I understand how the A/R is calculated. That the A/R represents the rate at which exhaust is forced into the the turbine, the smaller the area to radius ratio is the higher the exhaust velocity and the higher the back pressure before the turbine. That a specific turbine A/R will only be available for a certain series (size) of turbo's...

What I haven't been able to figure out, does A/R represent the volume of the turbine housing as well as the ratio?
Does a T3 stage 1 turbine (58.9026mm/2.319" inducer) .48A/R turbine housing flow the same volume as a T3 stage 5 turbine (72mm/2.834" inducer) .48A/R turbine housing?
Or would the stage 5 .48A/R turbine housing have a larger inlet/snail housing to flow more volume and just the same reduction ratio as the stage 1 housing?

My reason for asking is because I am contemplating running a larger turbo on my build, currently it's running a T3 stage1 60 trim mustang turbo at 30psi, I figure running a larger turbo that makes the same power on less boost and operates within it's efficiency range wouldn't be a bad idea.

I have a T3/T4 hybrid, garrett T3 stage 3 (t31) turbine and turbonetics super H T04B 76.2mm compressor side. The turbo came with a .63 A/R 4 bolt turbine housing, for my build I require a 5bolt turbine housing with internal wastegate hole (If the internal wastegate actuator won't fit between the comp housing and block I have a 5bolt flange O2 housing/down pipe with external Tial wastegate running off the internal wastegate hole). So I have to replace the turbine housing. I know the larger turbine wheel and rotating mass of the this turbo will generate more boost lag than the stage 1 60trim.

The motor is a 2.2L inline four cylinder.
12Valve single over head factory cam.
86mm bore, 94mm stroke.
7.5:1 compression ratio (down from the factory 7.8:1 by porting the combustion chambers).
The head, intake manifold and exhaust manifold are heavily ported, the throttle body is larger.
RPM cut is 6250 rpm.
These motors generate peak torque in the low 3000rpm.

The car is a Front Wheel Drive street car, it occasionally sees the drag track on cruise night or a race track course but is just built to drive on the roads, accelerate quickly, handle well, survive potholes, speed bumps, dirt roads and drive in winter storms. It is a sleeper that surprises everyone.
I am not looking to make the highest peak horsepower number possible near peak rpm on paper, I want to make as much torque as possible as soon as possible and carry it as far in the power band as possible. The way I see it, torque is torque despite rpm and that is what accelerates a car and that's what can be physically measured, horsepower is a mathematical equation based on torque and rpm representing the work done at that rpm over a certain amount of time and represents momentum (the faster something is rotating the less torque is required to accelerate it more) . What really maters is how fast the rpm's climb or if two cars race for 3 seconds the car whose wheels revolve the most times (provided the circumference x rotation = a longer distance) in 3 seconds wins, regardless of bench and chassis dynamometer numbers.

I can't find turbine maps for the T3 turbine wheels or turbine A/R flow rates.
I would like to run a .48A/R turbine housing and have the turbos characteristics stay the same as they are with the inevitable added lag of the lager turbo rotating mass and blade size and make more torque and power than the mustang turbo. But before spending more on a turbine housing than I paid for the turbo I want to make sure this will all work together.

 

I'm not super familiar with T3's, but you are correct, a/r is the area of the nozzle divided by the radius of the nozzles center to the center of the turbine hole.

So, if the stage 5 uses the same housing as the stage 1, but has the turbine hole bored out, then it will flow the same, because what defines a/r was never changed.
If the stage 5 uses a bigger housing but is also a .48a/r, then it will flow more than the stage 1.

Also, if it takes 30psi to make whatever hp you are at, then you will always need to make 30psi to make that same power. UNLESS the turbo you are currently using is so small that it's causing a major restriction to flow in the upper end, in which case bolting in a turbo with a bigger turbine section will free up flow, and will therefore bring down the amount of boost you'll need.

I ran some vague numbers just to see where your at. At 6200rpms, 2.2L at 100% ve with 30psi puts you at 48lbs/min of air, enough for ~480hp. So the compressor map needs to support 48lbs/min @ 3.0pr. To hit 30psi at 3000rpms your map needs to also support ~24lbs/min of air.

Turbine side puts you at 15lb/min exhaust flow at 2.7pr on the turbine map at 3000rpms. But when I go to 6200rpms, exhaust flow shoots up over double to 34lbs/min, which will require alot of wastegating on the top end. Gtx2867 with .57a/r will do what you want at 3,000rpms, but will definitely be in housing choke at the top end.

G25-660 .49a/r fills in almost perfect, same scenario as the 2867, but better. Using the sizes of these 2 turbos should help you decide what route you should go. Going larger a/r will help on the top end but you won't hit your 3000rpm goal.

 

Thanks for the post and info.
Still haven't found found an answer on A/R but your post leads me to question whether the large turbo will yield any gains.

I figured I am so far out of the T3 60trim efficiency range there must be room for improvement, but I have also always said as long as the turbine shaft doesn't snap and you control intake temps more intake manifold PSI = more power even if it's beyond the turbo's efficiency range.

Here is the flow map for the T3 45trim compressor I put on the car at the beginning.:
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It ran up to 21psi boost.

Here is the T3 60trim compressor map for the turbo the car currently has installed:
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Can't see this turbo flowing 48lbs/min at 3bar.

The engineered scientific way the set-up ended up running 30psi boost manifold pressure is:

-The car runs factory injectors and ecu, they are 33.333lb (350cc) each and batch fired 2X2.
-The car runs a Simple Digital System extra injector controller and two batch fired 61.9lb (650cc) injectors with a 2.5bar map sensor.
-The water meth system runs 6 variable pressure misting nozzles, they are rated to flow 66cc (6.3lb) each at 66psi, or a total of 37.7 lb (396cc) in an atmospheric environment. Because of the shape, size and position of the misting nozzles I am not sure if the passing compressed air inside the charge pipe has a venturi effect on the mist nozzles or they just flow in a pressurized environment.
-The car originally ran an autometer 20psi boost gauge.

So when I raised the boost above 21 psi after adding water/meth injection the Extra injector controller flowed the injectors at 100% duty cycle (progressively based on rpm but it was in the 8 A/F under boost). I could have swapped a set of 450cc injectors I have but instead I kept turning up the boost until the air fuel ratio reached about 10.8:1 . Eventually I got curious and connected a pressure gauge that went higher than 20 psi and found out I was at 30psi manifold pressure. So I installed a boost gauge that went above 30psi with overboost warning.

Bassackward tuning. Timing is set by the factory ECU and it has no idea what boost pressure the engine is running and stays the same above 15psi. Fuel was fixed based on exceeding the controllers Map sensors range. Air was variable so I adjusted it to match the fuel and timing.

On the new build of the car I swapped the injector controller 2.5bar map sensor for a 2.5bar gauge pressure sensor, 0-36 psi above atmosphere.
Purchased a MSD Boost timing master controller and swapped the 2bar map senor (0-15 psi control 0-5psi start point control) to a 2bar gauge pressure sensor (15-30psi control 15-20psi start point).

Here is the garrett T04B 60-1 compressor map (same size compressor wheel the turbonetics has:
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Here is the turbonetics map for the 60-1 (can't find the measurements for this wheel):
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A/r only represents the area of the housings nozzle, not the total volume of the turbine housing.

I wouldn't use any of those turbos, they were never designed for the higher boost you are running. Obviously they will do it, but are really inefficient.

I can get you a quality knockoff G25-660 for only $900. Sure it's not the $150 ebay special, but its much more capable of running where you need it to and will make the power much more efficiently.

 

I know A/R is not meant to represent the volume of the turbine housing but if all .63 A/R or X A/R turbine housings have the same volume (physical dimensions) regardless of turbine wheel size then turbine housing volume is fixed to the A/R number. And all X A/R would have the same volume.

I am surprised by how tough these junk yard Garrett T3's are, I have destroyed lots of IHI and Mitsu turbo's running far less boost, don't know how well the Turbonetics turbo would hold up, it's an older model and Turbonetics didn't have the best reliability or durability track record.

Looked up the G25-660 turbo, pretty amazing little turbo's with one of those I could run one of the larger A/R turbine housings. However I would worry about the small compressor housing, perhaps I'm wrong but my experience with these motors running large compressor wheels with small compressor housings is that boost/torque comes on too sudden, the huge torque spike at low RPM is hard on the transmission and axles and sometimes (this is where I could be wrong as to the cause) when flooring the car from a role in 4th gear the turbine is accelerated so fast that the large compressor wheel and small housing build pressure too quickly and before the wastegate can react the boost spike in the compressor housing causes the turbine shaft to snap, or the compressor housing or wheel to explode...

The reason the turbine housing volume interests me so much:

The factory IHI VJ-11 turbo is rated to flow 21lbs/min, the turbine housing is 20R = .78 A/R
The 45trim T3 with .48 A/R turbine housing and .42A/R comp housing is also rated to flow 21lbs/min.
The T3 has a larger turbine wheel and larger compressor wheel. The T3 Turbine housing A/R is smaller or the turbine housing has a higher rate of compression than the IHI housing but it's more than 2.5 times the size, if the .78 A/R IhI snail housing and inlet holds one cup of water the .48A/R housing holds 2.5 cups or more. 2.5 times the exhaust volume before the turbine wheel means exhaust 2.5X the wide open throttle exhaust pulses required to get the turbo spooling, the IHI with .78A/R housing felt like it to one exhaust pulse from one cylinder to start spooling.

The T3 is larger and less efficient than the IHI vj-11 but boost comes on at the same RPM and instantly but the torque curve isn't as sudden. All the port work to the head, intake and exhaust worked against the IHI but with the T3's.
Here is a dyno of a factory stock 2.2GT running the IHI VJ-11 turbo at factory boost, this car was also running the factory boost solenoid it lowers boost bellow 3000rpm and above 4000rpm, once removed torque comes on quicker move 2750rpm line to 2250rpm and doesn't fall on it's face above at 4300 rpm. But it will give an idea of where or how the engine breaths.
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With proper wastegate and boost control the engine holds power to redline cut 6250rpm.
Not a great drag track motor in FWD form (to much torque) but it's great fun on a role and set-up properly it will accelerate from 60mph rolling to 100mph less than 1 second slower than it does under constant acceleration. So I can let the GT500's, Rs4's, AMC 63's, ninja 1200's... have a early run at the car when I see them coming in the other lane (like the ricer drive by is the respectable way to win here in Gatineau Quebec), I cruise along and wait for their front bumper or tire to be at my rear pumper and floor it and before their rear pumper clears my front bumper I have made up the 30-40km/h (18-25mph) speed gain they had and am pulling ahead and keep pulling. I do this as revenge for trying to pull the ricer drive by, about 50% of the people around here do this. One kid who was a friend of a friend and sometimes was around my shop once drove past me in a broken ass cavalier on the highway while I was maintaining a constant speed, he seemed to be as well but the next time he was at the shop he apparently beat me in a race, he claims he saw me driving on the highway a mile ahead and floored it to catch up and drove past me under full acceleration and I ignored him so he won. The Frenchmen eh!

Anyway what I am trying to say is the T3's move the boost slightly down the powerband and the port work moved them back, the less efficient T3's spool as quickly as the VJ-11 and Mitsu Big 16G (36lb/min) but have less instant torque band that doesn't destroy the drivetrain or the turbo.
I guess it's not a question of when boost comes on or how fast it builds it's how steep the torque band is. Any steeper and it takes a tole on parts and gives the car a dangerous (fwd) torque curve that is almost unusable because no mater how much throttle you give it or boost you push trough the torque jump from none to there is instant and not the slightest bit progressive, sucks for breaking traction and cornering.
Slowing the torque curve of the car would take away it's best quality.

From what I looked up on the G25-660 BB turbo with small volume .82A/R turbine housing and supper efficient small sized compressor housing and awesome designed small frame, large flow turbine and compressor wheels, that have the ability with .82 A/R spool as fast as the tiny factory K turbo's on Volkswagen 1.8L motors (that is smaller and more efficient than the VJ-11).
I think it might be too much technology, too efficient for these engines, when I started looking at the G25-660 online I though it's the most awesome turbo in that power range ever built and I should start saving up but in a video review while the guy was commenting on how garrett achieved this in such a small efficient turbo and mention how fast they build boost on even small displacement 4cylinders and why I just pictured the torque band going straight up the chart to a big red X, looking like it wants to bulge back in the rpms and time on it's way there to something breaking.
It is an amazing turbo, it spools like a 20lb/min small A/R turbo but breaths like and flows 66lb/min like a large frame, large A/R turbo. Space turbo---

With a small efficient turbo this motor doesn't need a ball bearing turbo, perhaps on a larger slower spooling less efficient turbo BB could work with these motors, the long intake runners and piston stoke allow these motors to flow a lot more air at low rpm than 2.0L and 2.2L motors with square or shorter stroke that breath better in high rpm and put down higher HP. So it gets the turbo spooling quickly and holds boost to redline or the engine gets the turbo there then the turbo keeps the engine there. While VW fwd turbos are running launch control to build boost at idle next to me at the tree, I don't touch the gas pedal and worry I'm going to build too much instant boost when I touch the pedal and spin the tires.

 

The response of turbo can be adjusted using a stand-alone boost controller in closed loop, or via empirical testing in open loop for specific situations. There is also exhaust gas pressure tuning where a cutout style device can limit exhaust flow thus slowing turbo spool. I would worry less about the turbo spool capability and more about its efficiency and mass, then use control theory to control the rate of boost onset.

 

That is all very true and things I considered when looking at the G25-660 BB turbo.
I have a manual/mechanical boost control set up that works perfectly and cost me nothing. If I could go back in time I would have bought an Innovate Motorsports SCG-1 wideband/boost controller, rpm gain settings can be used as progressive boost control.

This cars build budget is basically 0$.
The good things about these motors is that they breath well at low rpm and can get a turbo spooling faster than most other 4cylinder front wheel drives. The factory pitons and rods can handle 30+ psi, so can the transmission and axles and cooling system. The factory ecu and piggy back fuel control with water meth can manage 30psi boost. All that's required is a low cost upgrade journal bearing turbo, 20$ boost cut chip, larger intercooler/pipes, exhaust and clutch.

Running a "2000$" ball bearing turbo that might spool too suddenly on this motor and then having to run electronic boost control to correct it sounds like money that could be spent elsewhere on this build.

The Turbonectics T3/T4 I was asking A/R questions about is for my higher budget 2door build that is on hold for this one, but I have been considering using it on this build and running a better turbo on the 2door.

And for that I will definitely consider the G25-660.

 

The size of the compressor housing has no affect on spool. Only the turbine housing.

Stop talking about volume of the turbine housing, your talking in circles with it and it means nothing. The only controlling part of the turbine housing is the nozzle, which is what the a/r is telling you, that's it.

Your comparing apples to oranges with different brands of turbos. Ihi's are usually designed for high flow/ low pressure, so a small turbo can flow pretty good. But it's not good at making high boost. A holset for example is the opposite, it's high pressure/ low flow so naturally the wheels have to be bigger in order to create the tip speed necessary to make high pressure. With bigger wheels comes bigger housings.

I would seriously go with the g25 and a large turbine housing. The spool will be linear and power on top will be clean and efficient. This is and will always be better than a large turbine wheel and really tight a/r housing.