#15296, "RE: S-FMU Disc's..." In response to Reply # 2
Approximately 6.5:1 (3.62 in), 5.4:1 (2.72 in), 3.2:1 (2.47 in), and 2.5:1 (2.22 in). In my experience, they generally give a little lower rise than you would think. The rise also depends on what spring you use. Just approximations.
#15298, "RE: S-FMU Disc's..." In response to Reply # 4
The ratios that I posted are taken from a graph with the S-FMU instructions. They do vary from that some. The stiffer spring will yeild a higher actual ratio. What I get is like 4.8:1 with the 5.4:1 disk. They are often a little low, like I said. To safely test it, you need a $25 electric tire pump, $5 needle valve, and extra hose. You start the engine and supply pressurized air to the boost gauge and S-FMU. You use the needle valve to bleed off some of the pressure. You read the boost gauge and adjust the valve to get the "boost" you want. Read the fuel pressure gauge and you can figure out the actual ratio. Here's what I use:
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