This is a random thought that popped into my head today... Since the ECU has no knowledge of what gear the car is actually in, how is it that it manages to limit boost in first gear? Does it use the speed sensor to limit boost bellow a certain vehicle speed? Or is it simply that since there is less load in first gear, the ECU ends up in a different part of the boost map which is mapped accordingly? Or is it something totally different? This question is directed at the various tuners who deal with the ECU's mapping directly.

Thanks
-- Ed

BTW, sorry if this is somewhat of a pointless question... let's give it one of these guys...
:banana:

It can know what gear you are in.

If you divide the RPM by the vehicle speed you can figure out what gear your in.

No idea however if this is what it actually does tho.

Uhm, boost is determined by engine load. Since there is less engine load due to the gear advantage in first you are not able to build boost as quickly or as high as you can in the higher gears.

Double posting n00b:furious:

I hate to tell you, but he ECU has NO IDEA what gear you are in. It has the capability I would guess, but its not set to read that info.
The ECU doesnt limit boost in 1-2 gear. It limits it to the exact same in all gears. Boost pressure is engine load dependant. this is why if you use aboost controller set in 3rd gear, you will overboost in 4th -5th.
Your engine just isnt put under enough load to build more than 7ish lbs in 1-2 gear. BECAUSE there is a little restrictor in the wastegate vacume/boost line. If you do the 3/16 mod you will see a couple more PSI in 1-2 gear. Not always full boost, some cars only go up 1-3PSI when they do it. The restrictor makes it harder to get the boost through the line to the FBC, which slows its response. this is why you get wastegate boost in the early gears.

wow that is really wrong

yes the ecu knows how fast you are going it even does little tricks like shutting off the cooling fans if you are over 60 mph

Your engine just isnt put under enough load to build more than 7ish lbs in 1-2 gear. BECAUSE there is a little restrictor in the wastegate vacume/boost line. If you do the 3/16 mod you will see a couple more PSI in 1-2 gear.

oh no it will make full boost in first put a mbc on an it will do it
the ecu just has lower duty cycles at lower speeds.. when you add the 3/16 restrictor the duty cycle is same but more air is passed keeping the waste gate closed longer

The restrictor makes it harder to get the boost through the line to the FBC, which slows its response. the smaller restrictor will creat a smoothign effect as it will allow a smaller amount of air to pass


this is why you get wastegate boost in the early gears

no not at all it is because the ecu has a lower duty cycle at lower speeds (not gear dependant, speed dependant)

FWIW the 3/16 mod is a BAD idea

Originally posted by Davenow
I hate to tell you, but he ECU has NO IDEA what gear you are in. It has the capability I would guess, but its not set to read that info. ...

Exactly how do you know this?

Just to throw some more controversy into the mix... the ECU doesn't necessarily restrict boost in 1st and 2nd... stock, I could hit 14PSI in all 5 gears. It all depends on how it learns after a reset.

Originally posted by Orson


Exactly how do you know this?

Yeah, nothing like stating something with such authority, then saying you guess something :lol:

Anyhoo...most modern PCM/ECUs have a gear selection input. This is especially nice if you are trying to do things like limit RPM or in the case of a factory turbo car: manage a boost curve.

The factory boost controller is electronic. Knowing inputs like gear selection, RPM, and TPS allows it to select duty cycles for the controller. Net result is desired boost.

This is why the factory ECU limits peak boost in 1st and 2nd. Anyone with a ECU reflash or MBC can see that the car is capabable of more peak boost in those gears.

It is good to note that given 1st gear whizzes by so quickly, it can be hard to get peak boost with larger turbos: you run out of RPMS and don't have enough load. But on a stock car it is capable of 14-15psi in 1st gear before needing to shift if the factory BC logic is not used/defeated.

- b

Alright... the lower boost is deffinately not because of the lower load in the first two gears... no way. My Access ECU makes ~13-14psi in first and usually hits full boost in second and this is with the stock restrictor hose and stock coupler so the lower boost is deffinately coded into the ECU. The speed dependency makes the most sense so far. I was also thinking it might be related to heat. The ECU can lower boost levels based on intake temp and coolent temp. So maybe in first gear, it simply sees too high of an intake temp since there's not enough flow over the IC and therefore pulls some boost. Any Ecutek tuners care to comment?

Thanks
-- Ed

The ECU's boost map is an 8x8 scaleable grid of 64 values, with axes being RPM and load.

Interpolation is used to determine boost levels in between those cells in that grid.

The 1st gear limited by load theory is easily tested by driving your car up a 10 degree hill in 1st gear.

Someone just go do it and see if you hit max boost :)

Originally posted by Vaus
The ECU can lower boost levels based on intake temp and coolent temp. So maybe in first gear, it simply sees too high of an intake temp since there's not enough flow over the IC and therefore pulls some boost. This is a good theory, and I'm not saying the ECU does not do intake-temperature-based adjustment (as much as I would like to outright say that right now, I won't), but you lose weight at the end there. This, too, is easily tested with a simple boost gauge and a 3-minute-warmed-up car. I'll throw $20 your way if the car pulls boost with IATs of 95F vs. 60F :)

Originally posted by bvl

It is good to note that given 1st gear whizzes by so quickly, it can be hard to get peak boost with larger turbos: you run out of RPMS and don't have enough load. But on a stock car it is capable of 14-15psi in 1st gear before needing to shift if the factory BC logic is not used/defeated.

- b

17 psi first gear.... Factory BC, utec, and vishnu restrictor...

:devil: :devil: :devil: :devil: :devil: :devil: :devil:

Originally posted by jblaine
This is a good theory, and I'm not saying the ECU does not do intake-temperature-based adjustment (as much as I would like to outright say that right now, I won't), but you lose weight at the end there. This, too, is easily tested with a simple boost gauge and a 3-minute-warmed-up car. I'll throw $20 your way if the car pulls boost with IATs of 95F vs. 60F :)

The ECU absolutely has the ability to pull boost based on intake temps and coolant temps. It depends on the coding, but it deffinately can. Heatsoak the car and make a WOT run... see if you hit full boost. My Access ECU pulls about 1psi during the day here when its in the 100's and hits full boost at night when it cools down. My previous ECU (Vishnu) pulled boost less agressively but it still did.

-- Ed

Ride the brake while pressing the accelerator in first gear. You will hit full boost.

Originally posted by Vaus
The ECU absolutely has the ability to pull boost based on intake temps and coolant temps. That's a pretty confident, concise, and bold statement to make just because your car saw 1psi difference.

You know this, concretely, how?

I'll go so far as to say that you have absolutely no idea why your peak boost fluctuated by 1psi and are speculating just as much as the next guy all of a sudden.

Originally posted by jblaine
That's a pretty confident, concise, and bold statement to make just because your car saw 1psi difference.

You know this, concretely, how?

I'll go so far as to say that you have absolutely no idea why your peak boost fluctuated by 1psi and are speculating just as much as the next guy all of a sudden.

Really? Well I understand your scepticism as I'm quite a sceptic myself. I've done a good amount of delta dash logging in different conditions and see this occurance EVERY time. I also didn't mention this, but during the day in the 100 degree weather, I can get full boost but only at higher speeds (4th and 5th gear runs) when intake temps come down another 10-15 degrees. And finally, I've spoken to both Shiv and Trey personally about this, and they confirm that the ECU will pull boost based on intake/coolant temps. So let me make that "confident and concise statement once more...

The ECU absolutely has the ability to pull boost based on intake temps and coolant temps.
:D

-- Ed

Originally posted by Rich10
Ride the brake while pressing the accelerator in first gear. You will hit full boost.

Have you tried this with a stock car or a reflashed ECU? Either way, its possible that by the time you hit full boost in first, the IC is no longer heatsoaked and therefore the ECU is no longer pulling boost. I've actually noticed that I see very close to full boost in first if I run through it from a roll or right after slowing down rather than from a stop light when I rarely see close to full boost.

-- Ed

I guess I'll have to "prove it" (and I don't really consider it proof of exacly what you're stating) to myself with my own DD runs in 3rd.

I already have logs showing peak boost hit in 3rd at 45F and 90F intake air temps.

I'll see what I get on a hot day after driving around... take it easy in 1st and 2nd, then floor it in 3rd at 2000RPMs and see where it goes.

Originally posted by Vaus
Have you tried this with a stock car or a reflashed ECU? Either way, its possible that by the time you hit full boost in first, the IC is no longer heatsoaked and therefore the ECU is no longer pulling boost. I've actually noticed that I see very close to full boost in first if I run through it from a roll or right after slowing down rather than from a stop light when I rarely see close to full boost.

-- Ed Heatsoak takes a minimum of 20 seconds generally to cool off IC-wise at 20MPH or so.

Also, the intake air temperature sensor is in the MAF assembly, not post-intercooler. Post-turbo air temperature is never metered.

I guess I'll have to wait for a 90+ day. I just did a 2.5 hour hard late night drive in 1st, 2nd, 3rd, and sometimes 4th with plenty of traffic lights here and there. I datalogged several 3rd gear pulls from 2000RPM.

IAT = 90F
Peak boost = same as always

For now, all I have are older logs from my stock ECU showing 102F IAT and solid 13.5psi of peak boost as expected.

jblaine,
Still not a believer ;)

Alright.. I wish it was easier to post DD logs but I'll just tell ya what I got and I can e-mail them to you if you like.

I have logs from my Access ECU showing IAT's of 110+ and a solid 13.8psi max boost. I also have logs showing IAT's in the low 90s hitting a solid 14.7psi max. I have several logs from each session and they're all consistent. All runs were done in third gear ~2000RPM to 6500RPM on the same road just varying weather conditions. Anyone can PM me and I'll e-mail the logs.

FYI: I have logs from my Vishnu ECU showing IAT's of 100-110 making 14.4psi max boost.

Is this enough to convince you that the ECU can and does pull boost based on temperature?? :p

For cold air intake temperatures the ECU cuts the duty cycle to the wastegate solenoid, but there is a full map there to 110 degrees Celcius which could be used to cut duty cycle at high temperatures.

There is a 2x2 map of with air intake temperature vs RPM which contains boost modifier lookups. This is inactive in the standard ECU maps I've seen.

Some STi maps have Integral as well as proportional boost control and also gear judge, as well as coolant temperature controlled boost pressure. Apart from the integral boost control the features are unused.

There is nothing I've seen that limits boost in 1st gear apart from typical loads and time involved. It is simply a desired boost by TPS and RPM and a maximum wastegate duty by TPS and RPM.

Even my 20G can get 24 PSI in 1st gear :) On the 99/00 ECU there was an Ecutek hack which took the defunct (on this model) IAT vs duty map and substituted a delta RPM for IAT, giving you a modifier to duty so that you could have full boost in lower gears. I once had my car overboost fuel cutting in 2nd and not in 5th. Better mated to a FMIC so that heatsoak temperatures are less of an issue, and... an uprated tranny :)

Great info! I'm still confused about one thing. My Vishnu ECU never made more than 10psi in first gear yet the Cobb ECU makes ~13-14psi in first. I'd atribute this to temperature correction but the strange thing is that the Cobb ECU seems to actually pull more boost at higher temps than the Vishnu ECU did (see my previous post). Still seems fishy to me. I guess I'll log WG duty cycles in first vs. 3rd and see what I can come up with.

-- Ed

Originally posted by Vaus


Have you tried this with a stock car or a reflashed ECU? Either way, its possible that by the time you hit full boost in first, the IC is no longer heatsoaked and therefore the ECU is no longer pulling boost. I've actually noticed that I see very close to full boost in first if I run through it from a roll or right after slowing down rather than from a stop light when I rarely see close to full boost.

-- Ed
I haven't tried this since my car was stock. When I was stock, I couldn't figure out why I couldn't get more boost in first gear. Someone posted this as a way to prove that the ECU wasn't holding back the boost in first gear and I tried it. I was able to get approx 14psi in first by riding the brake.

From what I have gathered of our ECU, there is a target boost map and a target boost control solenoid duty cycle map. If you floor it, it is possible the ECU goes right to the duty cycle number (a number set for 14 psi) and works its way back to obtain the desired boost. In first gear this setup limits boost (the turbo doesn't have time to really spool up with the solenoid trying to keep the wastegate open), while 3rd + it isn't (the computer also has time to further adjust the duty cycle it is using). I'll bet the difference between flashes is in the tuning of that duty cycle map.

Tom

That's a good theory. I'd really like to hear from cobb or an Ecutek tuner on this.

-- Ed

Ed, why do you think taking out the factory restrictor and using the 3/16" is a bad idea?I have a Cobb stage 2 and with the restrictor in place the car didnt really have the bang so I put the 3/16" thingy in and it made all the world of difference so I called Trey and he said that was perfectly fine to use it.

Rich

The 3/16" mod simply allows you to use the stock boost controller to run more boost. For instance, instead of running 90% waste gate duty cycle, you can run 60%, and get the same result. It's kinda like fooling the stock boost controller (same as an ABC, but not adjustable).

Using the stock boost controller and the vishnu restrictor, I am able to run 21 psi...:devil:

Originally posted by wyowrx
Using the stock boost controller and the vishnu restrictor, I am able to run 21 psi...:devil:

How in the holy hell do you do that?! ;)

Originally posted by masterrch
Ed, why do you think taking out the factory restrictor and using the 3/16" is a bad idea?I have a Cobb stage 2 and with the restrictor in place the car didnt really have the bang so I put the 3/16" thingy in and it made all the world of difference so I called Trey and he said that was perfectly fine to use it.

Rich

The 3/16" coupler just allows the solenoid to bleed off more pressure. Do you have a boost gauge? What kind of boost were you seeing before/after the 3/16" coupler? Are you getting any spiking now? If you have a little spiking but are closer to the correct boost target, you should try a 5/32" coupler. It seems to work really well, giving the solenoid a little help w/o causing any spiking. A friend of mine is running the 5/32" coupler on his stage 2 AECU with great results. He was previously running cobb's restrictor hose and seeing slight spikes and once he switched to the coupler, everything runs better.

-- Ed

Originally posted by Vaus
That's a good theory. I'd really like to hear from cobb or an Ecutek tuner on this.

-- Ed


Umm, you did hear from an ECUtek tuner on this.

John Banks has been an ECUtek tuner longer than pretty much everyone in the US. I'd believe what he has to say on the matter.

Similar to what Tom says, except that on cars without an "Initial Wastegate Duty" map (ie USDM WRX AFAIK), the boost "error" from target boost is used as a lookup to a table which controls the ramp rate to maximum duty cycle. In practice it ramps up pretty quick even in first gear, the limit is the maximum duty cycle in the map.

So yes, maximum wastegate duty is the main limiter to boost in lower gears - if you set it high enough to make target boost easily in lower gears you get a spike in higher gears, even if you use a 3 port solenoid for boost control which is much tighter on the control.

Hence temperature and gear compensation is the way to go IMHO. Icing on the cake would be learning.

I have to admit to chopping and changing between MBC and 3 port with gear judge. AVC-R would also be superb.

I think I deserve a good flaming for admitting I love MBCs ;) Adjust the bleed and actuator and you can get the part throttle and top end roll off you want :D

Originally posted by john banks
Similar to what Tom says, except that on cars without an "Initial Wastegate Duty" map (ie USDM WRX AFAIK), the boost "error" from target boost is used as a lookup to a table which controls the ramp rate to maximum duty cycle. In practice it ramps up pretty quick even in first gear, the limit is the maximum duty cycle in the map.


Ah, so we (USDM WRX) have some sort of ramp rate table, not actual maximums, or both?

Tom

Both. You don't have gear judge, or anything meaningful on temperature control.

Originally posted by john banks
Both. You don't have gear judge, or anything meaningful on temperature control.

If you say we don't have anything meaningful on temp control, how do you explain my logs under varrying IATs?

-- Ed

You're controlling wastegate duty cycle and not actual manifold air pressure.

Temperature fluctuations will cause the density and humidity of the air to change, which will change the interaction between the bleed, the manifold air pressure, and the wastegate.

Also, because the pressure source for wastegate control is the turbo outlet. It is conceivable that MAP is also dependent on pressure drop across the intercooler and intercooler temperature efficiency. I'm not positive that one has a real measurable effect, but several people with MBCs, UTECs, etc... have noted that the first thing I mentioned is definitely real.

The ECU has an actual boost target to hit besides just wastegate duty cycles. This is a third gear pull so the ECU deffinately has time to hit the target and consistently hits 1psi lower with IAT's of 110+. It still seems that there is a temperature correction for boost.

-- Ed

Ed,my understanding of the factory restrictor was more of a failsafe device so no matter what happened with the soleniod the lack of flow in the hose would allways open the wastgate.
With the restrictor in place the Cobb stge 2 could only manage around 14psi which was only slightly higher than it was stock with 3/16" fitting it hits a consistant 15.2psi with out spiking.
I asked Trey what it should be and he was abit vauge.
I was even thinking about a MBC to get it closer to 16psi.
(sorry for the post within a post)

Rich

I don't think the restrictor is a failsafe, some cars can make a good deal more than stock boost on reflashes with the stock restrictor. As long as you're not spiking, the 3/16" should be fine and 15.2psi is just about right for stage 2.

-- Ed

There is no temperature correction - merely that a higher IAT requires a higher duty cycle than your car is mapped for to achieve target boost. Same happens in lower gears. There is no fancy trickery involved!

The 3/16 mod a bit of an allusion. What you really doing is changing time intervals. There are two restrictors, the brass pea in the hose and the restricter coupler. When you change the restrictor your just changing when the wastegate opens, which equates to more boost.

The problem that this presents is that the stock ecu is tuned to performance and just because your increasing boost doesnt mean that your increasing power. As JB stated there are a lot of look ups that the ECU performs and when the boost is increased the Air charge is increased. That causes the ECU to obtain another value that may not be the most optium value. An altered map point in the fuel map can have a different ignition map point value. This can also cause the look up in the igntion map to be less and the ECU will appear to have puledl timing a bit. This is when you feel the bumps and jumps. Now when things get back on track in the map you may feel the smooth pull.

The fully stock car has a smoothness about it. It may not have the power but it is smooth. Now the key is to have the smoothness and power, When you have that combination you have an engineered mod anything else is just a change.

Most of the mods that are made take away from the smoothness of the stock ECU maps. BOV are just induced turbo lag.

One key thing about this ECU is that it has to ability to protect itself and learn. The ECU even knows to reduce boost if your at a higher altitude. Hence

LA MBC + HM Run = BE

Low Alitude MBC running in the High mountain run will blow the engine.

With that one should understand that any changes can cause a chain reaction in the ECU. The ECU may cover your mistakes but if it doesnt then ......

WRXzard

We're talking about using the 3/16" coupler on a Cobb reflashed ECU specifically not on a stock ECU. It has been noted many times that the coupler can have negative effects on a stock ECU but it is in fact a good way for people not seeing the correct max boost to give the solenoid a little help. It seems to work better than Cobb's smaller restrictor hose which sometimes creates spikes.

-- Ed

Originally posted by WRXzard

Low Alitude MBC running in the High mountain run will blow the engine.

WRXzard

That is, without seperate engine management and tuning!

Bumping this with a question:

after absorbing this info and thinking for a while, it seems that the ECU is basically open loop boost control; it is controlling the boost simply with BCS duty cycle similar to the UTEC open loop, although with the added ramp up rate table.

In addition, it has boost targets, but those are used for long term adjustment. They are not directly used in boost control, but to adjust the gain on the BCS duty cycle over the course of days/weeks. That's why the 3/16 mod works great for a while, then it is tuned down a bit. The BCS duty cycle is lowered, the ramp rate might be adjusted, but there isn't an immediate feedback system (PID) for boost control.

So am I talking out of my behind or is this an accurate description of our USDM boost control?

Tom

Unfortunately you are just about entirely incorrect.

Boost control is closed loop. Present Boost-target boost is a look up to duty ramp rate table to zero in on target. The values in this table determine the damping/gain.

Doh, I wasn't thinking of the ramp adjustment right. I guess it is the P in PID.

If there is a (current - target) boost correction, why would the 3/16 mod do anything? I remember having ~1 psi more boost with than without. If there is immediate boost correction, it seems the mod would only induce mildly earlier spool and spikes.

So we have a target boost (by rpm), a target BCS duty cycle (by rpm/load?) and a duty ramp table (by current-target boost?). which one (if any) is adjustable by the ECU?

I guess having a rate lookup table allows them to fine tune near the target level, but that same fine tune gain near target limits the ability to handle extra flow at the BCS.

Thanks for the help.

Tom

3/16 mod is just like running higher duty cycle maximums. So tends to lead to overshoot and higher held boost in lower gears - often "target" boost is limited by duty cycle not boost target in lower gears. The control is not very aggressive high gain closed loop so as not to cause oscillation.

Prodrive asserts the following:

The temperature correction map in the ECU has control over the duty cycle of the wastegate solenoid. This is used to stop over-boost if the ambient air temperature falls too far and as a safety device to protect the engine if the intake temperature air gets too hot. This primary safety device kicks in above 40C and lowers the boost pressure. This allows the use of higher boost when conditions are optimal (ie. below 40C)

This *may* be in direct reference to the Prodrive tuned ECU, so I was wondering if this is true for other ECUTek'd ECUs, or the stock WRX ECU. From reading john banks's post, I would assume this must be something privy to the Prodrive ECU then since he made the comment There is no temperature correction - merely that a higher IAT requires a higher duty cycle than your car is mapped for to achieve target boost. Same happens in lower gears. There is no fancy trickery involved!

On the standard ECUs I've seen so far, the tables to control for temperature are more sophisticated on STi models, especially JDM, but they are largely unused. With Ecutek tools, a tuner (including Prodrive) can modify these tables.

But as the standard WRX ECUs stand that I have seen there is indeed no fancy trickery.

Thanks John! :disco:

quick question since I'm a n00b - where do you work? (Just seeing your member number is enough to make me cower in my boots!) I feel like an idiot asking you, but you obviously have a lot of experience.

I used to map commercially using Ecutek tools.