[matty088]

Why does boost build so slow on these cars? It seems like boost steadily increases as Rpms rise and as you go thru the gears. It seems like we don't see "full" boost until 5th gear. Why just have full boost the entire time. I could see limiting first gear for traction purposes. But after that what's the arguement to limit boost?

[Aatish]

Originally Posted by matty088

Why does boost build so slow on these cars? It seems like boost steadily increases as Rpms rise and as you go thru the gears. It seems like we don't see "full" boost until 5th gear. Why just have full boost the entire time. I could see limiting first gear for traction purposes. But after that what's the arguement to limit boost?

Cars tuned for economy and performance balance, so boost by gear is used to optimize this. You can get a tune to have a higher target, and performance, but you'll sacrifice economy.

[Mike@N54Tuning.com]

With the JB4 you can get peak TQ pretty quick.. It does take some RPM to spool the turbo so a turbo car will always need some RPM to get going..

[matty088]

Originally Posted by Mike@N54Tuning.com

With the JB4 you can get peak TQ pretty quick.. It does take some RPM to spool the turbo so a turbo car will always need some RPM to get going..

Yea in my experience if you run say 15 psi. U may get there in 1500 Rpms but once there u are there. I don't know the boosts behavior in the n55 seems odd to me. Takes forever to get 15psi. Why not have it in second gear. Why do u needto wait to 5th. What's the arguement there?

[Mike@N54Tuning.com]

Boost isn't really gear dependant.. Once you are in around 2/2500 RPM you should pretty much have full boost..

Mike

[BMWILUVU]

"full boost" may be limited by gear and so gear-dependent. Mostly for smoothness of delivery

[XutvJet]

1) Turbos require load and in the lower gears, there isn't enough load in order to generate full boost. Most turbos will not see full boost in 1st or 2nd gear. It's just not possible.

2) BMW tunes there turbos to deliver a more naturally aspirated type power delivery. They intentionally make it so that boost increases as the rpms increase (to a point). They're basically trying to make the I6 turbos behave like a small displacement, decent revving V8 where power is progressive and linear and torque is flat.

When you add most any tune or piggyback, the device alters this linear power delivery and adds a substantial amount of power below 6000rpms, often times making that peak power is realized in the lower 5,000 rpms range vs the lower 6,000rpms for stock.

[matty088]

Originally Posted by XutvJet

1) Turbos require load and in the lower gears, there isn't enough load in order to generate full boost. Most turbos will not see full boost in 1st or 2nd gear. It's just not possible.

2) BMW tunes there turbos to deliver a more naturally aspirated type power delivery. They intentionally make it so that boost increases as the rpms increase (to a point). They're basically trying to make the I6 turbos behave like a small displacement, decent revving V8 where power is progressive and linear and torque is flat.

When you add most any tune or piggyback, the device alters this linear power delivery and adds a substantial amount of power below 6000rpms, often times making that peak power is realized in the lower 5,000 rpms range vs the lower 6,000rpms for stock.

Yea well they did a great job if the goal is to make a turbo car feel na.