Since any good manifold is expensive and somewhat mystical in the fact that most Vee racers don't have a flowbench or dyno, please sit through this to help you understand what you are investing in. I apologize if I bore you.
An engine makes HP based upon it's displacement and how much air/fuel it can get into the cylinders. The more it can fill the cylinder on it's intake stroke the more that it can deliver on its power stroke. There are many other items that determine the full efficiency of the engine. (compression ratios, spark timing, cam timing a/f ratios, valve lift, oil viscosity, etc.) On any prepped race engine those things are addressed and we are all pretty equal due to the rules and what we know works. . The remaining thing is induction. Heads, Carb and Intake Manifold. Assuming the typical Vee engine, the most important items are the carb and manifold. Not to say that heads flow isn't important, but the difference in HP between a mid-level set of heads and top flow heads is not nearly as significant as the intake and carb.
Just for reference I will give you some numbers from the flow bench. Don't get hung up on them, but it will help you understand more later.
We have been flowing intake manifolds for almost 20 years. A stock VW manifold might flow in the 52 to 56 CFM area. A prepped manifold called a "Vintage" or "Regional" flows in the 62 to 64+ CFM area. Prior to very recently a top "National" flowed in the 65 to 67 CFM area. If you had a manifold that flowed 66+ CFM on both sides, you were not going to be beaten by anyone else on HP alone. That has changed. From the above numbers you can see the range of how much manifold flow can be, and how it is more critical than typical range in head flow.
We now have manifolds that flow 68, 69 and even 70 CFM. After many flow bench tests we were quite impressed. However, we knew they were better, but what exactly did it do to the HP curve? I personally felt that it would increase the HP slightly out past 6100+ RPM. (Maybe .5 HP.) With that premonition we started doing some dyno tests on one of the new manifolds.
The Engine was a good fresh "National" with a good National carb and a manifold that flowed at 66+ CFM. Several runs were made on the engine to stabilize oil temps etc. Oil temp, head temp, A/F ratios etc were closely monitored to insure that each test was valid and comparable. The same tests were done with the newer manifold mounted. The tests were back to back within 10 minutes of each other with the exact same environmental conditions.
The above are representative of about 14 total dyno runs from 3000 to 6500 RPM. While the blue line clearly shows the gains, the most impressive part is the gain out at 6500 RPM. When most engine's pumping losses are forcing the nose dive in HP, the Monster Mani stretches the curve out much longer. BTW, the Monster Mani tested here was NOT the biggest MM we have. It was about a point down from others. Across all tests the MM's produced anywhere from .75 to 1.5 additional HP in the operating curve.
These manifolds are SCCA legal and the manufacture will stand behind them. You are eventually going to want or need one. Give us a call. (859-252-2496)