Tuning MBT

[Captain Bondo]

Interested to hear what sort of strategies that you guys who are attempting to tune your cars correctly are using for finding MBT (Minimum timing for Best Torque).

There don't seem to be many steady state dynos in my area- tuning for MBT seems like it would be tedious without a load cell equipped dyno.

Any thoughts? I'm a bit worried as acheiving an ignition map that's +/- a degree or so of MBT at most load point is also a pretty big part of my "master plan" along with low EBR.

I just can't see how you'd do it unless you had either steady state dyno or chamber pressure transducers.

 

[blkaplan]

Interested to hear what sort of strategies that you guys who are attempting to tune your cars correctly are using for finding MBT (Minimum timing for Best Torque).

There don't seem to be many steady state dynos in my area- tuning for MBT seems like it would be tedious without a load cell equipped dyno.

Any thoughts? I'm a bit worried as acheiving an ignition map that's +/- a degree or so of MBT at most load point is also a pretty big part of my "master plan" along with low EBR.

I just can't see how you'd do it unless you had either steady state dyno or chamber pressure transducers.

Find a better dyno? There are also companys that make driveshafts with built in load cells to give a torque reading. You could use datalogging and real time correction to tune the ignition table.

 

[Captain Bondo]

Find a better dyno? There are also companys that make driveshafts with built in load cells to give a torque reading. You could use datalogging and real time correction to tune the ignition table.

I just don't particularly want a 2 hour drive to the dyno if I can help it, but I guess it might be necessary.

Your other suggestions do not really apply to what I am trying to determine, to be honest. Maybe I have not explained the process correctly.

This isn't about "real time correction" - I don't think Megasquirt can accept some manner of analog input for torque and autotune spark, and a load cell in the driveshaft wouldn't tell me anything a standard dyno's torque measurment wouldn't- which isn't what I care about for tuinng.

 

[blkaplan]

I just don't particularly want a 2 hour drive to the dyno if I can help it, but I guess it might be necessary.

Your other suggestions do not really apply to what I am trying to determine, to be honest. Maybe I have not explained the process correctly.

This isn't about "real time correction" - I don't think Megasquirt can accept some manner of analog input for torque and autotune spark, and a load cell in the driveshaft wouldn't tell me anything a standard dyno's torque measurment wouldn't- which isn't what I care about for tuinng.

I wasn't really suggesting it for real time correction but as a method for tuning for maximum torque with minimum timing. It should be very easy to write a script that reviews the datalog and adjusts for minimum timing with maximum torque if you can input the the torque into your data logger.

Its much better then a standard dyno but a load holding dyno is the most straight forward way to get what your after

 

[JR-66]

Chamber pressure is the only proper way to determine proper ignition points. For diy tuners datalogging and tuning and datalogging and tuning gives reasonable good result, folks here with megasquirt and such logs data, calculate powercurves out of it, tune, log, calculate again and so on. With acceleration measurement gadgets one can also get pretty good results. Of course knowing when the engine knocks helps... Downside is finding proper place to beat the crap out.

 

[blkaplan]

Chamber pressure is the only proper way to determine proper ignition points. For diy tuners datalogging and tuning and datalogging and tuning gives reasonable good result, folks here with megasquirt and such logs data, calculate powercurves out of it, tune, log, calculate again and so on. With acceleration measurement gadgets one can also get pretty good results. Of course knowing when the engine knocks helps... Downside is finding proper place to beat the crap out.

What have you been using the chamber pressure measurement?

 

[JR-66]

What have you been using the chamber pressure measurement?

None, way too expensive for diy people, if I remember correct, just the plug with piezo element costs something like 2000 bucks or something silly like that, then you need electronics and softwares too.

 

[Captain Bondo]

Chamber pressure is the only proper way to determine proper ignition points.

Chamber pressure still means nothing if you can't hold the engine at a fixed load. If you are measuring torque or chamber pressure either will work, but you need to be able to run at a fixed point.

Of course knowing when the engine knocks helps... Downside is finding proper place to beat the crap out.

It helps you not blow the motor up but it doesn't help you tune correctly. This is a misconception.

What needs to be understood is that the optimal ignition timing value is not necessarily just before you get detonation. Sometimes the vlaue for MBT is 6 or 10 degrees lower than the value that induces knock.

That window in between just results in a lot of extra strain on the engine with no gain (or even a loss) in output.

 

[JR-66]

None, way too expensive for diy people, if I remember correct, just the plug with piezo element costs something like 2000 bucks or something silly like that, then you need electronics and softwares too.

Edit, pressure sensor prices start at 5000?

 

[JR-66]

Chamber pressure still means nothing if you can't hold the engine at a fixed load. If you are measuring torque or chamber pressure either will work, but you need to be able to run at a fixed point.




It helps you not blow the motor up but it doesn't help you tune correctly. This is a misconception.

What needs to be understood is that the optimal ignition timing value is not necessarily just before you get detonation. Sometimes the vlaue for MBT is 6 or 10 degrees lower than the value that induces knock.

That window in between just results in a lot of extra strain on the engine with no gain (or even a loss) in output.

True, I believe none that owns those sensors work at cheap dynos...

And the knowing when it knocks give you rough estimate when to back out, just to get some scale what range to work. With datalogging(and power calculation or other method) one can found the points where torque stops rising. I know that most tuners just haunts knock point and just pull back couple degrees.

 

[Captain Bondo]

. I know that most tuners just haunts knock point and just pull back couple degrees.

That's what I want to avoid. That isn't tuning IMO.

 

[Karl Buchka]

Call it what you want, but it works well enough to get the spark map pretty close to optimal. Sounds like you've got a 2 hour drive ahead of you.

 

[Captain Bondo]

Call it what you want, but it works well enough to get the spark map pretty close to optimal. .

Comparisons of cars road tuned using this method and then dyno tuned using this method would disagree with you. The only way to know if it is close it to do a steady state tune and compare them - otherwise you are guessing. You are assuming that the detonation threshold is near MBT and while it somettimes is, it is often not.


Here is an example from EFI101 - ferrai F40 that made 495hp with 32 degrees of advance.
After steady state tuning it made 591hp at 14 degrees. Same boost, the road tune was done by a well know Pectel tuner.

 

[Janne K]

So you do not want to drive to a load cell dyno, and yet you tell us that load cell dyno tuning is the only way to go? Hmm, i don't know man. Too much paint thinners at your garage after all the bodywork?

If you wan't to tune in an inertia-dyno, you can do a bazillion runs, make one change at a time, and see where power goes after each change. But i know that you already knew that, that would be the tedious job mentioned earlier. And if you're looking to get MBT timing for other than WOT conditions, the inertia-dyno is no good.

So find a load cell dyno and be done with it?

 

[blkaplan]

I have complete access to a load cell dyno 15 minutes from my house

 

[Captain Bondo]

So you do not want to drive to a load cell dyno, and yet you tell us that load cell dyno tuning is the only way to go? Hmm, i don't know man. Too much paint thinners at your garage after all the bodywork?

I am saying it is typically the most straight forward way to tune a car based on my criteria for what a good tune is.

And no, I'm not terribly interested in being hours away from home if something goes wrong.

Hence why I was looking for strategies people are employing to get something closer to what I am looking for ahead of time.

Sounds like everyone just cranks it till it pings and then backs it off. Not suprising I guess.

Is there something about my way of typing that is hard to understand?

 

[JR-66]

Maximum torque at any given load point, sounds like a bumpy ride, what about driveability?

Is there more behind that Ferrari dynoshoot somewhere? Should be fun to see what EGT and such it had.

 

[Captain Bondo]

Maximum torque at any given load point, sounds like a bumpy ride, what about driveability?

Seriously?

Of course. This is worse than the geometry correction thread. Of course you want the timing to produce best torque at every load point. Why wouldn't you?

Man I am seriously going grey here.

Ok the point of this thread was not to explain fundamental engine concepts but,

If every point is optimized, then the less throttle/map you need to to keep the car moving forward, this includes cruise and is therefore also the tuning method that will give best fuel economy and nice cruise.

Surely you can accept that the timing that makes the best torque is making the best use out of the volume of fuel injected. That inherently makes driveability good.

Neutering the ignition map intentially to tyr to improve part throttle response makes no sense.

 

[the poi]

2 hour drive (and know what tow company you can call)! It's so trivial once you get on a load dyno, there's no other method that makes any sense.

 

[TerribleOne]

If you're getting that serious about your timing maybe it's time to bolt your block up to an engine dyno.. Do you have AAA+ in canada?