No mine is faster
No mine is faster, oh yea, mine is faster and bigger
Look HP is great. However if speed is your goal, reducing drag is the way to go. Speed without fuel burn. There are many things you can do to reduce drag.
From Van's data (which is very accurate)
180 HP RV-7 can do 210mph (true top speed, sea level)
200 HP RV-7 can do 217mph (true top speed, sea level)
So 20 hp is good for 7 miles per hour.
If you use a plenum and Sam James style cowl alone you will pick up 7 mph. You can mod a vans stock cowl and baffles to achieve the same effect as Sam's cowl/plenum kit, however you need to read up on the aerodynamics. Sam's kit is pretty good, so if you copy it you will achieve similar results.
Recommend Kent Paser's book, Economy with speed.
Obviously 200 hp with a cowl/plenum will go faster than a 180hp.
I agree with Dan, if you are not turbo charged you will not exceed Vne if you can't exceed it at Sea Level. However Vne goes down (indicated airspeed wise) with altitude. I'll explain but trust me Vne, the red line on your airspeed gage is good for SEA LEVEL only. Still with out a turbo you will not exceed Vne or flutter margins in level flight for a stock RV. Decending out of 15,000 or 10,000 feet, watch it and don't fly red line because you will have negative flutter margin.
Cheers George