Originally Posted by actmobmar
hello, i'm new on here and looking to build up a 1968 gto convertible that i inherited when a good friend of mine passed away too soon. the car has a ys code block(400) in it that appears to match the car, along w/ #48 ram air 3 heads. the car has a 4 speed in it, and i am looking at taking the tremec 600 that is currently in my '69 camaro, and has a .6 overdrive, so i am considering 3.73 gears. i'd like the car to run mid 12's as most production cars these days do, and i want to keep the factory block and heads so it appears original. the car currently has headers, performer intake, demon 650, and hei ignition. any help to guide me in the rite direction in this build would be great, as i am not familiar w/ pontiacs! thanks!!
I ran mid 12's using a Holley 4777 and a Performer intake on a 455 w/6X heads in an all steel '81 Camaro, and went quicker than that using a 428 in a '68 LeMans (also all steel), so I see no reason you can't get into the 12's w/your 400 using a decent cam and the '69 #48 heads you have. I'd clean the bowls and give them a good valve job. No harm in port matching the intake and heads (not gasket matching, BTW), but full-on porting isn't necessary to run high 12's.
Whether your idea of stock appearing includes headers I don't know, but using long tube headers will make running 12's a lot easier unless you use the good manifolds- the low-po manifolds hurt power too much. The 400 spins higher than a 455 all else being equal, so using a bigger carb certainly won't hurt.
I'm guessing the pistons aren't flat tops, else the compression would be higher than 9.5:1.
Some reading if you're in the mood:
• Engine info