I am trying to get an idea of what the dynamic compression ratio is on my stock 390 but I need to know what the valve timing is. The Steve Christ book gives the lobe lift and valve lift for intake and exhaust, but no duration or valve timing numbers.

Specifically, I need to know at how many degrees ABDC the intake valve closes. Does anyone know what the valve timing is on a stock 1976 390?

 

Valve Lift
Intake, Exhaust
0.427", 0.431"

Lobe Lift
Intake, Exhaust
0.247", 0.249"

Duration @ .006"
Intake, Exhaust
256*, 266*

Intake Timing @ .006"
Opens 13* BTDC, Closes 63*ABDC

Exhaust Timing @ .006"
Opens 63* BBDC, Closes 23* ATDC

Overlap 36*

The stock timing set retards the cam by 4*

 

Thanks a lot BB. I figured it was a long shot that anyone would have this info and instead I get a complete answer within 15 minutes.

At the bottom you wrote that the stock timing set retards 4 degrees. I assume that means that as installed, the intake valve closes at 67 degrees ABDC rather than 63. Correct?

Thanks again,
Bob

 

You're welcome!

I'm surprised I had that info on the work computer, don't tell the boss.

Yes, all the cam timing events run 4* late with the stock setup (had to think about that for a sec).

 

I thought it was 8 degrees Barry?

 

Is it 8*? For some reason I thought it was 4*.

Anyway, is the timing right? For retarding the cam the intake & exhaust opening numbers get smaller and the closing numbers get bigger. The timing is all running late but it's just the way it's measured on the degree wheel.

Guess I need to think about this a little more.

 

You guys have me thinking now...Oooooch....that hurt! LOL!! I have allways thought they ran 4* retarded... So that would mean that the timing events happen 4* after thet should have happened? Right? Right!