I live in Utah, up at about 5,000 feet elevation. As a general rule of thumb, you can "guestimate" that for every 250 feet of elevation, you lose about 1% of the horsepower you would be making at sea level.

That said, any motor I run is going to be making about 20% less power than everyone else down at sea level, which is pretty significant. My BBC that would make 600 horses at sea level only makes 480 here, booo.

So that said, when putting together an exhaust system, headers in particular, do I want to choose my primary tube size based on my "actual" 480 HP output? Or do I need to run the same tube diameter as I would at sea level?

Same thing for choosing a muffler, the rule of thumb is 2.2 cfm per horsepower. But can I use quieter mufflers to support only 480 HP (About 1050 CFM total), or do I still need to size them for 600 HP (1320 cfm)?

 

Anybody?

 

Its not an exact science.. You just want it to be big enough that its not causing a restriction. Build an exhaust system big enough to support the max amount of power you want to make with it. For a 600hp big block, I'd go with a 2" or 2-1/8" primary, 3.5" collectors, and 3" dual exhaust or 4" single exhuast system.

 

That's what gave the best results on the dyno (at sea level), 2" primary tubes into a 3.5" collector.

Maybe I'm just overthinking it. But since it only will make 480 "actual" horsepower at my altitude, I was wondering if a slightly smaller diameter primary would be best, to keep the exhaust velocity and scavenging at maximum. Thanks for the response

 

Spray it, that'll make up for the lack of air up there, even a small shot would help out tremendously.