Precision Turbo and Engine BigStuff3 GEN3 PRO SEFI (LS1) System Hardware & BigComm Software - Manual (Page 36)

BigStuff3 Pro SEFI System (LS1)
Version 1.0 35
Crank Shaft (Pulse/rev)
This input screen allows the user to set the quantity of teeth on the crankshaft.
Return_to_Pickup_Wheels
Coil-On-Plug (COP)
Crank Reference Setting
To realize the full benefits of the GEN3’s precise timing and individual cylinder control, Top
Dead Center (TDC) for cylinder 1 (compression stroke) needs to be determined and marked on
the dampener.
Finding TDC
TDC is the point at which the number 1 piston reaches its uppermost position in the cylinder.
Ignition timing is usually expressed as degrees before top dead center (BTDC) or after top
dead center (ATDC). A timing mark on the crankshaft balancer or dampener corresponds to
the top dead center position of the number one engine cylinder. In order for the GEN3 ECU
to reach its full performance potential, it is important that TDC is verified. A simple process
for verifying TDC for number one (1) cylinder (compression) is outlined in the paragraphs
below.
Finding TDC Process to use when the cylinder heads are on the engine
One way to find Top Dead Center (TDC) is to use a piston stop and a degree wheel. Make
sure that the piston is down in the cylinder and then thread the piston stop into the #1 spark
plug hole. Securely fasten the degree wheel to the front of the crankshaft. Next, fabricate a
rigid pointer to point at the front of the degree wheel. Make sure that the pointer is solidly
mounted so that it will not move. Using a ½ breaker bar, very slowly and carefully rotate the
crankshaft until the piston lightly touches the piston stop. Write down the number the pointer
is indicating on the degree wheel. Rotate the crankshaft in the opposite direction again until
the piston lightly touches the piston stop. Again, write down the number the pointer is
indicating on the degree wheel. TDC will be exactly in between the two numbers that were
recorded. Remove the piston stop and rotate the motor the “middle” number on the degree
wheel.
A new zero point mark (white paint works well) needs to be made on the dampener. Once
made, this new line will represent true TDC when it is in exact alignment with pointer.
Crane Cams offers positive stops (brass), in 12mm (Part number 99410-1) & 14mm (Part
number 99412-1) sizes. GM also offers a piston stop (Part number 12364087). They are
made to screw directly into the cylinder head spark plug hole and are machined from brass to
prevent piston damage. They incorporate an air bleed hole to prevent compression build-up
while turning the engine over.
If the cylinder heads are off the engine, Use the same process as outlined above, except use a
dial indicator instead of a piston stop.