by Lith » Tue Oct 31, 2006 3:56 pm
The trim is basically a calculated number represents the ratio between the inducer and the exducer of each wheel. I'd assume if you are asking for some detail on turbos you have a basic understanding of what they are?
On the compressor, the inducer is the bit that draws air in from the outside world (and therefore is more or less the biggest defining factor in terms of defining how much air the turbo MIGHT be able to move), the exducer throws the air against the compressor scroll and as a result mainly affects spool and also the amount of boost producing ability (ie, outright pressure ratio) the turbo has. A bigger exducer (compared to inducer) will have a higher pressure ratio efficiency - and in turn often have a "safer" relative surge line. A smaller exducer will be more inclined to surge at higher PR and low air flow levels and probably be a bit laggier, but will also be less restrictive and therefore will be capable of flowing more when it gets up and going.
On the exhaust side, its a similar story except - the inducer is the "big bit" which catches the gas and its guided out the exducer.
Generally speaking, the "bigger" the trim, the more aggressive the wheel is - or should I say, the inducer and exducer sizes are closer together in size. The smaller the motor, the smaller the trim you should probably go for - as you're probably both more likely to need spool over peak air flow, and you're also more likely to be susceptable to surge.
With a T3/T4 on something like a 1.6l, you're probably going to want to run quite a small T3/T4 - ie, .48a/r turbine housing and some sort of <.50trim T04B compressor wheel or something like that.
An all important thing you should decide, or tell us - is what you hope to achieve from it??? A TD05-16G from an EVO will probably flow similar to "small" T3/T4s and be well efficient on a 4AGE, as well as spool at least as well.