FC3S Murray's never ending build.

NoDOHC · 09-15-2009, 06:07 PM

35 psi? I have never seen a pulse that low. Ever. (Except on a blown engine, which gives 25-30 with missing pieces of apex seal.) Maybe we do it differently. I simply take the check valve out of the bottom of the gauge and crank the engine with the plugs out of both rotors and the gas floored (about 400 rpm).

I tested a 120,000+ miles turbo II and got 90 psi bounces.

My 160,000 mile '91 has 110 psi bounces.

My 199,000 mile 6-port had 105 psi bounces even after the coolant seals failed.

I don't know if the pulse is actually 115 psi, I watch how high the gauge bounces (there may be overshoot).

The factory tester actually graphs instantaneous pressure on a chart. I have seen several traces and they usually run about 8 bar (120 psi).

The FSM recommends that no pulse be below 80 psi as I recall.

Think about this:

Starting air pressure 14.7 psi
compression ratio 8.2:1
final pressure = (14.7 * 8.2) = 120 psia = 105 psig (assuming constant air temperature, which is clearly not true, so the pressure should be higher). Any air lost past seals comes out of this total.

I can list a video of the gauge bounces if this would help.

What to you do for 35 psi readings?

09-15-2009, 06:07 PM	#11
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 18	35 psi? I have never seen a pulse that low. Ever. (Except on a blown engine, which gives 25-30 with missing pieces of apex seal.) Maybe we do it differently. I simply take the check valve out of the bottom of the gauge and crank the engine with the plugs out of both rotors and the gas floored (about 400 rpm). I tested a 120,000+ miles turbo II and got 90 psi bounces. My 160,000 mile '91 has 110 psi bounces. My 199,000 mile 6-port had 105 psi bounces even after the coolant seals failed. I don't know if the pulse is actually 115 psi, I watch how high the gauge bounces (there may be overshoot). The factory tester actually graphs instantaneous pressure on a chart. I have seen several traces and they usually run about 8 bar (120 psi). The FSM recommends that no pulse be below 80 psi as I recall. Think about this: Starting air pressure 14.7 psi compression ratio 8.2:1 final pressure = (14.7 * 8.2) = 120 psia = 105 psig (assuming constant air temperature, which is clearly not true, so the pressure should be higher). Any air lost past seals comes out of this total. I can list a video of the gauge bounces if this would help. What to you do for 35 psi readings? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic) Last edited by NoDOHC; 09-15-2009 at 06:21 PM. Reason: add video idea