I have a 1978 L82. So far here are the mods that have been made:

Accel distributor
Hedman headers, no cats, flow masters (no y pipe)
Removed A/C compressor, EGR valve, Air pump
Holley Fuel Pump

Just curious of where I sit at the present moment

 

This isnt meant to be rude, but if those are the extent of the modifications, then your interest in horsepower leads me to believe that you would probably be dissapointed with the real actual numbers.

The only item that is truly making more power is the headers, which you didnt specify are long or short. Is the holley fuel pump manual or electric? Either way, it isnt going to make more power, unless it is replacing a defective unit...same goes for the distributor.

While I cant give you a definitive answer, I would recommend changing your intake manifold, and possibly swapping the carb as a bare minimum of taking advantage of what youve got. If you really want to take complete advantage of your current long block, a well planned cam swap in conjunction with the manifold and carb swap, would give you some good numbers

 

nothing dramatic, maybe 10 -15 hp over stock. the weight reduction though by losing the a/c and air pump might reduce your 1/4 time by a .10 of a second or so. if you have a decent advance curve in the distributor, that might help a bit too.

 

There is much information on this topic on the forum and in the literature if you do a search on the internet. The 2 best examples I can think of are the comparison between a 74 L-82 vette versus a 75-79 L-82 vette, both of which are stock and an article I read comparing the GM y pipe exhaust system used on the 75-79 corvettes and a true dual exhaust.

The 75-79 y pipe exhaust is VERY restrictive and probably the worst exhaust ever put on a corvette. It simply was not designed with HP in mind. The 2.5 inch Y pipe exhaust is essentially a single exhaust pipe of 2.5 inches since the 2 into 1 into 2 design dictates that the exhaust's flow characteristics are defined by the portion of the exhaust that is the single 2.5 inch pipe. The stock mufflers were notoriously constrictive along with the pancake cat which was absolutely horrible for flow.

A 1974 L-82 was rated at 250 HP Net with a true dual exhaust (but still had restrictive mufflers) with no cat versus a 1975 L-82 y pipe exhaust with a pancake cat made 200 Net HP, no other changes-the engines are almost identical, just the exhaust difference. The exhaust alone was worth 50 net HP. No headers on either engine. The 74 dual exhaust flows roughly 4X the exhaust of the 75 L-82. Add long tube/shorty headers to this equation (not much difference on a street stock type engine for long tube versus shorty headers) and then you are adding 10-15 net HP with the headers alone on a true dual exhaust 2.5 inch setup.

An article that has been referenced on this forum that dynoed a late 70's GM V8 with the a single y pipe cat exhaust versus a true dual exhaust with no cat went from 152 HP to 230+HP with true duals and high flow mufflers with no other changes, which confirms my example above.

Lastly, my 78 L-82 which started out bone stock and I have owned for 27 years orginally had a stock Y pipe exhaust, pancake cat, and stock mufflers when I bought it in 1983. I made incremental changes to the exhaust 1 at a time over that time. In 1983 I removed the cat on the y pipe exhaust (test pipe), 1988 added Monza Turbo Mufflers, 2003 replaced all the pipes with 2.5 inch true duals (same Monza Turbo mufflers), and in 2007 added McJacks shorty headers to the 2.5 true duals. Every change resulted in more HP! The shorty headers probably added 10-15 HP alone on these motors. The total change is probaly worth 50+ HP in the mid to high RPM range. The single biggest change you can make to a 75-79 corvette (the 80 exhaust was redesigned and slightly better than the former) is to replace the OEM stock system pipes with 2.5 inch true duals, no cat, free flowing mufflers and a header of some kind which will net somewhere between 30-40 HP on these engines depending on your starting point.

Hope that helps!