1jzgte vvti removing cat

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1jzgte vvti removing cat

Postby JT » Tue Mar 06, 2018 5:13 pm

Brother has a clean factory spec chaser with single turbo ct15b 1jzgte. It looks it really good nick, still has factory air intake, ecu, exhaust, i/c etc and runs great. He's in the process of converting to manual including manual ecu.

He's read about people having an issue with the turbos once the cat converters are removed. I've done some research and it seems a bit hyped up but I could be wrong. A few people are saying only removing the cat will cause the seals on the turbo to start leaking within a few months. I can understand if you let the boost above 14-15psi, poor tune and drive it hard, its going to put a lot more pressure on the ceramic wheels.

On this engine/turbo combo how does the increased flow relate to shaft speed if he was to keep it at about factory boost?

Does anyone have experience with these ct15b turbos running 12 psi on factory 1jz for extended periods with a free flow exhaust? Is this likely to cause the turbo to shit itself?
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Re: 1jzgte vvti removing cat

Postby matt dunn » Tue Mar 06, 2018 10:19 pm

You would possibly find that if you free up the exhaust you may not be able to keep the boost standard,
as the extra flow will raise the boost.
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Re: 1jzgte vvti removing cat

Postby JT » Wed Mar 07, 2018 8:17 pm

Yeah we figured that was likely to happen. My question about keeping the boost factory could probably have been worded better..

How much of an increase in load on the ceramic wheels and bearings is there likely to be, if the boost was at a similar level but flowing more due to the removed cat?
If the boost was to stay at the same level, ie boost controller, how much energy or wheel speed is the turbo seeing?

As you say, its likely the boost will increase (a few psi max?) without making any other changes. Is this likely to be a major issue on ct15b turbo in reasonable condition?

I'm trying to identify what the actual issues are with removing the cat and what causes the weak points of this turbo to fail. Tired of reading "if you remove the cat your turbo will definately fail!" without all the facts.
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Re: 1jzgte vvti removing cat

Postby BlakeNZ » Wed Mar 07, 2018 9:45 pm

a boost controller can not help you lower boost back down to factory levels.
Sometimes a big exhaust will help the ceramic wheel last longer, as the exhaust gases can escape more easily, so the wheel is not subject to as much heat.
Why does he want to remove the Cat? I'm guessing he wants more power. Freeing up the exhaust will usually result in more power, due to more boost. This small increase in boost comes with an increase in shaft speed.
However, sometimes you can increase boost without causing turbo shaft speed to increase. How? by allowing the compressor side of the turbo to breathe more easily, IN and OUT. eg, a more free flowing air filter and intake pipe, or a bigger better flowing intercooler(less restrictive) and intercooler pipework
But let me tell you this, the ceramic turbos on a (say) 20 year old motor, are a total LOTTERY. Some people can run 19 psi for years on them, while others last 3 days at 14psi boost once a big exhaust is fitted. It depends on factors such as historical maintenance, mileage, driving style, and luck. A brand new turbo(if you could source one) will inevitably last a lot longer on a car with increased boost, if only for the fact that the ceramic wheel has been heat cycled so fewer times, and the new bearings don't allow the shaft to move sideways and cause the exhaust wheel fins to touch the housing.
There are steel wheel upgrades available for the CT15B ceramic wheel if he doesn't want to run the risk.
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