dbb280zx

I just installed my rb streetable header and presilencer today and holy ****. As soon as i started it I shut it back off. I have NEVER EVER heard anything that loud before! I put in some ear plugs and started it back up. The car (81 gsl) runs like **** (misses half the time) and most of the noise seems to come from the engine compartment. Now what comes out of the muffler is only slightly louder than stock and has a good tone to it. I don't think that there are any leaks in the new exhaust. I believe what is making all the noise is the plate that blocks off the acv hole. Has this happened to anyone??
Dennis