Question about full boost at partial throttle at lower rpm
 

I recently got an 88 TII (RTEK 1.7, 720 cc secondaries, SAFC II, S5 Turbo, at <10 psi, ported wastegate). The previous owner had the boost set at 12 psi w/stock intercooler (ive read this is bad), so i downtuned it to about 8-10 psi (autometer boost gauge) by adjusting the manual boost valve and was test driving it today.

Im new to turbo's, and I noticed that I can get full boost (~9 psi) when accelerating with partial throttle as low as 3500 rpm. Is this bad for the engine? The ecu isnt in full throttle mode, so is it going to lean out? Or does the ecu use the airflow sensor and automatically compensate?

the pressure sensor and afm take care of it. i was worried about the same thing... till i got a wideband.

No, not necessarily.
This is why you downshift. :)
Welcome to the world of "turbo lag".
Turbo boost is not instantaneous - it needs to "spool" up before it makes max boost.


[QUOTE]The ecu isnt in full throttle mode, so is it going to lean out?[?QUOTE]
No.


The airflow meter is the primary load sensor once the engine goes into + boost.
Yes, the (stock) ECU adds fuel the more the airflow meter opens up.


-Ted

so what is the difference between getting full boost at partial throttle and full throttle after its at full boost? I guess what im asking is, does the boost sensor get its signal before or after the throttle plates?

Boost is picked up after thr TB. Also your feul and timing maps depend on RPM and pressure not Throttle position.

Arent these symptoms actually indicative of surging, not lag?

Ignition timing...
...which is what the boost sensor tells the ECU to do.


-Ted

Surging?
The only surge I am aware of is trying to run too much flow through the turbo at too low a boost pressure?


-Ted

I was under the impression that surging was sort of the opposite... too much pressure for the engine's current flow requirements... this always made sense to me because the "surge limit" is in the upper left portion of compressor maps, where the boost is high and the amount of air is low...