Quote:
Originally Posted by Bad as L  I don't mean to nit pick but a long stroke short rod motor has a quicker moving piston with less dwell time at the top of the stroke (TDC) and a relatively slower moving piston with longer dwell time at the bottom of the stroke (BDC). In other words a 408 has a shorter piston dwell time and a quicker moving piston at TDC than a stock 351 does but a longer dwell time and a slower moving piston at BDC.
The timing the motor needs will be dictated by the combustion chamber shape/cylinder head (among other things) more so than piston speed. |
Bad as L,
Nit picking is OK. You are correct of course regarding the piston dwell at the top of the stroke ( I need to edit my own posts more carefully). However the low rod ratio of this combination means the piston moves away from BDC slowly trapping a higher % of cylinder volume. Regardless of combustion chamber shape if the intake valve is closing pretty early, which his cam will, the result will be some pretty high dynamic compression. Unless his static CR is under 9:5. Bottom line he's beating rod bearings and needs to either back up his timing or find some higher octane fuel. All the theory means nothing. Believe the results. The dynamic compression developed is directly related to the intake closing and it is going to be the most significant factor in determining the timing and fuel requirements IMO. Thanks for the come back.