Well, you said the HTA71 wouldn't be as responsive. That pretty much leaves.. .stock. I'm just trying to clarify your words, be it regarding threshold or response.

 

Fair, I'm inferring that the response for the 550 should leave nothing to be desired compared to stock - if it's as good as the marketing suggests it should be.

 

I hear ya. I wish there were data, because I'm still really interested in the 550 and maybe the 660. I love how my stock turbo acts and to make more power would be the best of both worlds.

 

You'll notice that they've released part numbers for T4 divided IWG housings. Most excited for the results from these. It may be nice to run a reverse rotation bottom mount, as the exhaust runners can be kept shorter and straighter.

https://www.turbobygarrett.com/turbo...series-g25-550

 

Since I'm locked into T4 IWG, I'm now curious is this is worth ditching the EFR 7670 for.

 

Well...... I think both the G25-660 and EFR7670 are 550whp turbos (along with Gen1 GTX3076R, Gen2 GTX3071R). I back of the envelope calculated the G25-660 has the same ballpark rotational inertia as the EFR7163. So I expect the G25-660 is have better transient response than the EFR7670. And the MarM turbine wheel of the G25 will let you get aggressive with EGTs. It looks like you can get the G25 in reverse rotation with the divided T4 IWG housing, so being reverse rotation will allow you to have a better flowing exhaust manifold on the 4G63.

 

I'm most interested to see what sized turbine they come up with next . If I had to guess I'd say something in the 57-58mm area and in a similar trim .
Teamed up with the existing 67mm compressor its in the EFR 6758 size range whilst still being fairly compact .
Garrett would have something to crow about if such a turbo could pump out 700+ Hp reliably and without the bulk of a GT3582R .

 

Yep, I'd bet something around 60mm. The 3582 is basically obsolete since the introduction of the 3584rs.

 

Finally the turbo is in. I can share the first impression prior to final map and dyno.

The kis is based on

-g25-660 AR .92
-Tial MV-R
-Custom manifold 42.7 mm
-Custom downpipe and elbow 76mm

This kit is designed for high rpm, 600+ Hp (at crankshaft), and high response. Particular attection has been taken for the elbow section removing the AC and mounting the turbo slightly tilted in oder to obtain an elbow straight as possible using every inch.

Full boost starting at about 4000 rpm which is not so bad considering that the saturation of exhaust flowing is equal to a gtx3076 AR 1.01. Transition from spool to full boost is quite fast but not so brutal as precion turbo. On the other side turbo lag is very small during the gear shifting make it very responsive in the 4000+ rpm range. A comparison between this little guys and similar (in therm of wheel) turbos as Arms, gt2 etc is not so easy, since that my kit is not designed for low rpm but i think that the AR .72 canbe competitive in the 3500-4000 range. Clearly the maximum compressor flowing of 60lib/min make the g25-660 in advantage in term of maximum power availble.
Finally, the tial MV-R is maybe to big for the 0.92 housing, the MV-S shound be more than enought.

I will share some real data/video as soon as possible.

 

I imagine the 0.72 would shift your boost curve 500rpm sooner. But like you said, your were targeting top-end power.

 

Without knowing what "full boost" is for you, I'm interested in when it teaches 20psi.

 

For me full boost is 1.9 bar (27.5 psi) but I test also with 1.35 bar (19.6 psi). In the case of 1.35bar, in IV gear, the full boost is reached before 4000 rpm. In any case I will post a video of the speedometer.

 

Yes, I think that the 0.72 can drastically improve the spool. The new exhaust housing and exhaust blade design allows to obtain an incredible exhaust flowing for the size. Here a comparison with the gtx3076.

G25-660:



GTX3076 gen 2:




Basically no one use the 1.01 AR in the gtx3076 because is not responsive, but on the g25-660, the 0.92 AR, which have a similar maximum exhaust flowing works great in the daily driving. For the same reason I can imagine that the G25-660 with 0.72 AR, which is comparable with the gtx3076 0.61/0.63 AR, would be ultra responsive on low rpm.

 

20psi before 4k is good news. I'd like to see 3400-3600. That would have me very interested, with the smaller AR.

 

Where X amount of boost comes in doesn't matter. It matters where it makes 200wtq, then 300wtq, etc. A turbo kit at 20psi makes more power/torque than a 71hta at 20psi.