Looks Like Garrett Slipped Another Gtx30 Variant In .

[discopotato03]

As far as I know the waste gate flat valve or disc is a bit larger and the hole it covers .

Group A rally engines of the 90s .

They tried all sorts of things to make a usable power range with the air restrictor which limited them to about 5500 revs . Mitsubishi had quite a few variations of their TD05s and they went reverse rotation and twin scroll when they turned the engine around in the Evo 4 . The first TS housing was 9cm in the 4 with an optional 10.5 in the 5RS and most 6s .

The 6 TMEs had an optional smaller 15G compressor to make them boost even lower down . I don't remember which Evos first used the 9.8cm TS housing but they were standard on most 7s and some 8s I believe . Evo 9s had a different head with variable inlet cam timing and improved cooling passages , smaller diameter plugs as well .

The VCT helped pull up the bottom end and let them use an updated 10.5cm turbine housing , sort of a bit like Neo RB25 enhancements .

I can't remember the build numbers but Evos 4 5 and 6 weren't made in huge numbers , I did read all up there were 7000 6s built . 8s and 9s were sold new in the States and here in larger volumes than the earlier cars . They were never going to be main stream because most people don't like real performance car characteristics .

Back to today and GTX turbos . As part of the range they do a "Rally Potato" GTX28 turbo which has a modified compressor wheel , its intended to work within the limits of a given restrictor size and available on special order .

A .

BTW this site won't let me edit my posts so please excuse the silly spelling mistakes .

[Dale FZ1]

Best info is they used a larger disc, and bored the hole slightly larger.

It seemed to have occurred reasonably early after they were put on the market, whether it was a retro-fix to existing units, or they ran out stocks and then did the fix probably won't be made known to customers.

I think that BHDave had the info at the time he got his upgraded.

[badhairdave]

Nah, I just dropped my housing at gcg and told them to take it out as far as possible.

I do remember one of the regular contributors mentioned it, just can't remember who.

[Dale FZ1]

Restrictor equipped turbos are off on a tangent, probably worth kicking off a different thread Adrian - I reckons there's some good areas of discussion available but maybe not really applicable to Skyline owners.

I see both sides of the ledger with the discussion in this thread, and I'm sure many others do too.

AngryRB hit the nail on the head with respect to chasing a wide rpm range. Frequent comments by those running various combinations of GT30 0.82 setups is that they are progressive, responsive, and allow the RB25 to make torque (and keep making it) at revs the OEM gear had already killed the fun. IMO it takes a ho-hum engine character and makes it into a cut-price weapon that would probably give a mechanically stock but boosted-up RB26 a good seeing-to in most situations. But still compromised, because they do trade that little bit of torque the OEM setup gave from 2000-3000. Those owners who experienced the transformation have rarely been negative, but I would recommend a diff ratio change to make the most of it.

Mark's comment about accessing torque at sane rpm is valid, and it it's 100% street use then it may be a good thing to have it torque rich up to 6000 but no further. Comes down to preferences, but its best to be properly informed before deciding what you prefer. Just because it can operate over a wider range, doesn't mean you have to - all the time. Licence preservation is a real issue here.

Water injection or ethanol fuels are good things, and shouldn't be ignored. But I don't see the point in a mechanical configuration for a daily driven that needs either of these simply to survive, or to be able to wind in reasonable ignition timing to make grunt. Weekend playthings and race/rally are a different story. Perhaps if Mark went with either of these routes, his performance targets will be met. Best response, boosting over 20psi anyway, and run aggressive ignition timing safely so it makes best grunt. The only existing reliable information we have is that his rpm range will remain similar to a stock engine - whether that is a problem is for him to determine.

Dave has the experience - recommends external gate even with a small compressor. Experience holds sway over wish lists IMO. Scott has a workable and cost effective solution for housing/gate combination. Both ideas are good, and my thinking is that the bigger/better flowing gate vs an integral gate is the big factor that will permit sufficient venting in that it controls turbine speed, and also turbine inlet pressure. Extension of that idea is that the engine will continue to scavenge efficiently, and make torque into higher rpm without necessarily resorting to ethanol or water injection. Relative simplicity is a good thing, and he still has the option of stepping into those setups later if desired. I'd be doing what I can - within cost limits - to get a result that responds down low without compromising high rpm breathing.

The decision for Mark is whether he views minimal visual change under-hood from stock as imperative, or desirable.

[hy_rpm]

Stao has told me that the mitsubishi housings won't work with garret turbos

As he has tested it something with the angle of the exhaust gas aiming at the turbine so the kando housing won't work with the gtx3067

[M@&k]

I'm a bit torn really. While I think the 0.63 housing is probably closer to what I'm after, I wonder if there is more to get out of 0.82 as well. Maybe first step should be trying stronger actuator and winding boost up...

[discopotato03]

Yep most people seem to agree that a higher poundage actuator will go towards keeping the gate shut if has been leaking or blowing open . The plus is that its the cheaper of the two alternatives and you probably need it regardless of housing size .

Dale the greatest failing of waste gates in principle is that most are regulated by boost pressure - often with little regard to hot side pressure/flow .

Something else to think about is that those Garrett turbine housing maps are very likely generated using non gated housings so total flow through the IW ones probably isn't common knowledge .

The MHI thing is a different story but the parallel is that to make the power they wanted in a limited rev range they used smallish compressor wheels in relation to their turbines - not unlike a GTX3067 in some ways . Many Garrett competition TR30Rs use miniscule looking compressors for their 60mm TR30 (Ns111) turbines and their turbine housings aren't exactly huge . Its all about making the turbine spin the compressor wheel fast enough to make the turbocharger boost in the desired part of the engines rev range .

As for race like , at this stage of life I doubt my car would ever see a race track and I'm not sure if Mafias ever did either . If you drove in such a way that you never saw less than 3500 plus revs then yes a 0.63 housing wouldn't be very useful on an RB25 with a GT30 turbo . Mind you you wouldn't be looking at much less than a GTX3071 or GT3076 either .

Also I notice you mention that Mafias car went off at 6000+ but made 700Nm of torque to 7000 - possibly 6800 . With that available from 3100 why wouldn't you change up at 6-6500 and wind it up again ? I can only see the extra revs making a not real close ratio gearbox harder to swap cogs with . I guess Evos get a leg up here because turbo lag , which they don't have std anyway , is less of an issue when the revs don't drop as far between gears and you're less likely to fall off the turbo so to speak .

A .

[Dale FZ1]

^^ Misquoted. I'd not suggested anywhere that Mafia's car made torque to 7000rpm, at any stage. The idea with it was that you'd pull a gear before it started slowing, and ride the wave in a lower engine speed range. That it came on song earlier than a 0.8 setup meant it could get up and boogie without as many downshifts. It never hit a circuit that I was aware of, but it did get a workout at the drag strip.

I wouldn't suggest either that a street only engine should perform like a race only setup, but I'll stand by the idea that producing best torque over the widest useable rpm range is a good thing. Wide ratio gaps and slow-ish shift changes are less of an issue that way. Perhaps off thread, but that issue could be covered in the thread relating to your 3076 upgrade.

[badhairdave]

I'm a bit torn really. While I think the 0.63 housing is probably closer to what I'm after, I wonder if there is more to get out of 0.82 as well. Maybe first step should be trying stronger actuator and winding boost up...

I would stick with what you have, for now at least. Go a better actuator, I'd suggest a big can one rather than the compact type that Garrett supply as, in theory, it will have a better chance of keeping the flap shut if pressure in the turbine housing sky rockets. Unlikely but why risk it?

Than jam 1.4 bar down its throat.

[discopotato03]

Actually that was his quote not yours . I'm not sure if he ever ran the 0.82 housing on the 25 before it became a 25/30 . Has anyone ever done a back to back on the same RB25 with the same everything except turbine housing - both being Garrett GT30 IW ones ?

Interesting how he says that with the 0.82 housing on his RB30 and I assume the same turbo RWKW didn't change just the torque - from 720 to 850 Nm . Since most peoples dick rulers have RWKW graduations on them I guess that says something .

The fella with the GTX3067R has to decide if the current set up with probably a higher rated actuator gets him what he wants . If that's a torquey responsive engine than doesn't need WOT and a smokes worth of "forplay" waiting for boost then the path is obvious .

Only he can know , A .

[M@&k]

Bit of an update for those interested. Had another tuner (Hyperdrive) look at my car today, as I wanted to see if it could run some more boost and also to get some other ideas on what might be holding it back.

The result is not much different from before (dyno plot below), as boost tapers and there wasn't anything they could do about it. What was more interesting is that they noted that the turbine housing would quickly get red hot followed by dump pipe. He said it's pretty obvious there's a restriction there, and when I asked if a better dump might help he was dubious as it was the housing which got hot first indicating that was the most restrictive point.
This seems strange to me with a 0.82 housing...

He also noted that the turn-flow cooler (Blitz SE) was also likely to be a major restriction and recommended that be the first thing to change, unless I wanted to go external gate path. That or go E85 lol.

Anyway, here's the other dyno plot. For some stupid reason I decided to get the one without the baseline run on it. Might have to see if I can get a copy with baseline on.

[wolverine]

Can you refresh me on the cat and exhaust you have hanging off the back?

A 0.82 GT30 housing is not a restriction at that power level.

[M@&k]

...

A 0.82 GT30 housing is not a restriction at that power level.

That's what I would have thought. I'm getting quite confused...

I've got a custom 3" stainless from turbo back. Large oval rear muffler and reasonable sized mid muffler. Dump pipe is a split design which merges shortly after outlet.

Cat is a high flow. Not sure on cell count.

Would a restrictive exhaust cause the turbine housing to heat up as described?

Edited August 13, 2014 by M@&k

[wolverine]

You need to be sure that you have 3" system right thru with no step downs...the cat is always a good place to start looking when you have a restriction.

[M@&k]

I'm 99% sure it's 3" all the way, I haven't noticed any step downs, but yeah not going to hurt to double check. I can't comment on restrictiveness of mufflers and cat though.

I'm getting real confused with this setup now, as I always seem to be getting conflicting information... like this housing being a restriction when there doesn't seem to have been previous examples.

I'm thinking of the following options:

- Get a 3.5" bellmouth dump made, maybe with higher flowing cat as well.

- Install different intercooler (most likely Plazmaman kit with gooseneck / Gibson style cold piping)

- Throw caution to the wind and just try 0.63 A/R IWG housing anyway

I'm not willing to give up on this turbo just yet, but at the moment it's not presenting itself as a compelling option, as at this type of boost response I probably would have been better off with GTX3071.

Any ideas on what to try next on stock manifold and internal gate are welcome!

[scotty nm35]

Get rid of that split dump first, everything else should support twice the power.

Once you have run that up, if you are still not happy, you may need an external gate off an external rear housing to push much further. Don't go to the smaller .63, you will be even more limited.

[Skepticism]

Would have thought tuner would have suggested just dropping the exhaust then seeing what happens on the dyno, otherwise too many variables to f**k around with.. dump, cat, mufflers, step downs, whatever. Intercooler could be plausible but I dunno the Blitz SE

I wonder whether tuner is right about the housing though.. bear with me on this. Maybe someone more knowledgeable than me can let me know what they think

Turbines extract energy out of the exhaust flow by the wheel via a pressure differential before and after the wheel. If there's an exhaust restriction after wheel then the pressure is higher so the difference before and after is less, so the turbine has to work harder to extract the same energy (i.e. spin the compressor to a whatever RPM). So more total exhaust volume would be needed for the same turbine rpm

If the wheel needs more flow to get the same RPM due to exhaust, then I'm thinking the demands on the housing is greater so it could become a restriction as a result and you'd hit a brick wall, housing starts glowing etc

Edited August 14, 2014 by Skepticism

[M@&k]

Get rid of that split dump first, everything else should support twice the power.

Once you have run that up, if you are still not happy, you may need an external gate off an external rear housing to push much further. Don't go to the smaller .63, you will be even more limited.

The split dump does strike me as being a suspect. The merge is very close to the turbine outlet (~100mm maybe), so I could imagine that turbulence generated might cause flow to get backed up in housing?

Just to clarify, I'm not necessarily chasing more power. Just that if I can't get boost on well before 4,000rpm then might as well gone with a bigger turbo like GTX3071 or GT3076. It's 100% street driven at the moment, so what I'm really chasing is getting boost on earlier. Removing restrictions to make it more efficient and get the most out of it is also highly desirable.

Would have thought tuner would have suggested just dropping the exhaust then seeing what happens on the dyno, otherwise too many variables to f**k around with.. dump, cat, mufflers, step downs, whatever. Intercooler could be plausible but I dunno the Blitz SE

I wonder whether tuner is right about the housing though.. bear with me on this. Maybe someone more knowledgeable than me can let me know what they think

Turbines extract energy out of the exhaust flow by the wheel via a pressure differential before and after the wheel. If there's an exhaust restriction after wheel then the pressure is higher so the difference before and after is less, so the turbine has to work harder to extract the same energy (i.e. spin the compressor to a whatever RPM). So more total exhaust volume would be needed for the same turbine rpm

If the wheel needs more flow to get the same RPM due to exhaust, then I'm thinking the demands on the housing is greater so it could become a restriction as a result and you'd hit a brick wall, housing starts glowing etc

Tuner was, I believe, quite convinced that the turbine housing was the restriction so probably why he didn't suggest dropping the exhaust. I'm thinking of getting back in touch for further feedback from him given no one else seems to have found issue with this housing.

Your thinking on turbine back pressure makes sense to me, but that could very well be because I want the issue to be something simple like restrictive dump pipe, lol.

P.S. talking to a friend about this yesterday, and he said a restrictive dump sounds painful. Much laughter ensued.

[discopotato03]

I think you can safely say that a GT30 turbine in a Garrett 0.82AR GT30 turbine housing is not restrictive at your power levels . Too many other people have made good power with this hot side combination to doubt it . If there is a restriction elsewhere it won't help the cause .

I personally don't like split dumps because they are difficult and expensive to make properly and I think the gains aren't there with these turbine housings . The flat valve is set in its own well so when it cracks open it isn't going to be firing gasses sideways into the turbines outlet stream anyway . IMO grab a decent XR6T flange and get a dump made from there . Mine is 3.5 inch back to the cat and my exhaust is not noisy . Bell mouth is much easier to form , basically weld the tube to the flange and make a fillet back from the gates side . Simple neat functional .

What remains to be seen is if you have to spin the compressor faster to get boost at lower revs , after the exhaust and tuning the only other place to go is the turbine housing .

It would be interesting to know the AFR and timing numbers you have in the low to medium rev area when it starts to boost . I'd like to think that the tuner isn't retarding the timing where it doesn't need to be and giving you high EGTs because of it . Some people have strange ideas about tuning turbo engines in the light to medium load/rev areas - that get used every day .

Biggest can area straight through mufflers work and can be quiet if properly designed . Mine are Redbacks and while its hard to get a centre muffler that takes up all the available space (Skylines a bit unique packaging wise here) mine is plenty quiet .

A .

[M@&k]

Got in touch with Hyperdrive yesterday. Turns out there was some confusion about the turbo and he thought it was a T28 based turbo (e.g. GTX2867), which was why he wasn't surprised at power level. Once we clarified that it was a GTX30 with 0.82 housing he said he feels like it should be making significantly more and that he agrees the restriction is somewhere in the exhaust.

Suggested next steps were a different dump pipe, larger open mouth as per Disco's comment above, and potentially check the cat to see if any restrictions there.

I need to take the car back to get a wheel stud replaced, so will discuss plan of attack for new dump and if anything else worth changing at the same time.