Hi fella's, first post. I would like to add something to this thread, having done a few sets of these. Don't get misled into thinking you can bolt these on "out of the box" and realize a huge gain because it's not going to happen. The base numbers are pretty dismal and are right there with the stock heads. They do, however, have an enormous amount of "potential". But they must be done by a reputable head porter that is willing to put the time in on the flow bench to get everything out of them.
Also, I have to disagree about the R heads not being a worthwhile change when staying with the stock manifold. Yes, it's true that a sheetmetal, or some trick injected manifold would realize better power from these heads but the same holds true for a really good set of ported stock heads also. When you've been doing this for a long time, like myself, you discover that steady state flow testing on a Superflow flowbench will sometimes mislead you on some things. Manifolds is one area where this happens. I have seen a phenomenom with these long runner manifolds with relation to performance versus cfm drop on a cylinder head where they run much better than they should, according to steady state flow testing. This became vividly apparent on an LS1 project I was involved with last year. Did you know that a bone stock black plastic LS1 manifold is good enough to run 9's on motor in a 3600 pound car? Well it is. The stock LS1 manifold will drop a 300 cfm head to 216 cfm. I witnessed one that was picked up enough to only drop that same head to 250 cfm, and it gained nothing on the chassis dyno or the track. It took a sheetmatal manifold to go faster and it was only .15 seconds better. Long story short is that the long runners already contain enough air to fill a cylinder and therefore don't gain as much power from porting as we have become accustomed to expect from other manifolds that have shorter(less volume) and curved runners. It's simply a situation where the runner volume makes up for lack of flow, or rather, the engine is relatively indifferent to how well the manifold flows because all of the air needed to fill the cylinder is already in the port, having re-filled during the three subsequent engine events after intake closing. This is where we go wrong relying on steady state flow tests because the flow in the engine is not steady, but pulsing. The port, as run on the engine, flows at a high rate for a short time, then rests and re-fills, waiting for the next intake cycle. The Viper manifold provides a relatively straight shot into the head and holds a lot of volume as well. The better the head flows, the quicker the runner is emptied. We at TNT have seen a substantial HP gain from these heads, regardless of the manifold type.
Greg
