Exhaust gasses gotta get out somehow. Reference "bananna in tailpipe" if you don't believe me - it really can stop a car.
The trick is to get them out of your motor in the best way possible, but not too good. Sounds strange? Read on....
When the exhaust leaves your motor, it absolutely positively needs some pipe to run through. A slight bit of back pressure is required to make your motor run. It's mysterious but true.
If there's too much back pressure, the cylinders don't scavenge enough, so the next intake doesn't get enough fuel and your power drops.
As a matter of fact, the so-called "back pressure" isn't really pressure per se, but what's known as the "scavenging effect." It'd take a physicist to explain it completely, but let me give it a shot at the basics, here. Take 30 seconds and see if it makes any sense!
When a car whips by you on the freeway, there's a buffeting wind behind it, because the car had a spot of low pressure behind it. So far, easy enough to understand. If the car whips by you and you're in a tunnel, the effect is much more pronounced.
When the exhaust stroke happens, there's quite a whoosh of gasses under pressure. That piston's moving pretty quick, see. This exhaust stroke is of a certain size and velocity, like a cloud moving down the exhaust pipe. It's not nearly as dense as a car, but it too has a low-pressure spot behind it. Then the exhaust valve slams and this creates another low-pressure wave to intensify the low-pressure spot. OK, it just got harder but I hope you're still with me.
As this cloud exits the collector, the low pressure spot tries to suck something in behind it. Like a piece of paper getting sucked into the tailwind of that car on the freeway.
And finally - remember that 4 cylinders are firing at different times. So, in an excellent exhaust system, each exhaust cloud will suck the next exhaust cloud along with it, increasing effeciency on getting those gasses out of there! Like stock cars drafting in a NASCAR race. This is the scavenging effect. If the pipe's too big, the low pressure spots are less pronounced.
Then, just to make things complicated, these pressure waves develop in closed-looped-exhaust systems. When one cylinder fires, it sends a pressure wave down another cylinder's pipe and this affects the exhaust of that cylinder. At high revs this creates dead spots.
So, the bigger the pipe, the less back pressure and the better top end (within reason). The less restrictive the outlet, the less back pressure and your low-end power might drop off. The wrong loop in the pipe at the wrong RPM and you suffer power loss.
It probably would've been simpler to say, "you need some back pressure, or your motor won't run, and you can vary the back pressure for different performance. My daddy told me this, and my daddy didn't lie - now I'm telling you and I don't lie."
All this converts to real application, of course! Would the SandLizrd carry on without good reason?
OK, let me rephrase that - would the SandLizrd steer you wrong on purpose? NO! Later in this article, see Styles of Baja Exhaust.
Heat risers are a secondary set of pipes that run off of the bottom of the intake manifold. They attach to the front two exhaust pipes, and have small holes in riser & pipe to allow small amounts of exhaust gasses to pulse through the riser, transferring heat to the intake manifold. These cylinders fire at different times, so the pulse runs back and forth, and does truly generate some heat. Heat risers vary in effectiveness, but in icy conditions every little bit of heat matters, considering that the intake is sucking cold air at an amazing rate... and anything that keeps my carburetor from turning into an ice block is OK by Me!
In the Arizona summer, most of us baja fanatics stick pennies in the heat riser's mate to the exhaust and try to limit the exhaust running through. Hey, we had to pull the intake & replace the rubber boots anyway, since they sun-rotted by the end of June!
The best part of heat risers is they serve to stabilize your intake system. Some people cut 'em off, but I've never seen a truly satisfactory stabilizer other than heat risers. The mount to the fuel pump bolt is OK, but it's been known to loosen the front bolt on the carburetor. The mount to the generator backing plate is just impossible to work with! Or, at the least, a royal pain. I'll choose heat risers any day.
Another common problem worth mentioning: Many aftermarket exhaust systems don't have the heat riser pedestals! Seems they're geared towards race applications & just aren't worried about 'em. As stated, I prefer heat risers for intake manifold stability.
So, what to do? Fabricate! Get a pair of heat-riser block-off plates. They're $3 a pair, and are designed for the opposite case - where the exhaust has heat risers but the intake doesn't. Fabricate a bracket from the top exhaust stud of #2 cylinder to the block-off plate, and weld. Bolt the bracket on, bolt the heat riser on, you are Stable!
Check out the cheap artist's impression:
Size does matter, but bigger is not always better. (Get your mind out of the gutter and back onto exhaust systems.) Karl's Custom VW recommends no bigger than 1 1/2" exhaust tube for anything up to and including a 1914cc motor. Sure, if your cam, heads etc. are out of this world you might have to bend the scale a bit, but it's a fact that no 1776cc needs bigger than 1 1/2" tubes.
As a matter of fact, I'm working on purchasing a closed baffle to increase the backpressure a bit and try to regain some low-end power. And that's only on stock heads, Engle 110 cam and 1 1/2" TriMill exhaust with the S&S Header! Not wild by any means.
Many class 5-1600 racers run 1 3/8" exhaust. Again, it's the backpressure thing. They also favor tiny single-barrel carburetors for intake velocity and torque - think about that, while you're at it!
It goes without saying, the type of header & baffle installed on said pipe makes all the difference in the world, so read on to the different brands/styles of exhaust system.
It's universally agreed, the Stinger is the loudest exhaust system. It only has a baffle insert and points up towards ear level or reflects off of buildings, and cannot be beat for raw noise.
It's fun. I ran a stinger for several years, and could set of car alarms at will. People could hear me coming from a mile away (literally). It's a raw noise that has VW tattooed all over its face!
However, the neighbors may grow to hate you.
The QuietPack line of exhaust systems are relatively tame. They sound like a lion purring, possibly - still power but friendly.
Anything that points downward drops the apparent volume to some degree. Even if it's reflecting off of concrete it still disperses the noise to some slight degree.
The question of noise vs. power is so arcane I cannot address it here. It's fair to say that a given exhaust setup produces certain power and certain noise. It is not fair to say that louder is more power, nor can I say that quieter is better. Pick your system and take the noise factor into consideration. You might even select for the noise factor and customize beyond that for the best exhaust you could ask for. I picked my setup because I liked the engineering, my friend has one and I got to drive it and it's great, and some of the racers use it too. Can't be all bad! (Then I bought a quieter baffle.) If your selection criteria goes along with this, you're on track, I suppose, but what did you expect me to say?
Do realize, many national forests require you to have a spark-arresting exhaust system in order to go there.
What does this mean? Said baffles arrest sparks. No forest fires.
Which systems qualify? I've tried researching this and it is hit-and-miss as could be! Some are advertised as such. Others are not advertised or listed as spark-arresting but when you ask you're told that they qualify. I believe that any closed-baffle system will keep you out of trouble but don't quote me on this!
Chrome is a plating that won't rust. It costs more, and some will tell you that chrome-plating creates microfissures in the metal and decreases strength. Chrome plate will blue, that is, turn funny colors due to heat. Looks Neat! A brand-new chrome exhaust system looks funny to me.
I've read about a paint that will coat an exhaust system and never cook, but I haven't seen it - I've seen the so-called high-heat paint boil away. Spotted a dead cylinder by which pipe wasn't cooked, so it's good for something! I understand that such paint should be cooked in - one of the guys at Karl's used to use a pizza oven for this.
Non-plated exhaust systems rust. Almost instantly, relatively speaking - I'm in Arizona and it doesn't rain much so what do I know about rust? If you're concerned about looks you have to go plated. Chrome plate is the only common offering. Take it from there.
(do notice, I've doged all questions about looks vs. function)
An uncommon offering was sent in by Mark in Ocean Springs, Mississippi... he informs me that "a company called Jet Hot Coatings, located in Pascagoula, Mississippi, will coat your exhaust system with the same coating used on the "Shell Oil" Bonneville Salt Flat Jet Car exhaust, of which they proudly display a picture of in their office. (Prices unknown.) The coating is good looking, even, and probably would withstand any punishment a gasoline powered engine could inflict upon it. They would need your sytem either raw or blasted raw to apply the coating.
If you would care to investigate this application further, you can reach them at (228) 762-9406."
I've read about such a coating in HOT VW's magazine and they said about the same thing!
Different exhaust systems route in different ways, obviously. Some even loop underneath the cylinder heads. To me, these look like rock attractors and heat radiators if you have any metal nearby, say a rock guard for the pushrod tubes.
Exhaust hooks on with 8 bolts, and requires 4 gaskets. Not brain surgery by any means, and $100 buys you what you want. The trick is, which one do you want?
The following are listed in alphabetical order. It's sheer coincidence that my favorite is first. If you know of other exhaust systems that deserve consideration here, email the SandLizrd and let me know.
S&S makes a complete line of pipes, headers and the like. A specialty you should know about is their S&S Silencer baffle. it's an aluminum can that mounts onto a Tri-Mill exhaust (or any exhaust if you're versatile enough) and just Sings!
It is available with both open- and closed-baffle designs. It points downward, so is not a rain attractor, and is aluminum so it never rusts.
The only problem isn't really a problem, just a maintenance issue - I've seen 'em blow the baffle out because the spirial-lock included is known to get carbonized, which is similar to graphite lubricant, and pop out on highway acceleration. It's a $40 baffle so you'd want to sink a sheet-metal screw into the can as a retainer.
The open baffle is still loud. The closed baffle is wrapped with steel wool, a superior material, and is comparable to the quiet-pack design.
The stinger is a classic. When baja bugs were new, it was the best exhaust ever! It's loud and brash, sticks up and out the back (like a stinger, see?) and is basically rude as hell.
Problems with the stinger: It catches rain. Anyone with a stinger wants a 1-lb. coffee can in their baja at all times, in case of rain - cover the exhaust! When you stop your motor, some exhaust valve or another is going to be partway open, and this cylinder could fill up with water. hard to start that way. Backing into things can also be a problem - it protrudes beyond your rear pushbar. Even odds whether you'd break the exhaust, break a cylinder head or just break a lug, but all of these are bad. And finally - I personally had problems with the stinger tube assembly liking to sag. The stingerpipe itself mounts onto a collector with either a 2- or 3-bolt pattern (3-bolt is newer and better) and said collector has junctions with 4 pipes coming off of the cylinders. This allows some motion. I had to drill a hole and set a screw to keep the durn thing stationary!
SuperTrapp makes some excellent baffles that install onto an existing exhaust system. The beauty (beauties) of the SuperTrapp are in the engineering. You add or remove these spacer disks to adjust the amount of back pressure and tune the scavenging effect! Changing your valves? No problem, add a couple of disks. Neighbors hate you? Fine, quit hammering gussets on their curb, and remove a few disks. The tuning process takes some time, but is infinitely variable!
I experienced the joys of SuperTrapp systems in my 3-wheeled days - when the Honda ATC 110 was the rage. Being the smart-ass kid I was, I put on every disk the threads would allow and ran like hell! Mucho power on that setup.
Also worth mentioning - SuperTrapp is advertised as a spark-arresting exhaust. No worries.
The Tri-Mill style of exhaust is pipes only, although they do sell a baffle. You should mount on a baffle of your choice. A major advantage of the Tri-Mill is that it angles all exhaust up and away, so there's minimal pressure waves going into other pipes. It routes fine, too. The only real disadvantage is that it's always in the way! Also, in its stock configuration it points upwards, so the noise volume and rainwater are issues.
I should also mention, anyone with a Tri-Mill should have extra springs in their spares kit, since the stock springs like to break.
TurboTubes are great for their two-into-one style. Harder to get bad pressure waves that way. This changes the scavenging effect, so let it be known: if you change from one exhaust setup to turbo tubes, the entire motor equation will change. They're tuned to a degree and run fine. The volume is up there a bit, as they point straight back. The set I'm looking at currently are routed under the heads, and I don't like that - rocks, heat, too close to the pushrod tube protectors, the total effect is not for me. Must be configured for non-baja or something where there's no room alongside the valve covers.
There's a whole variety of Quiet-Pack-style exhaust systems out there. What this means is, there's a conventional-style muffler mounted onto the collector point. Some weave around behind the motor and make your pulley inaccessible. Others angle downwards and are always in the way. I hate to generalize, but they typically increase back pressure a bit so are good for low end, and may be the quietest full-baja setup available.
But they're always rusty! And I've gotten more nasty burns from 'em, since they're so big they always seem to be in the way. But I've been saying that about lots of exhaust systems.
Thanks to Wes and all the good guys at Karl's Custom VW for their Assistance!
Are you breathing easier?