Si Stock Boot Pressure for real or misleading advertising?

[RehabJP]

Have been driving my new 2020 Si and watching the Boost gauge and I have not seen it boost over around 16 PSI even though the advertised max boost for the Si is 20.3 PSI. I have tried it in sport mode, in comfort mode, flooring it in 6th going 70, pulling the gears all the way to the top rowing through all the gears and the max boost I am seeing is 16 PSI. Is it one of those advertising "theoretical max boost" things or will a stock Si with the L15B7 engine actually boost to over 20 PSI?

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[arnoldo]

Have been driving my new 2020 Si and watching the Boost gauge and I have not seen it boost over around 16 PSI even though the advertised max boost for the Si is 20.3 PSI. I have tried it in sport mode, in comfort mode, flooring it in 6th going 70, pulling the gears all the way to the top rowing through all the gears and the max boost I am seeing is 16 PSI. Is it one of those advertising "theoretical max boost" things or will a stock Si with the L15B7 engine actually boost to over 20 PSI?

Honda advertised peak boost of the hatch 1.5T at 16 PSI and the highest I recorded in my datalog is around 14.

WIth the way the engine work, I think Honda advertise max boost recorded in the ideal test environment at Honda facility. I don't know how Honda set up their testing environment but most likely Honda use 93 octane fuel or even higher in a controlled environment that allow the engine to perform at its peak performance.

I wouldn't say false advertising. Some dynos even measured Civic 1.5T Non-SI/SI power figure higher than advertised figure.

 

[fenix-silver]

Have been driving my new 2020 Si and watching the Boost gauge and I have not seen it boost over around 16 PSI even though the advertised max boost for the Si is 20.3 PSI. I have tried it in sport mode, in comfort mode, flooring it in 6th going 70, pulling the gears all the way to the top rowing through all the gears and the max boost I am seeing is 16 PSI. Is it one of those advertising "theoretical max boost" things or will a stock Si with the L15B7 engine actually boost to over 20 PSI?

Flooring in 6th at 70mph is a pretty bad idea for your clutch and engine, FYI. As far as hitting 20PSI, it's going to be dependent on temperature, elevation, load, RPMs, etc.

 

[RehabJP]

Flooring in 6th at 70mph is a pretty bad idea for your clutch and engine, FYI. As far as hitting 20PSI, it's going to be dependent on temperature, elevation, load, RPMs, etc.

Fair point. Normally I would downshift to 5th for more torque and acceleration on the freeway I just wanted to see what the boost would do and it did spool up and hit about 16 psi in 6th on acceleration. Its funny Honda said the changed the gearing and made the 6th gear shorter to give the driver more acceleration on the highway without having to downshift which really defeats the purpose of driving a manual to me.

 

[Benster]

They may also have put another boost sensor right after the turbo and not in the intake manifold like where ours is. You lose PSI going through al the piping and intercooler and this may be where the 20.3 comes from. Dpn't quote me on this as I'm not sure but it would account for the pressure difference.

 

[Vic_L]

I don't know how "accurate" the boost gauge is on the Si.
The 1.5T Hatchback's gauge doesn't even have numbers...
IMO, best to use something like KTuner / Hondata, and run a datalog.

 

[Benster]

I don't know how "accurate" the boost gauge is on the Si.
The 1.5T Hatchback's gauge doesn't even have numbers...
IMO, best to use something like KTuner / Hondata, and run a datalog.

I had my laptop open on ktuner for a couple pulls on the stock tune and it would kinda spike to 15 and settle around 14, 14.5 on my hatch. My guess is the pressure loss in the manifold is not compensated by the computer. The ktuner does compensate for it as when I load a tune it will be right at the target boost level. I read somewhere even the stock ktuner tune(not stock Civic tune) is more powerful as you'll get the true 15 psi on the non-SI cars.

 

[fenix-silver]

I don't know how "accurate" the boost gauge is on the Si.
The 1.5T Hatchback's gauge doesn't even have numbers...
IMO, best to use something like KTuner / Hondata, and run a datalog.

It's accurate. I see the same values as through Ktuner.

 

[Vic_L]

I had my laptop open on ktuner for a couple pulls on the stock tune and it would kinda spike to 15 and settle around 14, 14.5 on my hatch. My guess is the pressure loss in the manifold is not compensated by the computer. The ktuner does compensate for it as when I load a tune it will be right at the target boost level. I read somewhere even the stock ktuner tune(not stock Civic tune) is more powerful as you'll get the true 15 psi on the non-SI cars.

Yeah, I agree.
From what I can see, KTuner does compensate for the loss and what-not.

I'd have to check my old logs, but with TSP Stage 1 on Map #3, I've seen TC Pressure peak at 24, and Converted MAP being 23.6. Supposedly that "custom tune" is up to 24 PSI. Seems accurate.

 

[RehabJP]

I don't know how "accurate" the boost gauge is on the Si.
The 1.5T Hatchback's gauge doesn't even have numbers...
IMO, best to use something like KTuner / Hondata, and run a datalog.

No tuner but I do have an Autel 906. It wont flash the ECM but I believe it does have a PID for max boot so it will register the maximum boost it sees during a drive so maybe I will give that a try and see what it says but my guess it your not gonna see 20 PSI on stock tune. IF you ask Honda they would probably tell you that is the boost pressure at the actually turbo and that there are losses between the turbo and the throttle body as it goes through the intercooler and such but if the stock Civic EX is also boosting to the same max then kind of negates the purpose of spending more for the Si since you are paying for the extra performance. I know there are other things you get with the Si that do not come in any of the the other Civics except the CTR but still if they tell you you are gonna get more boost than any other 1.5T you should get more boost than the other 1.5Ts

 

[JT Si]

No tuner but I do have an Autel 906. It wont flash the ECM but I believe it does have a PID for max boot so it will register the maximum boost it sees during a drive so maybe I will give that a try and see what it says but my guess it your not gonna see 20 PSI on stock tune. IF you ask Honda they would probably tell you that is the boost pressure at the actually turbo and that there are losses between the turbo and the throttle body as it goes through the intercooler and such but if the stock Civic EX is also boosting to the same max then kind of negates the purpose of spending more for the Si since you are paying for the extra performance. I know there are other things you get with the Si that do not come in any of the the other Civics except the CTR but still if they tell you you are gonna get more boost than any other 1.5T you should get more boost than the other 1.5Ts

I guarantee you the Si gets more boost than the other civics. Even if it didn't, however, we know for a fact the Si has different, stronger engine internals that mean sustained use under boost will last longer. Isn't that the point of the Si? Something approachable with a little bit of extra power that your can flog on day in and day out reliably?

 

[EkSean]

It's accurate. I see the same values as through Ktuner.

I second this. Even tuned at 28psi, ktuner reads low to high 28s and so does the dash but 28-29 depending if it gets over 28.5 or not.

 

[Hondanickx]

It depends on the outside temperature.I've seen almost 16psi on my non si and as low as 14psi with different temperatures.The ECU just says to make that much torque and it regulates the boost and everything Else to that.
As for going Wot in 5th and 6th ... There's too much bs stories going on about that.You can go WOT in 5th if you make enough rpm.
Those guys that only do it in 4th and below ...You only race up to 4th gear and then stop or what? Lol
You don't want go WOT in 5th or 6th at Very low rpm .

 

[fenix-silver]

No tuner but I do have an Autel 906. It wont flash the ECM but I believe it does have a PID for max boot so it will register the maximum boost it sees during a drive so maybe I will give that a try and see what it says but my guess it your not gonna see 20 PSI on stock tune. IF you ask Honda they would probably tell you that is the boost pressure at the actually turbo and that there are losses between the turbo and the throttle body as it goes through the intercooler and such but if the stock Civic EX is also boosting to the same max then kind of negates the purpose of spending more for the Si since you are paying for the extra performance. I know there are other things you get with the Si that do not come in any of the the other Civics except the CTR but still if they tell you you are gonna get more boost than any other 1.5T you should get more boost than the other 1.5Ts

There is no pressure sensor at the turbo on the L15. There is a pressure sensor in the charge pipe ahead of the throttle and one in the intake manifold. Not sure which one the ECU relies on primarily for achieving the calculated boost target (I'm guessing the manifold MAP), but the difference doesn't matter for this discussion. When the ECU is determining the boost target, it doesn't know or care about the pressure drop between the turbo and sensor. It basically says I need to keep the wastegate shut until I achieve a certain amount of boost, at which point the wastegate opens (oversimplified due to boost ramp and other ECU parameters, but the point stands). If it takes 23 PSI of actual boost to achieve 20 PSI at the manifold, it has no idea.

 

[Benster]

It's all about the kcontrol for how much boost you're getting as well. If your kcontrol is at .49 you'll see max boost but if you're over that, the computer will actually lower boost. I retuned once and for some reason the car reset to .89 and I only had 13psi on a 21 psi map.

Pretty much everything has been said though, the stock tune probably takes its reading from the charge pipe vs intake where the tuners most likely take the intake one to account for the losses.

As for differences in boost, the SI gets 20.3 and the non-SI gets 15. The SI has 9.6:1 compression ratio, a different connecting rod and turbo amongst other things where the non-SI have 10.5:1(I think, over 10:1 for sure), weaker rods and more blades in the compressor wheel of the turbo. We build boost faster but can't put out the CFM like the SI turbo does. There are quite a bit of differences for just 20hp that Honda went through, not just more boost.

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