Okay, so I'm a little confused on the exhaust housing A/R for turbos. If the smaller the number the faster the spool why wouldn't we all start swapping housings? I mean, how about a .60/.42 or something of that sort. We have seen the Holset with the .48 housing reaching full spool at 4K so why would there even be higher A/R?


JP

 

Because once you get the exhaust wheel spinning at full speed, it's kinda hard to get it to go any faster i.e. lost efficiency. Pretty much from everything that i've read it basicly ends up restricting the exhaust after that. Think about the 95+ eclipses with the little t-25's that are maxed out...yeah, they spool up fast...but they really don't produce as much past 5k. Even if you were able to swap a larger compressor wheel and housing, it's only going to make more volume at the same rpm range i would imagine. Isn't that basicly what a t3/t4 combo is anyway? t3 exhaust with t4 compressor...

 

If you have a small wheel on the exhaust side ( small diameter) it has less leverage to spool up a large wheel on the intake. you have to remember that AR just isnt the only dementions going on. you can have a 48 ar 60 trim and you can have a 60 ar 60 trim. the first one has a smaller housing and the second one has a larger housing but about the same size wheel. so be carful hearing that its a 60 trim exhaust. it might flow less than a exhaust with a 60 AR housing with the same size wheel.

 

Also here's a little trick that i did on my 14b that actually helped quite a bit...port out the exhaust housing. It takes a little bit longer to spool up, but it's well worth it at the higher rpm because now it actually produces power still due to increased exhaust flow.

 

Posted in the wrong forum. Sorry, but thanks for moving it. Thanks for the responds too guys. So the trim has to do with the wheel size? So the D-Series Holset isn't making the kind of power it would if it had the orginal hot side rather than the ported .48? Thanks guys, I appericate your time and thought I'm just trying to learn a little more.


JP