Diceman wrote:
There seems to be some misunderstanding of surge in some of the posts on here.
Surge is caused when the turbo compressor effectively falls off the left hand side of the compressor map, at this point the turbo (air pump) is trying to produce high pressure at low flow. The flow is however being limited by the engine capacity and volumetric efficiency at a particular rpm/pressure point. At this operating point adding cams/big valves free flowing inlet & intercooler will all help to increase the engines ability to consume the air (moving it back into the compressor map) or reducing the total pressure required (again moving it back into the compressor map).
When surge occurs it is basically the compressor stalling then starting to spin again until it falls off the compressor map again (hence the flutter noise as it bounces on/off curve and flow reverses).
Having spoken to TT a few times they did warn me that the options available with bigger compressor wheels to the original s148 (especially the s175) were a bit surgey unless you were running cams and had minimised pumping losses. (One if the guys used to run an mr2 turbo so r&d had been done.
Part if the issue IMHO is people buying hybrid turbos before they really need it/oversized units. It certainly doesn't help if TT didn't publish this.
This is a valid point but when TT advertise it as a bolt on turbo for a stock engine then it becomes an issue. This is where the TTS148 excels because it works with all the factory plumbing. The latest version went against this requiring potential head work to make it compatible rendering the turbo obsolete, for the same amount of cash as modifying the head you can have a much more modern turbo design with all the custom pipe work included for the same price.