Timing Difference

Why is the timing on a bbc head 36 to 41 and a pontaic or other big chief heads only 24 to 28,both motors have 1471's on alcohol. Thanks

[ May 31, 2004, 05:49 PM: Message edited by: Big Joe ]

 

Hello Big Joe
I'm not an authority on timming but the key factors seem to be (after changing our system last year) The amount of lead necassary to start the flame front in relation to the amount of time it takes the flame to propogate across the combustion chamber. Both your heads may have very different quench areas causing the difference in timming lead. It does seem like a lot of lead difference. Call JD at MSD mag tech to get the straight poop if your head manufacturer cannot answer your question.

 

I cant say for sure, but I did some time in an engine shop and the rule of thumb around there was the better the head, the less timing required. This is true on NA motors also, my Big Chief motor requires ALOT less timing then my friends conventional motor of the same size, if I were to guess I would say it has something to do with the intake ports as well as the combustion chamber, keep in mind the Big chief stuff has alot better shaped combustion chamber and requires a shallow dome in which both help flame travel across the top of the piston. No facts just my .02