went from a GT3071RWG AKA GT2971 with the T25 0.64 AR internally gated turbine housing. To an externally gated G25-550 with a 0.72AR Turbine. The G25 seems boost happy and responsive when in boost but RPM threshold is higher and the drive ability is not as good. it will hit full boost with ~40% throttle plate opening held steady. 100 less hp at 3800rpm feels quite noticeable followed by wallop of boost and torque rise make slow autocross corners challenging. kind of disappointing results. Red is old setup GT3071RWG blue is G25-550.

 

Are you on electronic boost control? I've kicked around the idea of changing over to boost target based on TPS to try to get power delivery to be more 1:1 with throttle position.

I'm surprised by those graphs simply because everyone I've heard has said the g25 series is a light switch as far as boost coming on. Any reason you didn't go with the smaller AR?

Also, damn that's some power and congrats on the Mazda Motorsports shirt feature!

 

Yea I'm surprised by it as well. The GT371RWG was a manual boost control and Hydra ECU. Never got an electronic boost controller to be stable and repeatable with that turbo and ECU. With the turbo change I went to a Link G4X Extreme and using its boost controller and a bunch of other features including Traction control wired in with MK60 ABS wheel speeds which really seems to be working well. I'm now also using E-throttle from a 2.0l BRZ (65mm) and a Honda Fit pedal. have had to put in a really nonlinear throttle relationship to make it more derivable. as I said it will make full boost with the throttle plate never opening much past 50%probably 60% throttle plate opening is the same result as being full open. I think it may need some form of TPS based boost control but I haven't figured out the best way to do it searching Link forums yet and I also signed up for Evens performance Academy.

The Biggest difference in spool seems to be from the Hot Side AR. The .72 is the smallest AR available with an external waste gate. surprisingly

I had lots of people advising going larger than I did. Im using a turbosmart straight Gate PSG40.

 

I will say once above rpm threshold the boost is nutty it just wants any excuse to be operating at boost target. It's like its too responsive to be easy to drive and it's not helping in making the car be a faster car.

 

Bob, I'm pretty sure you can setup your boost target table like shown below (not sure what max KPA you run) so while the throttle plate will open the same, the wastegate will bleed off less pressure as you increase TPS. I'm pretty sure a setup like this will need a really well tuned wastegate duty cycle table as well.

I think that would give you a more linear throttle. Another thing at play would be what the wastegate duty cycle is doing on spool up. If the duty cycle is at 90% when it's trying to get to the target then you're going to get that crazy spoolup regardless.

I'm just spitballing here (I'm sure @curly would have more experience with all of this), but you might also consider a table like below but with open loop boost control. Scale the wastegate duty cycle from 20% or so at low throttle up to the max you run at full throttle. It would probably be a bit easier to get up and running and give you an idea of if it works better or not.

 

Only problem is the guy who's turning his car is the guy who taught me most of what I spew out here. Kris is pretty knowledgeable, especially with Link and turbos

What simba said is definitely an option, you'd have to go through from 0-100dc EBC. The help file on CL EBC is helpful in showing you how to disable control by zeroing out PID and working your way up.

Kris probably already did this or perhaps you did, I need to do it myself and get CL EBC working, although I'm not doing anything as crazy as your setup.

 

I will say what worked on the dyno for boost control didn't work at all in real world. The target table was pretty close but in order to avoid overshoot I needed the stage1 duty cycle to be pretty close to the target table and to maintain it stable I needed way lower values on the integral and derivative gains in closed loop. Trying to hold it hard closed to speed spool up was a disaster. only way to make it work smoothly is to closely seems to mimic the behavior of a manual boost controller and the EBC only helps to keep it slightly flatter than a manual boost controller deep into the RPM range. I only got a few test days with it before going to Nats and my laptop stopped downloading data logs for some reason which I have yet to sort out.

Right now I have boost target table based on ethonol % and 4 selectable levels based on a can keypad input on the dash. Kris set that up for me. But yea basically once above the rpm threshold the turbo wants to hit full boost and doesn't seem to have much issue pushing through a partially closed throttle body. it seems Ideally Id want a boost target trim table setup vs TPS but I can't figure out a way to do it. you are stuck doing the main table as boost target vs tps. Here is an example of hitting boost cut with mostly less than half throttle.Might work great for a drift car not so much if you are shooting for low lap times.

 

Under boost setup where it says "GP boost Tables", set it to "always on", then set your axis to TPS. You can set a trim for target or WG DC, Ideally you'd do both so it jumps down in DC if you're lowering target.

 

has anybody actually run TPS based boost control? I haven't found anybody who actually got it working or showed it as a good solution.

 

something like this?

 

While I might be able to get boost control to make it more derivable above boost rpm threshold I don't think I can fix that huge deficit over my old setup at 3800-4000 rpm followed by a wallop of power at 4500 rpm putting it instantly into traction control mode. This is starting at 35mph and a common speed seen on slow autocross corners. It is too hard to drive through that transition unless the power is turned way down.

They make a .61AR external gate housing for the GT/GTX30 looks like it flows about the same as the .64 I was using. I see all the tests showing better spool with the G25 over that turbo but I think they were comparing the GTX3071R with the .82 AR housing to a G25 with a .72AR. The internally gated G25-550 with the .49 AR would probably work better for what I want. but maybe for me just the GTX3071R with a .61 external hot side housing.

 

Like in general? Yes I run TPS on MS3 with a 2867R gen II and it is extremely effective, and I have sequential compressor stages.

I have to think it is very doable on this setup.

 

Just out of curiosity, what were you trying to solve with the g25-550? Better responsiveness, higher overall power, better efficiency, just a "better" turbo? Just based on what I've heard (and having not looked specifically at either turbo's data), I would've expect the newer tech to outperform the older tech unless the compared turbo's were targeting significantly different markets.

I'd also be interested to see how that GP boost trim setup works out if you decide to test it.

I know you mentioned this above, but if you were having these issues at 35% Stage 1 Duty Cycle then I can only imagine how much of a handful it was while spooling at something like 80%

 

Honestly I was after better spool and more responsive turbo better ability to use and control the power. The turbo I was using was over 20yo technology and not even really in production any more. might even do a boost curve to flatten the torque out some. Much over 400hp is really not that useful in making the car faster.for my purposes Just makes more time into the traction control. Thus far I didn't get any of what I was after with this turbo change. The power is not as responsive off slow corners then its too boost happy to control well at higher rpms.

 

I'm still surprised by that. Even looking at this article that Garrett has on their website shows the 25-550 with a larger AR outperforming the GTX3071 with a smaller AR, and it gets to target torque around 700 RPM earlier. Consider your old turbo was a generation behind the GTX and wasn't using EBC it's even more surprising. Keep in mind that I'm not too versed on the in's and out's of turbo tech.

https://www.garrettmotion.com/news/n...e-sr20-engine/

 

Yea I watched that video too. I'm pretty sure their GT25-550 is a .72 AR where the GTX3071R they are comparing is a .82 AR or even larger, they don't tell you anywhere that I can see what the AR is on the GTX371R GII . Also GTvs, GTX I'm not sure if the GTX3071R though it has higher efficiency and more top end capability than my older GT3071R might actually be more lazy at making boost at lower rpms. My old GT3071R was pretty much maxed out at 450hp more boost at that point was not really making any more power it was sufficient. I also wouldn't run it on a track at that level. can't get enough heat out to not kill it. lower boost and ~350hp was reasonably reliable for lapping although 450hp on high speed straights would definitely make it faster.

 

I didn't actually watch the speed academy video (although I do watch a lot of their stuff), but the page on Garrett's site I linked to shows the following specs alongside that video. I have to assume that these are the turbo's being used in that video, otherwise it's pretty misleading.

 

Yea and nether of those charts tell you the Turbine AR. In the comments on YouTube they tell you the G25-550 is a .72 AR and about 10 people ask what was the AR on the GTX3071R GII and the question was never answered. The internally gated Vband G25 comes in eather a .72 or a .92.AR whereas the GTX3071R GII internally gated V-band comes in .61, .83, or a 1.01 AR. Turbine AR seems to make a huge difference in RPM threshold.

 

Also my old turbo was with an internally gated T25 housing. Apparently to do that they use the same wheel as the 3071 but trim down the turbine wheel further. They have since renamed it a 2971 because it is really not the same. 57 mm inducer 52mm Exducer. with a .64 AR. According to the graphs from Garrett the turbine on mine flows about the same as a 3071R with a .61AR housing and the G25 with a .72 AR flows a bit more. To get a 2876 to flow as much as a 3071 it neds a .82 AR housing. pretty sure the rpm it will spool at is closely related to how much the exhaust is throttled/nozzled and its maximum flow rate through the combination of turbine wheel and housing.

 

I'm not familiar with the link software, but this to me looks like you're never targeting less than 26.1psi? This could be the problem, especially before if you had MBC, so mechanically the system would be limited if you were say at 20psi and part throttle, but here, the wastegate is going to try and throw everything at it to make 26.1psi. Is there a way to have the boost target table against throttle position?

I have got closed loop running really well on my setup with an MS3, though it is quite complex and I have yet to make a post about it. I do not have a drive by wire throttle, so I haven't been able to fully tune it at part throttle, but effectively I think you should create boost duty sweeps at certain throttle openings to see what is the least the system can mechanically make. Like this plot I have made below, but obviously this is only for WOT, but if you ran it at 20% throttle, 40% throttle, 60% and so on, you could work out exactly what the minimum the system could make at different throttle openings, and tune it accordingly. It might be even easier to just go to 0% duty cycle and do sweeps of throttle vs rpm first.