surge what causes it

[Cossie col]

was runing 30 psi on t38 with no probs but have now got roller t4 and boost gauge is all over the place and you can also hear it as it's not a constant smooth delivery. If i disconnect autronic boost controller and go down road it's fine so whats going on

[mark shead]

was runing 30 psi on t38 with no probs but have now got roller t4 and boost gauge is all over the place and you can also hear it as it's not a constant smooth delivery. If i disconnect autronic boost controller and go down road it's fine so whats going on

If it hasnt been mapped for the T4 you should not be trying the boost as the T4 can supply so much more air,
It also may not be surge if the boost hasnt been mapped with the new turbo as it may be over boosting and pulling boost down and trying to then achive the correct boost,
Also as the T4 supplys more air than the T38 it could be surge so I recomend getting the map checked asap.

Mark

[Mike Rainbird]

Basically surge is when the turbo is giving the engine more air flow than it can use at that particular rpm point, so the excess rebounds back from the engine into the turbo compressor causing it to try and stall. Obviously it is then fighting against itself and makes that horrible fluttering noise. This can end up completely destroying the turbo if you are not careful (snapping the shaft as it tries to rotate from the exhaust gases, whilst the back-flow is trying to stop it).

As Mark has said, the surge can be eliminated by re-mapping, by limiting the boost at that rpm point, or the engine can be re-engineered by using different cams / cam timing and gas flowing so that it can consume the airflow at that point.

[Cossie col]

cool, going to take head off as gasket is on its way out, check port size and maybe a little more if needed then down to Marks for remap