No disrespect intended, but your original post said, “drag/street truck.” I just don’t think you will be very happy with this combination.
Again, what transmission? What size tire are you running? If you will be running an automatic and don’t already have one set in stone, consider a THM700-R4/4L60 which has a 3.06 first gear ratio and wont eat HP with a heavy rotating internals like a THM400 will. The THM200-4R can also be built bad ass and has a 2.74:1 first gear along with light weight internals. Consider 3.23 to 3.55:1 gears if you are running around a 26” to 28” tall tire. 3.73 to 4.11:1 or lower will kill your top speed unless you are running > 30” tall tires. I would run as much stall in the converter as you can live with.
If your block is not decked and has the stock deck height of 9.025, your KB pistons will be .020 in the hole. Depending on which pistons you have, 5cc or 7cc volume valve relief notches, and your head gasket choice, (without milling your block) you will end up with approximately 10:1 to 10.6:1 compression. With the block at standard deck height, you will end up with a quench distance of .059 to .061 because your pistons will sit .020 in the hole. Tightening up that quench will help promote a more even burn and, even though your compression will be higher, it will most likely make your engine more detonation resistant.
If you zero deck the block, your gaskets will determine the quench distance. For example, if you choose a Fel-Pro composition style gasket, you will then have a quench distance of approximately .039 to .041 according to Fel-Pro’s advertised compressed gasket thicknesses. Your compression will then end up in the 10.4:1 to 11.1:1 compression range.
With all that said, your cam selection and iron heads will probably be a detonating nightmare on pump gas. I ran a similar combo on a 340 Mopar a while back and HAD to run a mix of race gas and premium to calm it down. Going to a 242 degree duration @ .050 calmed it down further.
If I recall correctly, out of the box, those heads flowed about 238 CFM at 28” at .450 valve lift. After that, they stall real bad and the flow number drop big time. With those numbers, those heads are capable of ~450HP +/-, but everything has to be right to get there. At some point, you are going to want to upgrade those heads. A higher flowing head will like your 6” rod combination better. If you plan on upgrading your heads, switching to aluminum will cause a loss of heat retention in the chambers. All else being equal, the engine will act like it has lost a point of compression.
With your cam selection of 212/220 @ .050 tappet lift, that engine will turn about 5,000 RPM. I would really recommend a larger cam, especially one with a tighter centerline of 108. The cam that you have will sound “stock” and will also build lots of cylinder pressure contributing to your detonation problem.
With the small ports of your Vortec heads, your engine will produce a lot of torque, which will be good to help get your heavy truck moving, but will limit your RPM capability. You can install a larger duration @ .050 cam, but you will get to a point where it just wont RPM up any higher. Again, since you used the term “drag/street truck,” (I assume mostly street) try to keep your cam duration @ .050 under 235 degrees.
If you are doing mostly street driving with occasional track time, those Vortec heads will make a lot of low end torque on a 383, so you should build accordingly. Your Vic Jr. intake might give you a few more HP over an RPM AirGap, but in the RPM range where your engine will mostly live, it will hurt all around drivability. In my opinion, it just isn’t worth it to lose torque down low for 5 HP at peak RPM. If you have it, run it, but if you still need to buy it, consider the RPM AirGap.
Cheers,
Joe
