The Ugly Duckling
There has always been the ugly duckling of all of the bolt-on parts that everyone takes for granted or just flat out misses. That ugly duckling is the exhaust system. So far in these articles we have talked a lot about moving air in these articles BUT if air comes in, how does it get out? If there is a common thing I see all over the Internet it’s that no one puts any thought or money into the idea that exhaust is just as important as intake and internal flow. It’s important because prices of headers and other exhaust parts vary so much that it’s often easier to just pick the cheapest setup and call it good. Do we even realize the importance of the length of each tube in correlation to how our engine actually fires off each exhaust pulse? Did you know that there are many forms and styles of headers out there and that each has a unique way of effecting the way exhaust is channeled down the long road of tubes it must travel on? Yes, this is yet another form of go-fast science.
When I first started building combinations and tuning I was always so focused on the air intake and the filter. I mean, if you think about it it's still largely the same now, there are only off the shelf options for headers, meaning, one size fits all. But when you actually understand exhaust flow you realize that this is the worst way to look at the problem. Every camshaft you choose, every intake manifold you choose, every combination of engine build you choose and many other variables ALL affect the exhaust. Does one size fits all work? Sure, enough so that you never question it. But what if you did the math for your combination and the hard work of knowing the best exhaust setup was worth another 30-50 wheel horsepower on any motor? Would you start thinking about it more? I know I did long ago.
You know why this exhaust stuff is difficult? Because exhaust systems require a bunch of things. It requires you to understand welding, to know fabrication, to take time (lots of it) and to sit there and keep hacking away until it’s right. It is the most time consuming part of any engine and big power build. But here is the catch, it’s the one place where you can find power you had no idea was there! It is the make or break of why the camshaft you choose either works well or works REALLY well. The draw exhaust affects the pulses on a cylinder head so much so that they can either over-scavenge an exhaust port to the point where the exhaust gas temps (EGTs) rise due to the fact that it is drawing so hard on the intake side. Crazy! Did you know that a good intake is worth about 2-3% of the engine's suctions in power, while exhaust makes up for 7-10%? If you knew that it would, would you think about your exhaust more?
(Horse)Power per Dollar
The main issue with exhaust systems as it is with many important components is cost. Let's face it, you see two sets of headers, one at triple the cost of another and you almost always choose the cheaper of the two. Well, you most likely got the same results in terms of dollar-for-value. When I got into exhaust design and theory it was like a world where you could get lost in. The cost of it, the hours in it, the frustration and testing. It is all there and it becomes something that you can not sell to anyone easily. How can you sell a custom pair of headers and exhaust for 4 times the cost of what's off the shelf? That is a really hard sell even with the best data and a good salesman and you are not always promised to even get it right the first time. Guys who try this wind up with hours of fabrication time and dyno time just to move something 2 inches to see if power and torque changes. 2 inches... that's all it takes to make or break perfect power sometimes. Can you imagine that? Cutting a welding for just small space changes? This is the exhaust world and it is crazy if you wanna dive deep.
When I started building my own headers and other items I would get consumed in the process and it’s way too easy to do this. I would sit for hours and try to time the engine and camshaft specs I made to the length of the tubes and where they would meet at each pulse. Small changes in overlap in a cam changed the length of a primary tube before the collector and changes to the intake manifold would as well. Would I hurt this engine's power band or would I just have the right amount of it.
Needless to say if you’re searching for “good” power then off-the-shelf headers and plumbing is where you will likely land but if you’re looking to squeeze out that extra bit that we all now know is there there are other ways of doing so. They may not be the easiest or cheapest but when we start talking about dollar-per-horsepower, going with a quality exhaust system or designing one that fits your build specifically can make a lot of sense. If there’s a takeaway from this article I’d like you to remember it’s this. Don’t pick the cheapest. The cheapest is often both the worst fitting, hardest to install and the worst performing. The trifecta of terrible.