The Right Morgan Exhaust System

1. Don’t go too big. A lot of Morgan owners make a mistake when they "upgrade" their exhaust system in purchasing exhaust pipes that are much larger than the factory originals. Most Morgans or any other vehicles leave the factory with the correct size exhaust pipes. While Factory silencers might be cheap and restrictive, their people tend to do a pretty good job choosing the right pipe size and for that matter, it is most often chosen by the engine supplier. Therefore, stick pretty close to the original factory pipe diameter – don’t add more than a half an inch in pipe diameter. I went from 1.875 " to 2" on a Plus 8. I tried larger on a dyno and achieved nothing except a less polite idle.

Note: Exhaust TIP size doesn’t matter when it comes to performance. As long as your tip(s) isn’t some sort of muffler-tip combo, go as big as you can stand. Exhaust tips are a way to tune the sound. The size of the pipe between the catalytic converter and the exhaust tip is what matters.

Here is how to calculate exhaust and header pipe size diameter. Use the flywheel bhp of your Morgan to calculate what  pipe size you need. Larger pipes than that will have no effect. Please note that there are diffiernet sizes recommended depending on whether you have either a dual system (from the engine to the tails) or a single system. Whether you have branch manifolds or not is also a BIG factor. 
Stick close to the factory pipe diameter. A 2″ dual exhaust system has enough capacity for a 300 hp system without ceramic coating or any other advantages other than branch manifolds.  Adding 1/4 of an inch to each pipe adds capacity for nearly 400hp. Going any bigger than 2 1/4 inch pipe diameter is usually overkill (and will often cause your engine to lose power).

2. Think about sticking with the factory exit configuration. Are you thinking about adding a dual exhaust system to a vehicle that currently has a single exhaust pipe? If so, you might want to consider the fact that converting a single exhaust system to a dual system isn’t always a good idea. If you’re driving a 4 cylinder, adding a dual exhaust system is usually a massive step backwards as there is only one exhaust manifold exit on your engine. Unless you’ve got a VERY powerful 4 cylinder, there’s not enough exhaust gases coming out of your engine to necessitate a dual exhaust…and even then you probably don’t need a dual. Dual exhausts only makes sense if you’ve got dual exhaust paths coming out of the motor. If your engine doesn’t have two exhaust manifolds then it probably doesn’t make sense to go with a dual exhaust.

3. You can think of building your own system without doing your homework. If you want to avoid paying big money for an exhaust kit, you can definitely build your own. Here’s what you need to do:

I am dedicating this article to my deeply missed friend Bill Button, who died in a new sports car he wanted to try two weeks short of his 90th birthday. He designed and made his own Plus 8 wexhaust system at the age of 85.)

A. Design the system you want ON the car, so you get the measurements and bends right. The more bends, the less the power. Additionally the more severe the bends the less power. Buy mandrel-bent pipes. Mandrel bends are smoother and more aerodynamic than press bends. If the pipes aren’t mandrel-bent, any changes in direction will result in a restriction. The good news is that you can buy mandrel-bent pipes online.

B. Choose a silencer made for your model and engine. Silencers should be chosen by looking at flow rates. Basically, you figure out where your engine makes the most usable power, and then you optimize everything for that point.
Good Way To Estimate: Take engine RPM x engine displacement, then divide by two. This is the intake volume. Use this same volume of air for the exhaust system, but then correct for thermal expansion (you need to know exhaust temps to figure things out). Fortunately, Morgan silencer manufacturers have done the math and testing for us, so all you have to do is buy a silencer designed for your model.