First/Second Post

[svenskalice]

Hello! I'm new here, I have an R33 GTST that is currently being finished up! Last year was pretty rough, blew two stock turbos so I decided to build the car. Has been down since November, but I get it back next weekend!

[Duncan]

Welcome Alice......hope you have a bit more luck from here on!

What was done in the build?

 

[silviaz]

On 3/3/2025 at 5:49 AM, svenskalice said:

Hello! I'm new here, I have an R33 GTST that is currently being finished up! Last year was pretty rough, blew two stock turbos so I decided to build the car. Has been down since November, but I get it back next weekend!

Welcome! How much psi were you pushing I'm curious if you've blown 2 turbos? I was overboosting at one stage and went over 14-15 psi, surprised I didn't blow it right then lol.

[GTSBoy]

8 minutes ago, silviaz said:

I was overboosting at one stage and went over 14-15 psi, surprised I didn't blow it right then lol.

It's a lottery. I ran my RB20 turbo at 17 psi for a while. It survived, went on to run for many many more years at 14 psi. Was still good when the engine was pulled to make way for the big block.

RB25 turbo died as it came onto boost, never having been over 12 psi in my 10+ years of using it.

[silviaz]

19 minutes ago, GTSBoy said:

It's a lottery. I ran my RB20 turbo at 17 psi for a while. It survived, went on to run for many many more years at 14 psi. Was still good when the engine was pulled to make way for the big block.

RB25 turbo died as it came onto boost, never having been over 12 psi in my 10+ years of using it.

From what I remember, the rb20 turbos can take a bit more boost than the rb25det engines? Thought I read that somewhere for some reason.

[GTSBoy]

43 minutes ago, silviaz said:

From what I remember, the rb20 turbos can take a bit more boost than the rb25det engines? Thought I read that somewhere for some reason.

Yeah, but it's not "boost" that they can take more of. Well, I guess it actually is. They are the same turbine, driving different compressors. I think the failure is more of a turbine temperature and (probably mostly) speed thing. I think the RB25s end up needing the turbine to reach higher speeds in order to drive the compressor to achieve the same boost level. So they will fail at lower boost on a 25 because they've actually reached the same failure speed that they do on a 20 at a higher boost pressure. If that makes sense?

[MBS206]

1 minute ago, GTSBoy said:

Yeah, but it's not "boost" that they can take more of. Well, I guess it actually is. They are the same turbine, driving different compressors. I think the failure is more of a turbine temperature and (probably mostly) speed thing. I think the RB25s end up needing the turbine to reach higher speeds in order to drive the compressor to achieve the same boost level. So they will fail at lower boost on a 25 because they've actually reached the same failure speed that they do on a 20 at a higher boost pressure. If that makes sense?

The "ideal/formula" that used to be touted was death of the turbo is going to be caused by a combination of 3 things.

Heat

Speed of turbo (boost level you're pushing)

Time

 

Basically, you can get away with high heat and high boost for short periods. But start doing long hard pulls, or circuit driving etc, and now you've increased time as well which will shred things. From memory when Adrian was drag racing he was running 17psi, on a stock turbo, and running insane speeds. But he also had other additives helping in the setup too.

Some people have success at 14psi for a while, while others due to pushing the cars hard for long periods opt down to lower temps.

But also, generate a lot of heat (let's say bad tune), for a long time, and you'll be okay, until you try to spin that little guy up slightly. It's the one advantage of dumping a lot of fuel in, you'll be reducing EGT a bit and helping with the heat portion of the above 3 areas.

 

And these days, stock turbos are that old that there's the possibility of just outright failures due to material age. I'm not shocked that even when used in factory spec that a stock turbo fails when 30 years old. It's a worn out "precision" "balanced" performance item, that's likely no longer precise, or well balanced

[GTSBoy]

4 minutes ago, MBS206 said:

The "ideal/formula" that used to be touted was death of the turbo is going to be caused by a combination of 3 things.

Heat

Speed of turbo (boost level you're pushing)

Time

 

Basically, you can get away with high heat and high boost for short periods. But start doing long hard pulls, or circuit driving etc, and now you've increased time as well which will shred things. From memory when Adrian was drag racing he was running 17psi, on a stock turbo, and running insane speeds. But he also had other additives helping in the setup too.

Some people have success at 14psi for a while, while others due to pushing the cars hard for long periods opt down to lower temps.

But also, generate a lot of heat (let's say bad tune), for a long time, and you'll be okay, until you try to spin that little guy up slightly. It's the one advantage of dumping a lot of fuel in, you'll be reducing EGT a bit and helping with the heat portion of the above 3 areas.

 

And these days, stock turbos are that old that there's the possibility of just outright failures due to material age. I'm not shocked that even when used in factory spec that a stock turbo fails when 30 years old. It's a worn out "precision" "balanced" performance item, that's likely no longer precise, or well balanced

All of that is absolutely true. At any time in the history of these turbos the lottery has always been that it could die at stock boost treated exactly as the factory intended, or it could die when pushed to 10, or 12, or 14, or 16 psi, after a short time, or a longer time, or it could last seemingly forever. You have the combination of all the possible statistical (probably) normal distributions of manufacturing tolerances and quality outcomes, on top of the statistical distributions of failure modes (which might be normal, but are probably biased, like Poisson distributions). You get the lucky turbo and you can beat on it for years. You get the really unlucky turbo and it will crap itself as it rolls out of the factory gate. And every possibility in between.

But you can definitely still kill the lucky turbo. It's just that most people didn't try, once they knew they really shouldn't try.

[MBS206]

50 minutes ago, GTSBoy said:

All of that is absolutely true. At any time in the history of these turbos the lottery has always been that it could die at stock boost treated exactly as the factory intended, or it could die when pushed to 10, or 12, or 14, or 16 psi, after a short time, or a longer time, or it could last seemingly forever. You have the combination of all the possible statistical (probably) normal distributions of manufacturing tolerances and quality outcomes, on top of the statistical distributions of failure modes (which might be normal, but are probably biased, like Poisson distributions). You get the lucky turbo and you can beat on it for years. You get the really unlucky turbo and it will crap itself as it rolls out of the factory gate. And every possibility in between.

But you can definitely still kill the lucky turbo. It's just that most people didn't try, once they knew they really shouldn't try.

Yep, agree with all of the above added on too.

I just love the age old "what boost were you running?" Question without getting any other surrounding data. IE, may have ran 20psi, and lived for 12 years, but it was an 80 year old granma driving it to Bingo once a week and never took it over 2500rpm.