viper_boy403

iTrader: (1)

I'm running an RB25 OEM turbo on my H22 and was having an interesting discussion with one of the guys on zilvia about this; this turbo has a ceramic turbine wheel that is known to not like to run over 1 bar before it self-destructs. However, I've been told this is only the case on an RB motor and other large(ish) displacement engines (for imports at least, heh)

The reasoning behind their statements being that the turbo doesnt need to spin as fast on a smaller engine, such as an H22, compared to an RB25 to produce the same boost pressure. Is there any truth to this?

Mikey3000

boost pressure is a function of the turbo not the engine it's on. an engine that flows more air would spool the turbo sooner, most likely, than an engine that flows less air. an engine's flow is a product of the efficiency of the engine, engine speed, and displacement (there may be more variables). the bottom line is, if the wheel is ceramic and can come apart at high turbine rpm, it'll come apart no matter what engine it's on, provided that engine is a typical road-worthy engine.

i don't think a turbo manufacturer would design a turbo who's turbine or compressor wheel wasn't strong enough to handle the tensile loads created on it due to high rpm.

Schister66

This is a tricky discussion and I hope someone like TheShodan chimes in.

At any rate, 10psi on one setup and 10psi on another doesn't translate into the same wheel rpm since the efficiency of the setup can vary greatly. Since boost is a measure of resistance in a system, the turbo could be spinning a a variety of ranges to make a given pressure. Think about an extreme example where you run a turbo into open air where there is effectively zero resistance...the turbo will not build boost no matter how fast the wheels spin. This is the same case with putting a turbo on a honda that came from an engine/setup with more resistance.

If you got this turbo from a setup that makes for example 10psi at 50,000 rpm turbine speed and you put this on your H22 which flows better...you may make 10psi at 75,000 rpm. You're getting the same pressure but a different amount of flow. This is the reason that compressor maps look the way they do. They are a pressure over flow with overlayed rpm ranges. If you look, the rpm lines are not linnear, but rather change throughout the compressor map.

I hope this makes sense...

viper_boy403

iTrader: (1)

Thanks for the great info guys, that totally makes sense. I had a general idea of the theory behind it but couldnt really put it into words that sounded right lol.

Good stuff

Bailhatch

Well they did. The JDM version of the 2jz has the same issue with fragile turbine wheels along with a few other OEM turbo cars. Sucks to not be able to just turn up the boost.

Mikey3000

interesting. thanks for the info.