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Discussion Starter #1 (Edited)
Hello all. Normally I don't bother with reviews, because I was dealing with established and well reputed businesses or products, so there wasn't much point. I suppose the same can be said of Garrett, they make good stuff, so why the review?

Background on my car, I built it for road racing. Car has a built, dry sumped 1jz, old turbo setup was a Comp CT4-6265 0.70 dbb, on a tubular manifold. It made good power, and had a decent power band, but it was lazy on the street, and when it did hit, you sort of just got used to which direction it was gonna go sideways in, because that is what it would usually do. This was on a car with a great alignment, sorted suspension, and an OS Giken diff. The car was a lot of fun at highway speeds, but down low it was missing the "fun" factor that the stock twins had. In short, the throttle response was pretty awful.

Along the way, I got into autocross. Throttle response is a pretty high priority. I had a friend drive my car once, gave him some tips on how to keep it happy and going forward. He tends to be our fastest driver of the day in a middle ground Mustang, so the guy can wheel. His review of my car was both amused and bewildered, asking me how I manage to drive the thing as fast as I do, as its power is either EVERYTHING or nothing, there wasn't much in-between for him, he called it a "light switch" car. It wasn't until I took the car to a big-track autocross event that I realized I needed that "fun" factor back. In second gear, the car just had a dead spot between about 45 mph and 55mph, somewhere that you spend a lot of time in. There's only so much to be done with driver technique to overcome the deficiencies of a turbo engine... it was slow, no other way to say it.

So, after a lot of homework, comparisons, learning how to read and understand compressor charts better than ever, I had a choice to make. Go with a more established EFR setup, or take a chance on Garrett's newest offerings. My next choice came down to the housing. The 0.72 versus the 0.92 housing. It came down to a matter of 4 lbs/min of flow in the favor of the larger housing, so I went with the 0.92 housing. Spool versus top end... So, how did it turn out?

In a word, excellent. As a street turbo, this thing is absolutely awesome. Think stock twins spool and response, but with medium sized single power. In competition, I found that I was able to control the rear end much easier than with the old setup. I was able to spin the tires to the degree that I wanted. Definitely need to calibrate my foot again... If I were to floor it like I was driving my old setup, it would just fry the tires. Magic is, I was able to modulate the throttle to produces wheel spin as necessary. Loved it.

Size wise, it's about the size of a CT26, nice and compact. Unfortunately, it seems that v-band is about the only viable housing option currently. Garrett used to have a T4 option listed on their info page on this turbo, that it no longer on there as of today. Hopefully someone like ATP will fill in the gap.

Price, it's not cheap, but I have no regret in purchasing it. It gives me the throttle response I need for competition, and plenty of power. Dyno visit next month in Vegas should show us what the power band looks like. I suspect it will be pretty wide and flat, relative to a lot of comparable output turbos.

I have found my new default recommendation for 1jz owners. This turbo will be ideal for nearly anybody with a 1j, unless you're into drag racing and are chasing sub 10 second times. 2jz or 7m guys, this would likely make a nice option as well. I'm sure Garrett will be putting out something along the lines of a G30 in the future, that may be a solid option as well, if they indeed make such a turbo.

Edit: Apparently the G30 is now available. So there's more options in that small frame single market now. :)
 

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Discussion Starter #2
Update after a weekend of autocross on a medium sized track. This thing still rocks. If you're at low altitude, I suspect you'll be very happy with this same setup on a 1j or 7m. Might be perfect for a 2j if absolute response is what you're after.

What I was hoping to learn this weekend, is how this turbo responds to second gear autocrossing. Throttle response is everything in autocross (after handling and driver mods first), and you don't have the mechanical advantage that first gear provides, so you're relying on spool characteristics when in second. Is it a magical bag of unicorns? No, no it's not. However, my situation is probably a bit different than most, as I'm at 6500' elevation, so power and response are a bit down, we have to work for our air up here a bit harder.

That said? If you can learn to downshift to first, as appropriate (heel and toe is a valuable skill here), you'll manage. If you have vvti, you might be able to get by without a downshift. What's forcing me to downshift is what are essentially hairpin turns. You are not likely to see those on a road course or on the street. A nicely flowing autocross course is going to be a good time with this setup. I was seeing speeds of 60-70 mph with plenty of braking zone left. That's cooking on a cone course in a parking lot, folks.

What's that? You've never autocrossed your Supra before? I won't even ask what you're waiting on... if the thing is even somewhat reliable, you owe it to yourself to give it a try. It'll teach you skills and car control that you've never needed before, and will wonder why you haven't been doing this for years. :)

Future plans for me involve a vvti head swap, because I'm a sucker for wide powerbands relative to engine size, and a dyno session here in a couple weeks. Gonna guess now that it will put me around 460whp / 430wtq at around 18psi on pump gas. Will update you when I have more info.
 

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Great review. Im considering the g25-660 or g30-770 for my mk4.

My car makes 605 whp at 19psi on a BW s366 and it's laggy as it does nothing before 4500
compared to new turbo engines its not as fun hearing the worlds throttle control and turbo engine only = fun.

When do you hit full boost and what's is your set boost? Any dyno charts.
Thank you
 

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Discussion Starter #4
Great review. Im considering the g25-660 or g30-770 for my mk4.

My car makes 605 whp at 19psi on a BW s366 and it's laggy as it does nothing before 4500
compared to new turbo engines its not as fun hearing the worlds throttle control and turbo engine only = fun.

When do you hit full boost and what's is your set boost? Any dyno charts.
Thank you
Garrett also makes a G30-660. Why, I'm not exactly sure, but your exhaust housings and plumbing sizes are a bit different on that one. G25-660 is an excellent street turbo, but if you're used to a 605whp car, you might want to go with the G30-770.

I agree, throttle control on a turbo engine does make for a lot of fun. I'm not a fan of lag either.

Full boost comes on early, although that isn't displayed on the one dyno chart I do have. I'd say between 3000 and 3500, somewhere in there the car has hit full boost of ~20 psi in my case. As far as numbers, in Las Vegas at All Access Tuning for Supras in Vegas 2019, the car put out the following numbers:

Torque at 3000 rpm: ~200
Torque at 4800 rpm: ~350
Torque at 7200 rpm: ~245
AVERAGE torque: 278

HP at 3000 rpm: ~110
HP at 5250 rpm: ~350
HP at 7200 rpm: ~340
AVERAGE HP: 291

Why so many data points? To demonstrate how flat the curves are with this turbo. Sure, peak numbers get some people excited, but I'd rather have as wide a powerband as possible, and this turbo delivers that quite well. It makes over 250 wtq for nearly 4000 rpm... Not bad for a car still on 91 octane. I can imagine you could easily throw another 20% onto any of those numbers running E85, and perhaps deliver more torque through the midrange as well.

Also worth noting, this particular dyno is known to be on the conservative side, I've seen cars that put out 1000+ whp in Arizona put out around 800whp on the dyno at All Access. Not saying there's anything good or bad with any particular dyno, just saying that some discrepancy is to be expected.

Now, that said, my car is every bit as fast and pulls every bit as hard as it did when it was running the Comp setup, which dyno'd peak outputs of 125whp and 90wtq more, on the same dyno as the G25-660 was run.
 

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Great review. Im considering the g25-660 or g30-770 for my mk4.

My car makes 605 whp at 19psi on a BW s366 and it's laggy as it does nothing before 4500
compared to new turbo engines its not as fun hearing the worlds throttle control and turbo engine only = fun.

When do you hit full boost and what's is your set boost? Any dyno charts.
Thank you
The 770 makes 600whp at 26psi on a 3.0. Ethanol recommended. It's a 58mm turbo compared to the 66mm you have. If I were you I'd get the g30-900. It should match your current numbers but have much more response below 4500rpm. Note that it costs A LOT though....
 

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Discussion Starter #6
Appreciate the 2jz perspective JOutterbridge. My particular perspective is a bit different from most, so I tend to stick to the smaller end of the turbo spectrum.

I just wish ATP would release a T4 housing for the G25's already... Seems like a LOT of Supra manifolds are T4, certainly the couple I have. That said, v-band is becoming a viable option these days.
 

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Appreciate the 2jz perspective JOutterbridge. My particular perspective is a bit different from most, so I tend to stick to the smaller end of the turbo spectrum.

I just wish ATP would release a T4 housing for the G25's already... Seems like a LOT of Supra manifolds are T4, certainly the couple I have. That said, v-band is becoming a viable option these days.
If you have T4 you can still get the new G series. ATP makes custom V-band to T4 housings. No need to get another manifold, space shouldn't be an issue either
 

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Discussion Starter #9
If you have T4 you can still get the new G series. ATP makes custom V-band to T4 housings. No need to get another manifold, space shouldn't be an issue either
Happen to have a link that works with the G25? I've seen some of their T4 housings, but only in the G30 and G42 turbos.

G25 variants have either T25, T3, or v-band housings, unless you know something I don't. Hoping that's the case! :)
 

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They will make custom for you if you'd prefer T4 over T3. I wouldnt recommend the G25 though on a stock head unless you're going twins. It's simply too small of an exhaust housing. Go G30 660 over G25 for less back pressure
 

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Discussion Starter #11
They will make custom for you if you'd prefer T4 over T3. I wouldnt recommend the G25 though on a stock head unless you're going twins. It's simply too small of an exhaust housing. Go G30 660 over G25 for less back pressure
I had asked them about a T4 for the G25 a while back, perhaps it's time to email them again... Also, I already have the G25-660. Surprisingly the 0.92 breathes quite well, only gave up 200 rpm up top where the peak power happens, but picked up around 800 to 1000 rpm down low, compared to a MUCH larger turbo I was running before.

For the 3.0+L guys, yeah, G30 would likely be the way to go.
 

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Ok, I was only saying that because the G25 in its largest A/R (1.06) flows the same as the G30 at .83A/R at a better pressure ratio. It's not the end of the world if you aren't maxing it out and hitting 8k+RPM though. If necessary you can always swap the turbine side of it to match the compressor. You could keep the 660 and just have the bigger turbine supercore if you can't get a Vband to T4 adapter made for your exhaust manifold
 

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Discussion Starter #13
I can't recall the exact specs, but aren't the G25-660 and G30-660 using different wheel sizes?

As for the G25, where are you finding a 1.06 housing? I have the 0.92 on mine. Also, running a T4 to v-band adapter on mine, only way to put that together for my setup without changing a manifold.

Not too worried about it though, it's a fantastic setup, I just wish the T4 was an option. Who doesn't want a QSV on an already really quick spooling turbo? ;)
 

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Thanks a lot for the review, te72.

I love seeing people trying smaller than normal turbos, in the hunt for response.

Great results given its only on 91 octane too :)
 

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Discussion Starter #15
I have some other plans that should help response a bit further. I have a vvti 2j head sitting, needing a refresh, that will someday top my bottom end. Between that and E85, I would imagine this little G25 should provide all the power I need and as wide a powerband as is realistic from only 2.5L, but time will tell!

I'm looking forward to seeing someone test a G30-770 on a 2j. I think it will provide near-stock spool speed, but deliver a VERY healthy street friendly top end.

Appreciate the compliment Mr Ree! The tune was done by Tim at Xact Dyno in Mesa, AZ. We were shooting for something that would be road trip friendly but still put out the power. Other than the cold weather tuning (not something that's feasible in summer in AZ!) and a bit of low end tuning, it runs fantastic. I like being able to fuel up just about anywhere and not worry about whether or not I'll have to baby the car...
 

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I have some other plans that should help response a bit further. I have a vvti 2j head sitting, needing a refresh, that will someday top my bottom end. Between that and E85, I would imagine this little G25 should provide all the power I need and as wide a powerband as is realistic from only 2.5L, but time will tell!

I'm looking forward to seeing someone test a G30-770 on a 2j. I think it will provide near-stock spool speed, but deliver a VERY healthy street friendly top end.

Appreciate the compliment Mr Ree! The tune was done by Tim at Xact Dyno in Mesa, AZ. We were shooting for something that would be road trip friendly but still put out the power. Other than the cold weather tuning (not something that's feasible in summer in AZ!) and a bit of low end tuning, it runs fantastic. I like being able to fuel up just about anywhere and not worry about whether or not I'll have to baby the car...
I have the G30-770 on order with 0.83ar it should arrive next week finger crossed I'll keep you guys posted
 

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Discussion Starter #19
Glad to hear it! Fresh paint to go along with a fresh turbo? Sounds like a well pampered car. :)
 
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