Unfortunately, there isn’t a right or wrong answer to this question. By far 1-3/4” header on a stock or modified 5.0L Mustang will offer plenty of capacity for exhaust gases. They will be neither restrictive nor too big to hinder power. 1-3/4” will add to the top end (over stock headers) but should not lose anything down low either.
Again, a 1-7/8” header is only 1/8” bigger, but this added 1/8” adds a massive exhaust volume capacity. The consensus amongst experts is that unless you have a very large displacement engine or are pushing more than 900 HP, 1-3/4” headers are more than adequate for a 5.0 ‘Stang.
Keep these tips in mind to help you decide what size is right for your Mustang:
- Headers are categorized by the size of primary tubes/runners
- The primary tubes merge into a larger diameter collector
- Smaller diameter tubes produce more horsepower and torque at lower speeds
- Larger diameter tubes produce more horsepower and torque at higher speeds, but lose power in the low end
- Shorter tubes improve top end power
- Longer tubes increase low-end torque
- Going too large in diameter can be harmful by leaving some exhaust gases in the combustion chamber on the next compression stroke
For most street/strip duty Mustangs, a 1-3/4” size primary tube header size will be more than effective. Not to say that a 1-7/8” header will not work (it will work, but may not scavenge the exhaust as well), but keeping in mind the overall displacement and horsepower levels of most street Mustangs, a 1-3/4” header is a safer bet to meet your power needs all throughout the powerband.
If you really can’t make up your mind – call the tech line of the header manufacturer and a representative will be able to tell you exactly what you need.