Mindphrame

Current build and goals::
FD, GT35R 1.06 A/R T4 divided, mild street port, pump fuel, PowerFC, targeting 350whp for a street main with rare track session where boost will be turned up to make ~400 whp max. Currently running around 14-15 psi. I'm hoping for a quicker spool than the GT35 but with all the legs it had at the top.

I'm spiraling down the rabbit hole of analysis paralysis. After 3 days of reading through every post I could about these turbos, I'm finding myself feeling like I'm still missing something to finalize the decision.

Some have said the G30-660 will be fine for a rotary but then I see it's being discussed for an FC (maybe?). I'm honestly not sure that is the same when it comes to other variables to consider (G30 might be great for an FC but not for FD - I dunno). I see a few posts with the Renesis - but again, not sure if that translates as well. I loved the idea of a turbo that has a faster response than my current one and technically flows better as well.

I asked 4 different builders/tuners and I got different answers from each. One said the G30 will be great, the other said G30 is too small and will choke - I need to go with a G35, another said G30 is too small and G35 is likely ok but I should go G40, and the last said they haven't done a build with a G yet. Oddly enough, all pointed away from the Borg Warner route stating my targets aren't in their "happy zone" and other minor gripes.

All said, I think I've narrowed it down to the G30 or the G35.

From what I understand the maps and math says that a G30 flows the same/better than the GTX35R. Maps and math are one thing, actual results are another - is a G30 truly too small for my build? I'd like, at least, the same performance as the current build and I don't want to choke it.
G35 is the same size in terms of wheels to the GT35R, etc but flows better - does it spool faster than the GT35R or GTX35R and will it be happy around 14-15 PSI (I assume)?

Questions!
Is the spool substantially better/different between a G30 vs G35? Or, am I wasting time over-analyzing nearly imperceptible differences?
Does anyone have actual dyno/results from a G30 or G35 on an FD?
Have I totally gone down the wrong rabbit hole and I need to be looking at something else entirely?
Are my targets in the happy zone for these G turbos?
Are these fine to run with a PowerFC? I have seen mention of the speed sensor is damn near mandatory - can the PFC even deal with these?

I feel like I can't go "wrong" with either but this was an unexpected expense so I'm being overly critical as a means to justify the substantial investment in any of these options these days...if I'm going to spend this much, I'd prefer to make the best/right decision. There is a pretty hefty price difference between the G30 and G35, enough to make me curious.

j9fd3s

iTrader: (3)

here is what ive come up with.

the boiler plate stuff is that Garrett uses CORRECTED numbers. on the compressor side since the numbers are corrected to 60f and sea level, which isn't usually a big jump to reality, so corrected vs uncorrected are usually pretty close. i used a fixed VE and BSFC, in reality these would change with rpm, but we have no info, so you get a fixed value. i also use Garretts suggestion of 2psi of pressure drop in the Intercooler, and 0.5psi for the air filter. at 15psi, this puts you at 2.23pr

the GT35 is like this, dots are 3000, 4000, 5000, 6000 and 7000rpm right to left. 3000rpm is about 9psi

the G30-660, the smallest G30. again 3k to 7k




and the G35-900 is here, it is the biggest G35



if you notice both G series should spool faster AND be more efficient at the top end, which is cool. the surprise is that the G35 looks almost as good for spool as the G30

j9fd3s

iTrader: (3)

for the turbine side we don't have enough info. again Garrett uses CORRECTED numbers and while the correction is small on the compressor side, its big on the turbine side. also Garretts map only shows one efficiency island, so we literally have no idea what happens if you're not at peak efficiency. to get an accurate picture you NEED the pre turbo pressure, post turbo pressure, and pre turbo EGT. to get the efficiency number you need post turbo EGT, but not sure we really care.

for this i used FIXED backpressure values, and really the pre-turbo value is just a guess. (it would help if you had WG duty)
i used a pre turbo value of 20psi and post turbo of 5psi, which is kind of best case also it would change with RPM, and my number doesn't. it gives you a PR of 1.76. i assumed pre turbo EGT was 900c.

since Garretts maps are weird, the data looks weird. also the PR would in reality change with RPM and mine don't. so same break points as the compressor, but the TOP is 7000rpm and bottom is 4k
so keep in mind that the numbers will be different from reality, you can at least compare them.
GT35, again Garretts map is only peak efficiency


the G30:


and the GT35

so if you really want to find out what turbo to pick it would help a lot a lot to get pre and post turbo pressures.
also to get like peak flow at like 3pr out of the turbine, even with some magic exhaust that only had 1psi of backpressure you'd still need 33psi preturbo, and the engine won't run with that

so in conclusion the GT35 sucks, and both G series are better matches, lol

Brettus

I've had my G30-660 on a Renesis for a few years now . It's a fantastic turbo IMO and pretty much the perfect match for the Renesis. For an REW.... I feel it's a tad on the small side and could easily be over-revved (a boost leak would do it)- and these turbos have been know to fail catastrophically if that happens.
The REW flows a bit more to make similar power so IMO the G series of choice for that 350-400 range on an REW is the G30-770 with the 1.06 twin scroll housing . A guy on here tried that combo and had great success (until he bridgeported it).

TeamRX8

iTrader: (2)

feel like immajusabangin my head on teh wall around here …
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j9fd3s

iTrader: (3)

Mindphrame

Thank you - I must have done something very wrong along the way - I thought it was boost pressure + atmospheric pressure - psi loss / atmospheric pressure or 15 + 14.7 - 2 / 14.7 = 1.88 which put me smack dab into the sweet spot (i think?) of the GT35R at full song around 3500 rpm. A nice spot for the G30 and weaker for the G35. Man, I'm bad at these things but I'm trying to learn! Didn't make sense other than I assumed these were designed to run and be happiest at higher boost - this made sense with the generalized information I was being told and reading about the BW being happiest in the 18+ psi area.

So I was really hoping someone was actually running one of these in a 350-400 application so I could get something more than theory-crafting - not that there is anything wrong with that!

That's what I was reading as well for the Renesis but I'm curious about the G30-770 - isn't the hot side the same as the 660 and just a bigger intake side? I thought the hot side wheel was what was causing the issue of choking or clow restriction or... whatever. Perhaps I'm not understanding the sizing nomenclature or the reason for the "too small" advice I was receiving.

Aren't we all? Want my avatar?


All said, I talked to a few more random tuners with a questionable depth of research and experience as well as a few Garrett dealers. Almost all said the G30 series was "too small." Ultimately I ended up talking to Elliot at Turbosouce and he happened to be the final "you really should go with the G35" as I needed to get a turbo on the way to keep the project moving. Right or wrong, here we go.

Hopefully, I'll have some results to report once the build is complete.

Thanks again for taking the time to help! I always appreciate it when someone takes the time to help guide the most wayward of our little community.

j9fd3s

iTrader: (3)

first, i ran across Garretts equations to figure the turbo out, and then put it in a spreadsheet, so ive removed myself from the math's, which is good!
the loss of the IC works the way you say, but the air filter goes on the other side of the math's (my friend tells my that math's is a contraction for mathematics and not a plural, so not only am i bad at math, but still working on English too!)

and of course its better if someone had real world experience, we've seen a couple. nobody has really posted complete enough data though. it turns out if you actually have the data; pressure and temp for the inlet and outlets of the turbo, it basically will then tell you where your setup needs changes. some of this stuff, like post turbo pressure, can be super simple too. old timey tuners would have run a fitting to a gauge, and if it was bucks up, a couple. and in the 80's Racing Beats datalogger was a video camera (their sponsor made them) pointed at the gauges. so we're sort of spoiled nowadays.

Brettus

Anyone that is telling you the G30 is too small just doesn't understand the G series. You say you want 350-400 .... My G30 runs at that power level all day and has LESS EMAP (with same AR) than the GTX3582 I used to run. Honestly ...yes the 660 and 770 share the same hotside but whoever is saying it will choke at that power level has no clue.

I'm guessing you have gone for the G35-900 T4 1.06 twin scroll (which makes sense) . My guess is it will perform on par with your existing GT35 at your nominated power level . Lotta money to spend to retain the status quo .... IMO.

Mindphrame

You're probably right, but I guess it won't be me who proves them right/wrong this time.

This has been the really frustrating part for me (and hence why I came here). The problem is, I don't have the knowledge base to defend, confirm, or deny their claims. Each person I spoke with has exponentially more experience than me. Forums say they don't know what they are talking about and they say to be careful of forums and what people say - both are right(to a degree)! I'm not knowledgeable enough to tell the difference. Either way, I felt like I was coming to a doctor armed with WebMD stuff I researched the night before - sometimes it's right, and other times you're missing the multitude of interactions that could lead to the same presentation. I could regurgitate the data and examples here, but I could not defend or elaborate because that's where my knowledge ended.

The worst part for me was when I'd ask the question "why is the G30 too small?" Because your FD flows a lot more so you need to size up. "But what does that mean?" It flows more so it will choke it "How? Restrictive? Pulse? Is that an old mentality overridden by new tech/aerodynamics? I get it, 133% flow, whatever...looking at the maps seems like it would be fine. Why will it choke?" It's just different and here is my mile-long pedigree, just buy a $3k turbo you can't return if you don't believe me or go with one I know will work better.

I never really got an answer that really made sense. Or maybe I did but I'm not able to understand it. They may be dead on right or some shade of wrong.

It got even more fun - every person selling turbos said to go with the EFR, and every rotary builder/tuner I talked to said to go with Garrett. It was nearly perfectly divided.

So the debate will live on to fight another day!

Either way, it's a calculated risk...too bad I really suck at math.

And yes, I went with G35-900 T4 1.06. Honestly not sure about the twin-scroll though - that means divided or dual wastegates?

j9fd3s

iTrader: (3)

divided, the WG is not on the turbo

for what its worth, its tough to pick a turbo. i'm in the same boat, looking for a turbo
i went down the whole rabbit hole essentially because Garret gives us a turbine map with no explanation of what it means or how to read it.
i find Garretts documentation surprisingly uneven, the parts of the turbo go by different names depending on where you look!
so its not surprising its hard to figure out a turbo, we don't get any good guidance from the people that make them...
oh and BTW you'd need to add about 10% to the turbine flow, Team Rx8 pointed out that the turbine and WG flow is the compressor AND the fuel mass, i haven't added the fuel mass to the sheet (but 10:1 afr makes it pretty easy)

BW does much better here, although i haven't really looked at their stuff. its like a whole different rabbit hole.
i should note too that Garrett and BW both use corrected numbers, but Garrett uses SAE STD corrections and BW uses like SAE NET, its a small difference but 50lbs min doe not equal 50lbs min

Brettus

It would be fine and it wouldn't "choke" . What do they even mean by that ? It's just another way of saying it will create too much back pressure IMO. But you are right , the maps look fine because they ARE fine.
I think people (including salesmen) still struggle to understand what Garrett did with the G series. Great turbos that flow more and are more efficient than their predecessors , which means they make more power size for size. But to get the same power and better spool......................... you have to drop down a size.
Just remembered where I saw the g30-660 (not 770 as I previously stated) on an FD:
https://www.rx7club.com/single-turbo.../#post12554488

j9fd3s

iTrader: (3)

+1 the diameter on the G series is smaller, BUT the depth is bigger.
as usual we're stuck thinking only in diameter, and haven't considered the other measurement (red arrows) at all


its kind of funny, its essentially what Mazda did in 1999 for the 280ps turbos

TeamRX8

iTrader: (2)

just because someone is a tuner doesn’t mean they can guide you correctly

as I recently posted up a dyno result of, and argued countless posts over with other people wrt the G40-900 1.06 being either chosen or recommended by them, with it not being a proper selection for most 13Bs. The Garrett G-series turbos being a different design concept and not falling into the impeller size theory that many people are attuned to approximating by. You have to understand the flow stream values and correlate them that way instead, but not so easy to do when they don’t offer flow maps.

when the flow line on the turbine map is approaching and becomes horizontal is when it chokes for that particular turbine impeller design and housing A/R. Thus indicating that no matter how much more pressure is put into the turbine the flow through is not increasing i.e. it more or less chokes at that flow rate and can’t pass anything more. If the excess output exhaust flow from the engine isn’t able to be released through the wastegate properly is when emap goes through the roof.

Which again A/R only ranks the turbine housing flow capability within that particular impeller. You can’t just blindly choose a specific A/R number when changing frame sizes:

G30 1.06 flat lines around 30 lbs/min

G35 1.06 flat lines around 33 lbs/min

G40 1.06 flat lines around 39 lbs/min

You can get the -900 compressor with all three, but have to understand how and why it’s more appropriate to choose one frame size over the other and what the appropriate turbine A/R may be for it. Because the Garrett G35 0.83 A/R equates to the G30 1.06 AR, and the G40 0.84 A/R is close to the G35 1.06 A/R, and so on wrt flow capacity.

the turbine efficiency basically peaking the closer the flow through it reaches the flatline point, though possibly as not well understood by the bigger the better for lower emap crowd, in reality there’s a balance to shoot for within the overall basis of how the engine is configured with porting, compression, intake, exhaust, etc.

https://motoiq.com/turbo-tech-compre...e-map-details/

I might have suggested the G35-900 1.06 instead, but it will favor a higher sustained top end power level with less response down low than the G30-900. So it just depends on your specific goal, track type, etc.. I didn’t read all the posts or in depth and might have missed if you stated it specifically. Somebody has to be the egg in order for there to be chickens. Don’t be afraid to be first.
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TeamRX8

iTrader: (2)

once you start leveling them up based on results though that becomes apparent, because again the goal was never attempting an exact match, but rather to establish what an appropriate starting point is wrt initial turbine selection. That is; to be in the ball park. You might hit a home run and nail it, or only get on base and need to adjust. Either is better than fouling or striking out. Once you comprehend the basic flow stream values relative to output and configuration for a particular engine then you can basically cook up anything good enough to have a successful meal with.
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Brettus

Thanks for the explanation .... I have to admit I hadn't realised that's what it meant but it makes perfect sense now.

This sentence is misleading. Of course emap and boost go through the roof if the wastegate isn't doing it's job. This can happen on ANY turbo with insufficient wastegating.
I think you actually meant something else but I'll leave you to say what it was before I say any more on that.
He did actually specify 350-400whp with better spool than the GT3582 he currently runs. The G35 definitely wont be satisfying the 'better spool' part of that equation and the G30-900 would be marginal as well. IMO

j9fd3s

iTrader: (3)

you way of picking the turbo is really practical and actually makes a lot of sense. i had to go and actually bang my head against the textbooks before i really got it though.

if i might make a suggestion. 2.5pr might be the turbos happy place, but unless you are running a ton of boost, its hard to get there in any way where the engine will still run.
2.0pr would be more realistic, Mazda actually tells us how much backpressure (or engine pressure ratio) we can have.
you probably want to be to the left of the crossover point, especially with a port... 400mmhg = 7.7psi, there is (probably) a balance with response too

EDIT: for the example, 15psi boost. assuming 3psi for the exhaust post turbo, 15psi +7.7 = 22.7. this gives you a PR of 2.1

rx7srbad

I've got the biggest of the lot G35-1050 1.21 ar and make 14.5 psi by 4300rpm on a large street port.

I would suggest if you want good response get a g35 900. Even for track use you if you use the gears correctly your power band should be between 4-8krpm. I feel this will be a good setup for you. The G30 900 will come in a bit faster but also go off faster!

In all my 100-200 km/h or 62mph to 124mph testing...these speed are likely where you will be for most tracks....i'm finding when i shift up at 8krpm....im dropping back into around 6krpm. On a street port .....make sure you optimise power and turbo efficiency where you expect to be the majority of the time! So if you are only going to use 2k rpm to 5k or 6krpm because auto crossing on tight tracks then sure go for the smaller turbos....but if you're expecting to rev all the way to 8krpm....the g35 900 is the one i would go for in the biggest ar.

On the other hand if you want to get into 6s range for 100-200km/h of real world acceleration (none of this dyno crap) then I can confirm the G35 1050 will get you into the mid 6s range with great consistency on a large street port at 17-20psi boost depending on conditions. The G35 900 will have better response but not sure if it will get you into mid 6s range...only one way to find out! ha

Brettus

Why does everyone think he wants more power ? That's not what he said.
The G30-660 1.06 will make the power he wants with ease, the G30- 770 1.06 with some headroom. Both will spool quicker than a GT35 1.06 . Anything bigger ........ wont!

rx72c

iTrader: (8)

If you have no real world experience that's what happens.

rx7srbad

Ultimately, the decision between the G30 and G35 turbochargers will depend on the OP priorities regarding spooling characteristics, power potential, and budget considerations. I believe the OP has already chosen the G35 900 and in my experience this is a great choice of turbo for his application, based upon real world data. The G35 900 is expected to deliver excellent spooling characteristics, improved midrange and top-end power, and a significant performance upgrade compared to the OP's previous GT35 turbo. Granted the smaller turbo will spool even faster but I am skeptical of the overall growth potential, plus the additional heat they will generate in the cruise areas between 3-4krpm as they will constantly want to get on boost.

While smaller turbos may be capable of hitting the initial power goals of 350-400hp, I have encountered fellow FD owners who realized the desire for more power very quickly or in some cases after being beaten by modern OEM vehicles like an M3/M4/911 or even a stage 1 Fiesta/ OEM Focus RS/ OEM Golf R on a motorway pull. The G35 900 offers imo a greater growth/power potential for the future, allowing the OP to simply increase boost and achieve even greater performance. This turbocharger's overall capabilities outshine those of the smaller turbos, providing an exciting opportunity for the OP to explore and enjoy their car to the fullest.

If you are racing for tenths of a second on a very tight track/circuit where every bit of response matters and there is a limit to max power like 350-400hp for that class of racing. The smaller turbo absolutely makes a lot sense to remain competitive.

On the other hand if its just a street car being tracked....the focus on maximizing 4-8krpm power band is crucial as this is where you will win/loose races on motorway/high way pulls or on the track.

I am interested to see how quickly a G30-660 1.06 / G30- 770 1.06 at 15psi covers the 100-200km/h. Have you done any acceleration runs on your with the dragy gps?

Also just to clarify I am not saying these smaller turbos are not great. I know one guy running a pulsar G30 770 on a k24 in an awd rx7 running a 9.9s 1/4 mile on the street with pump fuel.

Brettus

I see your point re growth and potential and do agree that the 35 is def the way to go if that is desired. I also see on his forum where there are people using EFR7670s and raving about how awesome they are. To me the G30-660 is Garrets' answer to that particular turbo. Not quite the lightning spool up of the EFR but still great and a compressor/turbine combo better suited to the 13b up to that 400whp power point. It's been tried already (see my link above) and the results were pretty dang impressive IMO
As far as my own experience goes ...no I don't have gps but I have done maybe 150 roll races with all manner of performance cars in my Renesis/G30-660 0.83/RX8. It doesn't disappoint.

Here's a run vs RX7 running 430whp/16psi vs my rx8 running 12psi 360ish whp :

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rx7srbad

Sorry I misread the post. The RX8 does well against the rx7! haha. Looks like a fun turbo. I've tuned a race fb rx7 running a efr 7670 and the response is amazing.

If you get a chance to do a GPS run...do post up the results. When i was running 12psi approx. 400hp on my G35 1050 the 100-200km/h was around the low 9s range, which is very respectable.

Slides

he is the rx8

rx72c

iTrader: (8)

that rx7 is making 430hp in its dreams