[Shane@DBPerformance]

A/R is just a ratio like trim, they don't mean a whole lot unless you are comparing to other housing in the same family. A .64 A/R T25 housing is tiny compared to a T3 .63 A/R. A T3 .82 A/R probably falls into line some where between a .58 and .68 T4 exhaust housing for spoolup/power. The PTE Mitsu .63 A/Rs are a tad bit smaller than the PTE T3 .63A/R. A Garrett GT42R 1.01 A/R divided T4 housing sounds huge, but it's really comparable to a T4 .68 undivided.

Spoolup can often more come down to cams, exhaust manifold design(huge), intake manifold, boost leaks, ignition timing, etc. The worst looking pile of shit true log manifold will usually spool a turbo the quickest, but have a big performance hit in the upper RPMs. Long runner fancy top mount manifolds no matter how perfectly they are design are usually laggy, which is fine if you need to make power from 8000-10000 RPMs.

I did one car with 3 different kinds of exhaust manifolds on the same turbo and saw 1000+ RPM spoolup difference from the worst to the best. eBay manifold spooled ok, but power was blah. Tried a fancy top mount, gained about 40hp, but 500 more rpms of lag. Tried a short runner tubular and made the same power as the top mount but spooled 1000 rpms quicker than the top mount and 500 quicker than the eBay.

I haven't had any BW or Holset turbos on the dyno that really blew me away as spooling way faster or making huge amounts more power. Some of those turbos are quite good, but not anything magic. The huge BWs(S372 and bigger) do spool pretty good for their size, but we aren't talking worlds different than others. It's hard to compare different cars, dynos, setups, etc over the internet to each other. The FP setups are usually noticably quicker spooling than comparable Garrett setups, but a lot of people use the FP exhaust manifold with them too.