So everyone has stated that blacktop extractors are larger than the silvertop ones therefore are a perfect upgrade for any 20v S/T owner to get good gains from. You might ask "how can i tell just by looking at them if they're S/T or B/T? Well i thought along the same lines, luckily i had both sitting in my garage. You'll need tape measure and borrow someone's vernier calipers to measure the primary pipe sizes. here are my findings
Here we have two sets of factory 20v extractors, : silvertop on the left and blacktop on the right
If you look long enough or click the pic you might just be able to tell, blacktop has one stud still bolted in for reference.
Primary pipe measurement of silvertop extractors
Pretty safe to say it's 35mm
Measuring Blacktop primary pipe
Safe to say it's 38mm
Measuring Blacktop extractors port size
resulting in 34mm diameter at the flange
Measuring Silvertop Extractors port sizes
resulting in 32mm approximately, was carboned up.
Also measured the S/T head and had 29mm but again was probably due to a build-up of carbon.
Measuring the downpipe where the 2-1 section bolts up, Silvertop
And Blacktop
Both the flange ends are 40mm which could well indicate that the Blacktop extractors can bolt up to the silvertop head and appear to bolt up to the silvertop 2-1 section. (Previously tested this but didn't have any camera to test at that early stage. And you've got a great quick and easy enhancement for your Silvertop 20v