Tuning forced induction for part throttle...

[FloorPizza]

OK, so a very trusted source (Tim at CIS) has stated that it isn't possible to fully tune FI for partial throttle operation, and that it is possible to be operating in a partial boost mode with no fuel correction. And now that I think back on it, most all of the FI blown up engines were being operated at partial throttle when they blew. I remember alot of posts saying "I wasn't even getting on it when it blew".

As much as I want to go with FI, I'm not willing to take this chance. So I'm asking this question to the tuners... is it possible to set up either a supercharger or a turbo so that all of the boost is dumped overboard until the Throttle Position Sensor sends a WOT signal, at which point the boost is dumped into the engine, at the exact same time the PCU goes into WOT mode (I always get this mode confused.. it's either "closed loop" or "open loop" operation at WOT), which of course, would be properly tuned for the boost (which is, apparently, fairly easy to CMR tune for FI). So basicly, I'm talking about a FI system setup similar to N20: nothing until you ask for it. No boost at all until you are WOT.

I realize that I'd be losing a lot of power when not operating at WOT; the engine would be wasting alot of horse power spinning either a SC or turbo without getting any benefit in return. I'd rather be wasting that horsepower and not have to worry about blowing up an engine.

So what do you guys think? Is this reasonably possible?

I know Tim is working on a tuning solution system that is neither a piggy back nor PCU replacement for solving the partial throttle/partial boost problem, and it really does sound exciting, and I'll probably end up buying his system once it's marketed and de-bugged, but in the mean time, I'd like a means of *safely* running boost.

[1fastsedan]

You can tune part throttle boost in CMR from Diablo. Problem solved.

[FloorPizza]

You can tune part throttle boost in CMR from Diablo. Problem solved.

Neither statement is correct, what I have been working on is a modified stand alone designed to work with a factory PCM. Very easy to tune with by the end user. It provides direct injector control and the ability to control the other variables that can not be performed in the factory LX PCM because the stuff is not in there.

You can not show me a rewritten LX PCM for forced induction that has the ability to control fuel in a part throttle boost situation (the vehicle is still in closed loop), without simply jumping to a WOT condition regardless of the pedal position. Every tune I have run for a turbo would always have a window where I could be in part throttle boost and no fuel correction. That window starts at about a 33% pedal position on a turbo and extends up to wherever the particular tune has the throttle blade opening percentage set at to go to WOT fueling.

Forced induction PCM tuning is another ball of wax compared to tuning of an NA engine. The factory LX PCM does not have functioning boost tables in it, and it can not tell a vacuum state from a presurized state in the manifold in relation to fuel correction. Putting a 2 BAR map sensor on a factory LX PCM only prevents forced induction from overranging the MAP sensor signal and throwing codes. The fueling is performed by lowering the throttle blade percentage as to where to transition to WOT. It has also been found that certain adaptives must be turned off otherwise the factory LX PCM will overwrite the tune and the vehicles drivability will progressively degrade.

The Dodge SRT-4 PCM has a bank of three solenoids controlled by the PCM to reroute vacuum and boost pressures (controls the wastegate and Blow Off Valve as well as barometric pressure readings), and a very important Throttle Inlet Pressure sensor so the PCM can compare the pressure on both sides of the throttle blade and make the appropriate fuel correction for all driving situations. The factory LX PCM can not do this, it is not set up from a wiring input/output standpoint to be able to do anything with a presurized manifold state. Regardless if "turbo" tables have been found in the LX PCM, there are no wiring connections into or out of the PCM to do anything with them.

Since the PCM code can not be rewritten (only exisitng table variables can be changed or things turned on or off), there is no way to make the PCM do anything other than throw more fuel based on the throttle blade opening percentage.

The worst thing to do is tune forced induction on the dyno and call it a day. One must spend some time on the street adjusting the tuning to address the drivability issues that will pop up from a straight dyno tune. I have seen it time and time again, and have probably run 25+ PCM tunes on my own vehicle. The lower the WOT threshold is set, the touchier the pedal becomes, so much till you get to a point where the slightest touch on the pedal and the vehicle will immediately jump to WOT and take off like a bat out of heck.

There are some very good tunes out there that do a good job walking the fine line between dyno conditions and street conditions, but not all are the same for sure. When you jump in a vehicle and as soon as you touch the gas on the street and it immediatley takes off (and worse doesn't stop going when you let off the gas for a few seconds), well it may have been okay on the dyno, but it is scary on the street.

I could ease into 2-3 psi of boost and drive the car there in a steady state, remaining in closed loop, which would leave you with a 14.7 AFR on a PCM tune. Not a good situation. The unit I was working on and ran for almost 2 years of testing would immediately, upon seeing boost, apply fuel correction even without ever going into WOT. Part throttle boost fuel correction has always been the issue with trying to tune the factory LX PCM.

If you had the ability to control your injectors directly in all situations, why would you not want to do just that? Sure it would be nice to be able to just simply rewrite the factory PCM code to make it do exactly as one wishes, but that is not a possibility on the LX.

Maybe some will believe me, others will not, but I have lived with forced induction for over 32,000 miles on my own vehicle, and have worked with countless others with FI. I have tried a half dozen different tuning options, over three years. I know what I have seen, what it has done, and what can realistically be achieved. Don't get me wrong, I am not knocking the available tuning software, it works very well in the areas it can control. It is not limitations with it, it is simply the limitations in the factory LX PCM that causes issues.

Tim

The bold parts are very interesting, and what made me write the original post in this thread. It appears that all CMR Diablo FI tiunes simply lower the threshold of WOT to the same point that the boost starts to kick in. However, as Tim points out, there is still a small window where you could still be pulling some boost without fuel correction, CMR tune or not.

[HULK]

You can tune part throttle boost in CMR from Diablo. Problem solved.

Lol.... glad I wasnt the only one thinking that as I was reading his post.... Never heard anyone say you cant tune for boost in part-throttle since CMR tuning became available.

-Pat

[FloorPizza]

You can tune part throttle boost in CMR from Diablo. Problem solved.

Lol.... glad I wasnt the only one thinking that as I was reading his post.... Never heard anyone say you cant tune for boost in part-throttle since CMR tuning became available.

-Pat

Guys, please read post number three. I'm well aware of CMR tuning from Diablo. Without it, we'd still be running piggy back systems or FAST in order to run FI.

Edit: I can very easily see this thread going totally off topic, and turn into a "yes you can tune partial throttle/partial boost", "No, you can't tune partial throttle/partial boost" argument. And that's fine... a definitive answer to that question would be great. However, I would still like to know if the original question in the original post is possible and/or practical.

For a great explanation/discussion about partial throttle/partial boost tuning, please check out this thread: Starting my turbo project Reading from the start of page three to the end of the thread is very enlightening.

[HEMI~C~]

To answer the question relating to controlling when the boost comes in this shouldn't be a problem if you control the source of the vacuum operating the BOV. I am trying to do just the opposite as you, bleeding off boost to reduce power at the shift.

What we have come up with so far is to plumb to BOV into my intercooler hoses, both vacuum diaghrams associated with the BOV will be connected to vacuum solenoids that can be triggered/controlled via an rpm window switch similar to that used to control nitrous. Actually, I am considering the use a progressive nitrous controller, that I had already planned on purchasing to control the hit of my direct port plates. I will likely use the programmable rpm window signal coming from the controller to open the vacuum solenoids, bleeding off boost just before the shift.... as the rpm falls...the shift occurs...and solenoids click back open restoring full boost. In theory anyways.

In your situation I imagine the above scenario could also work using the TPS input going into the controller to sense WOT....therefore triggering the solenoids to open providing the vacuum necessary to close the BOV/build boost.

As for AFR at lows load/partial boost situations what would you be looking to tune towards?

THoughts?

[1fastsedan]

The bold parts are very interesting, and what made me write the original post in this thread. It appears that all CMR Diablo FI tiunes simply lower the threshold of WOT to the same point that the boost starts to kick in. However, as Tim points out, there is still a small window where you could still be pulling some boost without fuel correction, CMR tune or not.

From what I understand (and Diablo stated last year), the boost tables are in the LX PCM the tuner just has to use them. Again, I think you're reading too much into this. If you still have issues with this, talk to Steve from RDP or Mike (lafrad). They have tuned more boosted LXs than anyone I know.

[hemituner]

Guys, please read post number three. I'm well aware of CMR tuning from Diablo. Without it, we'd still be running piggy back systems or FAST in order to run FI.

Edit: I can very easily see this thread going totally off topic, and turn into a "yes you can tune partial throttle/partial boost", "No, you can't tune partial throttle/partial boost" argument. And that's fine... a definitive answer to that question would be great. However, I would still like to know if the original question in the original post is possible and/or practical.

For a great explanation/discussion about partial throttle/partial boost tuning, please check out this thread: Starting my turbo project Reading from the start of page three to the end of the thread is very enlightening.

I think the real question here is WHO can do REAL part throttle maping for boosted applications not just cheating the 1 bar scaling with a 2 bar sensor tune. The answer is there are only 4 tuners that I know that can do it PROPERLY. It is Both possible and Practical.
Hope this helps
A.J.

[STREET LIFE R/T]

I think the real question here is WHO can do REAL part throttle maping for boosted applications not just cheating the 1 bar scaling with a 2 bar sensor tune. The answer is there are only 4 tuners that I know that can do it PROPERLY. It is Both possible and Practical.
Hope this helps
A.J.

Which 4 tuners.....

[Tim@NCTSLLC]

A supercharger is rpm based so generally the boost comes on higher in the rpm range. A turbo on the other hand is load based, so the point boost comes in is variable. As I have mentioned before, I could easily drive at 33% pedal position and be in 2-3 psi boost. For an SC, the WOT threshold can be lowered to more closely aproximate where boost comes on. However, as you lower the WOT threshold, your pedal becomes more sensitive to movement as the effective range of movement before WOT is less.

When you hear someone say that the vehicle takes off as soon as they touch the pedal or in light load situations, this is what is taking place. It is a balancing act between too little and too much. There are some who do a very good job balancing that line, but it takes specific tuning for the vehicle, not a canned tune as there are too many variables in play.

In particular on a turbo, you can not lower the threshold low enough to cover the entire boost range since load is the driving factor. Possibly with an SC if the rpm based boost point is high enough.

Yes as I have stated, I am aware that some have mentioned that the boost tables are present in the PCM. But you have to keep in mind, that they are not in use, and the physical architecture in the PCM is not configured for them (pin outs and external leads to the required sensors and components). The PCM is the handicap, not the tuning software. That needs to be understood. Also, the PCM program is not being rewritten, but the variables in the tables are being changed. You are still limited by what can actually be changed.

A good example once again is the SRT-4 PCM which is designed for boost. Not only does it have the tables present and in use, but the PCM is also using the MAP sensor to read manifold pressure, a solenoid to switch the MAP sesnor to read to atmosphere for updating barometric pressure reading (at times even when in boost, a TIP sensor (Throttle Inlet Pressure) upstream of the throttle plate to compare to the MAP sensor reading, and two more solenoids associated with the factory BOV and wastegate so it can limit power based on other parameters programmed into the PCM such as vehicle speed, ESP feedback, environmental conditions, etc. And yes it has the ability to bleed boost or bleed exhaust gas through the wastegate to control power output. But, because of all of this, the PCM can detect presure in the manifold at any point, and therefore apply fuel correction throughout the boost range.

None of these components exist nor do the physical pinouts in an LX vehicle so they can not be added to make the boost tables function as intended.

If you can ease into boost below the WOT threshold, you will still be in Closed Loop mode and the AFR will stay in the 14.5 - 14.7 range. The PCM simply can not see a "boosted" state based on MAP sensor reading and trigger WOT fueling. You are either in Closed Loop or Open Loop (WOT) mode. On the LX, the trigger point to WOT is based on a percent throttle blade open setting.

If I can be in boost at say a 40% throttle blade open percentage, and the WOT threshold is set at 60%, do I have part throttle boost correction? No I do not as I am still in closed loop mode. It is that simple.

Over the past three years, I have run every single piggyback manufactured that is based on skewing the MAP sensor voltage. None are stable as the PCM learns around it. I have run countless PCM tunes some bad, and some very good, from a variety of sources. I won't get into a discussion of who is good and who is not, but I will say that some of them (the best ones) came from a source where you could get no better from anyone. I have pulled so many log files, I have lost count of them. I have studied many dyno sheets where the vital AFR versus boost plots are included.

On those dyno sheets, it is clear where boost is in and where fueling correction is applied. I have yet to see one where the two match up. I have seen some which were close, but generally those had serious driveability issues. WOT runs on the dyno are one thing, and generally you go into boost when the pedal goes to the floor and WOT fuel correction is applied almost immediately. But, out on the street in day to day driving is where the complaints and issues come from as you do not drive it (unless at the track) the way it is run on the dyno. Any tuning needs to be a combination.

The best I have seen have started with street tuning, moved to the dyno, and then back to the street for final tweaking. These have the least amount of overall issues.

As far as bypassing boost, I am working on just such a project. But, you must keep in mind, that on a turbo, if you simply dump the boost to the atmosphere, it is like running the turbo with no outlet connection. You can easily overspeed the rotating assembly in the turbo and it will grenade at some point very quickly. It takes very little exhaust flow to spin a turbo at 150,000 plus RPM if there is no back pressure (work) on the compressor wheel.

Tim

[Frozen_]

Which 4 tuners.....

i can tell you Hemituner is one of them.

[FloorPizza]

You can tune part throttle boost in CMR from Diablo. Problem solved.

Lol.... glad I wasnt the only one thinking that as I was reading his post.... Never heard anyone say you cant tune for boost in part-throttle since CMR tuning became available.

-Pat

I think the real question here is WHO can do REAL part throttle maping for boosted applications not just cheating the 1 bar scaling with a 2 bar sensor tune. The answer is there are only 4 tuners that I know that can do it PROPERLY. It is Both possible and Practical.
Hope this helps
A.J.

Hope this thread is turning out to be a bit more educational than you thought.

[FloorPizza]

To answer the question relating to controlling when the boost comes in this shouldn't be a problem if you control the source of the vacuum operating the BOV. I am trying to do just the opposite as you, bleeding off boost to reduce power at the shift.

What we have come up with so far is to plumb to BOV into my intercooler hoses, both vacuum diaghrams associated with the BOV will be connected to vacuum solenoids that can be triggered/controlled via an rpm window switch similar to that used to control nitrous. Actually, I am considering the use a progressive nitrous controller, that I had already planned on purchasing to control the hit of my direct port plates. I will likely use the programmable rpm window signal coming from the controller to open the vacuum solenoids, bleeding off boost just before the shift.... as the rpm falls...the shift occurs...and solenoids click back open restoring full boost. In theory anyways.

In your situation I imagine the above scenario could also work using the TPS input going into the controller to sense WOT....therefore triggering the solenoids to open providing the vacuum necessary to close the BOV/build boost.

As for AFR at lows load/partial boost situations what would you be looking to tune towards?

THoughts?

Thank you, sir, that's exactly what I'm talking about doing. I'd like the thing to run completely stock from idle to 99% TPS, then go into boost at WOT. I'd like to keep the AFR's factory through the RPM range until the boost kicks in.

[1fastsedan]

Hope this thread is turning out to be a bit more educational than you thought.

Nope. Just proves who can tune boost and who can't. I know my tuner can, obviously some people blame the tools and not the tuner's lack of skill.

[FloorPizza]

A supercharger is rpm based so generally the boost comes on higher in the rpm range. A turbo on the other hand is load based, so the point boost comes in is variable. As I have mentioned before, I could easily drive at 33% pedal position and be in 2-3 psi boost. For an SC, the WOT threshold can be lowered to more closely aproximate where boost comes on. However, as you lower the WOT threshold, your pedal becomes more sensitive to movement as the effective range of movement before WOT is less.

When you hear someone say that the vehicle takes off as soon as they touch the pedal or in light load situations, this is what is taking place. It is a balancing act between too little and too much. There are some who do a very good job balancing that line, but it takes specific tuning for the vehicle, not a canned tune as there are too many variables in play.

In particular on a turbo, you can not lower the threshold low enough to cover the entire boost range since load is the driving factor. Possibly with an SC if the rpm based boost point is high enough.

Yes as I have stated, I am aware that some have mentioned that the boost tables are present in the PCM. But you have to keep in mind, that they are not in use, and the physical architecture in the PCM is not configured for them (pin outs and external leads to the required sensors and components). The PCM is the handicap, not the tuning software. That needs to be understood. Also, the PCM program is not being rewritten, but the variables in the tables are being changed. You are still limited by what can actually be changed.

A good example once again is the SRT-4 PCM which is designed for boost. Not only does it have the tables present and in use, but the PCM is also using the MAP sensor to read manifold pressure, a solenoid to switch the MAP sesnor to read to atmosphere for updating barometric pressure reading (at times even when in boost, a TIP sensor (Throttle Inlet Pressure) upstream of the throttle plate to compare to the MAP sensor reading, and two more solenoids associated with the factory BOV and wastegate so it can limit power based on other parameters programmed into the PCM such as vehicle speed, ESP feedback, environmental conditions, etc. And yes it has the ability to bleed boost or bleed exhaust gas through the wastegate to control power output. But, because of all of this, the PCM can detect presure in the manifold at any point, and therefore apply fuel correction throughout the boost range.

None of these components exist nor do the physical pinouts in an LX vehicle so they can not be added to make the boost tables function as intended.

If you can ease into boost below the WOT threshold, you will still be in Closed Loop mode and the AFR will stay in the 14.5 - 14.7 range. The PCM simply can not see a "boosted" state based on MAP sensor reading and trigger WOT fueling. You are either in Closed Loop or Open Loop (WOT) mode. On the LX, the trigger point to WOT is based on a percent throttle blade open setting.

If I can be in boost at say a 40% throttle blade open percentage, and the WOT threshold is set at 60%, do I have part throttle boost correction? No I do not as I am still in closed loop mode. It is that simple.

Over the past three years, I have run every single piggyback manufactured that is based on skewing the MAP sensor voltage. None are stable as the PCM learns around it. I have run countless PCM tunes some bad, and some very good, from a variety of sources. I won't get into a discussion of who is good and who is not, but I will say that some of them (the best ones) came from a source where you could get no better from anyone. I have pulled so many log files, I have lost count of them. I have studied many dyno sheets where the vital AFR versus boost plots are included.

On those dyno sheets, it is clear where boost is in and where fueling correction is applied. I have yet to see one where the two match up. I have seen some which were close, but generally those had serious driveability issues. WOT runs on the dyno are one thing, and generally you go into boost when the pedal goes to the floor and WOT fuel correction is applied almost immediately. But, out on the street in day to day driving is where the complaints and issues come from as you do not drive it (unless at the track) the way it is run on the dyno. Any tuning needs to be a combination.

The best I have seen have started with street tuning, moved to the dyno, and then back to the street for final tweaking. These have the least amount of overall issues.

As far as bypassing boost, I am working on just such a project. But, you must keep in mind, that on a turbo, if you simply dump the boost to the atmosphere, it is like running the turbo with no outlet connection. You can easily overspeed the rotating assembly in the turbo and it will grenade at some point very quickly. It takes very little exhaust flow to spin a turbo at 150,000 plus RPM if there is no back pressure (work) on the compressor wheel.

Tim

Thanks for showing up here, Tim!

As Tim has pointed out, it's a physical limitation of the LX PCM that is preventing tuners (even the good/best ones) from tuning for boost without it being, at least partially, a hack: Lowering the WOT threshold to the RPM that boost comes on in a SC application.

Edit: Ouch.. I can see the "hack" statement being taken completely wrong. It is a necessary hack, since it is the only currently feasible way of overcoming a limitation of the LX PCU: it can't see boost. Tuners are doing everything they can, of course, but are limited by the hardware they have to work with.