overboost??

[blingsta]

Hi guys.. just need a couple questions answered re my set up.. firstly what is overboost and how does the boost cut work?? reason?= put foot down in 3rd gear, boost came in but at about 4.5k rpm the car held back a bit as if the soft cut kicked in?? when tried again a few mins later, it didnt do it? any ideas??

[Turbo-Brown]

Overboost is something that you only get on cars with electronic boost control.

Basically, it lets the boost peak higher than it would normally for a given amount of time, say 10s or something before knocking it back to a lower level.

[blingsta]

ok, thanx turbo-brown, so if i dont have this electronic boost control, does it mean that this little thing it sometimes does would be down to mapping??

[Ant]

boost delevered is dependant on load, load is expressed as rpm/throttle position so you can get more boost at lower rpm with a bigger throttle opening, make some sense ?

so say you're in 3rd @ 2k then floor it, the boost will rise steeply up to the preset on the wastegate , then slowly tail off, on yours the boost limit is set to 7.5 psi, so if the boost exceeds the preset the MS will shut down the fuel delivery to bring the boost back into the limited range.

we've just lifted your rev limit as you're miles have increased, so to some extent you're inot uncharted territory with this setup, thats the main reason the boost cut is there, to protect the engine from any damage due to excessive boost.

If you conect the laptop and get someone to monitor the inj pulsewidth, you can see where the boost cut kills the fuelling, you can also see the intake temps increase a little as boost is applied.

you'll be surprised @ what you can learn from watching the ECU in action, anything that promotes a better understanding is a good thing IMHO.

If you need a sounding board, gimme a call mate

Just moved to new premises ( 900 sq/ft this time) so if I dont pick up, drop me a text and I'll return the call ASAP

Now, back to the whitewashing

[Turbo-Brown]

Hmmmm, shouldn't see the boost tail off to be honest unless the turbo's fairly small.

Wish I could post up the graph of my power run as it's got a boost trace on it too

[blingsta]

Ahh, makes a bit of sense now Ant! , what your saying is that as my boost kicks in so early, as my revs go up, im getting to 7.5psi before my rev limiter soft cut/hard cut kicks in so the boost protector kicks in instead??? is that right, if it is then that makes sense now dude!, cheers.. p.s, mileage is now 900 odd, so very nearly due a small boost increase... ive sent you e-mail that you havent replied to dude!..

[Jon_Bmw]

I have over boost on my audi, its excellent...but short lived. I think it lasts for 15 seconds, gives you about 1.3 bar instead of 0.9. 15 seconds holding your foot flat down, gets you to highly illegal speeds anyway!

Not really very helpful to the question, sorry guys

[Turbo-Brown]

Think it's supposed to be for overtaking or something.

Personally I'd rather have something consistent that I can rely on rather than something that gets you 1/2 way through the manuver and then lowers the power!

[blingsta]

ive still got alot to learn about turbo and ms!!!

[Jon_Bmw]

Completely agree Alex, but 15 seconds is along time, unless you are overtaking 15 cars!

[Turbo-Brown]

You're probably right, but a truck I reckon could take a while!