As in the boost threshold is horrendously high

Im not sure

 

WOW I see everybody knows

Well lets make it simpler, DOES boost threshhold mean the RPM where the boost is? (or begins in any real sence)
And horrendously high boost threshold means the RPM where the boost is, well, horrendously high?

 

Boost threshold is what you would call lag. Bascially, it is the point that the turbo starts spooling, so if it is horrendously high, it is VERY high up the rev range before the turbo starts making boost (i.e. very laggy).

 

I wouldnt call that lag, thats what people who dont know what lag is would call it, id call it boost threshold

I just wanted to be sure as i was having a brain lapse

But i was thinking right, cheers mike

 

well i didnt know what it was even if steve likes to pretend he did!

cheers mike

 

Hmm..
Boost threshold is an ecu setting where we allow a certain drift of boost pressure before we try to automate its repair.

IE:
Std Esc Cos has an overboost allowance target of 14psi between 3000 and 4300rpm.. anywhere between those speeds and teh ecu will allow an over boost of 6 psi to make 14psi as std. The threshold there is around 2 psi so if it hit 16 the active maps would drop boost valve duty cycle to get the boost back within its target pressure.

That help?

 

that seem to make more sense, threshold means limit

 

Actually threshold means "the level or point at which you start to experience something, or at which something starts to happen" .

 

from the dictionary yeah??

 

Yep, just to make a point .

 

What mike said in the first place is correct with regard to common car terms

 

not being too technical myself, i'd of thought that the point where the turbo started to boost would be more a term like boost response ..?

 

Boost responce is Lag which is different again (tho most people think boost threshold is lag).

As an example, most people say T4s are laggy on a cossie as they dont give you any power till 4500 on most engines, but in fact that just mean they got a high boost threshold.

T4s ARE laggy to some extent tho, as in even when you ARE well within the above explained boost threshold, you still got a small waiting time between when you boot it (WOT), and when the power comes. THATS Lag

Im lame at explaining stuff, but i think that makes sence

 

steve, i'd just call that spool up time

spose theres no really 100% techy answer is there as we all just use made-up words to describe things... lol

chatter anybody?

 

so you mean, say you were at 5K and changed gear keeping above the 4.5K (threshhold) it still takes a moment to come back to full boost .

wunder why, if its to do with the inertia of the compressor wheel etc, it doesnt like to contine spinning (flywheel effect) or is it due to the interumpted air flow causing turbulence inside?

 

comes from your wastegate dont it jim?

 

i agree - you are crap at explaining things!!

 

Matt- And your a nobodys perfect

Dave- Yes thats it.
Reason? Inertia will be a bit off it (hence rollerbearing turbos), as will airflow causing it to stall (hence in "theory" part the reason for DVs, to stop the air coming back out the turbo when the throttle closed which could slow or stoip the turbo, in "theory"...), but i dont think thats all or even the main bit, its mainly to do with a more modern design, but fuck knows what that is exactly...

 

i thought i understood after stu explained it. now im lost again! will read it again when properly awake!

 

What Stu says is not what we on about tho! We on about what most people call a boost threshold you fool Stu is on about somthing to do with the ECU

No wonder your confused

sexually

 

now thats one thing i'm 100% sure of!!

 

Time to PM Graceland to ask if you can expererment i think mate

 

i heard that roller bearing turbos were not necesserily any faster on spool up , as there is actually more friction with the rollers than the shaft floating in oil, they just last longer and are less prone to excessive heat burning the oil around the shaft ??? dunnno?

 

Im on about the question you asked

A Threshold is a perimiter IMO, something to be achieved but not exceeded... so there

 

Dave- No idea, if they are more or less friction, but either way, the difference in spool up isnt noticable.

Stu-