Well, I knew I'd open up a can of worms if I get into the realm of cylinder head technology. The main problem is, you couldn't describe all the important factors in a 500 page book, let alone in a short post in this forum. I'll try to cut to the chase on several issues...with uncertainty if this will just muck it up even more. But, here goes.
1. No, normally you can't make a single change to the heads or any other system on a naturally aspirated streetable Viper engine that would result in 150 hp. You certainly could on the heads that are about to go on a Pro Stock drag racing engine.
That's why I stated that my plan was to add about 150 by combining a different camshaft, exhaust system, head work, and fuel system mods. I would expect to see 30-50 from the head mods alone, but the most critical aspect of engine design is getting all the parts to work together. Often, people say "this cam makes hp" or "that carb makes hp". Both are inherently false statements. The only true source of energy is the fuel--the rest of it is how well it's mixed, how much gets in, and other factors.
2. There is a lot of truth to the fact that the manufacturer must balance cost against power--this has always been the case. This is why there isn't a stock cylinder head in the world that's already "optimal". I put that in quotation marks because it also depends on the environment. Want to lose about 100 hp in a hurry by bolting on a piece that supposedly "adds power"? Put on a Pro Stock style tunnel ram with two 1320 cfm carbs on your engine and watch it lose about 100 hp...at least until the engine's twisting above 7000 rpm's. I'd stand back if you zing that V-10 up to 7 grand. In theory, there should be a different port design in place every time you make any induction system modification.
So...the manufactures usually cut the all-imporant venturi & bowl areas with machine tools...they know it's not right, so they usually leave some extra "meat" there for the head porter--usually VERY little. But thank goodness they at least leave some!
Another thing that's very misunderstood--the OEM engineers often don't have a clue about what to do as far as maximizing the performance from an engine they develop. This is primarily because they must reach a goal within the constraints of budget and production costs. Furthermore, cylinder head technology does NOT flow from the engineer down to the racers. It goes exactly the other direction. That's why a guy like Bill Jenkins was paid by Chevrolet for years...so he could explain to the people who designed the engines what they should to to make them optimal for racing.
Then there's a matter of a poor design becoming too established to get rid of it...kind of the way the Beta video format was never able to displace VHS, despite being vastly superior. Chevrolet is still stuck with those huge combustion chambers on the Big Block Chevies (small chambers are better...PERIOD!). But...if someone produced a small (less than 70 cc) BBC head, there wouldn't be pistons around to fit it.
Don't believe the small combustion chamber thing? Pull the head off of any of the "Hemis" running in the NHRA Pro Stock category and you'll find heart-shaped combustion chambers between 47-49 cc's and nearly flat-top pistons. Now, pull the head off of any of the GM engines running in the NHRA Pro Stock category and you'll find heart-shaped combustion chambers between 47-49 cc's and nearly flat-top pistons.
If you don't know...47 cc's is FAR smaller than even any stock Small Block Chev. chamber--they're around 65...and these things are on 500 cubic inch V8's! Smaller is far better (unless you're running Top Fuel and have to put about a cup of fuel in there), but we're stuck with some things...unless you have an unlimited budget. The NHRA Pro Stock racers start with aluminum castings that are basically chunks of solid aluminum (they weigh over 80 lbs. each before machining, about 35 lbs. after).
I stand by what I said before. Unless you have access to a truly elite head porter, you'll be better off having them do minimal mods to the heads. Fortunately, the farther you get from the valve seat, the less things matter, so a lot of questionable work doesn't really show up as lost performance...and it makes the heads look really pretty! Porters know they're selling the heads to people, not to the engines...
Hope this helps!
RC
