Borci88

Admittedly in that screenshot its doing about 13psi but later on in the log theres definitely spikes to 16. What is missing though is the massive peak, then a big drop and then a recovery. While it does go a little higher than I would like on base pressure, I think it's reasonably safe to assume that boost control via the mac valve should be a lot easier to control from here on out. I wasn't game to hook up the mac valve today as it's very wet and it's on the verge of fighting traction as it is.

So a further update for this one. Turbosmart were very gracious and took one look at the wastegate and said this is our original version, we will just replace the entire thing and send it back to you. So I fitted the new wastegate with its new revisions and took it around the block on spring pressure (9 psi spring). Appears the minimum it will do is about 16psi. Keep in mind this is only 2nd and 3rd gear pulls. I think the issue is fixed compared to what it was doing before however I'm happy to provide more logs if anyone thinks theres more to the story to uncover

I thought the same but to just run gate pressure and use one port, you put your boost reference through the top. When I took it for a blat while hooked up only to the bottom I let off the accelerator and at the last second I saw 46psi. When using the Mac valve I use both ports, in my picture I was only using the top one because I was testing it on gate pressure.

So a big update for those invested in here which I think might be our smoking gun in all of this and it's not something you would pick because it shouldn't have been an issue.. I pulled the wastegate actuator/canister off the valve and went to move the actuator arm on the butterfly valve and discovered it was extremely tight, I had to put a lot of force as shown in the video to get it to open the valve. I then loosened the three bolts on top of the valve there and suddenly the valve moved freely as you would expect as you can see in the second video. The turbosmart does not have a 'seat' for this bracket to sit nicely into and as such I assume that when you bolt it down, it can be off by a millimetre or two and cause a bind in the shaft. I spoke to Turbosmart this afternoon and they have acknowledged that they revised this design late December '24 and have asked me to send it in for diagnosis and likely replacement. We rigged up an air compressor and tested the valve with the bolts tightened down versus loose. With them loose the actuator started to push the valve open anywhere from the 10 to 12psi (with a 12psi spring). This seems to be perfect and as you would expect. We then tightened down the three bolts and tried again and the valve wouldn't start opening until at least 16psi. I can only assume that due to heat cycling and different boost pressures, this is likely our fault and causes inconsistencies between runs and how the wastegate and mac valve are fighting to control boost. Freeplay.mp4 Binded.mp4

I could definitely do some logs without the VCT enabled for sure. I believe we tried it on the dyno and it still spiked but wouldn't hurt to try again and have the logs I might be able to use some metal cable ties and hold the gate open entirely, I'd need to see about that one. What do we think about these marks on the cap of the actuator? This is where the two parts push together where the diaphragm spring is. To me they look like air has been sleeping past?? Specifically talking about those black stains above the lower rim/lip. They can be rubbed away as if it's just an exhaust stain.

I will endeavour to give it a crack sooner or later. I have the wastegate apart at the moment so I'll replace it with a smaller spring just to see what it does and if I have to go back then so be it. If it spikes to 23 but can then be controlled back to 20, then the gate must not be 100% open... So if it's not 100% open then why can't it drop the boost even further than 20psi (I understand it's not linear). What a headache this whole thing is.

The answer to this would be I followed the documentation from Turbosmart which said each spring pressure could achieve a maximum of 5x it's rated pressure so the included smallest spring being the 6psi had a range up to 30psi. I went with the 12 because I figured it'd likely hover around 15psi as a base pressure however I was obviously wrong. I have a log here that I'll dig out that is purely wastegate and no Mac valve controlling anything. If it can't hold anywhere near 12psi, does that mean the straight gate is virtually wide open during a run? Or am I thinking about this all wrong. I could Tee Piece into the cooler pipe pre intercooler where the wastegate gets its feed, and send that to the ecu and see how that reads, I just don't have a spare pressure sensor currently that's all.

Before I commit to it as I already have the wastegate off the car, would you change it to the 9psi spring instead of the 12, or whack it back on now and try your suggestion? Edit: Actually I might just swap the spring and see what the logs say after another few pulls, as we know it's still spiking without the Mac valve in the picture so I need more data without the Mac valve trying to combat the issue.

Not that I could tell no however we also only used racepaces version of a boost controller, and not an actual Mac valve.

I spoke with Turbosmart on Friday and they said the uptake in Australia has been quite slow because it's not a known item, however they've been selling in huge numbers in the USA so we should have heard reports by now if they were no good surely. While it may be the gate it still begs the question, why did this happen very similarly with the Twin turbos...

Not in front of a computer until later tonight so this is probably the best I can do for now. We are using both ports on the wastegate eith the 3 port Mac valve, I've just changed it to single in the photo as I was trying it out on gate pressure

Not a problem at all Lithium, I appreciate your help regardless. I've pulled a small part of a log where the target pressure was 28psi and it spiked to 36.4psi. I've only just begun using Data Log Viewer so if I'm sending this in the wrong format let me know.

I built this engine approximately 12 years ago so my own head (brain) is a little grey on the exact hardware in the RB head, however what I recall is. Stock RB25 NEO TURBO Intake Camshaft HKS 260 degree Exhaust Camshaft (R34 GTR) RB25 NEO Turbo Springs I ported/removed the exhaust stud humps found in the RB25 head so theres less turbulence but it wasn't ported/polished properly, just a hump removal. I've attached two pictures of the before and after to illustrate. The ECU gets its boost reference from the nipple on the rear of the head on the intake side, behind the fuel rail. The wastegate gets its boost reference from a nipple on the cooler pipe immediately after the comp cover. Could a decent pressure drop across the intercooler cause the wastegate to be seeing a higher PSI than what the ECU is seeing, and thus it can't control it accurately and quick enough? We ran a line to the actuator and watched it open and close using an air compressor, while we didn't have a gauge on the line to see when it was cracking open, it was opening smoothly. I just removed the gate now and even though the documentation says you need to open it in a vice due to preload (which I did), there wasn't any preload on the cap, which is something we noticed straight out of the box as well when new. This silver cap internally is threaded to the actuator rod that runs out the bottom of the straightgate. Not sure how I'm supposed to get this spring out to be frank.. Potentially but everyone else doesn't appear to have to stop at 500kw because of 6boosts design. I would, but I think I'm getting to that point where if I'm going to do the head and make another 100kw, then I'm going to need a fancy gearbox and quite a few other things and 10k becomes 20k becomes 30k within a few months. I'm not necessarily sold on the idea just yet that the head is restrictive at 4000rpm (and what.. 300kw?) and yet doesn't seem to be restrictive at 7000rpm when it's making 500kw, however I'm obviously not closing the door on that theory.

It could be in the tune but in both cases it couldn't be completely solved or eliminated by some of the best tuners in victoria so I'm DOUBTFUL that it's in the tune or ECU but stranger things have happened of course. I've pondered that theory too but is there any theories that thinner and smaller ports overall would cause a turbo to spike? I would've thought it would just restrict it in general if it was small enough to make a difference. I wouldn't expect it to make a different at what is essentially sub 300kw at 4000rpm anyway. I think the next step is going to have to be the 6psi spring to rule out the idea that the gate is cracking open far too wide initially. At least that is the cheapest (free) thing to check initially.

Not without making up a new screamer pipe from scatch I don't think based upon the angles of the current return. Backpressure shouldn't be an issue though as the straight gate isn't affected by backpressure in the same way that a poppet valve is, and on top of that the exhast system is 4" all the way through so there should be minimal pressure if any to begin with.