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Old 07-23-2003, 10:40 PM   #1
Equilibrium Tuning
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Default How does the ECU limit boost in 1st?

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.

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-- Ed

BTW, sorry if this is somewhat of a pointless question... let's give it one of these guys...
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Old 07-23-2003, 11:04 PM   #2
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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.
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Old 07-23-2003, 11:36 PM   #3
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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.
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Old 07-24-2003, 10:06 AM   #4
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Double posting n00b
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Old 07-24-2003, 10:06 AM   #5
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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.
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Old 07-24-2003, 11:44 AM   #6
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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

Quote:
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

Quote:
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


Quote:
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

Last edited by Jaxx; 07-24-2003 at 11:56 AM.
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Old 07-24-2003, 12:19 PM   #7
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Quote:
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?
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Old 07-24-2003, 12:37 PM   #8
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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.
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Old 07-24-2003, 03:32 PM   #9
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Quote:
Originally posted by Orson


Exactly how do you know this?
Yeah, nothing like stating something with such authority, then saying you guess something

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
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Old 07-24-2003, 03:32 PM   #10
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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?

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Old 07-24-2003, 04:43 PM   #11
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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
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Old 07-24-2003, 04:48 PM   #12
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Quote:
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
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Old 07-24-2003, 07:56 PM   #13
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Quote:
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...


Last edited by wyowrx; 07-25-2003 at 03:26 AM.
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Old 07-26-2003, 03:09 AM   #14
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Quote:
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
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Old 07-26-2003, 10:45 AM   #15
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Ride the brake while pressing the accelerator in first gear. You will hit full boost.
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Old 07-26-2003, 11:06 AM   #16
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Quote:
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.
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Old 07-26-2003, 03:45 PM   #17
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Quote:
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.


-- Ed
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Old 07-26-2003, 03:50 PM   #18
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Quote:
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
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Old 07-26-2003, 03:54 PM   #19
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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.
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Old 07-26-2003, 03:56 PM   #20
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Quote:
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.
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Old 07-27-2003, 01:48 AM   #21
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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
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Old 07-27-2003, 02:26 AM   #22
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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??
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Old 07-27-2003, 12:56 PM   #23
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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
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Old 07-27-2003, 07:14 PM   #24
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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
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Old 07-27-2003, 08:22 PM   #25
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Quote:
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.
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