Working with Hooker’s Adjustable Race Headers – Part 2

Click Here to Begin Slideshow In our last issue, we zoomed in on the header primary tubes. If you point your browser back to that segment, you’ll recall we provided you with some insight into what to look for in terms of both primary tube diameter and primary tube length. Obviously, with a good set of Hooker adjustable headers, it’s relatively easy to increase the length of the primary tube. Increasing primary length tends to move power production downward in the RPM scale. But you can also tune with the collector (in addition to the primary tubes, or combined with them). The collector system found on a set of race headers might have more to offer than you’d first think. When it comes to the collector, let’s start at the very beginning: The job of the collector is to take advantage of the "secondary tuning impulses" from the other pipes in the system. According to Hooker Headers, the influence of the collector is generally restricted to the RPM level below the torque peak of the engine in question. That’s important, and Hooker Headers also notes that size of the collector is actually more critical in engines that spend the majority of their time in the lower RPM ranges. Not counting the bundle of snakes that can make up an 180-degree header system (although impressive looking, they are well beyond the scope of this series), there are two different types of headers commonly used in drag racing: those with 4-into-1 collectors and those with a “Try-Y” or 4-2-1-collector arrangement. What’s best? Reher-Morrison sheds some light on this: “Conventional 4-into-1 headers collect the exhaust for one side of the engine into a single collector. Despite their simplicity, we have found no advantage in using any more complex header design for most race cars. “Try-Y and 4-2-1 headers collect the exhaust by pairs of cylinders that are as far apart as possible in the firing order. The idea is that the gases racing past the silent tube will scavenge a vacuum in it, reducing exhaust reversion. We have found no advantage in this design for the majority of racing applications.” Reher-Morrison’s David Reher has something else to add on the above: “Where header design is compromised due to things like shock towers and tight engine compartments, it may be worth testing a properly designed Try-Y (where the header design is coordinated to the firing order), particularly in applications with lower engine speeds.” Length and Diameter of the Collector: The length of the header collector is important, but the truth is, it’s not absolutely 100% critical. Sure, some racers take the time to adjust collector length for a given car combination (good news, we’re sure). The trouble is, there’s a false narrative out there that states the length of the collector can have a profound effect in the engine tune up. That simply isn’t correct. Reher-Morrison tells us that a collector length change is tiny in terms of performance when compared to the changes one can make in the intake tract, valve train and so on. The notion here is headers should compliment the engine in the car. If you build an engine and you find there is a need to revise it to better suit the car combination, changes in the valve train (for example, advancing the camshaft) will have a far greater effect than making changes to the collector. If you need more bottom end and you want to get it with the headers, adding primary tube length is often a better approach. Fair enough, but where should you start when it comes to choosing the right collector for your racecar? Reher-Morrison shares some insight with a range of collector diameters and lengths we should target: “Like primary tube diameter, the diameter of the collector affects the exhaust restriction and velocity. Many small block racing engines perform better with collector diameters between 3 and 3-1/2-inches. Large displacement, high-horsepower engines require 4-5-inch (diameter) collectors. The length for most drag racing applications varies between 8 inches and 14 inches.” Merge Collectors: A variation of the conventional 4 into 1 header is the merge collector. With a series of both exhaust waves and sonic waves entering the collector, it’s easy to see that there is more to collector shape than you might have anticipated. Hooker Headers advises that a merge collector minimizes the reflected wave, so it has less effect upon the inertia pulses. The internal hourglass shape of this collector configuration tends to regulate the high and low pressures. It is also designed to speed up the velocity of the gas flow. Something else to consider is the overall shape of the collector (particularly in the case of a merge collector); it helps equalize the transition of the individual exhaust tube gases. When it comes to merge collectors, the shape and angle of the tubes that physically merge inside is important. Ditto with the overall length of the collector. You'll also find a "spear" or "pyramid" inside a merge collector. The purpose of this spear is to control the exhaust gases so that they don’t re-enter the primary tube and then travel backwards into the cylinder head by way of the low-pressure area (this is typically exhaust gas dilution). If the collector has an hourglass shape, the neck is equally important. By reducing the size of the neck, the exhaust gas velocity will increase as it is carried into and out of the collector. As it turns out, some racers have experienced an actual increase in the EGT (Exhaust Gas Temperature) in certain applications with a merge collector. This is likely due to the header extracting more of the air fuel mixture out of the cylinder and burning it inside the collector. Given this scenario, it’s probably a good idea to review (and revise) the engine camshaft timing events, and take the same approach with carburetor jetting. Reher-Morrison pointed out previously that there are other types of collectors available. Some pair the cylinders based upon firing order. Essentially, these collectors simulate a Tri-Y header configuration, and for a few applications, there could be more performance with this setup. Aside from their unique configuration, it's interesting to note these collectors usually range in length from 23 to 25 inches, well beyond the length of many conventional or merge collectors. One has to ask if a car picks up (performance wise) with a Try-Y design, complete with a long collector, was it the configuration (Try-Y) or simply the car’s need for a longer collector that induced the performance improvement? In the old days, it was common to tune the length of a collector with a crayon. You’d draw a line on the collector with a wax crayon. Then you’d make a pass with the car, climb underneath and check the crayon mark. Where the mark discolored is the point you’d chop off the collector. Easy-peasy, but what if the tuneup is really messed up and the engine is burning raw fuel in the collector? Then the crayon mark means nothing. There’s a better idea: Simply watch the ET slip! If the car picks up with a shortened collector, you’re going in the right direction. If it picks up with a collector extension, you’re headed in the right direction. In the end, getting your headers “in tune” isn't exactly cut and dry. More often than not, it becomes a game of test and try. The ET and MPH of the car will tell you if the header changes you made are good or bad. It’s that simple.

Working with Hooker’s Adjustable Race Headers - Part 2

Click Here to Begin Slideshow

In our last issue, we zoomed in on the header primary tubes. If you point your browser back to that segment, you’ll recall we provided you with some insight into what to look for in terms of both primary tube diameter and primary tube length. Obviously, with a good set of Hooker adjustable headers, it’s relatively easy to increase the length of the primary tube. Increasing primary length tends to move power production downward in the RPM scale. But you can also tune with the collector (in addition to the primary tubes, or combined with them). The collector system found on a set of race headers might have more to offer than you’d first think.

When it comes to the collector, let’s start at the very beginning: The job of the collector is to take advantage of the "secondary tuning impulses" from the other pipes in the system. According to Hooker Headers, the influence of the collector is generally restricted to the RPM level below the torque peak of the engine in question. That’s important, and Hooker Headers also notes that size of the collector is actually more critical in engines that spend the majority of their time in the lower RPM ranges.

Not counting the bundle of snakes that can make up an 180-degree header system (although impressive looking, they are well beyond the scope of this series), there are two different types of headers commonly used in drag racing: those with 4-into-1 collectors and those with a “Try-Y” or 4-2-1-collector arrangement. What’s best? Reher-Morrison sheds some light on this:

“Conventional 4-into-1 headers collect the exhaust for one side of the engine into a single collector. Despite their simplicity, we have found no advantage in using any more complex header design for most race cars.

“Try-Y and 4-2-1 headers collect the exhaust by pairs of cylinders that are as far apart as possible in the firing order. The idea is that the gases racing past the silent tube will scavenge a vacuum in it, reducing exhaust reversion. We have found no advantage in this design for the majority of racing applications.”

Reher-Morrison’s David Reher has something else to add on the above: “Where header design is compromised due to things like shock towers and tight engine compartments, it may be worth testing a properly designed Try-Y (where the header design is coordinated to the firing order), particularly in applications with lower engine speeds.”

Length and Diameter of the Collector: The length of the header collector is important, but the truth is, it’s not absolutely 100% critical. Sure, some racers take the time to adjust collector length for a given car combination (good news, we’re sure). The trouble is, there’s a false narrative out there that states the length of the collector can have a profound effect in the engine tune up. That simply isn’t correct.

Reher-Morrison tells us that a collector length change is tiny in terms of performance when compared to the changes one can make in the intake tract, valve train and so on. The notion here is headers should compliment the engine in the car. If you build an engine and you find there is a need to revise it to better suit the car combination, changes in the valve train (for example, advancing the camshaft) will have a far greater effect than making changes to the collector. If you need more bottom end and you want to get it with the headers, adding primary tube length is often a better approach.

Fair enough, but where should you start when it comes to choosing the right collector for your racecar? Reher-Morrison shares some insight with a range of collector diameters and lengths we should target: “Like primary tube diameter, the diameter of the collector affects the exhaust restriction and velocity. Many small block racing engines perform better with collector diameters between 3 and 3-1/2-inches. Large displacement, high-horsepower engines require 4-5-inch (diameter) collectors. The length for most drag racing applications varies between 8 inches and 14 inches.”

Merge Collectors: A variation of the conventional 4 into 1 header is the merge collector. With a series of both exhaust waves and sonic waves entering the collector, it’s easy to see that there is more to collector shape than you might have anticipated. Hooker Headers advises that a merge collector minimizes the reflected wave, so it has less effect upon the inertia pulses. The internal hourglass shape of this collector configuration tends to regulate the high and low pressures. It is also designed to speed up the velocity of the gas flow. Something else to consider is the overall shape of the collector (particularly in the case of a merge collector); it helps equalize the transition of the individual exhaust tube gases.

When it comes to merge collectors, the shape and angle of the tubes that physically merge inside is important. Ditto with the overall length of the collector. You'll also find a "spear" or "pyramid" inside a merge collector. The purpose of this spear is to control the exhaust gases so that they don’t re-enter the primary tube and then travel backwards into the cylinder head by way of the low-pressure area (this is typically exhaust gas dilution). If the collector has an hourglass shape, the neck is equally important. By reducing the size of the neck, the exhaust gas velocity will increase as it is carried into and out of the collector. As it turns out, some racers have experienced an actual increase in the EGT (Exhaust Gas Temperature) in certain applications with a merge collector. This is likely due to the header extracting more of the air fuel mixture out of the cylinder and burning it inside the collector. Given this scenario, it’s probably a good idea to review (and revise) the engine camshaft timing events, and take the same approach with carburetor jetting.

Reher-Morrison pointed out previously that there are other types of collectors available. Some pair the cylinders based upon firing order. Essentially, these collectors simulate a Tri-Y header configuration, and for a few applications, there could be more performance with this setup. Aside from their unique configuration, it's interesting to note these collectors usually range in length from 23 to 25 inches, well beyond the length of many conventional or merge collectors. One has to ask if a car picks up (performance wise) with a Try-Y design, complete with a long collector, was it the configuration (Try-Y) or simply the car’s need for a longer collector that induced the performance improvement?

In the old days, it was common to tune the length of a collector with a crayon. You’d draw a line on the collector with a wax crayon. Then you’d make a pass with the car, climb underneath and check the crayon mark. Where the mark discolored is the point you’d chop off the collector. Easy-peasy, but what if the tuneup is really messed up and the engine is burning raw fuel in the collector? Then the crayon mark means nothing. There’s a better idea: Simply watch the ET slip! If the car picks up with a shortened collector, you’re going in the right direction. If it picks up with a collector extension, you’re headed in the right direction.

In the end, getting your headers “in tune” isn't exactly cut and dry. More often than not, it becomes a game of test and try. The ET and MPH of the car will tell you if the header changes you made are good or bad. It’s that simple.

Working with Hooker’s Adjustable Race Headers - Part 2 1

For naturally aspirated combinations, header collectors are necessary. There are a number of different collector configurations out there. This is a standard 4-into-1 setup from Hooker Headers.

Working with Hooker’s Adjustable Race Headers - Part 2 2

This photo shows the inside of a conventional Hooker 4-into-1 collector. Compare it to the merge collector shown in the next photos:

Working with Hooker’s Adjustable Race Headers - Part 2 3

In addition to the conventional collectors, Hooker Headers also manufactures a special “merge” collector.

Working with Hooker’s Adjustable Race Headers - Part 2 4

The merge collector’s format is still a 4-into-1 setup, but internally, it makes use of a special spear designed to smooth the transition of spent gases.

Working with Hooker’s Adjustable Race Headers - Part 2 5

In tuning a combination, keep in mind you can easily change the overall length of a collector, either by shortening it or by adding a collector extension (Hooker Header’s example is shown here). Hooker’s collector extension measures 15 inches long.

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