05BlackPony

http://www.youtube.com/watch?v=t45WWwCvjMY

Best sounding sixer I've EVER heard.

Jsierzega

taking the cats off of your v6 will reduce back pressure killing your low end torque and hp

Sancho805

negative....it will free the flow which will slow down velocity of the gases and thats what lowers your torq a tad, not hp. backpressure is bad.

basketballord

are you sure about that? I mean I know back pressure is something you want to keep to a minimum, but I thought you still wanted some backpressure and that too little backpressure can be a bad thing for your engine. Seems like I just saw somebody post a comment along those lines the other day.

CroDalmatinac

I currently have MAC Long Tube Headers, MAC Off Road H-Pipe, No CATS and SLP Loudmouths. While it sounds AMAZING at idle, it's too much for me to handle while driving since the whole car shakes. I'm keeping the setup and just putting back on the GT Takeoff mufflers to HOPEFULLY reduce the noise/shaking.

Wickerbill

Im sorry but that is incorrect. 1. Increase the flow, increase in velocity, one of newtons laws, but that has nothing to do with why you could lose tq.. 2. You need a certain amount of backpressure to achieve a "vacuum" effect to allow your exhaust gases to effeiently escape combustion chamber. Too much backpressure and it acts like a barrier and all the exhaust wont escape the combustion chamber. The key inst all about the air going in, butalso escaping all the used gases as completely and effeciently as possible.

Sancho805

ummm.....negative wickerbill. backpressure is "BACK" pressure. putting pressure back into your pistons does NOT help your car, makes it work harder which lowers performance. the vacuum you mention brings it back to the engine. how can that be good? zero backpressure is not likely but the least amount possible is the goal and the same time, maintaing high velocity of exiting gases. the faster those gases get out, the faster and easier your engine can work. explain how your vacuum theory pushes out becuase i'm not understanding your definition. the vacuum is actually bringing gases back in which is definately not ideal.

Wickerbill

Its not my theory, its how a engine works. I build these for a living so if I know nothing else I know engines. Im also a pretty good tranny man but thats for another post The vacuum Im talking about is created by the exhaust leaving the head into the header out the exhaust. This creates a vacuum effect at the head ports so that when your piston comes up on the exhaust stroke and the exhaust valves open to let it escape it helps pull the exhaust through the ports out the header, not into the cylinder. There is no such thing as a 100% effecient engine so you will never escape all the exhaust gases out of the cylinder. But with the help of a small amount of backpressure and a good polish port job on heads you can make that engine as effecient as possible escaping the bad unusable exhaust gases out of the cylinder and the good clean burnable air in. Simple mechanics of a engine, you make power by making a more effecient engine.

Sancho805

Wickerbill,.....OK, thats how i understand the "vacuum" effect happens also but how is that backpressure? that "vacuum" comes from high pressure entering a lower pressure area. if the pressure in the exhaust port is greater than the pressure in the cylinder, the "vacuum" effect would bring exhaust gases back into the cylinder which contaminates the air/fuel mixture, right? the only way i can understand how a minimal amount of backpressure is beneficial would be if the intake/exhaust valve overlap is long and air/fuel has the chance to enter straight into the exhaust port. the backpressure would block that clean mixture and keep it in the cylinder but also "leak" some exhaust back into the cyclinder causing contamination. seems to me that valve timing is critical so that backpressure is not used to keep air/fuel in. I KNOW that an engine isnt perfect but i can't understand how backpressure is a good thing. backpressure "pushes" gases back in, not vacuum out. basic physics can explain that. i'm sure your engine work experience puts you higher than many of us in the auto world but physics is physics and it doesnt take an engine man like yourself to figure it out.

basketballord

http://www.superchevy.com/technical/...t/0505phr_exh/
Scroll down to "Headers -- Primary Pipe Diameters"
"Big pipes flow more, so is bigger better? Answer: absolutely not." Same goes for the cats/no cats argument I would think - there is an optimal level of exhaust flow...too much flow = no scavenging, too little = too much back pressure and decreased performance. Taking the cats off would be too much flow for a non - f/i V6, at least that's how I see it.