Machining Turbine Housings

[BLSTIC]

Had an idea recently. I know some turbochargers have a small turbine housing for reasons of lag reduction, but this isn't always best for peak power because it means that there is a lot of pressure between the exhuast valve and the turbine. If lag wasn't a concern (as in you were happy to trade low end boost for a higher peak power) you would use a larger turbine housing, but sometimes cost is prohibitive or they are simply not available. I'm wondering about machining the outlet port of the turbine (not sure on exact name) larger to reduce it's effectiveness (by uncovering more of the turbine than is normally exposed). I'm figuring it should reduce the pressure drop needed to achieve a given shaft speed, while needing more flow through it, and so increase power. You couldn't do this too far (as there's only so much material there), and it isn't the best way to do reduce back pressure, but it should at least have an effect.

Thoughts?

[Dorifta]

dont think so, i believe it would weaken the structure, especially when the exhast is hanging off there and studs in there, the insides yes, but i doubt anyone would would do it , u could only get 1 mm or 2 and that barely make any difference. I personally wouldnt go there,, but i could be wrong,, ur better of doing the insides of the housing

[Cartman]

its late for me.. but isnt this known as back cutting or something like that... cant remember properly.. but if i've read what you want to do in the way i think i have it'll increase lag while providing minimally more flow up top

[aphid]

cropping

yeah it's common practice however you really want to put some decent research and know what you're aiming to achieve long before you start machining, essentially it's the poor mans way of getting a larger A/R on the turbine housing!

EDIT: ahh you mean machining from the exhaust flange!! I think you'd have to be VERY careful there as if you went even slightly too far the exhaust gas would simply bypass the turbine wheel creating massive lag with minimal pay off =(

Edited October 2, 2009 by aphid

[discopotato03]

There are a couple of ways to reduce the manifold or turbine inlet pressure but none are exactly cheap/easy .

Increasing the exducer size or trim is one way but you need to find/buy/fit .

Increasing the turbines exducer tip height makes for a wider nozzle passage but still find/buy/fit .

A lower number of turbine blades is another because you open up the gaps between the blades .

Provided the turbine housing casting is beefy enough you can extrude hone the internal volute passage .

Not always but usually this housing size problem arises when an OEM turbo has a unique application specific casting shape and was only available in one size . Generally provided the exhaust manifold has a reasonably common mounting pattern alternatives can be found .

Do you have a specific example of a housing that you'd like better flow through ?

A .