Comparing two Turbo's

Hey guys, just wondering what I can expect for 2 different turbos for a RB25DET.

I have access to another turbo (no name brand) Id like to try which has the following specs compared to the Garret GTX30/76

Compressor: GTX30/76 No Name

Inducer Diameter 58mm 52.7mm

Exducer Diameter 76.6 76.2mm

A/R 0.6 0.5

Turbine

Inducer Diameter 60mm 65.2mm

Exducer Diameter 48.2mm

A/R 0.63 0.63

Garret only list a Turbine size (60mm) so not sure if they are talking about inducer or exducer?

The measurement specs show them as fairly similar but the Turbine and Compressor housings are noticably smaller on the no name turbo compared to the garret when viewed side by side?

Garrett list their turbine wheels by inducer diameter. They also usually list a 'trim' though which defines the relationship between inducer to exducer, so if you know the inducer diameter and trim, you can calculate the exducer. Check this link - http://www.turbobygarrett.com/turbobygarrett/wheel_trim

Answering your question accurately is a little hard but I can take an educated guess - While the compressor wheel size will go a long way to defining the airflow capability of a turbo, there's a little more to it. Based on the the wheel diameters would be a pretty safe bet that the no name turbo will offer less airflow potential than the Garrett given the 5 mm smaller inducer and correspondingly smaller trim. This would ultimately mean less power potential.

The no name turbo has a much smaller trim turbine wheel than the Garrett and in general as the trim increases, so does the airflow potential of the wheel. Particularly with such a small exducer on the no name, I'd suggest this would be quite restrictive on a 2.5 litre engine. You would likely end up with a turbo that would spool reasonably early and then fall over in the top end when compared back to back with the 3076 is my guess. .

The 3076 has proven to be a pretty good performer on the RB25. Personally if it was me I would tend towards the 0.82 housing for a 2.5 litre. but then when it comes to turbos I've always been a bit of a 'bigger is better' kind of guy. I guess you can't beat the drag racer out of me :)

I went on my r33 gts-t from a GT 3576r singelscroll to a GTX3071r with ATP trwinscroll A/R 1.06 housing. It's so much better to drive! The gt35 was well to wet the pants of your passenger. :P It had a great sound and kicked in very late and very hard, which spined the tires in the first three gears. But it was that laggy that it wasn't possible to reach full boost in first gear.

The GTX3071r yet makes about the same power (my stock rods limit the power) as the gt3576r setup, but you will see full boost as early as 3600rpm in 5th gear. This setup gives really nice dyno graphs, of course its also great to drive.

To be honest if i have the chooise a second time, i would go with a EFR Turbo. A EFR Turbo with the same size as the gtx3071r will produce about the same graph on the dyno, but the throttle respons are better on EFR Turbos.

Throttle response is the only thing what I'm missing on the GTX 3071r. The A/R 1.06 makes it a bit slugish, the low inertia titan wheels on a EFR Turbo will response better. Means you get earlier boost on lower gears (which isn't ussually seen on a dyno graph.

I Guess I should have also looked for specs on the stock turbo as thats what Im upgrading from on my own car, Its only because I had built another car with a Rb25/GT3076 so had something to compare it with... That setup was abit too laggy for my liking in this application (daily driver) I only want around 350rwhp and down low response is more of a priority.

Unfortunately I cannot seem to find any wheel specs for the Stock Turbo

If you're only aiming for 350 whp then the GT3076 is probably overkill. A smaller turbo would offer better response and a wider powerband while meeting your target.