I see them all the time xx/xx/xx

what are the numbers and what do they mean

 

For example:

A super phat shaft 66 would a be a 66/14/71

That means it has a 66 millimeter diameter compressor wheel measured at the compressor inducer(air inlet) (looking at the front of the turbo).
Larger compressor wheels can move more air more efficiently but they are a double edged sword and can sometimes run into surging conditions when there is not enough turbine power to keep the wheel turning at a proper speed.
Smaller wheels will perform better with lower rpm's and less power driving the turbine but will be limited in the cooling and top end department.

The 14 (14cm2) represents the turbine (hot) housing size in Holset terms (this is exclusive to Holset turbo's but is used today so people can somewhat get a handle on the size of the current after market Borg Warner turbo housings).
Most turbo housings are measured in A/R sizes (ie .80 .90 1.28 etc). Stock 3rd gen 5.9 turbine housings are 9cm2.

Larger turbine housings (ie 14, 16, 18 etc)will allow for more exhaust flow and cooler EGT's at throttle and more power, efficiency on the top end. However larger housings can slow efficiency on the bottom end increasing lag time. Larger housings can also increase cruising and off throttle egt's.

Smaller housings (like a 12,13 etc.) will offer less lag time and better throttle response, with lower cruising and daily driving EGT's but will sometimes reduce wide open or top end efficiencies.

The last number represents the diameter of the turbine (hot wheel) at the exducer (outlet).
That means it would have a 71mm diameter wheel at the rear.

Larger the turbine wheel the more exhaust can leave the engine and the more drive power can be used efficiently to drive the turbo however this is also a double edged sword. If you have a large turbine wheel sometimes you will run into surge condition in which there is not enough turbine speed to power the compressor.
Smaller wheels will run at rated speed more of the time and will provide better throttle response but once again will suffer on the top end.

 

I love it when someone gives a good explanation so all I have to type is "what he said" instead of the whole thing.

Good explanation in terms everyone can understand.

 

Thanks for the great explanation.

 

How cool to have someone like PourinDiesel on this site. What he says you can take to the bank, or instead, like me, go out and spend money on something you learned from PourinDsl. Thanks PD, glad you are on here.

 

Thanks guys.
I appreciate the kind words.

Sorry for the terrible English. I patched that post together

 

That was a great post, Thanks.

 

Fantastic explanation! If I could add to your reputation I would!

 

Good explanation!

 

thanks,
that was a great reply.
been reading on turbos, but was never sure what i was reading

 

Excellent!!!!!!