The carb is made by "Quick Fuel" has mechanical secondaries, and is rated at 850 cfm. The spacer is there to tune for the space the nitrous plate will eventually take up.
The heads are Darts' Iron versions, with 230 cc runners and 2.08" intake valves. A bit more than a 355 needs in the air dept, but I may use them again on some larger displacement project.
The internals are all balanced Forged steel, with 4 bolt splayed mains, and the cam is of the solid lifter variety designed to make power from 3500 to 7500 rpm.
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for a 355 ci, i would have probably gone with a 700cfm, 750 tops. even with nitro. for the nitro, 2 stage seloniods are safer than a one stage with a spacer plate, but even with the spacer plate type, you can expect 100 to 150 more hp.
be carefull though. a leaky seloniod could blow the heads off your car. have seen it happen. check it often. if you have never played with it before, you should set it to open only in top gear, and only at full throttle. miss a gear with nitro, and you will be picking up pieces of your bottom end and transmission off the street. at least with the two stage seloniod, it is only open half way when you hit it at first, a small safety margine incase you mess up.
make sure it closes when you come off the throttle too. if you smell it after the car is turned off, DO NOT START THE CAR. fun stuff, but dicy to play with. most people just put the plate on with an empty bottle for show for the ohhs and ahhs.
had a set of dart heads on my 69 camaro ss. they work fine, i wouldnt port them. already more potential flow than you will be able to use on a small block.
MSD is better for street than magnito too. its idiot proof. gona eat some plugs though, and dont forget to get steel plug wires. the carbon ones just dont hold up long with the extra voltage. BTW, gona make your radio sound like crap. filters help, but not much.
if your gona run pump gas, im guessing 10:1 on the pistons at most. even then your gona need octain booster. given that, i dont see 450 hp, more like 400 tops. and with nitro, idealy, your better off with lower compression, like 8:1. given that, it is looking like 350 hp. on pump gass without the nitro, 450 to 500 on nitro.
put a small block 400 crank into your 350, and punch it out 60 over, you can get about 383 CI, you can get close to 450 on pump gass and have the torque of a big block. did that with an 85 vette once. just once.
also, if your running an automatic, think about a stall speed converter. with a power range between 3500 and 7000, it will help launch you to max torque faster off the line. will play hell on street tires though.
little side not some people dont think about. push rods. the alluminum ones you get from the factory will bend like a noodle at 7000 rpms. get titanium push rods. better safe than sorry. on the other hand, you get the timming off a bit, your titanium push rods will put a valve through a piston.
would go with gear drives for the timing set too. easier to set the timing that way and be sure. sounds kind of cool to boot. kind of like a blower the why it whines.
im sure you got locking rocker arm nuts, just remember to use locktite on them to boot. they vibrate loose some times.