Max Boost For Standard R34 Gtt Turbo

[Bugzs15]

When I broke the turbo in my R33 I found pieces of compressor wheel in my intercooler, doesn't take much imagination to guess how it might get to the engine!

yeah the compressor wheel makes sense, just always wondered how the exhust side makes it back inside the engine. but based on the threads in this forum seems to be quite common.

[GTSBoy]

It's because the turbine is spinning at about a bazzillion RPM when it dies. The rotation inertia in any given piece of turbine blade is many many times more than is needed to make it travel backwards against the flow of exhaust gases. A couple of bounces in the collector and you could easily project a piece into cylinders 4, 5 or 6 ....probably more so 4 or 5.

RB26s have even shorter and straighter lines of sight between the turbine housing and their closest cylinders. That's what makes them more prone to copping a bum full when they blow.

[Bugzs15]

so isn't the propeller on the exhaust side spinning the same direction as the flow of exhaust gasses and would just be flung into the dump pipe and is in a seperate housing to the intake (cold) side of the turbo?

or is it because of the design of our particular turbos that broken shrapnel bouncing inside the turbine shell is flicked back into the engine through the intake side of the turbo by the nylon compressor wheel which is sitll intact, thus causing engine damage.

i am just tring to undersatnd the weakness of the turbos in our cars, your explanation definitaly made it easier to understand though, appreciate it.

It's because the turbine is spinning at about a bazzillion RPM when it dies. The rotation inertia in any given piece of turbine blade is many many times more than is needed to make it travel backwards against the flow of exhaust gases. A couple of bounces in the collector and you could easily project a piece into cylinders 4, 5 or 6 ....probably more so 4 or 5.

RB26s have even shorter and straighter lines of sight between the turbine housing and their closest cylinders. That's what makes them more prone to copping a bum full when they blow.

[GTSBoy]

In the specific case of turbos mounted on RB engines (** see note below) the turbine shaft is aligned parallel to the engine. That is to say, the turbo shaft is parallel to the axis of the case, or the crankshaft. The turbine is thus spinning around that axis. Now imagine that the only parts of the car/engine/turbo arrangement that are still present are the turbo shaft, the turbine and the exhaust manifold. We have subtracted the rest of the turbo and engine and car from the picture, so you can see a turbine spinning madly a few inches away from the outlet of the exhaust manifold.

Don't make the mistake of thinking that the exhaust gases flow through the turbine as if the turbine was a desk fan. The turbine is not an axial flow device. The exhaust gases flow into the turbine by entering at the tips of the blades and flowing inwards towards the shaft. It is only once the exhaust gas has started flowing inwards that it can then start to flow out through the exducer, which is parallel to the shaft. The exhaust gases make a kind of 90° direction change in order to follow this path. It's actually a little more complicated than that because the gases first flow around the volute of the housing and they end up flowing inwards through every blade opening at the same time.

If at any time the turbine were to disintegrate then you can imagine that the centrifugal force would send the broken fragments flying directly away from the turbo shaft in all directions. These directions are up, down, left and right, and all angles in between. They travel radially away from the shaft. The outlet of the exhaust manifold is located radially away from the turbo shaft. Now you can imagine the turbine housing back into the picture. The fragments now cannot travel very far away from the shaft because they are trapped in the volute of the turbine housing. They will bounce around. There is one direction, though, where they are fairly free to travel away from the shaft, and that is in the direction straight back out through the inlet to the turbine housing and through the outlet of the exhaust manifold. Some pieces have an opportunity to make that trip direct, or with only a slight bounce. Pieces that flow off in other directions still have the opportunity to bounce a couple of times in the housing and make their exit back through the in door, instead of out through the exducer. All in all, there is a reasonable chance of getting pieces up into the exhaust manifold, and depending on the layout of the manifold (ie the differences between RB26 and RB25) you stand varying chances of getting a bit to go all the way up an exhaust port and into the engine itself.

At no time is there any question of the turbine pieces making it into the engine via a route that includes the compressor housing and the intercooler. If a plastic compressor wheel explodes then the pieces will have to go via the intercooler to make it into the engine and this somewhat reduces the chances of them making it all the way there without getting stuck. That's a whole 'nother problem.

**This is actually true for the majority of engines, even FWD ones. The turbo is usually mounted on the exhaust manifold so that it is pretty much parallel with the engine. Aftermarket installations may or may not include some angle in order to make the dump work better or a variety of other reasons. WRXs and other similar shitheaps may have the turbo in a strange place. But most are effectively the same as the RB standard installation.

[Bugzs15]

Thanks GTSBoy, makes perfect sense when you think about it actually.

I was just confused as i thought the only way it goes into the engine is via the intake, but pieces flicking back inside through the exhaust manifold is quite possible based on your explanation.

Its a pretty bad design i guess (maybe a longer manifold runner could minimise it), as the chances of a turbo failing is quite likely when they get old, even if you dont run extra boost.

But then something as simple as a leaking radiator hose or a snapped auxillary/timing belt are also likely to blow an engine, so this is just an added risk you need to be aware of when buying a turbo car i guess.

In the specific case of turbos mounted on RB engines (** see note below) the turbine shaft is aligned parallel to the engine. That is to say, the turbo shaft is parallel to the axis of the case, or the crankshaft. The turbine is thus spinning around that axis. Now imagine that the only parts of the car/engine/turbo arrangement that are still present are the turbo shaft, the turbine and the exhaust manifold. We have subtracted the rest of the turbo and engine and car from the picture, so you can see a turbine spinning madly a few inches away from the outlet of the exhaust manifold.

Don't make the mistake of thinking that the exhaust gases flow through the turbine as if the turbine was a desk fan. The turbine is not an axial flow device. The exhaust gases flow into the turbine by entering at the tips of the blades and flowing inwards towards the shaft. It is only once the exhaust gas has started flowing inwards that it can then start to flow out through the exducer, which is parallel to the shaft. The exhaust gases make a kind of 90° direction change in order to follow this path. It's actually a little more complicated than that because the gases first flow around the volute of the housing and they end up flowing inwards through every blade opening at the same time.

If at any time the turbine were to disintegrate then you can imagine that the centrifugal force would send the broken fragments flying directly away from the turbo shaft in all directions. These directions are up, down, left and right, and all angles in between. They travel radially away from the shaft. The outlet of the exhaust manifold is located radially away from the turbo shaft. Now you can imagine the turbine housing back into the picture. The fragments now cannot travel very far away from the shaft because they are trapped in the volute of the turbine housing. They will bounce around. There is one direction, though, where they are fairly free to travel away from the shaft, and that is in the direction straight back out through the inlet to the turbine housing and through the outlet of the exhaust manifold. Some pieces have an opportunity to make that trip direct, or with only a slight bounce. Pieces that flow off in other directions still have the opportunity to bounce a couple of times in the housing and make their exit back through the in door, instead of out through the exducer. All in all, there is a reasonable chance of getting pieces up into the exhaust manifold, and depending on the layout of the manifold (ie the differences between RB26 and RB25) you stand varying chances of getting a bit to go all the way up an exhaust port and into the engine itself.

At no time is there any question of the turbine pieces making it into the engine via a route that includes the compressor housing and the intercooler. If a plastic compressor wheel explodes then the pieces will have to go via the intercooler to make it into the engine and this somewhat reduces the chances of them making it all the way there without getting stuck. That's a whole 'nother problem.

**This is actually true for the majority of engines, even FWD ones. The turbo is usually mounted on the exhaust manifold so that it is pretty much parallel with the engine. Aftermarket installations may or may not include some angle in order to make the dump work better or a variety of other reasons. WRXs and other similar shitheaps may have the turbo in a strange place. But most are effectively the same as the RB standard installation.

Edited September 30, 2013 by Bugzs15

[GTSBoy]

Not a "bad" design, not when you consider the assumptions that Nissan were working under. In Japan most cars only get a short life expectancy on the road. After that they are no longer worth considering because it becomes expensive to keep them on the road. So Japan is far worse (in some ways) than even most other countries and car manufacturers from the point of view of design life of components. Most cars are disposable enough these days (and I really mean from the mid 80s onwards). Jap cars are 10x more disposable, at least from the engineers' point of view. So a turbine that will hold together for much more than long enough at stock boost is not going to cost them (m)any warranties. A few people will wind the boost up and maybe a few will explode that way and get warrantied. That's manageable. As soon as these cars are on a boat to Australia or NZ, they are no longer the problem of the Nissan engineers, so it doesn't matter what sort of foolishness gets done to them.

The fact that the majority of RB20 and RB26 ceramic turbos can live quite a long life at quite a lot more boost than standard says that Nissan didn't do a bad job of over engineering them even with the disposable car mentality.

[niZmO_Man]

Not a "bad" design, not when you consider the assumptions that Nissan were working under. In Japan most cars only get a short life expectancy on the road. After that they are no longer worth considering because it becomes expensive to keep them on the road. So Japan is far worse (in some ways) than even most other countries and car manufacturers from the point of view of design life of components. Most cars are disposable enough these days (and I really mean from the mid 80s onwards). Jap cars are 10x more disposable, at least from the engineers' point of view. So a turbine that will hold together for much more than long enough at stock boost is not going to cost them (m)any warranties. A few people will wind the boost up and maybe a few will explode that way and get warrantied. That's manageable. As soon as these cars are on a boat to Australia or NZ, they are no longer the problem of the Nissan engineers, so it doesn't matter what sort of foolishness gets done to them.

That's probably one of the reasons why USA-spec cars (e.g. USDM JZA80 Supra) got steel wheel turbos.

[Tabs]

I st my gtt back in nz to 16-17 psi and after 15,000kms it did a turbo bearing and through the exhaust compressor blades into the exhaust pipe drifting on a cold motor :S

replaced it with a r33 turbo and dropped it to 14-15 psi and from what ive heard still going strong