Eaton M90 Supercharger Boost Pressure
Can anyone advise if it is possible to directly measure the Boost pressure on an M90 as fitted to a GM3800 L67 V6 ? If so , where do you connect the boost gauge ??We can only ever seem to get a negative (vacuum) pressure reading , even under heavy load conditions ? Is this normal ? Any advice would be greatly appreciated.
Roots type superchargers (Eaton) are positive
displacement pumps, just like 4 cycle engines. Your boost is determined by the displacement of the SC (1.5 liters/revolution for a M90). Check out this site for RPM/CFM and displacement specs.
Then you apply the formulas from this site to get the pulley ratio (or if you have the ratio, reverse the calculation): http://mg-tabc.org/supercharger/sc-harry-pyle.htm. This calculation basically looks at 1/2 the displacement of your engine (its a 4-cylcle engine) and compares the ratio to how many liters/rpm the supercharger pumps.
That will tell you how much manifold pressure to expect.
(email me if you have questions)