Yes, that's one reason. Also, a smaller wheel flows a lower volume of air than a larger wheel at the same pressure differential(assuming the same wheel design.)
compare a T60-1 http://www.turboneticsinc.com/comp_maps/fig9.html
to a T66
http://www.turboneticsinc.com/comp_maps/t66.html
A T60-1 might make 580rwhp at ~24psi ~= 2.6 PR (this is a stretch for the T60-1)
A T66 will make 580rwhp at ~20psi ~= 2.4 PR
The T60-1's peak efficiency island of 76 percent? is from a PR of 1.5 - 2.0. So if one runs at 2.6 they miss the peak efficiency completely and therefore heat the air more causing less mass of air to be forced into the engine.
The T66's peak efficiency island of 76 percent is from a PR of 1.7 - 3.4 and is nice and wide at 2.4. Obviously it will heat the air less causing more air mass to be forced into the engine.
Steve
compare a T60-1 http://www.turboneticsinc.com/comp_maps/fig9.html
to a T66
http://www.turboneticsinc.com/comp_maps/t66.html
A T60-1 might make 580rwhp at ~24psi ~= 2.6 PR (this is a stretch for the T60-1)
A T66 will make 580rwhp at ~20psi ~= 2.4 PR
The T60-1's peak efficiency island of 76 percent? is from a PR of 1.5 - 2.0. So if one runs at 2.6 they miss the peak efficiency completely and therefore heat the air more causing less mass of air to be forced into the engine.
The T66's peak efficiency island of 76 percent is from a PR of 1.7 - 3.4 and is nice and wide at 2.4. Obviously it will heat the air less causing more air mass to be forced into the engine.
Steve