Timing / Spark Plugs

[MACH1MUSTANG]

Why would you set initial timing to fire ATDC? When I bought my car it was set 4* ATDC. Engine is a 351W with 11:1 comp. Also, how long do spark plugs need to be in an engine before you can pull them to get a good read on the engine's performance?

 

[SoCalCruising]

The only reason I can think of is that the dizzy accidentally turned. I mean, that's a performance killer. Well, actually I do know that some engines in the early smog days were set with retarded timing for emissions reasons. I don't know if that applied to your motor, though. The other reason might be that there was detonation, for some reason, and retarding it was necessary, but that doesn't sound reasonable ... unless, maybe the PO was trying to use 87 octane with an 11:1 engine??? What are the cam specs? If the cam is small, that compression would make lots of dynamic compression. Usually that kind of compression would be matched up with a fairly aggressive cam when used with pump gas. Anyway, that's what comes to mind.

 

[MACH1MUSTANG]

I believe it was purposely set to that because of wanting to use pump gas by the PO. The car is a 1969 so no emissions issues here. Here are the cam specs, 238-248 @ .050, .512-.536 lift, 112 LSA, 5* advance ground in, .025 hot lash. I currently run a 50/50 mix of 110 octance race gas and 93 premium pump gas with the timing set at 10*. As soon as the weather warms up here in the mid west I am going to bump it up to 14* initial which will give me 40* total.

 

[SoCalCruising]

That's a lot of advance (40*). What kind of heads are you running? Iron? Aluminum?

 

[MACH1MUSTANG]

Whatever original heads are make out of, they are Iron I guess.

 

[D.Hearne]

Why would you set initial timing to fire ATDC? When I bought my car it was set 4* ATDC. Engine is a 351W with 11:1 comp. Also, how long do spark plugs need to be in an engine before you can pull them to get a good read on the engine's performance?

To try to run it on lower octane fuel. Did you ever try straight 93?