Boost Level Vs. Throttle Pedal Position

[fabrizzio71]

I have about 12,500 miles on my Si, and have only tried going WOT recently. I normally drive the car with the boost gauge visible as I like to monitor what’s going on with the engine. The first time I put the pedal to the floor it was in 2nd gear and I was surprised that the boost never went higher than 14-15 psi. I felt that was strange as previously I have seen boost go as high as 18 psi a number of times and 19psi twice. Just this evening, I tried again and did an experiment. I revved to 4,000 rpm in 3rd gear, put the pedal to the floor and held it, letting off before redline. Boost never went higher than 15psi. A little while later I did the same thing, but instead of putting the pedal all the way down I pushed it maybe 80% and boost went up as high as 18psi. I did this several times to confirm and got the same result. I am used to pedal to the floor meaning maximum acceleration, but it seems that isn’t the case here. This is my first turbo car and my first car with drive by wire. I recognize that the computer goes to 100% throttle before the pedal gets to the floor, I have even tested that with the car off but the display on. Why would boost be limited with pedal to the floor? I do have the Acuity Throttle position spaced but it is in position C which I didn’t think would cause an issue. Any insights?

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[Gotch]

I’ve noticed the exact same thing and have done the experiment you did several times. Most of my tries were in second gear where part throttle in “normal “ mode, boost would hit 18-19psi consistently with the odd 20psi spike here and there 2500-3500rpm. Foot to the floor and only 15-17psi. Factory boost control is all over the place even causing slight surging after 3500rpm. I think is is the ecu trying to hit a power target and not go beyond that.

 

[Gotch]

https://www.civicx.com/threads/wheres-the-boost.26666/

 

[COOL COUPE]

When I used to visit the Mazda Speed 3 forum everyone knew everything about everything you know how it goes. Back in 2008 those folks were taking the position that since the stock by pass valve was made of plastic - it would leak boost. I bought into the hype and did have a Turbo Smart BPV on my Speed 3. What specifically is the "quality" of our stock valve? ...assuming also it is plastic and not metal?

 

[Micah]

Boost builds based on load among other factors. Google is your friend.

 

[waterudoing]

Boost builds based on load among other factors. Google is your friend.

I'm sure OP knows this. Did you even read past the title?

 

[Micah]

I'm sure OP knows this. Did you even read past the title?

Yep. Would you kindly elaborate?

 

[360glitch]

I have about 12,500 miles on my Si, and have only tried going WOT recently. I normally drive the car with the boost gauge visible as I like to monitor what’s going on with the engine. The first time I put the pedal to the floor it was in 2nd gear and I was surprised that the boost never went higher than 14-15 psi. I felt that was strange as previously I have seen boost go as high as 18 psi a number of times and 19psi twice. Just this evening, I tried again and did an experiment. I revved to 4,000 rpm in 3rd gear, put the pedal to the floor and held it, letting off before redline. Boost never went higher than 15psi. A little while later I did the same thing, but instead of putting the pedal all the way down I pushed it maybe 80% and boost went up as high as 18psi. I did this several times to confirm and got the same result. I am used to pedal to the floor meaning maximum acceleration, but it seems that isn’t the case here. This is my first turbo car and my first car with drive by wire. I recognize that the computer goes to 100% throttle before the pedal gets to the floor, I have even tested that with the car off but the display on. Why would boost be limited with pedal to the floor? I do have the Acuity Throttle position spaced but it is in position C which I didn’t think would cause an issue. Any insights?

This is normal ECU behavior and not related to your throttle pedal spacer. You can change this behavior with an ECU tuner such as Ktuner.

 

[fabrizzio71]

This is normal ECU behavior and not related to your throttle pedal spacer. You can change this behavior with an ECU tuner such as Ktuner.

Thank you!

When I used to visit the Mazda Speed 3 forum everyone knew everything about everything you know how it goes. Back in 2008 those folks were taking the position that since the stock by pass valve was made of plastic - it would leak boost. I bought into the hype and did have a Turbo Smart BPV on my Speed 3. What specifically is the "quality" of our stock valve? ...assuming also it is plastic and not metal?

Thanks for the reply. One of the things I enjoy about this forum is the collective knowledge people bring from previous automotive experience.

I’ve noticed the exact same thing and have done the experiment you did several times. Most of my tries were in second gear where part throttle in “normal “ mode, boost would hit 18-19psi consistently with the odd 20psi spike here and there 2500-3500rpm. Foot to the floor and only 15-17psi. Factory boost control is all over the place even causing slight surging after 3500rpm. I think is is the ecu trying to hit a power target and not go beyond that.

Thanks, I’m glad to hear I’m not the only one to question this. Also, thanks for the link; I had actually read through that a while back. I’m still not sure I understand why Honda tuned the ECU that way, why not have it hit highest boost with foot to the floor? Today accelerating through an on-ramp, I floored it in 3rd and then by lifting my foot a tiny bit I actually got a bit more acceleration through the slight increase in boost.

Boost builds based on load among other factors. Google is your friend.

Yes, Google can be quite helpful. A forum specifically for automotive enthusiasts who drive the exact same vehicle as me is also quite helpful, hence why I posted on here and received numerous constructive responses. Sharing knowledge and enjoyment of our vehicles as well as debating and questioning its quirks seems to be the point of this forum.

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