What to Know About Installing a New Exhaust

We put a HackerPipe on our Victory

I’ve never been wild about aftermarket pipes. In my opinion, most of them produce too much noise and not nearly enough power. Apparently I’m in the minority. The pipe business appears to be booming (no pun intended), and at least half the letters I receive are related to exhaust systems.

Consequently, when HackerPipes asked us to test a version of their “Track-Tuned Header System,” I was ambivalent. After all, there was the noise issue, and the last thing I felt the Victory KingPin needed was more power. On the other hand, I realized that a pipe article—particularly one that featured hard numbers—might be of great service to our readers.

What transpired next sealed the deal. During one of our conversations, Hacker’s PR guy mentioned that dyno testing wasn’t part of their program. In fact, HackerPipes didn’t even own a dyno, but based on seat-of–the-pants testing and customer feedback, they felt their pipes made more power than a stock setup.

Victory KingPin, HackerPipes, Exhaust installation, Dyno
If Hacker supplied the pipes and the Anger Management Fuel module we decided to put them on the Victory KingPin.Photo Courtesy of HackerPipes

That got my attention. Back in August 2003, we ran an article titled “Pipe Dreams,” wherein we dyno-tested some of the more popular aftermarket exhausts. The results were interesting to say the least; the majority of pipes delivered less than stellar results. I’d long wanted to do a follow-up.

So I made the guys at Hacker a proposal: If they’d supply the pipe and one of their Anger Management Fuel Modules, I’d install it and do all the tuning—mimicking what an over-the-counter purchaser would do. The catch was that the pipe and fuel module would be the only changes. There’d be no airbox or ignition modifications, and win, lose or draw, we’d report the unvarnished results. To their credit, Hacker agreed.

Victory KingPin, HackerPipes, Exhaust installation, Dyno
The Victory KingPin was all set to go with the HackerPipes so onto the dyno it goes.Photography by Mark Zimmerman

Step One
To establish baseline numbers, the bone-stock KingPin was delivered to John Tavolacci at Dyno Solutions in Danbury, Connecticut. I chose Dyno Solutions because its only business is dyno testing. John doesn't sell parts, he doesn't build engines and he doesn't offer any sort of tuning services beyond some custom mapping; he simply runs a dyno, and as such, could be counted on to be completely unbiased.

After three pulls we had our numbers and there were no surprises. As you can see from the readout, the KingPin’s best run produced 72.95 horsepower and 93.45 pound-feet of torque. While not outstanding, the numbers are healthy and right in the ballpark for a big-inch cruiser. We also sent a copy of the chart to Polaris; they confirmed our King was hale and hearty and our numbers right on the mark.


The torque curve (represented by the upper line) is fairly smooth, with just a few hiccups in the delivery. Just above idle we’re making over 80 pound-feet of torque, which rises quickly to the maximum of 93.45 pound-feet and, despite some peaks and valleys, stays fairly constant up to 4200 rpm. After that, cylinder filling becomes less efficient and torque starts to drop off. As an aside, the horsepower continues to rise slightly because horsepower is torque multiplied by rpm, and the extra rpm more than compensates for the reduced torque. Similarly, the bottom line representing horsepower shows a nice steady climb toward its maximum of 4500 rpm before leveling off.

With the baseline established, the OEM system was replaced with the HackerPipes Track-Tuned Header and open megaphone, along with the Anger Management Fuel Module. The module was dialed in per the instructions and the bike test-ridden on a 10-mile loop. During the ride, two things became apparent: First, the noise level—while loud by my standards—wasn’t totally obnoxious as long as some right-hand restraint was used, and second, the bike was running way too rich at the bottom, but that was something we’d sort out on the dyno.

Baseline, Victory KingPin, HackerPipes, Exhaust installation, Dyno
The Baseline. The torque curve is represented by the upper line.Cruiser

Dyno Run 2

Track-Tuned Header Open Muffler Anger Management Fuel Module (base settings)
For the sake of illustration, we made our first dyno pull using my seat-of-the-pants fuel module settings. Surprisingly, things don't look too bad. We picked up 2.58 extra pound-feet of peak torque, and the curve is almost identical to that of the stock pipes. Toward the end of the run there's a drop in horsepower as the bike starts to run rich.

Dyno Run 2, Victory KingPin, HackerPipes, Exhaust installation, Dyno
Dyno Run 2: Black line HackerPipe, blue line stock. The bottom graph illustrates the fuel/air ratio.Cruiser

Dyno Run 3

Open Header Corrected Fuel Settings
In essence, this was a breakeven situation, and with no other modifications the Hacker wasn't going to set the world on fire. But at least it hadn't cost us any real performance; it in fact offered measurable gains in horsepower and torque.

What we have here is a bolt-on pipe that changes the look and sound of the bike and provides a modest performance increase at some points of the powerband. Since it’s lighter than the industrial-strength OEM unit, you can also argue that some performance is gained through weight reduction.

Dyno Run 3, Victory KingPin, HackerPipes, Exhaust installation, Dyno
Dyno Run 3: With the air/fuel ratios resolved, the power curve begins to look better. Although there’s a small loss at the bottom of the scale and the curve is a little shaky compared to the OEM pipes (black and red lines), it’s not too bad. We lost a little bit of torque at the bottom of the curve, but we picked up horsepower at the far end, and the peak numbers are slightly better than stock.Cruiser

Dyno Run 4

Quiet Option
Knowing that I prefer a quiet exhaust—quiet in this case being relative—Hacker included a traditional reverse cone megaphone that purportedly made less noise and only slightly less power than the open pipe. Replacing the open pipe with the "muffler" took all of three minutes, and they were right—it was noticeably quieter. The bad news was that on the dyno, it folded up like a deerskin wallet.

Compared to the stock pipe (black and red lines), the Hacker (blue and green lines) is behind on both torque and horsepower throughout the entire curve (the only exception being around 2900 where parity is achieved for a few rpm). But from there, it’s downhill all the way. Making matters worse is a torque crater at 3500 rpm where the Hacker makes 11 pounds less torque than the stock pipe.

Obviously, any torque loss is cause for concern, but a 12 percent drop is serious business as it negatively affects every aspect of performance. Torque holes like this also make the bike difficult to ride because the power drops off as you accelerate past 3000 rpm, and then it comes back on with a bang at 4000 rpm—which can light up the rear tire if the road is slick. It’s entertaining the first time it happens, but after that it’s just nerve-wracking.

Initially, we thought fuel mapping might be the problem, but as you can see from the air/fuel chart, the ratios—while not perfect—aren’t far off the optimum of 13 to 1. As installed, this combo was unacceptable.

So what's going on?
Neither pipe performed as expected, and in fact the quiet version was downright pitiful. Though we felt we'd honored the test parameters, we also felt that in fairness to HackerPipes we owed them a chance to set things right. So we did the logical thing and removed the airbox lid. The change was dramatic.

Dyno Run 4, Victory KingPin, HackerPipes, Exhaust installation, Dyno
Dyno Run 4Cruiser

Dyno run 5

Quiet Pipe, No AirBox Lid
The green and blue lines represent our first pass with the quiet pipe. Torque and horsepower are down compared to the stock bike, and there's that huge hole at 3500 rpm. The black and red lines show what happens when the airbox cover is removed. With no other changes, power instantly increases, and that gaping hole in the torque curve disappears. Better yet, we pick up torque and horsepower compared to the stock setup and in fact end up making 4.7 more pounds of peak torque—a five percent gain.

With the airbox mod, the HackerPipe isn’t bad—there’s an overall increase in power and a decent increase in torque. No doubt that if we pursued this tuning avenue we’d see even more of an increase.

Dyno Run 5, Victory KingPin, HackerPipes, Exhaust installation, Dyno
Dyno Run 5: With the airbox lid removed, the HackerPipe (red and black lines) perked right up. There’s a vast improvement over the first pull (blue and green lines) and a decent improvement over the OEM set.Cruiser

So did we learn anything? In truth, no. As we found in our original "Pipe Dreams" test, merely installing an aftermarket pipe isn't going to get you much of a power increase. Understand that modern intake and exhaust systems are extremely well thought out and extensively tested. The OEMs know exactly what they're doing, and any shortcomings are generally the result of EPA meddling. Yes, some extra power may be found by bolting on a new pipe, particularly if you're not overly concerned with current noise and pollution regulations, but don't expect miracles.

Remember the Golden Rule: Changes in either the exhaust or intake affect airflow through the engine, so in most cases a change in one demands a change in the other. Before laying down hard-earned cash, figure out exactly what you hope to gain. If it’s simply to make noise or change the way the bike looks, then by all means bolt on a new pipe and cross your fingers; maybe you’ll pick up a few ponies, maybe not. However, if your goal is to boost power, chances are you’ll need a pipe, fuel module and airbox/air filter modifications before you realize any genuine increases. And even then, you’ll be lucky to see a 10 to 15 percent gain.

My last piece of advice: If you really want to know where the bear went in the buckwheat, book some dyno time and quantify your handiwork—anything less is just guessing.