Cm870 upgrades

[Lostfarmboy]

Rawze Wrote:Grinding out the outlet port on the cold side of the turbo and polishing it does make for slight gains. Polishing the 90 degree elbow that attaches to it does too. This is true for any model Holset I have seen. The rough cast has its place in creating a wall-flow barrier, and improving flow, but the joint is just not quite big enough, and the bend just steep enough at higher flow rates, causing the effect to become unstable. Polishing out the rough surfaces to a high degree (close to mirror finish) proves to have a better effect in every case I have seen it done, including my own truck when I tried it. - Mine gained almost 0.3 mpg. Very difficult to get gains out of a truck that is already breaking 8+ all the time, so it definitely worked.

Rawze, I for one would be very interested in hearing more about how you did this and what you used to do it.