F8X G30-770 N55 M2 Boost Control Options

[ChrisD]

Aa far as AR goes, I don't think you'll have spool problems with that turbo and the 1.01, and going smaller will limit your power potential up top. I'd probably save my money and not order an additional housing until you can try out the 1.01 and see if it spools good enough for you. Then if you feel you've got some spool to spare, you could try the larger AR to get a little more power up top.

Yeah if anything I'm starting to think that turbo is going to be a bit on the small side even with the 1.01 AR, so seems like spool certainly won't be an issue if I stick with that.

I could maybe return the the G30-770 and swap it for a G30-900 or G35-900. Would moving to a G30-900 even make much difference though? I assume on pump gas the limiting factor is knock, so does a bigger compressor (same exhaust turbine) do anything to change that? I guess it means slightly lower IATs?

If the turbo itself was the limiting factor, surely that would mean we could max the G30-770 out and according to the compressor maps that should comfortably make the 600 bhp I'm looking for. The more I look into it the more confused I get

Tempted to just try both a G30-770 and a G35-900 and then sell whichever one I don't like the power curve of. Somehow they both have the exact same v band sizes for the inlet and outlet of the exhaust housing, and both are the same physical size, so should be easy to swap them without changing anything (other than intake pipe size)

 

[ChrisD]

@CalvinNismo I'm in Lincolnshire.

Oh and as for the CSF radiator yeah I do already have it. Bought it ages ago and never got round to installing it but figured this would be a good time. I'll have a read of that thread but hopefully the CSF one should at least be better than stock... Also if it makes any difference, I'm probably going to remove the air con condenser and pipework as the pipes get in the way a bit in the engine bay and I very rarely use the air con anyway.

I'm also going to add a bigger oil cooler cos I have one sat here anyway and I need to delete the oil/coolant warmer thing to make room for the turbo, so I'll make new AN lines from the oil filter housing that just go directly to this new oil cooler. I only do the occasional track day and tend to only do 15 to 20 minute runs before letting everything cool for at least 30 mins so I'm not expecting temps to be a huge issue for me tbh but I guess we'll see

 

[wheela]

Yeah if anything I'm starting to think that turbo is going to be a bit on the small side even with the 1.01 AR, so seems like spool certainly won't be an issue if I stick with that.

I could maybe return the the G30-770 and swap it for a G30-900 or G35-900. Would moving to a G30-900 even make much difference though? I assume on pump gas the limiting factor is knock, so does a bigger compressor (same exhaust turbine) do anything to change that? I guess it means slightly lower IATs?

If the turbo itself was the limiting factor, surely that would mean we could max the G30-770 out and according to the compressor maps that should comfortably make the 600 bhp I'm looking for. The more I look into it the more confused I get

Tempted to just try both a G30-770 and a G35-900 and then sell whichever one I don't like the power curve of. Somehow they both have the exact same v band sizes for the inlet and outlet of the exhaust housing, and both are the same physical size, so should be easy to swap them without changing anything (other than intake pipe size)

If you want to stick with Garret G-series, I'd go to the g35-900 over the g30-900. You're exactly right, you'll be limited by knock on pump gas only. That bigger turbine of the g-35 should help keep back pressure down, and the higher flow 900 compressor should be at a higher efficiency area of the map, so not needing as much energy from the exhaust to flow at boost. This should all help get more exhaust out of the cylinders and improve knock threshold.

I like your idea of trying both!! I do think g30-770 is a tad small though for this engine with no ethonal or meth.

 

[ChrisD]

If you want to stick with Garret G-series, I'd go to the g35-900 over the g30-900. ...

I was starting to think the same but then I watched this video and now I'm not so sure

I know its not the exact same engine, but its still a 3.0L inline 6 on pump gas so probably the closest comparison I'm going to find that's tried the exact 2 turbos I'm considering.

TL;DW They preferred the G30-770 over the G35-900 and said the G35 900 was giving absolutely nothing until nearly 5k RPM and then came on really aggressively. Whereas the G30 770 kicked in about 700 RPM earlier and was more progressive but still felt really fast. The only issue is everyone's definition of "feels really fast" is different...

As for the bigger turbine allowing more exhaust gas out of the cylinder to improve knock threshold, I hadn't considered that. I was only thinking about intake temps affecting that.

 

[houtan]

That was a helpful video. From my experience, I think the option that spools at 5k would be the wrong choice.

My turbo, which I believe is a GTX3582R ball bearing, is spooled up around 4,200 rpm when starting a log around 3k rpm, and I think it’s perfect. Definitely spools slower than something like a PS750, but I don’t need the power any earlier because I won’t have traction and I don’t want to put unnecessary strain on my bottom end.

If I got wot at 4k, in the correct gear, I’m at full boost in about 800rpm.

Hopefully that helps.

 

[ChrisD]

My turbo, which I believe is a GTX3582R ball bearing, is spooled up around 4,200 rpm when starting a log around 3k rpm, and I think it’s perfect. Definitely spools slower than something like a PS750, but I don’t need the power any earlier because I won’t have traction and I don’t want to put unnecessary strain on my bottom end.

See that's weird cos your turbo is the exact same turbine size as the GT35 900 that in the video they said was only coming on at 5k. Only difference is your compressor side is a bit larger and also the newer G series are supposedly more efficient and slightly better all around. So in theory theirs should have been either the same kind of response as yours or if anything a bit better.

 

[houtan]

Here is an example of the response going wot from 4k. Not a great log, but it gives you an idea of the turbo response.

Log-06-14-2024-19-06-16

Uploaded by API.

www.spoolstreet.com

 

[wheela]

I was starting to think the same but then I watched this video and now I'm not so sure

I know its not the exact same engine, but its still a 3.0L inline 6 on pump gas so probably the closest comparison I'm going to find that's tried the exact 2 turbos I'm considering.

TL;DW They preferred the G30-770 over the G35-900 and said the G35 900 was giving absolutely nothing until nearly 5k RPM and then came on really aggressively. Whereas the G30 770 kicked in about 700 RPM earlier and was more progressive but still felt really fast. The only issue is everyone's definition of "feels really fast" is different...

As for the bigger turbine allowing more exhaust gas out of the cylinder to improve knock threshold, I hadn't considered that. I was only thinking about intake temps affecting that.

Wow, those were spooling slower than I'd have thought. Maybe you'll be at a sweet spot with your g30-770. Excited to see how this turns out!

 

[ChrisD]

Wow, those were spooling slower than I'd have thought. Maybe you'll be at a sweet spot with your g30-770. Excited to see how this turns out!

yeah same but idk maybe they're on a much lower compression ratio than us or something. Looking at houtan's logs from his G35-900 equivalent, it doesn't seem to add up at all with what they were seeing in that video.

They did a dyno video here too directly comparing the two as well as some different AR housings:

 

[CalvinNismo]

It also depends what cams are in the 2JZ, they could be contributing to it spooling later than houtan’s N55 for example.

Also, you’re not far away from me, I’m only up in York.

 

[wheela]

yeah same but idk maybe they're on a much lower compression ratio than us or something. Looking at houtan's logs from his G35-900 equivalent, it doesn't seem to add up at all with what they were seeing in that video.

They did a dyno video here too directly comparing the two as well as some different AR housings:

Yeah, I hear you, not sure what their compression ratio is, and as @CalvinNismo mentioned, who knows what affect their after market cams are having. And that first video you posted where they were driving around town - hard to tell watching a tach on a video, but it my opinion some of their comments didn't really seem to square with what I was seeing on the tach

 

[ChrisD]

Just to add even more confusion to turbo sizing considerations, I got a message on IG from a guy who is running a G35-900 (0.82 AR) on an S55 M4 and he says its really laggy and wishes he'd gone for a G30-900 instead. He did make 570 whp on pump gas with a safe tune and no upgrades to the fuel system though (I guess S55 stock fuelling setup is a lot better than N55).

One thing that surprised me is he said the opposite of what SpeedAcademy said in their video about the G35-900. He said because its so laggy it helps with traction, whereas SpeedAcademy said it was scary to drive as it was breaking the tyres loose all the time.

So yeah I have absolutely no idea what will be best really so just going to stick with the G30-770 and see how it performs on the dyno and the street, then take it from there.

 

[wheela]

The s55 should be a pretty close comparison to n55 - same bore, stroke, compression ratio, and intake & exhaust valve sizes and lifts. But higher redline, and I suspect the cylinders have better cooling, since they're aluminum with a thin iron coating vs. iron sleeves like n55. It's disappointing to hear the g35 was so laggy. 570whp on pump is pretty good though. Yeah, s55 has dual hpfp, so much better fueling than stock n55.

I think your plan is good, you already have the g30-770, just run it and see how it goes

 

[houtan]

Took the 1er out for a bit yesterday. Grabbed a couple logs in case it helps.

Third gear log from low rpm.

Log-08-04-2024-23-43-19

Uploaded by API.

www.spoolstreet.com

Log from higher rpm maybe against someone else

Log-08-03-2024-17-03-50

Uploaded by API.

www.spoolstreet.com

I think it helps understand needing to be in the right gear. If you are in the correct gear the spool isn’t an issue.

 

[houtan]

The internet must be listening to me haha. This popped up on Facebook for me, says it’s a g35-900 and logs are posted in the comments. Looks like it spools around 5k.

https://m.facebook.com/groups/BMWN55/permalink/2786014728240231/?

 

[wheela]

The internet must be listening to me haha. This popped up on Facebook for me, says it’s a g35-900 and logs are posted in the comments. Looks like it spools around 5k.

https://m.facebook.com/groups/BMWN55/permalink/2786014728240231/?

Yes, Facebook is definitely listening I'm not on there, but my wife is. Anyway to share the content you linked to for those of us without f-book?

 

[houtan]

Honestly. I have no clue. I’m not really on there either. The only reason why I signed up is there seem to be a lot of groups that every once in a while share useful information. Most of it gets lost in a black hole, but sometimes I learn something.

Also, for whatever reason, a lot of stuff gets posted in the marketplace there so I search for stuff I’m looking to buy.

 

[ChrisD]

I kept thinking the smaller turbo might be a mistake... so I've now also got a G30-900 with a 0.83 AR as well, so I can test both and also swap the different AR housings between them. Both have the exact same size for every inlet and outlet on them so will be nice and easy to swap everything.

I know some people say G30 is "too small" and G35 is what I should be using on this engine but I think a lot of those people are focused on peak power figures, drag strips, and highway pulls... which is not at all how I use my car. I keep coming back to the guy with the S55 and a G35-900 saying that he finds it a bit too laggy to enjoy doing the exact kinds of things I like doing.

Also as there's no plug n play kits for the Motiv Reflex for N55 in stock anywhere at the moment (and no ETA when they'll be made again) I decided to just go for the GFB boost controller. For some reason my tuner also didn't seem interested in me installing the Reflex, which seems odd to me as I would have thought they'd prefer to be able to control boost from the ECU like normal but hey, less wiring for me.

 

[CalvinNismo]

From the video you linked with the Supra, the 1.01 A/R spooled earlier and produced more power than the 0.83 (in other words the 0.83 was a restriction). Would a 1.01 on the G35 maybe be a better option?

Edit: The 0.83 and 1.01 comparison was on the G30, with only the 1.01 on the G35. My bad! I’d be curious about the same turbine housing comparisons on the G35 for sure!

 

[CalvinNismo]

Either way I’m interested to see how it works out for you. My hunch is that 1.01 G30-900 will be the best. Most potential and least restriction.