CT26 Overboost Problem (56K warning)

[richzx]

I don't know if this will help you but I think it might. On SAU there has been a huge thread on the Jaycar boost controller using the factory Nissan boost solenoid to control boost. The thing with this set up is that the solenoid controls the wastgate opening etc and bleeds off air keeping the wastegate shut until the solenoid controlled by the boost controller, wants it to open. Obviously this would work in reverse in that air would be directed to the wastegate to keep it shut would it not? I am about to try this set up in my cressy with 1J and hopefully I have the same success as them.
http://www.skylinesaustralia.com/forums/t61207.html refers.
I hope I'm not barking up the wrong tree but I believe by enlarging or soldering the boost solenoid hole then greater airflow or more restricted airflow can be gained.

I hope this helps. The link contains a seriously long thread BTW.

Cheers
Rich

[The Real Roadrunner]

Yes - I've read about people porting their wastegates to get around the overboosting issue. Sounds like a very 'delicate' operation!

I guess an actuator with lower pressure setting might be a solution - haven't heard of that one before.

as far as porting the wastegate holes goes there's not much delicate about it, make sure you have at least 2mm of overlap for the lap and diegrind the christ out of the rest of it.

lower actuator pressure wont do shite as its a flow problem (factory one is 7psi so if that doesn't hold a lower one wont either)

cheers
linden

[Gold28]

Sounds like the exhaust housing and wastegate were just never designed to flow that much. Porting would help but I think it would be minor at best.

Just out of interest, does anyone know if a 7M CT26 a bolt in solution? Their exhaust should flow a lot more than a 3S CT26.

[The Real Roadrunner]

Just out of interest, does anyone know if a 7M CT26 a bolt in solution? Their exhaust should flow a lot more than a 3S CT26.

With some filling of the 4bolt flange to get the studs to line up, then change the dump flange and rotate the comp cover and mod the actuator to suit, then it fits.

but for all the crap to do that and just put some inefficient not to mention laggy antiquated POS why bother?

with a gt2871 you will see boost earlier as well as having a more efficient turbo that is eleventy million times better in both design and performance and it wouldnt be that much harder to put it together.

not having a go just pointing out a better way to skin the same cat.

cheers
linden

[Gold28]

No fair point, I have never looked into the differences between the two. I had heard that the 7m compressor is a good upgrade for the 3S turbo but that wouldn´t help the wastegate flow.

[Matty P]

a more efficient turbo that is eleventy million times better in both design and performance

Is that exactly eleventy million

Thanks for the suggestions guys.

So there is no support for my suggestion to disable the TVSV? That should prevent the extra 2psi being allowed in 3rd-5th which should make my boost the same (lower) pressure in all gears?

Surely that should enable me to keep the boost below 14psi? Even with that crappy wastegate design

[Gold28]

If the wastegate opens earlier, you ain't gonna make as much power and hence less exhaust pressure, so I guess it would help the problem.

But why would you fight boost creepby sacrificing power???

[Matty P]

I don't think I would be sacrificing power. If I can acheive a fairly reliable 10-12psi max boost in all gears, the car will feel a lot faster than when it hits boost cut whenever it is under load.

Also forgot to mention that I temporarily "solved" the problem a little while back by fitting a more restrictive muffler that I had. Car felt much quicker because it would boost up and not hesitate/shudder when under load.

For some reason the apparent boost cut returned

Reason I am looking to disable the TVSV is that none of the other options are particularly appealing at the moment:

• Porting the wastegate sounds like a lot of stuffing around for possibly little result
• External wastegate seems like a waste of $$$ on a standard turbo with mild power requirements
• Aftermarket turbo is not an expense I want to incur at the moment
• I may fit an EBC at a later date, but I would be happy with mild boost levels at this stage

Thanks again for all your assistance

[MRGen3SW20]

Got the same over boosting problem with my SW20. Got a high flow CT26 boosting up to 21 PSI and obvisouly hitting fuel cut. Checked and tested vaccum lines between compresser and actuator, blocked of vsv line at both ends (second hose off actuator). Checked actuator with 10psi pressure - rod moves fine.


Also got an issue with retarding and advancing timing while boosting in any gear. Feels like crap.

Anyone had these issues b4 cos I am kinda stumped.

[Matty P]

I put a small football pump onto the actuator and the wastegate opened almost fully with just one pump! Not sure how much pressure it was, because it has no pressure guage.

I noticed the actual flap which seals over the wastegate is quite loose - is that normal? It opened quite quickly and then slowly closed - I guess that's what it is supposed to do

So it looks like the wastegate is fine, so my problem is likely a combination of inefficient wastegate design and the effect of the Turbo VSV. Perhaps a slight boost leak somewhere there as well.

With the TVSV properly blocked off, I should be less likely to have a boost leak.

I will give the wastegate area and the fittings a good clean up and lubricate the actuator rod before I put it all back together.

[RobST162]

wastegate flap should not be loose when it's just sitting there... car off etc..

Rally car has a small washer sitting under the wastegate actuator mounting arm and the manifoldy bit where it bolts onto.

This reclaimed the slack in the actuator and tensionsed the gate.

We've had no problems.

[Stomps]

Hey, this is a fairly common problem, with 3s's, 7m's and 2jz's especially..

2j's have only one pissweak wastegate for two turbos which cant cope with excess airflow once an exhaust if fitted..

another solution to this problem is to fit a small restriction device in your exhaust.. only about 8cm long but which restricts the exhaust to about 1.5" in that section... Bolt it into a spot where you have a flange so its like an insert..

The short drop to 1.5" from 3" will not restrict your power much but will eliminate your boost creep problem.. We have recently fitted such devices to a couple of 2j's and a 3sgte MR2..

Its not an ideal solution but it is a shitload cheaper and easier then modifying wastegates or porting housings..

Good luck

Stomps

[Matty P]

Thanks for the input guys

The flap is not loose when the wastegate is closed - but I noticed when it opened that it is a little loose on the opening mechanism. Seems to close firmly once closed.

Rob - you mean that you put a washer on the mounting for the actuator to the turbo housing - to space it out more to take up slack in the actuator arm? There is no slack in my actuator rod, so should not need to do this.

Stomps - I was hoping to avoid having to introduce some more restriction into my exhaust system. I have already put a more restrictive muffler on which seemed to resolve the issue for a while. After paying big $$$ for an exhaust with Aussie dump, hi-flow cat and flexi it would be a bit sad to put a restrictor in it!

It is surprising that the wastegate capacity is so shite considering how much Toyota overengineer other parts of the car

Matt

[RobST162]

ok I understand now. I thought you were saying there was slack when it was shut. Which was just weirding me right out with your problem.

Yeah, we slotted a small washer between the turbo housing and actuator mount because we had some slack (aftermarket dump also).

Rob

[Matty P]

I tested the wastegate using a pump with a pressure guage. Not entirely accurate, but the wastegate began to open at about 8-10psi but did not open fully until the pressure was higher than that (maybe 12-14psi).

Does that sound about normal? Should the gate open fully at 8psi, or only start opening at that pressure?

Also checked that the outlet from the turbo housing was clear and unobstructed. No problems there.