View Single Post
TurboKraft TurboKraft is offline
Registered User
TurboKraft's Avatar
Join Date: Mar 2005
Location: Phoenix, AZ
Posts: 2,655
Originally Posted by MikeD94 View Post
I'm not an expert in turbo graphs but as you can see the graph on the left has more effeciency range (i.e. fatter area within the curves). Also, surge happens when the turbo operates to the left of the most left curve. So, the surge is less likely to happen on the left graph at the same air flow for a given pressure ratio. This can happen when the turbo is too large for a given engine dispacement under certain condition such as when the turbo starts to build boost at low engine rpm creating a phenomena where more boost builds than the engine can ingest. I'm sure this happens rarely on our 930 since our engine is relatively large for typical turbos used on these cars. I hope my lame explanation helps.
A spot-on explanation.
The more developed a 930 engine, the less necessary the ported shroud is because the engine is more efficient at lower revs and can consume all the airflow generated by the turbocharger.
On a more stock engine -- 7:1 pistons, stock ports, stock cams -- we have had surge on the dyno and on the road. The turbos boost up quickly and produce more airflow than the engine can use, thus the surge. It makes a real distinct shhh-shhh-shhh sound, and a honking or chirping sound in really bad instances. It's really hard on the turbocharger.

Later spool up? We haven't seen it on these engines.
Chris Carroll
TurboKraft, Inc.
Tel. 480.969.0911
email: -
Old 06-22-2011, 08:42 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)