CT26 Overboost Problem (56K warning)

[Gold28]

If that is the case, maybe you could change the actuator location and push rod length to open the gate further. Ie change the mechanical advantage that the actuator has on the gate.

Alternatively.......

I wonder if using an actuator with a smaller pressure would help. It would open the gate sooner and be at full extension earlier. You could then use a boost controller to set your peak.

Just brainstorming for ya..........

[The Real Roadrunner]

problem is the wastegate holes dont physically flow enough, so it wont matter how much you open thhe gate it wont work. (tried it and have the logging to back it up)

its not the actuator pressure as it creeps higher and higher as you rev the engine more. ie the more gas flow the engine makes the worse the problem gets.

cheers
linden

ps i just got this turbo back from a few mods so ill give you an update when its on the dyno.

[Gold28]

No I realise that but I was thinking that if you get beter control of the gate and get it opening all the way a little faster then it may have a better chance to regulate the pressure before it spikes to a point where it can't control it.

My thinking is that maybe it might have a better chance at regulating it if it only made 8-10 psi but with the slow acting gatem it spikes to 12 psi or more and is generating too much exhaust gas to regulate.

[Matty P]

Not sure where I would be able to find a wastegate actuator that worked on a lower pressure? The stock Toyota turbos would all be about the same wouldn't they?

As far as I can see, disabling the TVSV should do the trick because I am not getting boost cut in 1st and 2nd, so if I get the same boost level in the higher gears I should not hit it then either.

If that doesn't work, I will either put a restrictor in the exhaust or fit an EBC to try and gain better control over the pressure at the actuator.

Thanks again for all of your assistance (including those I can't rep because the bloody thing tells me to spread the love )

[Gold28]

I am fairly sure the nissan ones are only 4-6 psi but they have an ecu controlled solenoid working them.

Definitly try the TVSV though.

[The Real Roadrunner]

As far as I can see, disabling the TVSV should do the trick because I am not getting boost cut in 1st and 2nd, so if I get the same boost level in the higher gears I should not hit it then either.

it doesnt have the time to build up the pressure in the first 2 gears but third takes a while to wind out therefore providing enough time for it to build pressure.

turbos on now so ill find later this week.

cheers
linden

[Matty P]

True - but I still think that if the wastegate is opening 2psi earlier, there must be less chance of overboosting!

I can't discount the fact that I had a leak between the actuator and the TVSV as well. That little hose is a real b!tch to get on Blocking off the TVSV should assist with that.

What did you get done to your turbo Roadrunner? Were you experiencing overboosting issues as well?

[The Real Roadrunner]

What did you get done to your turbo Roadrunner? Were you experiencing overboosting issues as well?

all 21psi of it, no matter what we did it wouldnt drop.
i even went to the extent of putting a piece of sheetmetal (with a 50mm hole in it) between the flange on the dump and the exhaust to see if it would go away but alas it was still very much there.

ive just had the wheel backcut (or clipped as some would say) so we shall see if it solves the problem in the next week.

cheers
linden

[Matty P]

Well I have had the turbo looked at to determine whether it requires a rebuild.

Turns out that there is damage to the exhaust wheel (chunk out of a blade ) and shaft movement suggesting damage to internal bearings. In short - requires a rebuild!

Also, they reckoned the wastegate was opening with just 3psi of pressure, which would suggest to me that I should be getting low boost rather than overboosting!

Anyway - currently looking into options for my turbo - so hoping whatever happens there will help with the overboosting issue

[OnAll-FOUR]

Thanks Guys for the input - it is greatly appreciated

I considered external wastegate, but that really seems like overkill for a mild stock setup. If I was putting on an aftermarket turbo I would, but for CT26 it seems like a waste.

Just to clarify, the boost (according to my Autometer guage at least) does not spike but seems to build slowly. The shuddering occurs even when the gauge only shows low boost (ie. less than 10psi).

One solution may be to disable the Turbo VSV. As I understand it, this would cause it to revert to the lower boost setting in all gears. The problem does not seem to occur in 2nd gear, so perhaps this might manage to keep it below boost cut?

I am also planning to get the turbo inspected to see if it needs a rebuild. It is 150,000km old, so may be a little worn out. Will also try to make sure that the wastegate is opening properly (once I work out how to do it without measured compressed air )

Thanks again guys!

Food for thought, I have just recently fitted the aussie dump pipe and I have no overboosting problems persay. It creeps slighty at higher RPM but nothing like your experiencing and all I have is a manual bleed valve.

I had massive boost control problems until I DID diable the Turbo VSV. This is a must do if you want to control the boost althoug as you have said you will have to correct it with a boost controller.

The Turbo VSV bleeds air off the waste gate to give you the higher boost in the higher gears. This created havoc when I installed my boost controller. After cutting the pipe that goes to the turbo VSV from the wastegate and blocked both ends. Then I put my boost controller in the usual spot in between the turbo and wastegate and it has been great since.

[Matty P]

Thanks for that Ben.

What is the rest of your exhaust like? I found that I only had a problem when I did the rest of the exhaust. 3" mandrel bent with 3" hiflow cat etc.. I think being so free flowing is contributing to it.

Someone suggested the dump might have been causing the problem by not flowing well enough from the wastegate. I noticed the flange overhanged the pipe in that area, so I ground it back a bit to try and improve the flow.

Here's the result:


In addition to this I will be blocking off the TVSV and my turbo has been freshly rebuilt. Hoping these things will help!

[OnAll-FOUR]

I have only done the dump pipe so maybe I haven't experienced the worst of it yet. I plan to do this soon so I will let you know.

[Matty P]

Well my plan of attack for resolving the overboosting issue was threefold:
1. Mods to Aussie dump as shown above to improve flow around the wastegate.

2. Turbo freshly rebuilt, courtesy of Turbologic (thanks guys )


3. Blocking off the hose leading from wastegate actuator to the Turbo VSV to limit boost in 3rd-5th gears


The result? So far so good. On my test drive it boosted to 10-11psi in all gears and no signs of the hesitation that was occurring before during overboosting.

Not sure which of the above three items was most effective!

[OnAll-FOUR]

sweet good to hear. My bets would be the hesitation was probably due to the fubard turbine and the spiking due to the vsv not being blocked and/or the bit you cleared around the waste gate.