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PostPosted: Thu Dec 11, 2014 3:57 pm 
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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.

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PostPosted: Thu Dec 11, 2014 7:43 pm 
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JP, there's a lot of background to this so happy to compare notes over a beer at the next curry meet ;-)

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PostPosted: Fri Dec 12, 2014 10:37 am 
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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.


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PostPosted: Fri Dec 12, 2014 12:55 pm 
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I don't disagree with that although I still think the problem is primarily due to a badly matched compressor housing and wheel. As others have pointed out on the OC and Celica Club threads discussing this issue you can run a Garrett GTX30, 35, Borg-Warner and other larger turbos on the stock ST205 plenum, head and extractors without experiencing any on-throttle surge such as you got on the S148-3. Whilst modding the head may help with the flow downstream I'm not convinced it would make enough of a difference to eliminate the problem completely. To me the fact that TT have withdrawn it from sale is almost a tacit admission that they didn't match the housing and wheel on this latest version of the S148. The fact that they have offered you a rebuilt S148 with a 66mm wheel underscores this. Hope you get sorted soon and can enjoy the car :)

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1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp


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PostPosted: Sun Apr 14, 2019 7:23 pm 
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To avoid making any new thread, where has everyone tapped for installing water injection on a non-wrc while keeping the WTA IC. Whenever I search for it, my results tend to just be about the wrc having water injection.
I was thinking about tapping the same place in the manifold, but I am open to other options.

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