Picking A Performance Exhaust
Picking out a performance exhaust system can be, well, exhausting. There are almost endless options and how do you choose? Do you choose based on size, sound, fitment, or what your buddy suggests?
A few months ago we covered the Perks Of A Performance Exhaust. We covered weight savings, increased horsepower, better gas mileage, and sound. If you’re really wanting to reap these benefits though, you’re going to need to pick out the correct performance exhaust.
The first step is knowing what type of engine you have. If it’s a basic 350 SBC, it’s going to need a much different exhaust system than a supercharged BBC. One misnomer with the exhaust is that bigger is always better since it will flow better. While there is some merit to that, just like anything else too much can be a bad thing. Too big of headers or exhaust can hurt more than it helps.
What is back pressure? In essence, back pressure is the pressure of your exhaust pushing on the atmosphere. Some people try to eliminate it completely in an exhaust system, but in reality, your engine needs a little bit of it to function its best.
Another way to look at this is the exhaust gas flow velocity. The correct size piping will cause the fastest flow through your exhaust. If the piping is too small, it gets choked up and it’s like a traffic jam. If it’s too big then it slows down the exhaust velocity. The idea is to get the exhaust out of the engine fast so the engine doesn’t have to work to push it out.
What Size Exhaust?
Each application will be different, but there is a general guide below on what size piping you should have with your engine.
Single Tube Exhaust
- 150-200HP = 2.5″
- 200-250HP = 3″
- 250-300HP = 3.5″
- 350-425HP = 4″
- 425-500HP = 4.5″
True Dual Exhaust
- Up to 400HP = 2.5″
- Up to 500HP = 3″
- Up to 700HP = 3.5″
- Up to 850HP = 4″
- Up to 1000HP = 4.5″
X-Pipe, H-Pipe, No-Pipe?
Without a doubt, connecting your exhaust pipes together is going to give you extra power. Having the exhaust connected will equalize the pressures and help with scavenging and removing the exhaust from the system. Generally speaking, an X-Pipe will give a little higher-pitched sound, whereas an H-Pipe will give a lower rumble.
From a performance perspective, both are about equal. However, the X-pipe does do a better job at scavenging the exhaust out of the system. Due to space constraints, an X-Pipe isn’t always feasible though.
Placement of the X-Pipe or H-Pipe is crucial as well. Generally speaking, you’ll want the crossover to happen as soon as possible for the best performance.
Headed A New Direction
There’s no doubt that a set of headers will greatly increase the flow of your engine to increase power. There’s a lot that goes into the design of the headers and depending on your engine will help determine what’s the best performing for your engine.
With header design, there are primary tube diameter, long vs. short tubes, and collector diameter. Going back to engine performance, a basic SBC won’t need huge primary tubes and it can actually hurt performance.
Long tube headers generally build more power in the mid-range and top-end. Shorty headers generally build the most power in the low end. But remember ground clearance and fitment can play a role in which headers you choose. If you have a lowered car, then a set of long-tube headers might hang down low and scrape the ground.
As you can see, there are a lot of different factors that make for great performance exhaust. It’s not a one-size-fits-all category and really depends on what engine you have, the space available, and even intended usage. Exhaust built for low-end grunts will be different than exhaust built for high-end horsepower.