ive been looking on this site and a few others for this information
can somebody please shed some light on what is the ideal compressor a/r for a stock port fd and would a .70 a/r compressor housing be suitable
not looking for massive power as of yet but want an a/r size that could enter into the mid 400bhp+ fly wheel mark
thanks

 

A/R is only a ratio, and depends on the size of the turbo. A T6 1.00 A/R is much larger than a T3 1.00 A/R.

I assume you'll be using a T4 turbo? Is it divided or non? I've had good experience with a 0.84 A/R T4 divided turbo with an o-trim exhaust wheel for response, and not choking the top end. General opinion seems to be not to go much if any smaller than that though on a rotary.

The A/R on the compressor side does not factor much into turbo sizing, it mainly just dictates the size of the outlet on the cold side.

 

it will be a t4 not too sure yet if going to be divided/undivided what are pros and cons?
would a 1.00 be too big or better to stay with .84

 

Divided leads to better spool, possibly even better top end. This all relies on the design of your manifold too though. I would say anywhere between .84 and 1.00 A/R divided would be a good choice for you. With stock ports, the smaller would be better for spool, and I personally don't think it would hurt your top end.

 

thanks for the help ill look at some .84
on a side note i was looking at a list with a lot of turbos and what mods and seen a few with stock ports with 1.06 exhaust that would be too laggy??

 

1.06 A/R turbine housing on a T3 hotside isn't bad for stock ports.

 

i take it there is a big-ish difference between t3 and t4

 

If you run a T4 you will have more options later down the line should you want to upgrade your turbo. A T3 1.06 will work well with the only downside being your kinda stuck with T3 framed turbo's at that point.
A .84 divided T4 will work very well on stock ports even non BB and allow for mid to upper 400whp depending on turbine wheel size and desired boost level. It will also not drop off up top as well as long as it is a P or O-trim as mentioned.

~S~

 

O-trim's aren't that common anymore, I would go with a T4 divided framed, P-trim exhaust wheel around 0.84 A/R. Not sure if you had a specific turbo in mind, but a 60-1 or 35R compressor wheel would be perfect for your goals too. A-Spec has the GT3574 turbo which is just that. Great turbo, especially for the $$$.

 

i have a garrett t04s ball bearing...stock port with a 0.84 divided t4 turbine housing...spools nice and quick very responsive...

 

around about what rpm does it hit peak boost and does it hold to upper rev range?