Hi all — new swede here. I'm looking for dyno results either with the G25 or G30.
I'm currently looking at a Garrett G turbo for my Evo 3. I'm aiming for around 450 WHP, and the car will see mostly road use but also some track driving.
Right now I have an HX35 with a twin-scroll manifold that works quite well, but I'd like something that's a little more responsive and effective.The G25-660/700 looks promising, but I've heard complaints about compressor and exdusor being mismatched and excessive backpressure; some recommend the G30 instead.

Car spec:

• 2.0 6-bolt, CP pistons, Carillo rods
  
• Kelford 272 cams, Supertech double valve springs
  
• E85
  

Anyone running a G25 or G30 — dyno sheets, impressions on spool, midrange, and top-end, or thoughts on matching for my goals would be much appreciated.
Also have anyone tried the new G25-700?

 

Hey, welcome! Sounds like a really solid setup you’ve got there — the 6-bolt with Kelfords and E85 should give you plenty of headroom for either turbo choice.

I’ve seen a few Evo builds running the G25-660 and G25-700. The G25-700 definitely spools faster than the older HX35, but you might find it runs out of efficiency a bit sooner around the 450–470 WHP mark. The G30-660 seems to hit a nice balance — slightly slower spool than the G25, but it keeps pulling harder up top and holds boost longer on track runs.

If your priority is strong midrange and fast transient response for street use, the G25-700 is still a good call. But if you want a bit more breathing room for track sessions without worrying about backpressure, I’d lean toward the G30-660.

Would be great to see what you go with — please share your dyno once it’s done!

 

Thanks, yes, I’ve got the same feeling — especially since I’ve chosen the 272 cams.
It would be really interesting to have some information on how early or late the G25 vs G30 spools, and how their top-end performance compares. I also see a lot of SR20 builds going with the G30 instead of the G25.
What makes me doubt the G30-660 is that a lot of people are going the G25 route — both Adam LZ and Krebsbach Racing (even though he’s running a 2.2 and making good power) are praising that turbo.
So, back to my point — it would be really interesting to see some dyno curves with the G30-660, because I can’t really find a dyno sheet from a 4G63 2.0L setup. I’d like to compare how much better the top-end is and how much worse the spool might be. But as you said, it really depends on how top-end heavy I want the power to be — still, it would be nice to know what I’d be missing on the bottom end.

I’ll definitely share the final dyno sheet once it’s done

 

Here are some results with a g25-660 but on an evo x. This car has a stock bottom end, stock head, stock cams. Just regular bolt ons.

 

A G30-660 in 0.83 A/R will spool as quickly as a G25-660 in 0.92 A/R and free up about 30whp or so. The 660 compressor is a bit too big for the G25 turbine which is why Garrett released the G30-660 a bit later. The new Gen2 G-series is actually a step backwards; the compressors are much too big for the turbines. By too big, they flow too much for a given shaft speed which results in a poor blade speed ratio. That in turn results in poor turbine efficiency = high turbine back pressure. This video shows it perfectly. You can see the G25-700 has much lower shaft speeds than the G25-660 for the same boost which results in higher back pressure, less power, less response. On top of that, the newer compressor wheels have lower peak efficiency than the Gen1 design. As you're going with E85, I'd actually recommend a G25-550 in 0.72 A/R as a super fast spooling and responsive setup that will can hit 450whp on E85. Definitely install the speed sensor kit to make sure you don't overspin the turbo though as 450whp is at the edge of what the G25-550 can do on E85. It will absolutely be the most fun street turbo.

 

An updated video with a lot of data between: G25-660, G25-700, G30-770. I'm glad they also tested the G30-770 which spooled the same as the G25-700 and made more power than the G25-660, of course. What's really important is the comparison of the turbo shaft speeds. The G-series Gen2 compressor wheel flows a lot more mass flow for a given shaft speed compared to the Gen1. So, the Gen2 behaves effectively the same as a larger diameter wheel of the Gen1 design. This is the root of the performance issue of the G-series Gen2, at least in this G25-30 frame sizes. The 'too big' compressor for a given turbine diameter results in a poor blade speed ratio. A bad blade speed ratio results in lower turbine efficiency. The turbo math is simple, for a given compressor power requirement, lower turbine efficiency means you need more turbine pressure ratio assuming the same turbine mass flow. Lower turbine efficiency means a more sluggish turbo and more back pressure.

In the comparison of the G25-660 and G30-770, you can see the compromise in spool-up for power gain in going to the larger G30-770. Where this particular car is operating can't take advantage of the larger compressor wheel. In this case, you can visualize where the G30-660 is the goldilocks combo for this engine where it would spool up similarly to the G25-660 and free up the power to be where the G30-770 is. Or potentially more power than the G30-770 even as that turbo may be a bit out of it's sweet spot being too big.