i have a 66 chevelle 396 pro built with all the goodies.it has 450-500 HP on 10.5:1 comp.and i'm running 93 octane pump gas,and runs at 170-180 degrees. i runs great from idel all the up.but when i shut it off,it sounds like it still wants to run. can some one out there give me some hints,as to whats wrong!?!?!?!?
Check your idle. If it is too high for your engine setup, it may cause that problem. As my new engine has broken in, I adjusted the idle to correct the same problem you described and it turns off without any extra turnover.
Are you running an electric cooling fan? It may sound stupid, but I have had it happen more than once. If an ignition wire is used to turn a fan/relay combo on, when you turn off the key, the fan acts like a generator and will back feed the ignition for a bit. The end result is run on.....
1992 Firebird 355/Six Speed (Soon to be LT1)
1991 RS 350 / 700-R4
1987 Toyota Pickup 383 / 500 + HP 10.963 @ 119.95 Slicks / 11.997 @ 114.23 Radials
"Speed KILLS, so drive a FORD and live forever!" http://personal.lig.bellsouth.net/~racer383/
Try adding a can of octane boost next time you fill up. If the problem goes away, your gas has too low an octane rating for your compression ratio. 10.5:1 is kind of pushing it on 93 octane especially with iron heads IMHO. (I had the same problem with my 383 - running 10.4:1 compression and aluminum haeds)