing engine components, that factory R&D becomes less relevant.
If timing is way off, you will feel the difference a few degrees makes. If you are within a degree or two of ideal, you might not feel much of a difference in the seat of the pants. There are too many other variables. The best we can affordably do is chassis dyno testing and monitoring the knock sensor. That and some common sense will get you a reliable, powerful tune.
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Steve @ VersaTune
- Lead tuner
- Posts: 1157
- Joined: March 29th, 2010, 12:58 pm
Re: Boost Vs Timing Power
Even shorter answer:
If the boost air temp is so high that you have to retard timing so much that you lose more power than you would have gained from the increase in flow, then it's not worth it.
If the boost air temp is so high that you have to retard timing so much that you lose more power than you would have gained from the increase in flow, then it's not worth it.