MAP or Throttle Pos?

[Mike Hart]

After speaking with a few people at FSG I've been thinking about whether it would be worth using MAP as the load indicator as opposed to Throttle Pos. The implication was that when using MAP it's possible to achieve a low idle which is not possible in my experience with Throttle Pos.

I do however remember reading a while back that the may be some issues due to the restrictor causing odd pressures at higher rpms making mapping difficult.

So if anyone has any opinion as to which is best and what the advantages and disadvantages are then I'd be interested to hear them.

[Mike Hart]

After speaking with a few people at FSG I've been thinking about whether it would be worth using MAP as the load indicator as opposed to Throttle Pos. The implication was that when using MAP it's possible to achieve a low idle which is not possible in my experience with Throttle Pos.

I do however remember reading a while back that the may be some issues due to the restrictor causing odd pressures at higher rpms making mapping difficult.

So if anyone has any opinion as to which is best and what the advantages and disadvantages are then I'd be interested to hear them.

[MikeDutsa]

We are running a P.E. ecu. last year we hooked up both the map and tps, but we could never get the car to run on the map. the tps turned out to be very driveable. and we were able to achive an idle of 1200rpm on an f4i

[Erich Ohlde]

I've personally done tuning for the last four KU cars (all on an AEM), on each of those cars we have run a speed-density fuel/ign map with throttle based fuel enrichments. I've never had any problems tuning at high rpms with this system. I think you would do ok if you went speed-throttle as long as you did transient enrichments with the MAP (this is much harder to do). Keep in mind that your calibrations with a speed throttle setup are only good for a few hundred feet of elevation, you will have problems with lean/rich after that, speed density doesn't have that problem.

[BryanH]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jayhawk_electrical:
Keep in mind that your calibrations with a speed throttle setup are only good for a few hundred feet of elevation, you will have problems with lean/rich after that, speed density doesn't have that problem. </div></BLOCKQUOTE>

Erich, this is actually incorrect information. An engine with low manifold vacuum/long cam overlap running in speed density mode is dramatically effected by altitude, leaning out as altitude increases. eg 6% drop in baro = 25% leanout. Delco pcm's use wot maps with baro correction to get around this.
On the other hand AlphaN calibration is much more elegant, using constant baro correction and calculating the qty of oxygen molecules in the cyl on throttle plate position and air temp near the point of injection, which endless testing by many has proven to be very precise.

Which is the big drama with speed/density, as you are estimating air flow based on manifold vacuum, It is NOT an accurate measurement of the actual airflow.....
Cheers
RMIT fanclub

[murpia]

If you are mapping a single engine, and not planning to make any significant changes to the intake system, especially anything that will affect throttle flow, then alpha-n (throttle position) control will serve you well.

Otherwise, speed-density mapping can allow you to make certain changes to the system, and not need to re-map, as long as the engine port volumetric efficiency is not significantly affected. An example, changing the throttle body size should not need a re-map, as the engine will consume the same amount of air for equal MAP, even if this occurs at a very different TP.

In control system terms, speed-density is more robust, which is why OEMs use it.

Regards, Ian

[Erich Ohlde]

True, while Speed-Density is an estimating of total airflow through the system, the exact amount of air is not needed...thats what the dyno is for. Based on manifold pressure you say to inject a certain amount of fuel. So if you change altitudes the manifold pressure will drop for a given throttle opening, depending on what you have seen on the dyno for that manifold pressure controls how much fuel is injected.

Now if you did the same thing with alphaN you have to have the pressure sensor to give an overall adjustment to the fuel map. If you are going to have it anyway you might as well tune from it instead of the throttle. Using the throttle for accel enrichments is generally the way to go.

[murpia]

There is a lot of info on the Megasquirt (http://www.megasquirt.info/) site about the justification for speed-density as a design choice for that system.

I think this subject can be a touchy one for some... My opinion is that the best choice for a throttle-body plenum engine (as FSAE) is speed-density with throttle-position based acceleration enrichment. If altitude is an issue for you (maybe your dyno is up a mountain) then get a system that supports a separate barometric sensor. Exhaust back pressure changes with altitude can affect your engine VE, for the same MAP. That way you can get a good base map on the dyno (steady state) which hopefully won't need to change too much once you install the engine in the car. If you need to swap or change the air filter, throttle body, restrictor or associated pipework your base map should still be OK. Maybe even if you change the plenum a bit. Tune the transient enrichments on the track (wideband O2 sensor).

If you have a single, you might need to be careful how the MAP signal is sampled by your ECU, as there are likely to be large pressure fluctuations in the plenum. If your engine is not FSAE and has separate throttle bodies, I think the trouble you will have in getting a clean MAP signal is not worth it (there is no 'M'...), so go alpha-n. If you have a turbo, you need speed-density for sure.

Regards, Ian

[Mike Hart]

Thanks for the responses guys. I think I perhaps understand it a bit better now. The main thing that prompted me to ask was a comment about it by one of the design judges. I might have a little play around if I can find a pressure sensor to see what results I get.

Out of interest, what kind of idle speeds do you all get? We run a 2001 R6 (designed for carbs) but are changing to the new 2006 spec this year and it'd be nice to get a good low speed idle. It seems even TU Graz idled at around 4k and ours is around the 3.5k mark at the lowest. One of the guys at L'borough said their CBR ran happily at 1200 without the restrictor but would then refuse to sit below 3k with the restrictor in place!

[Grant Mahler]

Wouldn't the more prudent question be what your tuner is most comfortable with and what you can get to run best with your setup?

[Wesley]

We ran a MAP based speed/density setup in '06, and it never idled well, and had some issues below 8,000RPM. Now part of that is probably tuning - not much time was spent at any kind of part throttle tuning, and I think the idle was called good. It "idles" at probably 2,500.

On '07 we're running a TPS based system. I haven't driven it, but I have seen it driven and heard drivers talk about it, and it is an absolute dream compared to the '06. Part of this is that a lot of time was spent with part throttle tuning, but what it seems like to me, feeling the '06 car in action, is that throttle enrichments are MUCH easier to get right. While you can indeed log lambda on a track and adjust the enrichments on the fly, in a lot of school's cases, (ours included) you don't have a lot of available in-car time for that sort of procedure. It's really hard to dyno-tune it (at least on a simple dyno - there are fancy-pants ones that we don't have) with a MAP setup. '07 idles smooth at 1500, and starts and re-starts easily.

They are both running the Performance Electronics ECU.

With that said, we're going with a TPS-based system again this year. While it is true, there is more versatility available in a speed/density system, because we are in the same relative elevation at all of our competitions (give or take a little,) we don't have to worry too much about changing altitude.

BUT! I would agree completely with what Grant said. What can you get to work best, for the time and money you have, and which is your tuner more comfortable with? I'm lucky in that the guy who did last years system is still around to give me instruction, whereas the guy who did '06's isn't.

[Erich Ohlde]

tuned properly, either system will function well. However, a speed density system has much more robustness than the speed throttle system.

[Charlie]

Unless someone is using an Alpha based calibration without MAP compensation (rare), or a MAP based calibration without Alpha compensation (even more rare), it doesn't really matter. Both are actually using both inputs. It's just 'how do you want to go about the tune' at that point.

If one method fails and the other turns out a great calibration, maybe your available tools just cater to one method rather than the other, or maybe the person doing the calibration can't figure out how to wrap his head around one of 'em. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Igor]

Just curious, are the people running a MAP based system using their sensor right on the plenum or connected with a length of hose with a restrictor? And did anyone try both to see the difference?

It would seem that mounting a sensor directly on the plenum would give a more erratic signal than if you make a low pass filter with a hose and a restrictor at the plenum. I wouldn't think that would create too much lag.

Any thoughts,
Igor

[Mike Hart]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Grant Mahler:
Wouldn't the more prudent question be what your tuner is most comfortable with and what you can get to run best with your setup? </div></BLOCKQUOTE>

LOL. Our tuner?! Our team isn't big enough to have a tuner. There are usually only about 2 to 3 people who are on our engine group (it will be more next year) and previously the information hasn't been passed down so we all have to learn how to use it and make the decisions as what to run as a group.

[Chris Allbee]

We use Alpha-n....pretty sure MAP is useless...

P.S. this is just me poking Erich in the eye with a big stick http://fsae.com/groupee_common/emoticons/icon_smile.gif

[B Lewis @ PE Engine Management]

This seems to be a common thread and I agree that both methods done correctly can give acceptable results. I would encourage anyone who is thinking of going the speed-density route to consider where the pressure will be measured in the manifold. Even better would be to log manifold pressures, at a high sampling rate, at proposed locations and observe the fluctuations. At lower speeds, these can be significant for these small restricted engines.

[Grant Mahler]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Igor:
Just curious, are the people running a MAP based system using their sensor right on the plenum or connected with a length of hose with a restrictor? And did anyone try both to see the difference?

It would seem that mounting a sensor directly on the plenum would give a more erratic signal than if you make a low pass filter with a hose and a restrictor at the plenum. I wouldn't think that would create too much lag.

Any thoughts,
Igor </div></BLOCKQUOTE>

Yea - I've seen both work - not a significant difference so long as you ensure that the onboard map sensor has a good vacuum signal (no kinks).

[Drew Price]

Speaking from personal experience with Saab Turbos, MAP/intake air temp systems are a little more forgiving with restrictions in the intake, vacuum leaks (mine don't seem to care hardly at all), and hardware changes.

The mass air sensing systems are very sensitive to vacuum leaks (even small ones, big ones will make the engine not even run), the mass air sensor can sometimes be an intake restriction, and requires planning as to where it will be mounted, vibration isolated, etc., as they are fragile compared to MAP sensors. Clumsy diagnostics, or wiring problems can fry them pretty easily. They do not compensate for major hardware changes, like intake & exhaust changes, and cam changes are almost out of the question without re-mapping.

That said, both I]can[/I] be made to be elevation compensating, and both have been shown to work well.

Some ECU packages come with one or the other, or neither, which can be a cost or parts sourcing issue.

Saab switched back and forth a few times over the years, and I have a mass air sensing '85 900, and a MAP based '93 9000, both tuned, and both work well when everything is set proper.

For standalone systems, I was more concerned about what parts we could get quickly, and reasonably priced, and would be easy to keep working.

Our MS runs MAP based.

Best,
Drew

[Chris Allbee]

Ok, i suppose i should contribute something serious. MAP vs TPS...honestly, if you have the tie to tune them properly the driver will never know the difference. anyone that knows me will understand that my design and testing philosophy revolves around driver experience and confidence. As long as the driver has what he wants when he wants it and is confident using it, he will be faster. period. As far as the engineer goes, if you have all the equipment to do both then use what you are comfortable with. TPS has a "natural" acceleration compensation in that properly tuned it is less sensitive to transients than MAP based. MAP is more forgiving with differences in system setups, either from dyno to car or from changes after the fuel map has been set. I believe it has already been mentioned that as long as the VE curve does not drastically change then a MAP based system will be more adaptable, but you have to tune the hell out of the throttle enrichments to get it to come out of corners with any urgency.

If you wanna know which to use, then look at your resources, your knowledge base, and which way makes sense to you (or the tuner) and make a decision. Then test the hell out of it and get the driver in the car. Above all else, GET THE DRIVER IN THE CAR. you would be surprised with what a driver can do with a half tuned car if he is used to it and comfortable.

And if Erich read this...TPS RULES!!!!

[Erich Ohlde]

Let me just point out that OU used speed density last year and finished both events. this year they went to speed-throttle and DNF'd BOTH endurances....yeah, how bout that....

p.s. Chris I'm telling your wife to withold for the next couple of weeks. SHAZAM!

[Wesley]

We also switched from white to black zip-ties! http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Poe]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">[Mass Air flow load sensing] do not compensate for major hardware changes, like intake & exhaust changes, and cam changes are almost out of the question without re-mapping. </div></BLOCKQUOTE>

How do you figure?

[formula_wally]

We switched from MAP to TPS for the 2007 event.

Dyno tunning seemed to happen much quicker as we were using electronic throttle control on the dyno to set the engine on the selected load site.

Our design judge asked me why our team made the switch, and I listed my reasons to him. He agreed and had a few good comments, and I had a chat with him afterwards outside of the garage.

MAP based tuning to me is not the true race method of detecting load, because the load sense is a response of what the engine is currently doing, and not the drivers demands. Torque separation and partial throttle tunning is harder to accomplish with MAP because it was nonlinear to us in the regions where the driver required good modulation of power during corner exit. I have seen MAP pressure start to decrease near 12000 rpm, which is the indication of choke/sonic in your plenum.

TPS suffers from nonlinearities above 50% open. In our 2007 setup, we saw 90% of the power come at 50% throttle. (butterfly TP). We were able to lean some of the sites near the beginning of this knee to produce something a little more part throttle friendly, and then continued with of (XX.X %) over stoich for full power on WOT. Steady state, all of these systems will work. TPS requires the third degree of control, which is barometric compensation. Its too bad we can't change the pressure in the room of our dyno cell to simulate this.

From my observations, both methods work if the calibrator understand the control theory well enough to spot problems whilst doing there work.
If you trust yourself, stand by what you believe in and fess up if you made a mistake. I really enjoyed moving to TPS this year, because we were able to calibrate in under 8 hours, and get back to work on the rest of the car.

[Grant Mahler]

Does anyone have any experience with any "hybrid" tuning solutions - i.e.

AlphaN up to 5k RPM (some preset switchover), then MAP to redline?
Averaging what AlphaN and what MAP would give you?
Some combination thereof?

Any ideas on whether this would work reasonably? Any significant drawbacks?

[Fabrik8]

Bringing this back from the dead after a month..

What most all of you guys are missing is that there is no "magic" engine management control strategy that all of the engine management companies use. PE's control algorithms are probably quite different from Motec, AEM, etc. Thus corrections and strategies for dealing with sensor inputs can be wildly different. Some company's spd/density algorithm might work much better or worse than another company's AlphaN algorithm, or vice versa. You're just buying a black box from an embedded software supplier, you don't really know how what is going on under the covers.

I will say that speed density and AlphaN can both work very well for race engines, and speed density is often unnecessarily complex for non-emissions controlled engines. Again, this has everything to do with the sophistication and execution of the control strategy. AlphaN is the nice simple choice for race engines, but don't expect to cope very well with transient temp and pressure changes. I would not recommend basing the fuel directly off of the MAP sensor, there are too many weird and fast transient conditions that the control strategy may not be able to cope with.

Barometric pressure should be sampled with either strategy and used for calibration. Going off of the MAP alone for real time baro pressure to run the engine at a non-native altitude is reckless and usually won't work very well. Chances are your MAP and TPS readings will fight (try to use a stock ECU with a restrictor and see) and no one will win.

Any decent ECU should be able to have the TPS characterized for flow, which is the easy way to correct for flow non-linearities. It's half strategy, half diligent tuning.

Per Grant's question:
Most of the time there are multiple inputs considered in a 'hybrid' a-N and spd/den system. Usually RPM, engine load, and other things dynamically affect where the handoff is done. It doesn't really switch from one to the other, but rather transitions (gracefully if you're careful). There aren't really any drawbacks for a 'hybrid' system, except for complexity. For most offroad/race applications, it could be argued that either strategy could easily be effective as the combination of the two.

We're up at about a mile above sea level, and we're looking for ways to accurately model what will happen at competition altitude. I'm originally from the coast, and I don't like the altitude here, it makes everything a PITA.

[Pete M]

For the motec at least, the algorithms aren't a black box, and i imagine most of the other ECU makers explain how their system works too. How it works is extremely simple (well, there are a lot of steps but none of them are complex). You have a table of whatever you like vs whatever you like. Usually the axes are RPM and either MAP or TP. This table is used to select a value, using linear interpolation if you are between sites (most of the time). This value is a percentage and is multiplied by IJPU (the pulse width corresponding to a 100% fuel table value). Then, this number is multiplied by all your compensation tables to determine a number called the effective pulse width. This is the pulse width the ECU would send to the injector if it could be opened and closed instantly. The dead time table is then added to the effective pulse width to determine the actual pulse width. This is the length of the electrical signal sent to the injectors in ms.

There's no difference between speed density and alpha-N in this, other than the channel on the y-axis of the table at the start of the process. I'd be surprised if other manufactures took a radically different approach. Whether alpha-N or speed density performs the best will depend more on your mechanical setup than the ECU you use. For most NA applications, alpha-N will be easiest and give good enough results (if a baro sensor and an air temp sensor are used). If you're turbocharged, speed density is traditional, but you can make alpha-N work too so long as you compensate for manifold pressure.

I have to say i don't really understand the religious arguments made by some people on this topic. Ultimately they're both pretty decent at estimating mass air flow and hence the fuelling needed. Give both a go and figure out which you like best. There are more sophisticated methods too. The motec allows 4D fuel maps, which means you can have TP vs MAP vs RPM if you want and get both at once. That's more a turbo thing though, as on an NA engine, TP+RPM=MAP (you know what i mean).

[Wesley]

Now there's a challenge. I wonder if they have a graphical description of four-dimensional tuning.

I'm reminded of Doc Brown. "Marty, you're not thinking fourth dimensionally!"

[Pete M]

Nah, unfortunately there isn't a good visualisation of it. You just get 11 normal-looking 3D fuel maps and it'll interpolate between them based on the z-axis channel.

And btw, who the hell decided that a table with 2 axes was 3D. It's 2D... with a value at each co-ordinate. That's not a third dimension! They draw a 3D representation of it, but so what. A true 4D fuel map (4 axes) would truly be interesting to try to visualise...

[ad]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Pete M:
Nah, unfortunately there isn't a good visualisation of it. You just get 11 normal-looking 3D fuel maps and it'll interpolate between them based on the z-axis channel.

And btw, who the hell decided that a table with 2 axes was 3D. It's 2D... with a value at each co-ordinate. That's not a third dimension! They draw a 3D representation of it, but so what. A true 4D fuel map (4 axes) would truly be interesting to try to visualise... </div></BLOCKQUOTE>

how about colour? however crude it may be

[Pete M]

Colour would help for 3 axes (and even then you'd have to make the cube partially transparent so you could see the inner parts), but for 4? An animation of a partially transparent cube? Ha!

[formula_wally]

You need a special Matlab license to have access to scatter4() and scatter5(), and some of those 3d glasses that come with your next box of Trix.

I don't know how many teams have a proper dyno facility where they can control temperature, and pressures....... we didn't..... I think if you include more of these things as part of your tunning strategy, the judges will see that you are thinking about the bigger picture.

Put some time into validating you can cold and hot start. Having a calibration that can start in these polar opposite conditions is a good indication that you are controlling your fuel and timing past the 3rd dimension.

[Wesley]

Hooray for Oklahoma for testing temperature extremes. I ought to have plenty of opportunity to work on cold start and hot start conditions, with the weather varying from 100+ to 65 in the course of a day or two.

Pressurizing/Climate controlling a dyno cell is no small feat though. Just make sure you log your ambients when you make a pass so you can build up a correction list.

The funny thing is, I've seen so many different intake and exhaust combinations, all making relatively the same amount of power, it seems to me that, as they say, God is in the details.

That is, no matter what your setup is, as long as it's reasonably well engineered to flow the proper amount, tuned properly you're going to hit 60ish HP no matter what with a 4-cyl. I'm a firm believer that any one of the cars at competition has a good 5HP waiting to be discovered with some time on the dyno.

Which is why I'm hoping that Santa brings me a fancy new setup this year.

[N_Pennella]

Good info. I was going to switch to a MAP setup with our Motec but it looks like the time will be better spend on fine tuning the existing TP setup. Not much would be gained from what i understand.