What exactly do the turbo A/R numbers mean?

[arveetek]

The Garret turbo I have in my possesion has an exhaust housing A/R of 96, and a compressor housing A/R of 60. What exactly does this mean? What are the Banks and GM turbos rated at?

Casey

[gmctd]

It is Area of the nozzle divided by the Radius from the center of the turbine shaft to the center of the nozzle area.

Larger A/R reduces exhaust velocity and turbine rpm.
Takes more exhaust to make boost, as from larger engine, or higher rpm.

Turbine housings are sized for various displacements\flow rates, but the A/R in each size allows fine-tuning to desired output.

Similar on the compressor end, but relates to rpm, flow rate, and pressure developed by wheel diameter vs housing diameter to center of outlet.

The GM series have been variously described as being T-3 equivalent, which would be for a smaller displacement engine.
This improved driveability from a low rpm engine of larger displacement.
Noone has yet come forward with design-specifics, tho grape has sized them at 60-1, a spec used to describe the same relationships.

[grape]

a 60-1 is just the compressor side of the turbo.....that I'm using. A 60-1 has a 60 mm inducer, 62-1 has a 62 mm inducer and so on. The standard 60-1 wheel is able to be placed in a standard T04B housing with some machine work, and it becomes the 60-1 hifi. All big compressor wheels including the 62-1 all the way to the T-76 require the T04S housing which is very distinctive, 4" inlet and 2.5" outlet, it's huge. I've never measured the gm series stuff on the cold side. The inlet on the gm is T04B based due to the 3" inlet 2" outlet but the exhaust is T3 based, like 99.9% of all internally wastegated exhaust housings. Problem with the T3 is the exducer of the turbine wheel is only 2.75", which is basically the total diameter of the exhaust. So that's where the banks voodoo turbo comes in. It has a P trim T04 based turbine wheel which is more free flowing but at the cost of quick boost. But for some reason banks went to the trouble of having an exhaust housing cast with the standard T3 exhaust inlet bolt pattern, which is dinky and restrictive. Yet they had a huge 1.00 A/R, I guess so we could not blow our own stuff up even if we wanted to. My system is the manifolds off of a later 6.5, but the right side has been cut and a T04 exhaust flange welded to it. I'm gonna use an .81 with a P trim wheel along with the 60-1 inlet. With a 40 mm external wastegate on the crossover. I'm still not sure about the exhaust sizing, it may take a .69 because I want full boost up by 1500 rpm with it just sitting on the gate.

[gmctd]

Good info.

I have actual dimensions from the GM-4 thru -8 compressor and turbine somewhere in my files. I'll post them for ref when I find them.

Yeah, I write this stuff down in case I forget it, then forget where I wrote it down. :rolleyes:

Later -

Compressor wheel is 70mm (2.75") with 55mm (2.03") inducer dia, 0.250 tip height, very high flow profile.
Inlet is 3" into 2.3" (60mm) inducer
2.5" Radius to center of 1.25 x 2" Area for approximate A/R of 1.0. May be less - depends on actual area location and dimensions.
Outlet is 55.5mm (2.187").
Basic housing dia is 6.5".

Turbine housing (snail) exducer dia is 60mm (2.3"), wastegate dia is 35mm (1.3").
Radius approx 2", Area unknown without sectioning snail.
Inlet is 47.5mm (1.875") x 57mm (2.250").
Basic housing dia is 5".

Close approximations good enuf fer gummint work! ;)

Updating for posterity, as I take fresh measurements.

[ 03-16-2004, 03:45 AM: Message edited by: gmctd ]

[arveetek]

Thanks for the info, gentleman, although I'm still not quite sure what it all means.

If the GM 6.5L turbo has a compressor A/R of 1.0, and my Garret turbo has an A/R of 60, what does that tell me?

Caey

[gmctd]

Your turbo is a .60 compressor and .96 turbine A/R.

Should tell you rpm vs flow rate of the compressor and turbine, but you still need to know which size housings and trim you have to use the proper maps.

If it is not marked, you can take measurements for comparison.
Or, you can call Banks, and etc, for more info.
And there's more info in the Turbo Forum.

Measure the o.d. of the inlet, and the inducer i.d., where the blades are.

Measure the id of the outlet, then measure the radius from the center of the shaft to center of the housing, at 90deg to a line parallel to output.

Lay any thing with 90deg corner, vertical edge across the shaft centerline, with the horizontal upper edge parallel to output flow.

Approximate the center of the housing where the 90deg vertical edge crosses it.

Measure from the shaft center to this point, to get the approximate R value.

Multiply this with your .60 to get the approximate A (area). A/R

These figures will give some comparison to the GM compressor.

Same with the turbine dimensions.

Basic compressor housing diameter is 6.5", turbine is 5".