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209 | What Is Compressor Surge?

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Hi there,

I'm following HP Academy for couple years now. It really helps me with my own build, which I'm grateful for! Recently I've finished assemblying everything and started to tune the engine. It is Abarth's 1.4 litre T-jet engine we're talking about with GT2871 turbo fitted. The car is built for quarter mile races mostly.

I've mananged to get it running nicely up to 20psi of positive boost, but if I raise the boost more I start to hear compressor surge. I would like to do something about it as I'm aiming 30psi as a target. I've listened the webinar about the surge. It looks like the best solution would be change to GT2867 or even GT2860 however I leave it as a last option.

But, what about ported compressor housings? I was surpriced nobody actually mentioned them in a webinar as a solution. Is that because they are not so effective? Does it have any disadvantages? I tried to read as much I could find about those ported shrouds, however there's one thing I don't actually get. The compressor housing is ported so the excessive air which engine is not able to swallow have a way to escape. But....does it mean that the air is escaping through these holes also when the engine is NOT surging, just operating in a normal conditions under boost? If so, how much turbocharger efficienty is being "taken" by this?

Another idea that came to my mind and also hasn't been mentioned in a webinar. If the engine is surging because it can't swallow all the air turbocharger is pumping, should I try to raise the ability to swallow more? Would a head porting actually raise the flow enough to escape from the surge?

I would be very thankful for any advises. I'm a self learner and would love to get any tips on my problem from more experieced colegues.

Kind regards,


Good questions

im going to start at the bottom

yes porting and camshaft changes can dramatically improve compressor surge

a ported housing does not mean there is extra holes it just means it is more efficient

at what rpm are you getting compressor surge ?

I was taking about ported compressor housings which actually have extra holes.

It is surging somewhere around peak torque 5300-5500rpm

Seems to be a minor confusion between "ported" meaning the overall shape is improved for better airflow, and "ports" meaning drillings/passages/openings, which are used to bleed off the air to control surge?

I can back up what Ross said, 100% reduce the choke point post compressor, port the head, bigger valves, higher lift cams - more overlap/duration isn’t the most efficient as it throws boost out of the exhaust

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