How does small compressor housing affect the wheel map?

[tryingbe]

How does the smaller compressor housing, ie T4 50 wheel in T3 .42 housing, affect the compressor wheel map?

Laggier? Less laggy?

[puppet]

I don't think it matters all that much from what I've read. I remember reading a post by Larry ... the fella making 500+ HP in a Spirit ... pretty sure he ran a T4 wheel in both housings, dyno'd the same.
Apples to apples boost level will probably see higher outlet temps in the smaller housing though. Don't know how much.

[contraption22]

Higher outlet temps... poor spoolup. This isn't theory, or conjecture, this is personal experience.

[jckrieger]

Higher outlet temps... poor spoolup. This isn't theory, or conjecture, this is personal experience.

I agree. Putter has experienced the same laggy thing. I think he's getting 20psi by say, 5000+ RPM with his on a 2.2L.

My 60 trim in the native housing spools faster than the 50 trim in the stock housing. The difference is enough that I'd NEVER go back to the stock housing unless it was a T3 wheel.

[Dave]

Maps are plotted off CFMs (though they may show rated HP, but BHP is given off xx% of engine efficiency). The larger housing will flow more CFMs versus a smaller housing.

[jckrieger]

Maps are plotted off CFMs (though they may show rated HP, but BHP is given off xx% of engine efficiency). The larger housing will flow more CFMs versus a smaller housing.

Brake horsepower (bhp) is the measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump, and other auxiliary components. Thus the prefix "brake" refers to where the power is measured: at the engine's output shaft, as on an engine dynamometer. The actual horsepower delivered to the driving wheels is less. An engine would have to be retested to obtain a rating in another system. The term "brake" refers to the original use of a band brake to measure torque during the test (which is multiplied by the engine RPM and a scaling constant to give horsepower).

What you said makes no sense at all. It would be correct to use brake horsepower when sizing the turbo though, as you need to know the engine's power output, not the useful output you get to the tires.

[Dave]

Power is a function of efficiency. If you read Maximum Boost there is no relation in the choice of a turbocharger in regards to brake horsepower. Just sharing what I read. I just slapped on a known well working before I knew how to choose one. I'm not pronounced on how to properly choose one, I need to reread the chapter.

[jckrieger]

Ok, that makes more sense now. You're talking about going the other way around... BHP to CFM. I was thinking you meant BHP was a calculated value from its actual power output. You're right, If you know BHP you can calculate CFM if you know the engines BSFC and volumetric efficiency, among other factors

[Dave]

Ok, that makes more sense now. You're talking about going the other way around... BHP to CFM. I was thinking you meant BHP was a calculated value from its actual power output. You're right, If you know BHP you can calculate CFM if you know the engines BSFC and volumetric efficiency, among other factors

Among lots of other factors. It gets really confusing.

[johnl]

So ..... a GNX wheel, or a S70 wheel, in a T3 cover is gonna be more laggy, than a standard/small T4 wheel in a T4 cover?

[jckrieger]

So ..... a GNX wheel, or a S70 wheel, in a T3 cover is gonna be more laggy, than a standard/small T4 wheel in a T4 cover?

The S70 isn't terribly large, so it's hard to say how much of a difference the housing would make. I'd say you probably won't lose much response with just a S70 wheel. It's a lot easier to compare housing to housing while keeping the wheel family constant.

[contraption22]

The S70 isn't terribly large, so it's hard to say how much of a difference the housing would make. I'd say you probably won't lose much response with just a S70 wheel. It's a lot easier to compare housing to housing while keeping the wheel family constant.

A GN wheel is going to be a T3 wheel, so it's really not an issue.

[puppet]

You guys sure your not confusing the comp side with the turbine side? A/R on the comp side means very little having almost no effect on turbo performance.

"Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings."
ripped from the guys that make these things:
http://www.turbobygarrett.com/turbob...o_tech102.html

[jckrieger]

That quote is pertaining to a single family of compressor wheels. The T3 compressor housing is not only a .4x A/R, it's also MUCH smaller in size. The area of the discharge in a TO4 housing is at least 30% larger, so even if you had the same A/R the housing would look much different as a TO4.

[Directconnection]

I agree. Putter has experienced the same laggy thing. I think he's getting 20psi by say, 5000+ RPM with his on a 2.2L.

My 60 trim in the native housing spools faster than the 50 trim in the stock housing. The difference is enough that I'd NEVER go back to the stock housing unless it was a T3 wheel.

What turbo? That has to suck for anything less than a high rpm drag race engine. 5k.... ouch.

[puppet]

That quote is pertaining to a single family of compressor wheels. The T3 compressor housing is not only a .4x A/R, it's also MUCH smaller in size. The area of the discharge in a TO4 housing is at least 30% larger, so even if you had the same A/R the housing would look much different as a TO4.

I don't think the quote means that at all. We wouldn't look for a larger housing within the same family of wheels so why would they mention that ... especially since they're contrasting the A/R choices of the compressor side with the turbine side (very next section of same article).

Anyhow, less efficient from a heat standpoint I can see ... more laggy? nope. Common sense says that we're filling a small space with a bigger wheel. Boost will come on sooner. Might even be uncontrollable if the turbine side is too small for the comp wheel. Just for discussion let's say we could put a small wheel inside a big housing. What would that do to our boost? I'll go out on a limb and say it'll reduce boost and be laggy. If that's true the reverse should also be true ... no?

Not arguing ,,, just can't wrap my head around the "more laggy" part.

[contraption22]

Anyhow, less efficient from a heat standpoint I can see ... more laggy? nope. Common sense says that we're filling a small space with a bigger wheel. Boost will come on sooner. Might even be uncontrollable if the turbine side is too small for the comp wheel. Just for discussion let's say we could put a small wheel inside a big housing. What would that do to our boost? I'll go out on a limb and say it'll reduce boost and be laggy. If that's true the reverse should also be true ... no?

Not arguing ,,, just can't wrap my head around the "more laggy" part.

I don't know if the reverse is true. I don't know the theory or the physics behind it. The reality is tho, a T4 compressor wheel in a T3 compressor housing is laggy.

I had a "half-assed hybrid" turbo: a T04E 50-trim compressor in a T3 compressor cover with a S2 turbine wheel and a .63 turbing housing. The thing was so laggy on my 2.2 it was just about useless.

Going from that to a turbo with the same exact wheels, but with a T04E compressor housing in place of the T3 housing netted much faster boost response and more top end power.

[Frank]

I see your point puppet, but you gotta remember that what goes in, must go out. Remember that the compressor wheel is driven off of the turbine and depending on "how well the combustion cycle goes", is a direct contributor to the forces thru the turbine house. So the more efficent the motor, the better the energy in the exhaust. The more efficent the motor, the less the compressor housing has to work.

[jckrieger]

The reason I interpret the article as keeping the housing family constant is because you couldn't even think about changing turbine housing families for a given turbine wheel. I know for certain Garrett's factory hybrid turbos don't offer a T3 compressor housing option... period.