This is the starting point...
This is the starting point for many racers. Building your first stock car can mean using a set of headers that was originally made for street car applications. Though not designed for racing, these still may have to do for a large number of racers.
Editor's Note: Last month, contributor David Vizard discussed the technical properties of headers. This installment is intended to assist grassroots racers in the selection of this key component.
Headers have a specific purpose in the search for horsepower. But there is a balance between function and cost. The old saying "speed costs, so how fast do you want to go?" is especially applicable to headers.
They have a seemingly simple makeup from a philosophical perspective: a flange bolted to the cylinder head, tubes welded to the flange, and a collector welded to the tubes. All in all, headers do not seem that complex-until you want to make horsepower. That's when factors such as the length and diameter of the primary tubes and the type and length of the collector make a difference in the power that can be developed.
These views show a collec...
These views show a collector.
If you choose to build your own headers, the complexity of their design begins with the selection of materials. Will you use mild steel or stainless steel? When working on the primary tubes, you have to determine the diameter and the length. The goal is to make the primary tubes the same length, but this is sometimes difficult due to limited space in the engine compartment. Will they have a merged collector or a stamped collector? How long will the collector be? The header's construction isn't as simple as the completed product looks.
We sought the advice and council of those who have a vast amount of knowledge about tubular exhaust headers and the accompanying exhaust system as a whole. We spent some time with Billy Boat of B&B Fabrication. You may have heard his name before, as this is the same Billy Boat who sat on the pole of the 1998 Indy 500 when he was driving for A.J. Foyt.
This one will not end up as...
This one will not end up as a merged collector...
Billy has been building headers for many years, and his career began in his father's fabrication business. Now B&B Fabricators is a major player in the high end of the header industry, supplying headers and exhaust systems for top-of-the-line street cars as well as racing headers.
We also talked with Jere Stahl of Stahl Header fame. Jere has been building headers for over 40 years. His knowledge about the design and fabrication of headers came the old-fashioned way-he earned it. Jere is responsible for many of the developments in header design that have become commonplace within the science of exhaust system design, such as adjustable primary tubes, stepped headers, exhaust adapter flanges, exhaust reversion collectors, flow booster collectors, and velocity boosters.
...as the primary tubes will...
...as the primary tubes will be welded in.
SCR: What is the biggest mistake racers make when selecting headers?
Boat: The biggest mistake racers make is [they take on] a "one size fits all" mentality. Headers are a crucial part in the production of power for the engine. Headers are part of an overall system, and they are just as important as the intake manifold for tuning the engine. It makes sense that different tracks and track conditions may warrant a different type of header to match the requirements that the track places on the engine. If you are running a class with a restricted engine or a spec-type engine, it may make sense to do a bit more experimenting with the exhaust system to develop more power. Or at least try to tune the powerband to the track you are racing.
The difference between a merged...
The difference between a merged collector and a simple welded collector is obvious, as is the amount of effort that goes into making this part.
Stahl: Most of the Saturday night racers today have engine restrictions. These restrictions are achieved through a carburetor of a specific size, a set of heads or some other type of inlet restriction, or engine claiming rules. An even greater demand [is placed] on the exhaust system due to these restrictions and the fact that the majority of the racing takes place below 6,000 rpm. There is nothing you can do to an engine below 6,000 rpm that has as much effect as an exhaust system. It is what you do with the headers and the rest of the exhaust system past the headers. Racers' inattention to the driveability of the car has everything to do with the torque curve. The biggest mistake racers make is paying more attention to the price of the headers than the driveability. The exhaust system is such a strong contributor. It is also common for the racer to not pay attention to the variation in the primary tube length. This variation should not exceed 2 inches in length between the primary tubes. We have seen some of the "convenience" headers have as much as 15 inches of variation in primary tube length.
Although financially out of...
Although financially out of reach for most Saturday night racers, stainless steel is the preferred material for headers.
SCR: So, does it make sense for the racer to have multiple headers for different tracks?
Boat: It makes real sense if you race at multiple tracks. You are leaving some speed on the table if you are not maximizing the exhaust system for the track. It is completely possible that one track has some very tight corners that require more low-rpm power to get you out of the corners and another has very fast corners and does not require as great a range in the rpm over the course of a race. The selection of headers you use will affect the powerband of the engine. You need to speak with your engine builder to see what he recommends for your particular application.