The C5 header index is a numeric reference guide for us to quickly size your header compared to a known standard (usually the stock manifold).
How would you potentially use this number?
If you increased your engine size and wondering if your existing manifold/header would still work, you could run the numbers to compare Index numbers.
If the Index number shifts greater than 0.5 you will see a noticeable change in peak torque rpm. Larger Index number = higher peak torque rpm.
We hope this provides you with a better understanding of how a change in engine size or target rpm affects the intake/exhaust math.
We are creating an online quote that will be used to simplify orders. Until then, please contact us via