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Divided turbine houses only work with specially designed exhaust manifolds. Here's a quote from the book "Turbochargers" By Hugh MacInnes:

"Gary went on to experiment with axially divided turbine housings, an option from most turbo manufacturers. He found that if the exhaust pipes were connected to the seperate sides of the divided housing so the exhaust pulses entering each side were evently spaced, throttle response improved even more. Though this arrangement didn't add power, 'turbo lag' was all but gone."

In order to get the pulses equal length you would need either:

a) Equal length tubular headers (out of Inconel or 321 stainless to stand the stress) such that, since the firing order on a Saab is 1,3,4,2 cyllinders 1 and 4 shared one port, and 2 and 3 shared the other port. This would ensure even pulsing and reduces the time for possible exhaust reversion around the turbine, thus decresing lag.

B) Tune a header or manifold to do the same thing, but not be equal length. This is only possible with many complex formulas, and it only works at one specific RPM band. You simply tune them to do the same thing, but at the RPM region where spoolup is an issue. I don't know of any manifolds like this in existance on a production car. The factory Saab one is shaped the way it is for clearance issues.

Higher flow intercoolers can also drastically decrease lag. Between the two, lag can be reduced to nearly zero ... at which point you now must go one size up on turbine housing to keep from getting "compressor surge" at low RPM. Though doing so does allow for extra top end.

Hope this is helpful.

Dubbya~
 

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My first post

Originally posted by Mark in Ireland:
[qb]Would this piece of kit fit onto my T25??

 http://cgi.ebay.com/ebaymotors/ws/eBayIS...TRK%3AMEWA%3AIT  [/qb][/b]
Hi Mark, that's the same kit I bought when I was building my turbo - AFAIK it won't fit a T25 as the cores are different...You can pick up second hand Saab trim 40's or 45's (same turbine/core) very cheaply though - which you could then rebuild....

The other turbo's core (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2480306274) looks only oil cooled...Also the turbine might be a bit radical...With my .48 A/R turbine (and the exact same compressor/housing detailed there) lag is 'acceptable' (full boost by 3000ish) I wouldn't want it any worse...

With my t3/t4 I've found that torque is produced much more progressively due to the slower spool-up, so a bit of that Saab 'WACK' of torque is gone But you do eventually end up going much faster


T3/T4 is an easy, cheap solution - even with the balancing/core rebuild by Turbotechnics, mine totalled at under £250

P.S sorry I missed you at Elvington, it's always nice to put faces to names I was a bit caught up in the
 

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P.S sorry I missed you at Elvington, it's always nice to put faces to names      I was a bit caught up in the  :fawlty:      [/b]
Too busy tearing the tyres off my T16 more like
 
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