Reply With QuoteThe A/R describes the geometry of the scroll housing. Turbos like the T28 came in a variety of configurations, from ones made to boost to higher pressures and lower flows (those fitted to the twin turbo skylines) to ones made to flow more air at lower boost pressures.Originally Posted by rijidij
The A/R ratios on the compressor cover can be used to identify which one you've got.
But besides that, a given family of turbos (say T25 family) can have an assortment of different sized turbine housings (different A/R ratio) for different applications. Smaller builds boost at lower revs but chokes of a little higher end power. Bigger loses the low end but provides less restriction at the high end for more power.
But you can only use it to compare if you've got exactly the same wheel sizes inside. Otherwise it gets complicated.
There are a whole range of turbos that'll work on the 4BD1's depending on your goals. I'm using a T25 with a turbine A/R of 0.49 which is as small as you can really go.
It builds boost really early, I can have 17psi at 1500rpm.
The biggest I'd want to go is the T28 which Isuzurover has fitted with the 0.86 A/R turbine housing.
In between we have T25's with a 0.64 A/R, T28's with a 0.64 A/R and a lot of other options (T3's, IHI turbos, MHI turbos, Schwitzer etc).
I like the T25/T28 series because they have a high degree of interchange and they are dirt cheap to rebuild. There is also big support for them through the ricer crowd.
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