View unanswered posts | View active topics It is currently Wed Jun 19, 2019 9:48 pm

Reply to topic  [ 2 posts ] 
Turbo Lag? 
Author Message
LQFP144 - On Top Of The Game
User avatar

Joined: Sun Jul 18, 2010 2:35 pm
Posts: 302
What is turbo lag or what do you consider turbo lag. I would think its the time it takes to make the turbo output the most possible at the set boost.
Any thoughts on this. I also believe turbo lag is more of a problem in lower gears, esp cars gear short from the factory that didn't come with a turbo.

Thu Aug 08, 2013 2:40 am
User avatar

Joined: Tue Jan 15, 2008 2:31 pm
Posts: 15271
Location: Home sweet home!
At a fixed RPM lag is the time between a change in throttle and the steady state boost matching that throttle arriving. It's the time it takes the turbo to go from a lower speed to a higher speed in order to build pressure in the intake manifold, at a fixed RPM, with a change in load/required output.

Not to be confused with boost response curve AKA boost threshold which is the fact that you get 1psi at 3k, 3psi at 3500, 10psi at 4k, 18psi at 5k+. This is what idiots refer to as lag. This is not lag.

In my truck, at 5k, trailing throttle, NO boost, big turbo barely spinning, I stand on it, the lag is very short indeed. On the other hand, if you stand on it at 1500 RPM you can listen to the turbo wind its way up to the 1kPa you might make (if you're lucky), and it takes some seconds to do this (if held at 1500). On anything OEM the lag is almost imperceptibly short.

On the other hand, the figures I quoted above, which are from my truck, mean that if you are accelerating through a gear, and you start at 3k, you feel like the engine's power "lags" your command, because it takes N seconds to get to 5k where full torque is available.

Like your comments on AFR and gears, gears have nothing to do with it, just ramp rate of RPM. It is due to actual lag that the boost response curve varies with RPM ramp rate.

I bet someone in particular jumps in here to argue about this anyway, though.

Why such an elementary question?


_________________ - where Open Source means Open Source, and Free means Freedom - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!

Thu Aug 08, 2013 11:33 am
Profile WWW
Display posts from previous:  Sort by  
Reply to topic   [ 2 posts ] 

Who is online

Users browsing this forum: No registered users and 2 guests

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software for PTF. ColorizeIt.