Why does turning up the boost help with spoolup?

[Spoolin4Ever]

I'm not really new here, but this question is quite elemental:

I noticed when the boost is set at 16-17, that the spool up seems to be a bit quicker then when it is set on a lower setting such as 12. Why is that? Or does it just seem like it is but it's just faster overall making it seem to spool up faster.

 

[Defiant]

I think your key word is "seems". There shouldn't be any relation between where the wastegate opens, and when spool becomes palpable. However, the payoff in higher boost (until something blows up) may give more of an impression of overall performance.
Very little real road work goes on below boosting revs. Most have downshifted before they've left the boost band.

 

[Steve93Talon]

It's because the MBC/gate begins to bleed off boost a few psi before target boost to prevent a spike. So if you're targeting 12psi, it might start to open at around 9-10, but if you're targeting 17 it's staying completely shut until like 15.

 

[turboglenn]

It's because the MBC/gate begins to bleed off boost a few psi before target boost to prevent a spike. So if you're targeting 12psi, it might start to open at around 9-10, but if you're targeting 17 it's staying completely shut until like 15.

And Steve calls it for the win!!!!!!!!

 

[dsm-onster]

^ I was going to say the same thing. . . This has happened to both my turbo cars.

 

[Defiant]

That's true for where it begins to bleed off pressure to the turbine, but what effect would that have on spoolup? In both cases, you're supposedly starting with no bleed. The extra pressure of a higher bleed pressure should come into play after the turbine's spun-up, shouldn't it? WTF

 

[Mikael SS]

That's true for where it begins to bleed off pressure to the turbine, but what effect would that have on spoolup? In both cases, you're supposedly starting with no bleed. The extra pressure of a higher bleed pressure should come into play after the turbine's spun-up, shouldn't it? WTF

i'd stick with it just "feels" that way

turbos building boost gain exponentially- meaning it may take 10sec for 1psi, 5sec for 2, and 1sec for 8. (made up numbers for example sake)

so if its going all the way to 17, you might start your count at 3psi, and the "feel" from 3-17 is more dramatic than the "feel" of 1-12.

 

[nightracer91]

i'd stick with it just "feels" that way

turbos building boost gain exponentially- meaning it may take 10sec for 1psi, 5sec for 2, and 1sec for 8. (made up numbers for example sake)

so if its going all the way to 17, you might start your count at 3psi, and the "feel" from 3-17 is more dramatic than the "feel" of 1-12.

Very well put!

 

[tkelly27]

The pressure that the WG cracks at a few psi before the target boost. If you have a mbc set at 10psi, the wg might crack open at 8. If you have it set at 20, it will crack at 18. I do agree 99% of it is feel, but the one set at 20 should go from 8-10 faster than the one set at 10.

 

[T9S1i]

The pressure that the WG cracks at a few psi before the target boost. If you have a mbc set at 10psi, the wg might crack open at 8. If you have it set at 20, it will crack at 18. I do agree 99% of it is feel, but the one set at 20 should go from 8-10 faster than the one set at 10.

well put.

Hypothetical situation. You are driving a 16g car. YOu are doing a pull in 3rd gear starting at 2000 rpm.
When you do the pull and are running 10psi, you will start to see boost (1psi) say at 2500rpm, then you reach full spool 10psi at say 3000 rpm. Since the mbc starts to bleed pressure off at 8psi or so it feels slightly slower from 8-10psi.

Then you turn the boost up to 20psi. Start at 2000 rpm agian, and boost starts again at 2500 rpm, but you will probably probably see 10psi at 2800rpm 15psi at 3000 rpm and 20psi at 3200rpm. Since the mbc doesnt bleed off until about 17-18psi you get a faster spool.

Defiant, i dont think anyone was saying that the start of spool would be sooner, its just that the spool doesnt slow down and then stop until a higher psi, so spooling to 10psi will slow down about 2psi before the targeted boost, whereas running 20psi will fly past 10psi and then not start to slow till a stop until around 18psi or so. The 16g in either case will start to spool at the same 2500rpm, but it wont slow until a few psi under the targeted boost pressure.


Hope that isnt confusing, but thats the way i see it. And i do agree that it will "spool faster" with higher boost. (running a bleeder type MBC)

 

[Mr Peepers]

Tuning the LET - Wastegate creep

It doesn't seem like it is going to answer the OP's question, but tangents off and does a pretty good job.

Short answer: It will not affect boost threshold(lowest rpm to build boost often confused as lag) but will affect spool up. I *think* Defiant thought you meant spool up sooner as in a lower boost threshold.

--------

Look at dyno graphs comparing different boost levels on the same chart. The higher boost runs will reach the previous psi quicker after boost sets in(or torque, however you want to look at it)

Example: http://www.slowboyracing.com/downloads/dyno graphs/E16G 15-20-25-30psi.JPG

 

[90laserRSfwd]

to the OP, are you saying your car will make 12 psi sooner (rpm wise) when the boost controler is set for target boost @ 17 psi, then it's set to target boost @ 12 psi?... Example..

You get the full 12 psi @ 3100 rpm with the boost controler target set to 12 psi. When you set the boost controler to 17 psi (target) it makes 17 psi by 3100 rpm's, or when it's set to 17 psi you see 12 psi before 3100 rpms? That sounds kind of confusing just read it slow and let it sink in for a second. Or rephrased, when the boost controler is set @ 12 you see 12 by 3100, when it's set for 17 you see 12 @ less then 3100?

 

[xveganxcowboyx]

I'm going to try and reiterate what several others have said in a simple way.

There is no difference in time or RPM to achieving some boost. IE, you will always see 1+ psi at the same rpm. The bleed effects may (and this is where speculation happens) cause your 12 psi to come a tiny bit later when set to twelve than when set to 17, because the last few psi will not climb so quickly with the lower boost setting. It would of course slow down for the last few psi when set to 17 as well. If there is a difference it is probably tiny.

The "feeling it" effect is much more significant. Since boost does rise exponentially the time it takes to go from 1 to 12 and from 0 to 17 is similar, only taking a tiny bit longer to reach 17. The power difference between 12 and seventeen is large. That much power coming on so suddenly makes the revs climb much faster, which not only "feels" different, but gives the appearance of early spool.

 

[Spln_Hrd]

After I hit 8 psi on my gt35r it just pegs what its set at real hard like, I guess I can't tell. But I can't go any lower than 15 psi.

 

[90laserRSfwd]

xveganxcowboyx said what I was trying to say!