To help us out with our header tech in the November '13 issue of PHR, Hedman Headers gave a short list of 9 things that everyone should know about their project before calling to talk about headers.
What engine does it have now, and more importantly; what did it originally have?
You might be dropping in a big-block or late model engine, but many cars have chassis and suspension differences between 6-cylinder, small-block, and big-block cars.
Is the engine in the original spot?
All off-the-shelf headers are designed with the factory engine location in mind (unless otherwise stated), so if any repositioning has been done it may create interference problems.
How much horsepower and torque, and where do the peaks occur?
This isn't super important on most street combos, but can become critical on really high horsepower race combos where extracting every last bit of power is necessary. If you had the engine built, ask the builder for recommendations on primary tube diameter.
Transmission and shifter type?
Some headers will not clear both automatic and standard trans linkage.
A/C, power steering, and steering type?
A/C boxes on the firewall can cause fitment issues, as can the power steering ram (common on vintage FoMoCo cars). Also, the GM 825 series quick-ratio box is larger than standard and can create fitment issues. If you've done a rack and pinion conversion, this can also change what header will work do to the steering shaft.
Full size starter?
Some headers will require the use of a mini-starter. Mopars are notorious for this.
Suspension or front clip upgrades?
Most bolt-on suspension upgrades will be fine, but subframe or cradle swap should be noted since they may not have the same clearances as stock parts.
How low will you go?
This is often the dividing line for street cars on long tubes vs. shorty or mid-length since even the best long tubes will sacrifice some clearance.
Have you replaced the motor and trans mounts?
Old mounts can sag by as much as .5-inch, which can make an otherwise perfect set of headers not fit. Robinson says this one comes up more than you might think.