I have a 1984 Camaro with a 305 LG4. Engine code H. I have found a direct replacement high flow converter. Claimed horsepower gains of 8 to 10 hp and 12 pounds of torque. It is not a Random Tech which flows at 382 cfm for this particular application but flow is dead comparable and half the price. Can a good cat give me this boost alone. I will get a good cat back at the same time. Stock is 2 -1/4 and I guess new system will be 3 inches on back from the converter. Give me total assumable gains for quality cat and mandel piping along with a topline muffler.

 

I don't think I'd do it. That would still retain some of the significantly restricting parts of the LG4 system - the manifolds, y-pipe, and cat.

The L69/LB9 system would be much better, w/2-3/4" y-pipe & cat, 2-1/4" exhaust manifolds and downpipes.

But, headers and direct fit high-flow cat for the '86-'91 TPI single cat application and appropriate catback would be even better. Sure, more money, but now you're talking 25 or better HP improvement, with a bunch of room to grow (cam, heads for instance). If you settle for the 10 HP of a high-flow LG4 cat, you're basically stuck with that.

FWIW, the single snorkel LG4 air cleaner is another "gotta go" item. A dual snorkel will let that poor thing breathe in as much as an improved exhaust will let it breathe out. An open element will also improve flow, but won't be as good for general driveability as a dual snorkel would be.

If/when you improve the cam, upgrade the ignition at the same time (module, coil). Wouldn't hurt to do it now, either.