I see all the turbos have an a/r .xx, what does it stand for? What does it do? Thanks.

 

A/R = Area/Radius

Area = area of the inlet of the turbine or the outlet of the compressor

Radius = radius from the centre of the turbo wheels to the the centre of the area of the turbine inlet or compressor outlet.

Compressor performance is comparatively insensitive to changes in A/R. Larger housings can be used to optimize low boost applications.

Exhaust performance is greatly affected by changes in A/R. A smaller A/R increases throttle response and a larger A/R increases overall power.

General description from the Garrett site Turbo Tech 101

 

That would be AFR not A/R...LOL

 

Lol...delete delete delete!!!

 

I think I get it now. Like a 5000lb truck from a roll would want a smaller a/r to build boost quick and make the torque to get a bunch of weight going. Where a lighter vehicle (camaro) from a roll would want a larger a/r to pull hard on the top-end. Right?

 

Maybe. It depends a lot on how you size the turbos. A lot of guys size turbos the way they size cams IMO -- too big. Yeah, a smaller turbo will make less comparative power, but it's that same old "under the curve" argument.

If your turbo is too big for the application, you will get crazy *** lag -- but since lag is expected from a turbo, a lot of people just accept it or try to fix it with a smaller A/R housing (which chokes the turbine effectively on the top of the efficiency curve).

Soap box aside, with the turbo sized "correctly", a smaller A/R gets you into boost sooner, but at the expense of top end power. A larger A/R gets you into boost later, but with more top end power.

I have what I think is going to be small A/R housings on my twins now because I wanted Radix like lag on the street (where 1000+ hp is a liability anyway ), if I am not satisfied with what they crank out, I will put on two larger housings for glory track / dyno days.

To put it another way, I couldn't do variable vane technology like on diesel rigs (where the computer controls the vanes), but wanted similar performance -- grunt when having fun, powah when being serious about things.

 

hell yeah lol.