Flowtech's Terminator Exhaust for Project 11.99

Coming up with an exhaust system for a strip car is a bit more challenging that for a street car. On a car that is predominantly used for the street, your concerns may be, in this order, sound quality, power, ease of fitment, and perhaps durability. Let's face it, most people who get an aftermarket exhaust do so for the sound. They want a mean, aggressive sounding tone on the outside, but not too invasive and "drony" inside the car.

When considering an exhaust for a strip car, the priorities change. Sound is still a major factor, but in a different way. This time it's the track officials that are imposing the sound requirements. Many tracks have a rule, imposed by surrounding communities, that cars must not exceed 95db, measured at 3500 rpm from 50 feet from the car. Also many classes of bracket racing require the car to be "fully muffled." However rarely is the sound actually ever measured. In fact we have never seen a db meter used by an official at the track. Rather the officials simply use their discretion and authority to determine if a car is too loud. This typically means that all cars must have mufflers, even if the car can meet the 95db requirement through open headers. Most officials simply peek under the car, and if it has mufflers, it's okay to run, regardless of how loud it is. In fact we usually see open-bodied dragsters with huge 5" mufflers, which are clearly louder than 95db, being given the go-ahead nod. Yet when we tried to run Project 11.99 through open headers and 18" extensions, we were told to get mufflers or go home.

So we decided that it was time to get an exhaust system under the '67. When it comes to putting an exhaust system on a strip car, first and foremost you want an exhaust system that does not rob horsepower, and thus hurt ET's. While a few cars may actually see a gain with a well designed exhaust system, the fact is many, if not most, will run better numbers with open headers. With the previous 289 engine, we ran a consistent 2 tenths and 2 mph faster through the headers than compared to a 2.25" exhaust. While it is easy to say that an exhaust system is restrictive, that is not the sole factor contributing to the loss of power. Exhaust systems are added weight, as much as 60 pounds. They also change the air/fuel ratio and scavenging characteristics of the cylinders. There is also the debate over backpressure, and whether engines benefit from slight backpressure. Most experiments have shown that backpressure typically increases low-mid range torque, at the expense of power at the top end. On a street car that operates between idle and 4000, 90% of the time, back pressure is desired as it puts more power in the usable range. On a strip car, operating at no less than 4000 rpm, you'd rather have the top end power.

Our goal for Project 11.99 was to put together an exhaust system that lost no more than one-tenth versus running open headers. We decided to go with a three inch system, that ends at the mufflers, just shy of the axle housing, as opposed to having tail pipes bent over the axle and under the rear bumper. The less bends in the exhaust system means less restrictions and reduced back pressure. Because the car is driven 150 or so miles round-trip to the track, we also needed a system that was somewhat quiet. In reality, if sound was not a concern, we could have simply bolted on two "bullet" style mufflers directly behind the collectors, and had virtually zero restriction. However we've done this before, and it is LOUD. With the drone and resonation under the floorboard this turns out to be louder than open headers.

We contacted Flowtech (Holley) and told them about our engine combo, and they suggested their new X-Terminator pipe and Terminator mufflers. We decided on 3" because it is slightly less restrictive than a 2.5", plus if we go to a larger displacement engine in the future, it will still be up to the task. The 3" pipe will be louder than a 2.5", and it's more difficult for the exhaust shop to work with. For a street car, 2.5" would be preferred. The Terminator mufflers are their highest flowing mufflers, and are claimed to outflow the "F" brand. Besides, we didn't want our car sounding like everyone else's! It is a steel design, fully welded, and utilizes chambers and perforated tubes for sound control, rather than glass packing which tends to burnout. They are not light, nor are they compact. At 15 lbs a piece and 5"x11"x15", they are on the bulky side. You'll want to make sure they fit under the car first!

We took our mufflers and crossover to Mel and Sons Mufflers of San Pablo, CA. These guys are artists when it comes to fabricating custom exhausts, and they have a great reputation around here. Choosing a competent exhaust shop is just as important as buying the right exhaust components. We've had shoddy exhaust systems put together in the past, and they suck. Poorly bent pipes, bad welds, asymmetrical pipes, etc... it not only looks bad, but robs power and eventually falls apart. It's worth driving a bit farther and paying a little more to have it done right.

What we ended up with was an incredible looking and sounding system. The sound of the X-Terminator pipe is very unique; at high rpms it emits a higher pitched note, very similar to something you'd hear at Daytona. To be honest, the system is louder than we thought it would be at idle, but the X tends to quiet out the note at part and wide open throttle. F/M

Read all about the track results here!

Flowtech Terminator
Part Number: 50130
(3" Center/Offset)
Looking down the 3" barrel of the Terminator muffler above, and X-Terminator Pipe below.
A Division of Holley Performance Products


X Versus H
It's long been known that connecting the two sides of a dual exhaust system, shortly after the headers, increases power and reduces sound. However in a traditional "H" pipe, only sound and pressure waves cross through the connection. Gasses take the route of lowest pressure, which is straight out the pipe, rather than making a 90 degree turn in to the H.
Indy and Nascar teams have been using "X" type crossovers for quite some time. In an "X" pipe the gasses from both cylinder banks actually pass through a common area. This not only provides the benefits of some sound wave cancellation, but also increases the scavenging effect, helping draw out spent charge from the combustion chamber.
So how much of an increase does an X gain over an H? It's hard to say, especially considering that every combination will yield varying gains. In theory an X will work better as rpms go up. Considering the Flowtech X-Terminator pieces are priced under $50; you're much better off getting that, rather than having a shop fab up a crude 'H' piece.

click for larger image!<1>Fitting a 3" X under an early Mustang proved to be a challenge. The exhaust techs spent a half hour trying to layout ideal positions that would not interfere with the driveline, and yield minimal bends in the pipes. click for larger image!<2>Once the x was located, mandrel bend pipes were cut and tack welded into place.
click for larger image!<3>With the x setup with inlets and outlets, the rest was down hill. Note we also installed a driveshaft safety loop at this time. It should be six inches from the front u-joint. We had ours welded to the floor pan.

click for larger image!
<4> The intermediate pipe is then run back to the muffler.

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<5>Once all the pipes and mufflers are tacked into location, the whole system is dropped down and completely welded.
click for larger image! <6> The completed system, ready to rumble. The system is held up at the header flanges (we used Flowtech Aluminum gaskets) and rear hangers. This allows the whole unit to drop out for transmission work, etc. We left the ends of the mufflers as shown, no turndowns or tail pipes. We'll show you why in the next issue!
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