More about smog and emission

Hey folks and constant readers! Hope you all had a fantastic New Year and kept it all above the board and safe. I know for a fact the loud obnoxious bus drivers didn't but alas it will have to be a people's revolution before things ever change in this country. Remember if the French and the Russian could wipe out their respective royal families, then the bus maniacs ain't nothing! Now onto my last bit about headers, heck by now you all could start header production facilities ….or so I hope.

When a pulse travels down the primary of a Tri-Y header to the collector, i mostly go down the main branch of the primary. When it reaches the collector, the reflected wave also travels back up the main primary to the exhaust valve and back out again. However in a Tri-Y, the branch that goes up to the opposite cylinder, since the exhaust valve is closed for that cylinder, acts like an interference branch, creating a pulse and an assisting wave of it's own, slightly out of phase with the main pulse and wave. This widens the bandwidth of rpm that the additional scavenging is effective by making the pipe less sensitive to rpm induced pitch.

The pipe becomes "in-tune" for a longer band of rpm, widening the engines power band at the expense of slightly reducing peak power over a 4-1 design. Since some of the pulses energy is dissipated in the interference branch, the main pulse is not as strong and scavenge is not as total for the Tri-Y. Peak scavenging efficiency is compromised for having good scavenge over a wider range of rpm. That is why many full race engines where peak power is important use 4-1 designs, while many headers that are designed for best drivability like street engines or rally engines use Tri-Y headers.

We feel for the most part, the majority of you street performance freaks are better off either with a Tri-Y or a 4-1 with either long runners, small runner diameters or both and a merged collector.

For street cars it is essential that the headers you purchase have provisions for all of the vehicles stock O2 sensors, EGR fittings and any other emission controls that the vehicle originally had fitted to the exhaust manifold. Most modern emission controls do not rob any wide open throttle horsepower. The common EGR valve, which reduces toxic oxides of nitrogen, closes and has no effect at wide open throttle. Most air injection devices only usually operate either on cold start or under closed throttle deceleration on most modern cars. Removing these controls does not help power and pollutes the air. This is not good for a street car as we must all do our part to help keep our planet clean.

Just because your headers have provisions for all of your smog equipment, don't assume that it is street legal. Due to the intelligence of some of our local government agencies, unless an aftermarket part is CARB approved with a CARB EO number, it is not legal in some states no matter how clean the gasses coming from the tail pipe are! So if no smog certification hassles are important to you, either check your local laws before installing or make sure that the part you buy has a CARB EO number. Your parts dealer should be able to answer that question.

You can expect a power gain of about 6-12 hp at the wheels from a well-designed header on most cars depending on how bad the factory exhaust manifold was. If you drive the same, not exploiting your newfound power too frequently, you can expect better mileage with a header due to the improved volumetric efficiency it produces. In buying a header look for thick wall mild steel tubing, at least 16 gauge, and preferably 14 gauge. Rust and heat resistant ceramic coated or stainless steel primary pipes are preferred for longer life. Look for thick flanges also as these will resist exhaust leaks and last much longer.

Hotshot, Stillen, AEBS, S&S and many others make good quality headers for most popular Jap cars. There are a few others out there but generally the quality is much lower.

Well that's it for this episode feel free to e-mail me with your questions on plasmaim@yahoo.com and I will do my very best to answer your queries.