which spark plugs??
 

I need to get a new set of plugs for my 89GT. I am planning on going with Autolites but I am not sure which ones to get and what gap to use. I believe the AP25's gapped at .054 are what I was using when my stang was stock but I would like to know if I should change plugs or gaps with my new mods. Thanks

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Chrome Yellow 99GT -Flowmaster DF 40 series mufflers, Steeda tri-ax shifter, Steeda sport springs, Tokico HP shocks/struts, K&N w/ cut silencer
Black 89GT -Cobra intake, E-303 cam, 1.7 roller rockers, rebuilt/balanced short block, 75mm Pro-m, 65mm TB, BBK headers, BBK h-pipe, Flowmaster Am.Thunder, TrickFlow valve springs, K&N, 190 pump, adj fuel press regulator, hurst shifter on T5, MT 26x8.5x15 ET Drags, 3.73 or 4.10?

The plug gap should be about .045" for a high performance street car. When a blower or nitrous is added, you need to drop the heat range on the plugs and reduce there gap to about .035", depending on level of boost or how much nitrous is added. The above is not for certain, you will have to read the plugs in order to make the proper determination, but it will get you in the ballpark.

which plugs should I get...24 or 25???

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Chrome Yellow 99GT -Flowmaster DF 40 series mufflers, Steeda tri-ax shifter, Steeda sport springs, Tokico HP shocks/struts, K&N w/ cut silencer
Black 89GT -Cobra intake, E-303 cam, 1.7 roller rockers, rebuilt/balanced short block, 75mm Pro-m, 65mm TB, BBK headers, BBK h-pipe, Flowmaster Am.Thunder, TrickFlow valve springs, K&N, 190 pump, adj fuel press regulator, hurst shifter on T5, MT 26x8.5x15 ET Drags, 3.73 or 4.10?

I don't have a clue as to what's the difference between the the autolite plugs you mentioned. I don't have a parts catalogue. Get the ones that are the same heat range as factory and then gap them yourself. Gap them to .045".