Thats funny that you think some shop or distributor can re-engineer a Garrett turbo by drilling "speed holes" in the cover inlet and get the same anti-surge benefits that Garrett does by engineering their slotting technoloy which is cast into the cover rather than an afterthought. I believe HKS is the only company who casts the "speed holes" into the cover.

The speed holes dont hurt top end because their anti-surge benefits are minimal at best. Garretts anti-surge slots do affect compressor effeciency because of the air flow disruption at the inlet. Anti-surge technology not only will extend the surge line further (the left side of a compressor map), it aids in boost transition, part throttle and gear shift boost response.

The big advantage to having the anti-surge slots by Garrett over the drilled holes is, the bigger inlet diamater associated with Garretts anti-surge. There is always going to be a disruption of air flow around the inlet due to the recirculation of the antisurge technology. Garrett opens up the inlet diameter to compensate for this.

 

muckman, nice write up. i thought the same thing just not so in depth. i was told the drilled holes dont do nothing by some, but even precision tried to convince me that the drilled holes did the same function as the slotted. btw, ams came through and got me a brand new slotted anit surge cover. only shop that could get me one and i tried lots of shops over 20, big thumbs up to ams

 

What was the cost of the garrett cover?