What A/R housing size for 66mm turbo?

right now I'm running a temporary single turbo setup. Un-tuned low boost.

I'm doing my final upgrades over the next month or so.

In brief mods are/going to be,

SARD 800cc injectors

Walbro 400 pump

3" downpipe, HKS carbon exhaust

ARC 2-row intercooler

tubular manifold and 40mm wastegate

On the fuel I have here, I'm able to run about 1.45-1.5 bar no issues on pump gas.

So I believe I should be able to hit 580-600bhp or so easily on a bit less boost.

I'm running a bullseye 66mm (basically a Borg Warner S366)

It has a T3 .63 housing, hits full boost at 3500rpm.

I bought this turbo used from another guy who ran this on his Supra.

The response and boost Is brutal on the low end but at the top after 5800rpm it really dies off.

I'm changing to a T4 housing now. I am leaning towards 0.68 A/R as that seems like a reasonable size to retain some lower end boost?

I also have the option of a 0.58 A/R , for a A/R size like this I was wondering if it would be too restrictive up top?

I just want the car to pull a pit more up top but still have good low end boost.

I would change to a 60-62mm but I'll keep this turbo for now.

Also I have been considering a log/cast style manifold but then I would need to redue my downpipe and intercooler intake pipe.

Cheers

I tried .68, .81 and .96 on my t67,

.68 had high egt and felt asthmatic, the .96 was a lag monster but cold and meaty but throttle response was poor, .81 was by far the best of both worlds..

I used a cast manifold and that helped a lot on response and spool over the tubular.

`i`m using the t4 s366 batmowheel turbo with 1.00ar and hks tubular mani and tbh lag was an issue until i fitted an auto diff recently, so mike`s spot on with 81 ish a/r.

If you had a divided manifold i would say .84 is perfect

I don't have a divided manifold, just a normal one.

was the .68 really that bad ?

I'm coming from a T3 setup, and love the way it spool on the low end.

I still wanted to keep it spooling well on the low end, the larger AR I go with the more lag and later it will spool?

so I figured .68 will be better over anything larger down low, and will be good 'enough' up top ?

Are you running stock cams, they won`t be doing you any favors after 6k, a set of 264`s will allow more power higher up the rev range but increase lag on spool slighly, its always a tradeoff tbh.

just to jump in here, are we saying .81 ar for hot or cold side ? and if it is a .81 hot side what cold side trim suits for best of both spool time/ power

Are the different housing divided or not?

in my case undevided

My .81 is hot side, and non divided.

yes.64 was a disaster, asthmatic, hot, and spools only marginally quicker, shortly followed by a lack of power and once the revs get really high, it's like a diesel ;-)

My .81 is hot side, and non divided.

yes.64 was a disaster, asthmatic, hot, and spools only marginally quicker, shortly followed by a lack of power and once the revs get really high, it's like a diesel ;-)

my .68 seems just fine , but i am running low boost 1.3bar, i also dont have anything to compair it to so it would seem fine lol