Originally Posted by BobH
I was thinking of getting a couple of gauges for my twin FLs as soon as I can locate a fitting in the intake and figure out what kind of weird British thread it is.
I can't help you with the boost on the FL's, but the thread on the fittings are BSP. I expect it is a tapered thread, which would make it BSPT (British Standard Pipe - Tapered)
In the US, fittings are normally NPT (National Pipe Thread)
BSP threads have a 55 degree angled thread cut, vs 60 degrees on NPT threads.
Also - a BSP thread is slightly finer (19 threads per inch vs 18 TPI for NPT) on 1/4" and 3/8" fittings.
To confuse the issue, on 1/2" and 3/4"fittings, both NPT and BSP have 14 threads per inch and appear to be a match but the sealing integrity will be compromised due to the difference in thread angle.
In other words, don't mix them or you'll end up with possible leaks and cross threaded fittings.
By the way guys - BSP aren't weird threads, -Its what the rest of the world has standardised on.
Heres a link for more info.
NPT vs. BSP Pipe | Pipe and Hose