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Hot Air 29/03/2003 (V8 Headers) PDF Print E-mail

The other day a customer, whose car was in for muffler replacement, looked through some photo’s of performance exhaust mods on my counter and commented after a while:

 

“These are photo’s of brand new cars!” pointing to pics of an Audi TT and a Mini Cooper S, “How come they need exhaust replacement already; anyway, aren’t these latest exhausts of stainless construction?”


He had always been under the impression that exhaust replacement was just a necessary evil, a grudge-buy! So he was amazed at my answer to his question, which was that a lot of new vehicles are brought in for performance enhancement through the use of custom-fabricated performance exhausts. He had no idea that a car’s performance can be improved by means of an exhaust!


The fact of the matter is that in most cases, a well-tuned exhaust is the cheapest way of increasing horsepower. This is definitely the case in virtually all V8 systems that I have encountered, especially American V8’s.


There is awe about V8’s. They evoke great memories of Cadillacs, Mustangs, Nascar racing and drag racing and the notion of the American dream – bigger is Better! Who can blame them!

 

Who of you can remember the feeling of pure muscle power when the gentle exhaust burble at idle turns into instant blue smoking rubber by simply flooring the accelerator pedal!


V8 motors are generally big bore 5 litre and bigger capacity motors, which are inherently torquey by nature. The primary factory exhaust design considerations are:

  1. To optimize power and torque relative to the engine’s characteristics.

  2. To direct the burnt exhaust gases into the atmosphere away from the driver and passengers.

  3. To minimize vibration and noise output

  4. And lately, to minimize harmful exhaust emission.

 The exhaust design for these vehicles, almost without exception, until recently has been biased towards the noise abatement aspect. This non-performance related requirement assures the exhaust tuner near exceptional scope to improve power and torque.


Cross-over header pipes

The V8 motor is generally regarded as two 4-cylinder engines joined in a V-form driving off one common crankshaft. This is not the case. Most V8’s are four V2’s joined together in a 90° sequence. The resulting uneven exhaust cycle spacing on each 4 cylinder bank causes a certain limitation in power potential of conventional 4-1 or 4-2-1 branches on each bank of cylinders.

 

To obtain even exhaust sequence spacing, i.e. the required firing order on the converging 4-1 collectors, some of the header pipes must cross over to the opposite bank of cylinders.

 

This system is called the 180° crossover header system because an exhaust pulse occurs in each collector every 180° of crank rotation.

 

There are some disadvantages to the crossover headers:

  1. The header lengths are critical to the required power band. It is not always possible to cater for equal length headers due to routing constraints.

  2. On high revving motors the required header lengths are so short that this system cannot be used.

  3. Where do you install crossover headers under the bonnet? This application is only practical on racing vehicles with the motor location and body panels designed to accept crossover headers.


Conventional 4-1 headers

Theoretically, bank separated 4-1 headers are generally not as efficient as the 180° set-up, but are not as sensitive to header pipe length, which simplifies fabrication in the engine bay, maximizing the use of available space. However, for high performance motors, large diameter header tubing is required, which, in some cases is impossible to install without re-arranging the body-work.

 

The answer to this problem is (can be):


The 4-2-1 (TRI-Y) headers

The main advantages of this type of V8 header systems are:

  1. They are even less sensitive to length than the 4-1 header pipes

  2. They often produce a wider power band

  3. They produce only slightly less power than a good 4-1 header. So they can be used in moderately modified engines with cam duration up to 270 degrees.

  4. They can be installed in much more confined spaces. Smaller header diameters can be used, which simplifies fabrication around obstacles to a greater extent.


However, if the V8 motor is going to be fitted with camshafts of substantially longer duration than 270°, a 4-2-1 header system is going to produce less peak power than a good 4-1 header system.


So, if you are one of those enthusiasts contemplating a V8 installation into your bakkie or kit car, include the following in your planning stage:

 

Pick a vehicle with considerable space available to the sides of each bank of cylinders and both sides of the gearbox bell housing to ensure sufficient freedom for exhaust header fabrication options. (Theo Marcolefas, take note!)


That’s all for now!

Abel dos Santos

 
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