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Garrett G Series


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On 9/6/2021 at 10:22 PM, BK said:

Yep, with the Mitsubishi cores. They were the GTIII-SS, RS, 2530, 4R and 5R turbos.

Almost went a 5R myself as the T51R replacement, until the SAU faithful shot me down in flames and slapped some sense into me 🤣

Be interesting to see how the HKS G series turbos compare, as they obviously realised they made a mistake and mustn't have sold well.

The RS/2530/4R/5R all looked pretty mediocre IMO, looks like they recently announced something that is no longer based on the MHI cores as well: https://www.hks-power.co.jp/product_db/turbo/db/29690

I've yet to figure out what could possibly replace the GTIII-SS for the weird corner of "basically stock but not ceramic turbine". Basically the same "design concept" as what HKS says for the GT4135 in that link. Nismo is busy rehashing R34 N1 turbos and calling it a new turbo, only Garrett makes bolt-on turbos and the designs are decades old at this point. Tomei has the T550B but nobody has tested them and talked about it on the internet and their old ARMS M7655 was just garbage. 

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Hi all, been a long time lurker of this thread, ultimately leading me to a G30-770 w/ 0.83 T4 flange. Just wanted to share the results I've gotten so far; though compared to the last dyno chart shared by Lithium, I feel like there's something off or inefficient about my setup. Now that ATP has a T4 twin-scroll housing available, that might be my next move to try to fix the laze (not soon) and reduce the number of cheap parts on my build. Also, sorry about the low-res image.

Important parts:

Altitude! 1519m/4984ft

RB25 neo (stock longblock & cams)

G30-770 0.83 single-scroll T4, normally at 20psi (the run at 22 was a quick one to verify there's still headroom)

Haltech Platinum Pro

E70 ish ethanol

CXRacing exhaust manifold (unsure whether an inefficient manifold would cause this much laziness)

OtakuGarage intake manifold

3" exhaust with cat

240_rb25_g30_770_flex.jpg

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Yeah, I did a basic test of VCT at idle, and have it configured to be ON from 2000 - 5500, though I forgot to do an ON/OFF comparison on the dyno, so it's possible that's still a factor.
 

I'll also share how this looks in Autocross, where the lag is far exacerbated -- in my data-log, I was only seeing ~14psi peak and 5900 RPM in 2nd (barely into the meaty part; also possible I should just run a smaller turbo for this application; looking at you G25-660). Gear ratios are pretty close to stock R34 GTT 5speed, which is fairly long for autox as well -- lots of factors that are not ideal, ever a work in progress.

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On 19/09/2021 at 2:55 PM, gik0geck0 said:

Altitude! 1519m/4984ft

G30-770 0.83 single-scroll T4, normally at 20psi (the run at 22 was a quick one to verify there's still headroom)

Haltech Platinum Pro

E70 ish ethanol

CXRacing exhaust manifold (unsure whether an inefficient manifold would cause this much laziness)

OtakuGarage intake manifold

240_rb25_g30_770_flex.jpg

Wow, that's lazy - definitely not right for that kind of setup. 

I personally am not a fan of the ATP T4 housing and actually have no idea how you have a T4 open housing G30 - Garrett don't have a native T4 open housing so I'd wonder what that housing spec and quality is and how much it could be contributing to that result.   Otaku intake manifolds seem to have a pretty dodgy reputation at least from what I've heard, I'd make sure there has been no sneaky cracks for boost to leak out of.   I know nothing of the CXRacing manifold either, but the smorgasbord of cost cut spec parts and a sub-par result definitely make it feel like this could turn into a "the poor man pays twice" kind of story.

I would at least be going through a diagnostic process to rule out the typical "something ain't working right" process.   A genuine Garrett G30 with a .83a/r exhaust housing on a stock cam RB25 with VVT working, and quality intake and exhaust manifolds with no leaks should NOT be that lazy.   G30s are a little later in boost threshold than other turbos with the same wheel sizes, but no way near that later - twin scroll or otherwise.   I know of an G35 1050 running an open housing on an RB25 and it's significantly less lazy than this.   

That altitude wouldn't help, but I wouldn't expect it to hurt THAT much.   Something that is catching my eye is how linear the spool is - it doesn't seem like it's getting into a proper "ramp" like you'd normally expect.   

Just to rule out something very obvious that I've definitely seen other people miss, and end up with this kind of lag (if not actually being outright unable to build more than a few psi of boost) - did you definitely install the valve seat/fire ring/whatever you want to call it in the wastegate?  Without it you effectively end up with the effect of the wastegate being constantly slightly cracked, the exhaust will sound fairly pitchy/angry the whole time and it makes the turbo a lot laggier.

Valve Seat Fire Ring for Precision 39mm Wastegate - AGP Turbo

 

Edited by Lithium
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FWIW I have an older, albeit larger GTX3576 Gen 2 with a 1.01 divided housing and all 2bar comes in before 4500RPM on a 2.5L RB25DET NEO with 260/9.15 cams.

I believe your CX Racing manifold and turbine housing are to blame, also @Lithium's suggestion of the fire ring not installed properly OR missing altogether could be a contributing factor.

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Thanks for confirming my suspicions that something isn't right. I've pulled vaccum and pressure on the intake manifold and held it to check for leaks, so I'm confident the intake side is fine. I have verified that the WG fire ring is correctly seated and that the flange gasket appears to be holding, though I've always suspected how flat all the manifold flanges are. I stuck a smoke machine in the turbine housing, and at least at 0 pressure, it's sealed. The CXRacing flange is drilled for both T3 & T4, so that has me suspicious of that seal, but I'm not sure I'll know until I switch manifolds.

Your comments about ATP housings make me consider switching to v-band & Garrett housing, but T4 twin-scroll is still alluring; I have yet to decide on manifold choice, but I've been thinking T4 TS because it'd give me incremental confirmation of the single bad part; if it's better, then the ATP housing is fine and it was either poor manifold design or leaky flange at higher pressure.

Here's a link to ATP's listing of the T4 G30 housing: https://www.atpturbo.com/mm5/merchant.mvc?Screen=PROD&Store_Code=tp&Product_Code=GRT-TBO-M30&Category_Code=Garrett-Turbo-GSeries-G30-770

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This would be perfect for you, twin scroll manifold, with the scroll split to the gate seat

https://www.sincocustoms.com/shop/product/209348/rb20-or-rb25-t4-twin-scroll--turbo-manifold/

Then next logical step is to get a T4 TS turbine housing and come back to tell us it is all in by 4000RPM :D 

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