Technical Information About Headers

There are two different types and designs of headers:

  • Interference Header
  • Equal Length Four into One Header

There are of course slight variation of these designs, and there are specific benefits of each headers design, in terms of application.

Interference Header - Historically this is the type of header design that HM Headers manufacturers. A form of science is applied to design these headers, thus it is technically more difficult to design and manufacture.

The interference header is flexible in its design allowing it to be fitted to vehicles that are either heavily modified or standard vehicles. The interference design means that the primary pipes are married to the secondaries following the firing order of an engine.

Due to the primary pipes being married together this develops a scavenging effect, which enables the headers to scavenge the exhaust gas from the engine, allowing the engine to be more efficient in discharging the exhaust gas, and developing more kilowatts and torque at a lower rpm range than any other header. In fact interference headers develop their kilowatts and torque within a more useable power band; well designed interference headers, such as HM Headers, typically develop kilowatts and torque from approximately 1800 RPM onwards, thus interference headers provide better "street drivability".

In fact HM Headers are designed to be fitted to standard non modified vehicles as well as highly modified vehicles with engines that develop in excess of 350 kilowatts.

Equal Length Interference Header - Fuel Economy - A common misconception in fitting interference headers is that, due to the increase in kilowatts and torque it will have a negative impact on fuel economy. This is in fact not true and the vehicle may achieve better fuel economy, if the engine is in good working order as the headers allow the engine to work more efficiently as previously explained. This in turn betters the fuel economy.

All HM Headers are supplied with fitment kits which includes, when required, clamps, nuts, bolts, gaskets and flanges.

Equal Length Four into One - This particular header is relatively easy to manufacture and very little science is used in the design of it. The design lends itself to marrying all the primary pipes, which are of equal length, into one large collector. This design of header and its benefits strictly apply to engines that are designed to operate above the 5000 - 6000 RPM and onwards; hence they are not suitable for road going applications. In fact to gain significant increases from fitting equal length headers many fitters of this design will suggest a performance camshaft, PCM recalibration, differential ratio change and hi stall torque converter be fitted as well as the header.

Equal Length Four into One Header - Fuel Economy - Due to the benefits of these headers not being achieved until 5000 to 6000 RPM with many vehicles, any fuel efficiency gains are relatively rare.

Catalytic Converters

Our Perry Exhaust systems use Delphi catalytic converters. Delphi is the manufacturer of many Original Equipment catalytic converters for Manufacturers of Australian vehicles as well as many vehicles sold overseas. The Delphi catalytic converters are of the highest quality, and Perry Exhaust converts them to a high flow catalytic converter that is able to withstand turbo and supercharged engines that produce over 350 kilowatts.

Delphi's superior quality compliments the HM Header and Perry Exhaust range well therefore we only use Delphi products. To this end Delphi has selected us as the only aftermarket supplier of their product for the Australia Aftermarket Exhaust Industry.

Exhaust Systems

Perry Exhausts offers a large range of performance exhausts and our main achievement has been to introduce a high standard of quality in the industry for performance exhaust. Due to our extensive work as an Original Equipment Manufacturer we are able to offer similar quality at an affordable price. Our exhausts comply with aftermarket regulations and do not suffer from booming that is apparent with many aftermarket performance exhaust systems. We offer a range of mild and stainless steel with mandrel bends to ensure maximum performance, the right look and fit.

All Perry Exhaust systems are fitted with chrome tips, they use original mounting positions of existing exhaust systems and all exhaust clamps, nuts, bolts and gaskets are supplied as part of our fitting kits.

Mild Steel Vs Stainless Steel

Traditionally, all headers manufactured by HM Headers, prior to 1986 were built from 16 gauge, mild steel tubing. However due to the introduction of catalytic converters with the advent of unleaded fuel many of the vehicle manufacturers required stainless steel exhaust components. This was due to mild steel contaminating catalytic converters as a result of excessive corrosion caused by the higher temperatures that unleaded vehicles run, thus causing an increase in mild steel oxidization. The use of stainless steel was used to overcome this concern.

HM Headers and Perry Exhaust were quick to adopt this new standard in material application, for the supply of vehicle manufacturer's original equipment and the manufacturing of our own aftermarket product.

"I never read fitting instructions."

Sometimes reading fitting instructions can seem like a waste of time for the expert exhaust fitter. But the fitting instructions that come with the HM Headers and Perry Exhaust product are more than just step by step directions on how to fit a header. They are constantly being updated with new advice, fitting shortcuts and "tricks of the trade".

So, please take the time to quickly read through the fitting instructions contained in the header package and take advantage of any fitting tips coming out of HM Headers and Perry Exhaust Research and Development team or from other exhaust fitting professionals.

If the Header does not have fitting instructions please phone our hot line on 1800 442 337 and seek our assistance.

Headers - Do not fit gaskets!

(Unless the vehicle has aluminium cylinder heads or is a non-cross flow configuration.)

Fitting instructions advise the installer not to fit gaskets to nearly 80% of the product range. This is due to the extremely high standard to which all HM Headers header flanges are manufactured. The use of an appropriate sealant on all flange faces is all that is required for a successful header installation.

This "no gasket" policy is valid for all V8, V6 and cross flow 4 and 6 cylinder engines. With non-cross flow engines the fitting of an exhaust manifold gasket is advised for the sake of sealing the inlet manifold.

If a gasket is required to be fitted, Use an original equipment gasket or a quality after market product.

"If I don't have to fit gaskets, what type of sealant should I use?"

Do not use a silicone base sealer of any type in front of your O2 sensor or Catalytic converter.

We recommend the use of an automotive grade product for sealing all flange faces. Ordinary automotive grade paste is able to withstand the high temperatures generated at the exhaust port of an engine and is less likely to "blow out" and begin leaking like some silicone exhaust sealers can do.

When fitting a set of headers to a vehicle with a catalytic converter and oxygen sensor, it is recommended that the installer does not use a silicone product which if used incorrectly can damage or poison the cat or oxygen sensor. There are several brands of quality non-silicone pastes available from local auto parts suppliers.

Once the header installation is complete, do not immediately start and rev the engine. This could lead to "blowing out", as the sealant would not be cured. If the vehicle needs to be driven as soon as the header is installed, start the engine and let it idle for 2-3 minutes. The exhaust heat from the idling engine will help speed up the curing process without the risk.

Welding On Vehicles

It is recommended that if any welding is required during the installation, the vehicle's battery be disconnected, however you will lose radio codes etc if you choose this option. Furthermore, it is highly recommended that any engine management computer system be disconnected or the appropriate engine protection device be used. The vehicle's owner's manual will usually indicate where the engine management computer is located.

The best advice is to avoid welding on the vehicle.

Emission Control Devices

It is important to note that while fitting a set of Headers or sports system it is the fitter's responsibility to reconnect and make operative all relevant emission control devices. These include catalytic converters, oxygen sensors, EGR pickups and air pump connections.

As most of the HM Headers and Perry Exhaust product range comes complete with the relevant connections, it is simply a matter of re-installing the appropriate emission control devices.

We Appreciate feedback!

If you feel, at any time, that you have some constructive information that you wish to pass on concerning the HM Headers and Perry Exhaust product range, please feel free to contact us.

The contact numbers are:
Phone - 1800 432 337
Fax - (03) 9792 2223