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Tuning a/f on BBSC or other Blown NSXs

Joined
22 November 2001
Messages
301
Location
Woodland Hills, CA
Disclaimer:

First and foremost let me iterate what I belive is the current and most accurate advice of Mark Basch: Leave the tuning to him. A/F tuning (changing the ss fuel maps on a BBSC) can very easily result in a blown motor. I am not advocating that anyone do this on their own. However, if you do want to know methods on how to do it correctly - you may have some benefit of my own experiences.

I have cut and paste here from what I have written in the general discussion board. First, you should know that tuning for a/f requires special tools. Trying to tune using stock O2 sensors is TOTALLY useless... there is virtually nothing you will discern from a stock O2 sensor. You see a lot of these gauges and such for a/f and it is likely the biggest scam going. How a stock O2 sensors works is the following: when a/f is below 14.7:1 there is one voltage and when above 14.7:1 there is a higher voltage. Your stock ECU, similar to ECUs in other cars, simply uses the stock O2 to "hunt in" on the desired (ideal) a/f which is 14.7:1. In other words, there is really no way, for example, that these O2's can tell the difference between 10.0:1 and 14.0:1.

If you are trying to use the stock O2 for tuning forced induction motor, you likely want to target an ideal (under bosst) a/f of 12.5:1. If you are running under 11:1 you're too rich and if you get North of 13:1 you may be in trouble. The stock O2 or even the available aftermarket gauges CANNOT discern the difference. An a/f of 12.5:1 (under boost) is generally recognized as an ideal value for providing optimum power while being justa tad rich. A/F values over 13.5:1 are too lean and can cause detonation and ultimately holes in your pistons. A/F values between 11.0:1 and 12.0:1 are not bad but are on the rich side and will not provide you the optimum power. If you could achieve a flat line on 12.5:1... you, IMO, would have an ideal set-up. If you have known boost pressure (6psi in the current BBSC config) and you can achieve 12.5:1... then HP is just a by-product.

OK, so how do you do the tuning short of spending hours of time at a dyno... complicated by the necessity of doing a lot of analysis, planning and checking between runs as you modify fuel tables.

The good news (sort of) is that there is a solution. In fact it is a very good one, albeit expensive. I am using it now to tune my BBSC. The kit consists of a 5-wire O2 sensor and a black-box brain/controller. Once installed, it will let you display instantaneous a/f ratios (accurate to 1/100) and, more importantly, it will let you datalog for virtually any period of time. You can then playback the datalog or, using the supplied software, you can generate a/f graphs. There is a provision for a RPM-in (mandatory) and an auxilary in (0-5v) for a Map-in voltage, for example.

All values are datalogged.

My testing has consisted of modifying the fuel maps and then doing 4 or 5 2000-6000 full-throttle acceleration runs. (6K-8k can be tuned in after you get the hang of it.) I use 3rd gear and will use 4th gear for final tuning. It is almost essential to have a passenger with you. Have the passenger watch instantaneous a/f to make sure no values over 13:1... while datalogging the whole sequence. Next, return home and view the graphs. Make changes to the table and repeat the process.

If you are careful and methodical, I believe that this method with the right tools is the BEST way to tune a forced induction car like the BBSC. In my mind, many advantages over the Dyno.

I have made some pretty significant improvements to the tables in my car - but one size doesn't fit all - hence the need of MB to individually tune cars... or leave you with something known to be comfortable... i.e., conservative.

If there's enough interest from Forum members to go down the path I have gone, I'd certainly like to help. For example, the pre-requisite to a/f tuning is either a lot of dyno time, lesser dyno time with MB present with his experience, or purchasing the system I have and having the capability to tune without a dyno. (Another significant advantage to what I am doing is looking at 1-2 and 2-3 full throttle shifts and analayzing a/f ratios.) It's all in the details.

Chime in if you're interested. This is not limited to BBSC as it applies to all forced induction situations. This set of tools will give you very accurate data collection and analysis and the difference will be what tools you have available to modify the a/f numbers. For BBSC, this is the ss box. For Comptech this is the fuel pump voltage inverter and FMU, for many other FI cars this is only an FMU or potentially other sophisticated electronic boxes.
 
Bravo - Great Post!

Questions:

- Did you feel the need to further enhance Mark's tuning?

- Is this something, once perfected, that would be an upgrade to a tuned NSX?

- Does the black box take the place of the ECU (and thus loose traction controll, VTEC controll, etc.)?

Great start to a great thread!

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids
 
Let me try to address your questions.

1. Yes, I felt the need to tune the BBSC to my car. MB is pretty busy these days and I truly believe the table can be tweaked to suit individual cars. The generic table, by definition, needs to be conservative. However, too conservative can be bad too in that over time it is not good to have your car running too rich. I also have been very curious to a/f under different conditions - something hard to do on a dyno.

2. Tuning, IMO, needs to be done on individual cars. For forced induction this is primarily a/f and timing. If you get the a/f and timing right over the rpm range, then you have all that is possible out of your particular config. A trip to the dyno will give you the HP bragging rights... but you don't have to use it as your primary tuning tool.

3. The SS Black Box has tables for both "fuel" and timing. Each has the same grid - basically 500 rpm increments from 0 to 8000 rpm on the y-axis and .5lb increments from idle vacuum to 16psi of boost. Each cell contains a value that corresponds to a MAP sensor voltage input to the stock ECU. To oversimplify, the SS box tries to "fool" the stock ECU by intercepting the stock MAP sensor voltage and adjusting it depending on this table. Think of it as "telling" the ECU that you're at 10,000' when not under boost and as boost increases, the car begins to think it is at a lower elevation - thus needing to richen the fuel. The biggest limitation here is that this is a very indirect way of controlling fuel... as no one really knows the algorithm in the stock ECU and specifically how it interprets these values, rationalizes the differences (hey, did I just fall off a cliff?)and ultimate changes injector pulsing. The bottomline is that the system works... but we're all still learning how it reacts to different inputs.

The second table in the SS box is a timing table. x and y axis are the same as the fuel tables (RPM X Boost) but the control is presumably direct. The values in these cells are literally degrees of ignition retard for given rpm/boost increments.

The SS box does not replace the stock ECU - it just lies to it
smile.gif
Yes, an advantage is that VTEC and everything else is retained. Most important, IMO, is that 90% of the time you are in closed-loop mode and everything works normally i.e., pretty much perfect.
 
Nick, sound familiar? This is what I was telling you is my top priority. Dynos are great fun, but they don't reproduce real life very well. Sure you can simulate many conditions if you have the time and money, but some you can't. In the end, this is the right approach to tuning and I think it will uncover some major shortfalls in my current system

kpond, I'm glad to see you taking this approach. I left you some questions on that other thread.
 
Is there anyone in the St. Louis area that can perform this kind of tuning? I don't mind spending the $$$$ for a top notch tuning as such. Damn people in California have all the luck. But seriously anyone in this area, Chicago, Kansas City, Tenn.,Kentucky, I don't mind the drive for quality.
Let me know.
Len
 
Originally posted by len3.8:
Is there anyone in the St. Louis area that can perform this kind of tuning? ...

I'm purchasing a wide-band unit as soon as I find the right one. Everyone in town will be welcome to use it, but that will require at least one extra sensor so I don't need to pull one of mine. Then you'll need to install the "bung" in your exhaust to accept the sensor, or a plug when not using the sensor. Perhaps we can all have them installed together by a guy I know that works magic welding SS.
 
Hey Steve - yes "Obi One" I was listening and sounds exactly what we were talking about. If everything was "steady state", with all the same mods, with all the same engines, and only on a dyno it would be a lot easier! Unfortunately what works on a dyno may have limitations on the street or at idle!

As for the mod - sounds great! I would kill to know 1/2 as much as you do and will need all the help I can get when / if I take the FI plunge. Problem with St. Louis is few people we can trust OR know what they are doing. I feel we have to support each other and be self sufficient (or buy a small plane and fly tuners out from California 3 times a year!)

BTW - Steve - was that you screaming by sonic on Big Bend (heading east past Sulpher Springs) last night?

I was treating the kids to Sonic and my head snapped to the left when I heard that unmistakable sound of a boosted NSX near WOT.

Can't wait to see everyone next Sat. night!

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids
 
In a related thread, a question was posed about the necessity/practice of tuners to re-address a/f tuning after psi mods, etc. Following is my response to that question - hopefully supplying some insight to common a/f management techniques:

Different sc/turbo installs employ different approaches to address a/f. Fundamenatlly, we all understand that a sc/turbo is adding more air at each stroke of the piston... so the challenge is how to add a corresponding amount of fuel, in most cases by "trickery" of everything else that your stock ECU is handling...

One of the most common methods (because of the inherent simplicity) is to employ a mechanical fuel management unit (FMU). Here's how an FMU works. Nearly all port fuel injected cars utilize a pressurized fuel rail with a return line going back to the fuel tank. The (in most cases) static fuel pressure in this fuel rail is a programmed constant in the ECU. So, in stock applications your ECU increases the pulse width of the fuel injectors to add more fuel under full throttle conditions. Now remember, under WOT vehicles including the NSX are in open-loop mode - unable to rely upon O2 sensors for precise optimization of a/f. Instead WOT causes the ECU to use stock internal tables that have been derived by the engineers designing the desired engine characteristics. Back to the FMU.

An FMU is a mechanical device that is installed in series on the fuel rail return line. The FMU is connected to a manifold vacuum line. As the FMU begins to see boost pressure, it begins to restrict the fuel return line... which has the direct effect of increasing fuel pressure on the fuel rail. The more boost pressure, the more the restriction, the higher the fuel rail pressure. The ECU doesn't know this. Remember, the fuel rail pressure is an assumed constant in the ECU... it is not measured and it is assumed to be flat.

So, the effect is that as boost pressure begins to increase, the pressure on the fuel rail begins to climb unbeknownst to the stock ECU. The ECU is telling the injectors a pre-determined pulse length. However, since there is more pressure on the rail, this same pulse length will result in more fuel being injected into the engine.** Pretty slick, huh?

**Well, that is the theory and, as usual, there are a few gotchas. First, experimentation will have to tell you the right fuel pressure and the slope of the curve needed to provide the desired a/f over the boost range. However;

1. Your stock injectors may not have enough flow rate to deliver the needed fuel.
2. Your stock fuel pump may not have enough volume to provide all of the fuel (and psi) needed.

Bottomline: An FMU is a simplistically clever device. I believe an FMU along with running the stock fuel pump at a higher voltage (volume & psi) is what Comptech employs to manage a/f.

To finally answer the original question... yes, when people are adding intercoolers or modifying boost psi curves, you will have to go back and minimally measure the a/f with a high probability of also needing to make several adjustments. Adjustments are needed first and foremost to be safe (neither too rich nor too lean) and secondarily for greed (power) where a/f's are optimized.

Sorry again for the long post - but if y'all aren't interested in this stuff don't read it or tell me to shut-up.
 
sjs, et. al,

I will post the details about a group buy potential for what I believe is the best wideband on the market. I did a lot of research before settling on the one I chose - and I couldn't be more satisfied with the quality, support, supplied software, datalogging options, etc.

You can read about the solution I chose at www.fjoinc.com/automotive

FJO doesn't sell directly but I have been working with these guys a lot as well as with one of their largest distributors. I'm pretty sure we can get some savings if we get together 6-10 orders or more.

I'll do a little sales pitch in a post later on today (I have no vested interest, financial benefit, etc.) and I'll ask for a show of hands and we can go from there.
 
OK - here is the big IF question.

If one was to get the wide A/F and timing characteristics available with this system then POTENTIALLY would they have the capability to tune any system?

What I am asking is - if I could source an inexpensive whipple super, vortex super, or quality turbo and had someone locally (let's just call him "Steve" for now), could you potentially design a high quality FI yourself at a low cost and tune it safely to the NSX?

What would be the benefits or concerns of taking on this project?

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids
 
Nick,

Good question. There are fundamenatlly two challenges with FI (let's all assume that fi - forced induction in this thread and not the usual "fuel injection"). The first is all of the physical, mechanical design characteristics. This is something, BTW, I think that MB has done very well. Even so, there are compromises. (The BBSC makes the oil fill cap a challenge to get to and the polished aluminum overflow bottle directly covers the factory "California compliant" vacuum/smog diagram.) Both of these are minor considering how well the system is packaged overall.

The second, and potentially more challenging, aspect of a FI system is the design, implementation, and tuning capabilities to achieve correct a/f and timing attributes. Of BBSC, GroupM, and Comptech, each uses very different approaches to try to provide the right tunability. I know the least about the GroupeM implementation but from the little I know from Alex - it seems that it is the most sophiticated and makes the best use of sophisticated and proprietary electronics complementing the existing ECU. In a previous post, I briefly described Comptech's approach.... and I am quickly becoming very intimate with the current BBSC implementation.

You said "If one was to get the wide A/F and timing characteristics available with this system.." I don't know what you mean by "this system". I am an extremely happy customer of FJO's wideband controller - but this system and accompanying software is only for measurement and datalogging and not for controlling.

I assume that maybe you were referring to the SS Box when you said "this system". At this time, my answer would be no, the SS box is not the cure all. The primary limitation in my experience is that the SS box is trying to fool the ECU... but keep in mind that the ECU in the NSX is ADAPTIVE.
So, the NSX tends to give you different a/f results over the next 4-5 start stop sequences after loading a new table. This is another BIG reason I like the "on-street" tuning approach I am using rather than a dyno. At this time, I would strongly urge that those of you dyno tuning use multiple pulls between ignition off sequences BEFORE being comfortable with the maps that you have loaded. I believe that this is yet another reason that MB prefers to do this himself.

Perhaps the best approach would be to use an aftermarket ECU in place of the stock ECU. The HUGE advantage is that you have DIRECT control over fuel (injector pulse widths, for example) as well as timing. The HUGE disadvantage is that I cannot even imagine the tuning time that would be required to get one of these right. There are just soooo many parameters and variables to consider. Forget about being boosted, I'm talking about just getting normal driving characteristics right for idle, throttle tip in, warm start, cold start, different air temps, shift points (throttle close to WOT), etc. etc.

There's another thread where someone has just purchased the AEM ECU. I am very excited to know how that project goes. A lot will depend on how good the base config is (if any). IF there is a good, driveable base config in that ECU (based on the NSX), then doing the additional tuning for FI will be a DREAM and the ONLY way to go. I guess we will soon find that out.
 
Kendall,

Thank you very much for all this information. To be this knowledgeable and not condensing is truly a gift! I know owe you at least one beer at NSXpo and will be fighting for the chairs next to you throughout the week!

OK - next point of interest. If you believe these systems need to be tuned / mapped to have adequate results - do you think vendors will ever be able to mail these to customers with meager skills in a "one size fits all" solution?

Also - do you ever see a piggy back system that can learn, adapt, and self tune so it can empirically derive what the ECU is doing to always stay at the optimal f/a mixture?

Finally - how often should one revisit performance tuning? After a tune up? After a new mod? Just after a certain amount of time?

------------------
Nick M

91' Red/Black with Many Mods
99' Honda Odyssey with Many Kids

[This message has been edited by matteni (edited 18 August 2002).]
 
Nick,

I believe each of BBSC, GM, and Comptech have a baseline a/f mgmt system that they deliver. BBSC, being the newest of the kits, is still getting MAP improvements as MB and the users begin to learn more and more cars are installed.

The real motivation for me to invest in a on-board wideband solution was twofold: First, I wanted to have the ability to see and the ultimately to modify the a/f for my car. I envision installing the aftercooler when available - which will necessitate additional tuning, etc.

The second reason was simply on-board monitoring. What happens if the ss box fails? What happens on those really cold wet mornings when FI is really at it's best? What do the a/f numbers do in thses situations? Without monitoring, how will anyone know? Sure, one way is to find out when it's too late but I don't want to have THAT condition!

I don't think everyone needs to monitor but at least if some of us are and providing feedback to MB and others - then the knowledge base around the BBSC will grow faster.

As for you other question, the answer is no, I don't see an adaptive solution on the horizon. Right now I'd settle for a more direct way to address specific RPM/af anomolies!

How often do you need to change the a/f? Well, only when you're doing something that really effects air/fuel ingestion like increasing boost, decreasing air temperatures (aftercooler) or similar. In theory headers and/or exhaust will have a minor a/f effect but I don't think any of us have been able to tune so close to the edge that we can really account for that. Well, not yet anyway.
 
I am currently using an FJO to tune my Supra.It is dead on to dyno A/F meters.It also comes with all the associated datalog software but does require you to have a bung welded into your exhaust as it uses its own 5 wire o2 sensor.

Joe

------------------
97 NSX-T BBSC Spa Yellow
93 Supra TT T-61
97 Viper GTS w/Corsa,K/N
 
After a lot of investigation of different options, I too went with the FJO. It is really a great system. You can monitor and/or datalog with a laptop...
or, better yet, you can monitor & datalog with a Palm Pilot and then just "sync" the files with the PC for analysis.

[This message has been edited by kpond (edited 19 August 2002).]
 
Well Kendall/kpond, thanks for the great posts. You have said many of the things I’ve been trying to find the time to put in writing as a baseline for more in-depth discussions on this topic, which is clearly critical to boosted systems. Since you have already laid the foundation, I’ll jump right ahead to my primary concern with tuning these systems for real-world use. Since I don’t yet own a wide-band analyzer I’m forced to work only on theories here, but perhaps you can test those at least with respect to an SC.

What concerns me the most about the common approaches is achieving correct AF ratio at less than wide open throttle (WOT). I can put my car on a dyno and get the mixture just the way I want it under WOT. Given sufficient dyno time I could then simulate at least some part throttle conditions and see how it looks, but things like hills are not so simple. This is why I want my own wide-band sensor and logger.

Even with the relatively predictable nature of an SC where a given RPM yields a known amount of boost, it seems that the throttle position sensor (TPS) needs to be in the equation at a minimum. Now, as already noted the stock ECU is monitoring that and may be reducing the injector pulse accordingly, but we don’t really know how much, or if perhaps when it sees zero vacuum (as it is tricked to believe whenever on boost) it decides to ignore the TPS and assume WOT. I really don’t know, but even if it still attenuates the pulse compared to WOT, is it as a % of total or a flat amount, and how does that combine with the SS adjustments? As also noted by Kendall, this type of grey area in our understanding is why the trial and error is necessary and time consuming. I’d like to see your AF ratio plots for part throttle runs as when rolling in just enough to pass someone on a 2-laner. I’m not sure at what throttle position the boost is allowed to build rather than bypass, but obviously that would be the minimum for the tests.

Now consider a turbo system, where fuel and timing maps can’t assume that a given RPM corresponds to a specific boost level. (This is where the greatest strength of the Aerodynes, building boost so easily even at low RPM, can also be a weakness.) I can easily adjust the AF ratio to look good during a typical dyno pull, but that’s only good enough if all I do is drag race. In the real world I can find myself at a given boost level at a much lower or much higher RPM than I did on the dyno. For example, if I’m going up a hill I’ll get boost very early so the ratio will be too lean at first. Going down a steep hill it will come on more slowly so the mixture will be too rich. If that weren’t enough, I can get the same boost/RPM combination at ¼ throttle that I see at full throttle. For that matter, I can get a higher boost at a lower RPM with ¼ throttle than I do with a WOT drag race. How can a simple map based on just RPM & boost cope with that? I think the answer is, it can’t. At a minimum I need to add the TPS to my fuel map.

I say at a minimum I need TPS because even that seems crude these days. The real question (it seems to me) is good old CFM. If you could measure the volume (and density) of the air passing the throttle body then tuning would be much simpler, or at least theoretically possible. The beauty of carburetors is that they automatically draw in fuel through the jets in proportion to the amount of air passing through them. With injection we need to measure or estimate CFM. There have been various schemes over the years to accomplish this including a “barn door” at the throttle body (actually hinged at the top) that is pushed out of the way by incoming air, with the angle of that door indicating the amount of the air being ingested by the engine (CFM). Another is the hot wire anemometer which applies voltage to a piece of wire running through the throttle body, causing it to heat up, then measuring how much it is cooled by the intake air. With that you can do a pretty good job of calculating the effective CFM including the element of air density. There are limits to this technology as well, but it seems to work.

Today I think Mass Air Flow meters are accepted as the best solution, using a built in venturi and smaller sample tube to calculate CFM and output a variable voltage corresponding to that measurement. I think the important thing here is having one sized right so it can handle the required CFM without being a restriction itself.

If I were designing a bolt-on turbo NSX system I would probably start by finding a suitable existing Mass Air Flow meter. I would also try to retain the stock ECU for all the things it does well, but add a piggyback system that monitored RPM, boost and CFM so I can modify the fuel maps only when on boost. I would certainly avoid the auxiliary injectors, replacing the stock parts with larger ones. In other words, something similar to the BBSC setup but with the addition of airflow metering. In the end a full ECU replacement may be necessary rather than the piggyback setup, but hopefully not. The other option is to find someone who can substantially rework the stock ECU, but I still think true CFM needs to be factored in to do it right and a Manifold Absolute Pressure (MAP) sensor such as the NSX uses just isn’t an adequate substitute for a turbo system.

Well it’s late and this post is plenty long already, so I’ll save the rest of my thoughts including why I think this is so important beyond the obvious HP greed, till next time.
 
I'm glad to hear more people chiming in on the FJO unit! That's one of the first I looked at and exchanged a few emails including an attempt to get a group buy going. (I think I even stated a group buy thread for it and got zero response) The best discount I got was 10-15%, so worthwhile but not a deal maker/breaker. I have since looked at other possibilities including more general data acquisition systems that track Gs and GPS coordinates as well as multiple sensors such as AF ratio. Still digging.

So, exactly which model and options did each of you purchase, and what else would you want to add?

I guess that there is no reason a person couldn't get buy with just the sensors and a voltmeter for simply checking the AF ratio and doing basic tuning. A good analog meter would be the easiest for a passenger to watch and you could probably do a very decent job on the cheap.

BTW, besides being slow to load for us with dead-slow dial up connections, those huge pics made the page too wide to read the posts easily.
frown.gif
Perhaps resize the pics or just se links?

[This message has been edited by sjs (edited 19 August 2002).]
 
Ok you guys use A/F meters to see what A/F the cars running but what do actually use to tune the cars A/F. A SuperAFC, or like a stand alone Haltech, AEM, Hondata, Tech 2? I have a SuperAFC on my car and thats what I tune my car with on the dyno but I've heard that the NSX learn's the fuel maps. Lets say you dyno the car and it makes 290rwhp before tunning it with the Super AFC, and then after tunning it with the SuperAFC the car makes 300rwhp. If you take the car back a week later the car will dyno exactly what it did before 290rwhp again. The car learns the maps? If anyone has a S/AFC try it.
 
Well, I took the pics off as it seemed to slow people down... and it's really annoying that it lengthens the x-axis requiring you to scroll to read posts.

SJS - you pose some interesting observations... it'll probably take some iterations to address them all with hopefully others joining more in the discussion.

One of the first things you will notice after using a datalogger is how much of the time your car spends in closed-loop mode. It really takes very near WOT to break to open-loop. I think that many of your various "worry" conditions can be addressed by closed-loop mode. However, I do think that you are right in that in a turbo application, boost is not "as" linear with RPM. The first steps for you will be to datalog boost levels (a simple GM MAP sensor will convert boost to a 0-5v voltage so you can datalog it). You will need to understand the characteristics of your curves. Although turbo applications can generate more boost at lower rpm's... I'm thinking you will still see more "rpm linearity" than you think.

Regarding MAF vs MAP, each has advantages and disadvantages and can likely generate a lot of opinions... I'm not sure if I would agree that a MAF is needed.

The amount of air ingested by the engine is straightforward to calculate if you know:

1. Displacement
2. RPM
3. Air Temp
4. Air Density (ambient)
5. Manifold Absolute Pressure (MAP)

Fundamentally, this is how MAP-based fuel injection works. The only additional parameters we've introduced is inlet air temperature (potential to be much hotter after compression) and the fact that MAP may be positive. Nevertheless, everything remains easily calculatable. (Is that a word?)

It's late, and I have a long day tomorrow - I'll re-join tomorrow night. Later.
 
Originally posted by sjs:

>Even with the relatively predictable nature
>of an SC where a given RPM yields a known
>amount of boost, it seems that the throttle
>position sensor (TPS) needs to be in the
>equation at a minimum.

The 2nd BBSC fuel system design using the Factor X / Hondata system for the NSX used the assumption of known boost vs. RPM (without actually measuring MAP above atmospheric pressure). I'm not sure if it also used TPS for part throttle operation. From experience, the Factor X system DID have problems at part throttle, and this is (presumably) the major reason MB switched to the Split Second box which can measure boost.

TPS is typically used to sense throttle changes for dynamic enrichment (so the engine will not stumble when the peddle is pressed quickly). I can't think of much else TPS is useful for; the MAP sensor is a much better indicator of load (ie. air flow).

>Now consider a turbo system, where fuel and
>timing maps can’t assume that a given RPM
>corresponds to a specific boost level.

The BBSC with Split Second box does not assume any fixed relationship between RPM and boost. It should work equally as well with a turbo. The MAP sensor can handle pressure from "full" vacuum (idle) to 16 psi of boost (quoting Kendall).

>For example, if I’m going up a hill I’ll
>get boost very early so the ratio will be
>too lean at first. Going down a steep hill
>it will come on more slowly so the mixture
>will be too rich. If that weren’t enough,
>I can get the same boost/RPM combination at
>¼ throttle that I see at full throttle.
>For that matter, I can get a higher boost
>at a lower RPM with ¼ throttle than I do
>with a WOT drag race. How can a simple map
>based on just RPM & boost cope with that?
>I think the answer is, it can’t. At a
>minimum I need to add the TPS to my fuel
>map.

If you know RPM & MAP, you can create a single 3 dimensional table for injector duty cycle that will handle all of the conditions you described. Air temp is also needed to compensate for air density changes, but this is a single correction factor not based on RPM. For fixed throttle position, TPS adds no significant new information.

>The real question (it seems to me) is good
>old CFM. If you could measure the volume
>(and density) of the air passing the
>throttle body then tuning would be much
>simpler, or at least theoretically
>possible.

It would be simpler in that the AFR tables that you start with could be directly calculated from the known mass air flow. But once you have that, some tweaking would still be required to achieve the desired AFR. Another advantage is that small changes in volumetric efficiency of the engine (ie. adding headers) would automatically be reflected in higher mass air flow readings and the AFR would automatically adjust.

Honda/Acura use speed density EFI. This means the actual mass air flow is indirectly calculated by measuring RPM, MAP and intake air temperature. This system works just fine assuming that the volumetric efficiency of the engine does not significantly change during its life. Even small changes can be detected by the ECU (ie. learned) when in closed loop mode, and the ECU can apply a global correction factor. I don't know how sophisticated the Honda PGM-EFI system is, but I have read that the newer Ford ECU's have complex learning algorithms.

>The beauty of carburetors is that they
>automatically draw in fuel through the jets
>in proportion to the amount of air passing
>through them.

Yes, Weber carbs are very beautiful to look at. But... I believe that carburetors can not compensate for air density changes, so they are really responding to velocity changes, not mass air flow changes. Hardly ideal for a boosted application. Imagine the air density / air temp changes that can occur between winter with a nice cold intercooler to summer with a heat soaked intercooler.

>Another is the hot wire anemometer which
>applies voltage to a piece of wire running
>through the throttle body, causing it to
>heat up, then measuring how much it is
>cooled by the intake air. (snip)
>Today I think Mass Air Flow meters are
>accepted as the best solution, using a
>built in venturi and smaller sample tube to
>calculate CFM and output a variable voltage
>corresponding to that measurement.

Both the hot wire & hot film meters that you described are mass airflow meters that are capable of directly measuring mass air flow and compensate for air density changes. I believe Ford uses them on most of their lineup. Others do not, presumably because of cost. For high HP applications, they are definitely a disadvantage because of the added intake restriction.

>If I were designing a bolt-on turbo NSX
>system I would probably start by finding a
>suitable existing Mass Air Flow meter. I
>would also try to retain the stock ECU for
>all the things it does well, but add a
>piggyback system that monitored RPM, boost
>and CFM so I can modify the fuel maps only
>when on boost. (snip)
>In other words, something similar to the
>BBSC setup but with the addition of airflow
>metering. (snip)
> (snip) but I still think true CFM needs to
>be factored in to do it right and a
>Manifold Absolute Pressure (MAP) sensor
>such as the NSX uses just isn’t an adequate
>substitute for a turbo system.

The speed density EFI method of the stock NSX EFI and also the BBSC system aren't a substitute for anything, they ARE the system. The Split Second box has its own MAP sensor that replaces the stock NSX MAP sensor, so it can measure boost.

My only gripe with the Split Second box is that you are trying to fool the ECU by supplying it with different MAP voltage values, and you have no way of knowing the actual result on injector duty cycle for any change in MAP voltage. This is in contrast to other piggy back devices that stretch or shorten the injector pulses directly (after the ECU), and you know exactly by how much you are changing the injector duty cycle.

Bryan Zublin

[This message has been edited by BryanZublin (edited 19 August 2002).]
 
Bryan,

Ha, I never noticed the intake air temp sensor. I see it now, a thermistor with a range of ~ -4 to +250 F. Unfortunately the response it not linear so it will be tougher to build a little gauge for it. I also see a barometric pressure sensor. Those explain how the ECU gets enough information, the MAP sensor alone was obviously inadequate.

OK, that’s fine for the stock setup, but those factors aren’t part of the Split Second box maps, or any of the auxiliary injector controllers I’ve seen. So that still means they should be inadequate, using only manifold pressure and RPM, and all the more so since they magnify intake air temperature variations.

That takes me back to the fact that, for example, I can get 5psi boost at 4k RPM under WOT acceleration but I can also get 5psi at 4k RPM but just ¼ throttle. Leaving air temp out for a minute, I’m trying to convince myself that fuel demand for a given RPM and boost is constant regardless of throttle position. On the one hand it seems obvious, same displacement, same strokes/minute, same pressure = same CFM. And yet, it seems illogical that a dramatic difference in the main throttle butterfly position has no bearing on the fuel required. I guess that’s the problem with relying on the seemingly logical. Part of the key may be that MAP is taken downstream of the throttle butterfly. Still troubling is the reality of my own car. I got it dialed in nicely on a dyno, but out in the real world at part throttle as boost builds it goes decidedly rich. I’ve tinkered with the map trying to resolve it but without an AF meter it’s pretty tough, which is why getting a wide-band is my top priority. I haven’t given up entirely on the possibility that an acceptable solution can be reached with the parts at hand, but something about part throttle boost still worries me.

Comments on a few of your other points:

You said “This system works just fine assuming that the volumetric efficiency of the engine does not significantly change…” How does the volumetric efficiency of a boosted engine compare to the same engine normally aspirated? As I recall, it is typically somewhat different.

Trust me, I’m not advocating that we go back to carbs, I was merely pointing out that they meter fuel automatically according to air flow, but I made no suggestion that they accounted for air density. That’s one of the many reasons why a good injection system is better.

I’m not clear on why the hot wire method should be restrictive, particularly if it is designed from the start for the anticipated CFM and HP. However, I think that they may have limitations in responding to very high flow rates and rapid changes.

It sounds like you are saying that the BBSC/Split Second setup still utilizes speed density on boost. But since you can’t send the ECU anything above the voltage that equates to atmospheric (zero vacuum zero boost) then it can’t ever calculate the actual airflow on it’s own (on boost). Or am I missing something? So as soon as you get to positive manifold pressure, what are you changing to increase fuel delivery? Must be either duty cycle or pressure. Sorry, I just don’t know anything about how the SS box is supposed to work, so please feel free to enlighten me.


[This message has been edited by sjs (edited 19 August 2002).]
 
We are all talking about the threads of running lean. But can somebody tell me what will be the effect of running (to) rich.

Furthermore, I want to use octaneboost. It will probably help me to avoid pinging. Is this true? And I heard that you can obtain more horsepower with a higher octane.

Gerard
 
Originally posted by Gerard van Santen:
We are all talking about the threads of running lean. But can somebody tell me what will be the effect of running (to) rich.

Furthermore, I want to use octaneboost. It will probably help me to avoid pinging. Is this true? And I heard that you can obtain more horsepower with a higher octane.
Gerard


Taking them one at a time, briefly. (lunch break)

Actually, my concerns have been mostly about running too rich (fat) because I tuned the mixture just fine on the dyno for full acceleration conditions, which is the highest demand. My problem is that I did not tune for part-throttle low RPM where boost has time to build up to levels higher than they do at WOT for the same RPM. The result is a rich condition because the boost tells it to pump more fuel even though I’m not standing on it. This is particularly pronounced up hills where the load is greater. But I still didn’t answer you question. The most dangerous consequence to running rich is that excess fuel can wash down the cylinders and then the rings wear quickly. This can be very fast or more gradual depending on the severity and duration of the rich condition. Other than that you can load spark plugs and possibly damage the catalytic converter, not to mention pollute the atmosphere.

Octane boost is not an economical solution to detonation if purchased in the typical retail containers. It takes a bunch of it to raise a few “points” (93.0 to 93.3 for example) so a significant increase is expensive. There are people who buy toluene in bulk at paint stores and use that, but that’s a discussion in itself. It will only yield more HP if the lack of sufficient octane is specifically reducing power. That may sound “duh” , but the point is that it doesn’t contain more energy, it just prevents power from being lost to things like the fuel igniting too early (detonation) or the ECU dialing back the timing, which is really the same thing since it responds to detonation. If you have an SC or turbo then cooling the intake charge is also beneficial. That can be done with inter/after coolers or even water injection. So the best bet for street purposes is to build/tune for available pump gas in your area.
 
Originally posted by sjs:



Thanks for the explanation. I have a CTSC 91 NSX with comptech headers, no cats and a comptech supertrap exhaust

I have another question related to running rich. My A/F ration is from 2,500 rpm to 7,300 rpm always between 11 an 12. My tech says that's ideal for a boosted engine.

I have the following problem. When I shift up from 3 to 4 and 4 to 5 under WOT, I hear a bang coming out of my exhaust and sometimes big flames come with it. At first I thought it was because of running lean (much O2), but after I did a run I and checked my A/F ratio, it turned out that I certainly wasn't running lean. Can this hurt my beloved NSX?
 
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