[Goldenblack440]

I have a warm 360/904 going into a 73 Challenger, hi lift cam (2700-5800). The heads are small port smog heads. i have port matched the Edelbrock Performer inlet to the untouched heads. I have just got some headers. They are 1-5/8 primary. The exh ports are smaller, so should i port match these as well? Someone told me not to- to leave the step which creates an "anti-reversion" effect. Any idea if this is correct- benefits? etc

What do you reckon Eddie?

PS, the exhaust system is going to be a twin 2-1/2 with X pipe and low restriction mufflers eg Lukey straight through or Flo Master. It won't be anything fancy like mandrel bent. I hope all this will still have enough backpressure to give the torque i need? As i want driveability, its a heavy 3800+ car. i'm hoping the inherent torque of the 360 will still be there

Thanks, Steve

[dave-r]

Don't open up the exhaust ports.

Here is some reading for you; http://victorylibrary.com/mopar/header-tech-c.htm

Note the bit that says "If the primary pipe inside diameter is more than 1/8” larger than the actual port opening in the head, the header flange bolt pattern can be slotted slightly to raise the centerline of the primary pipe above the center of the port, until the bottom of the pipe just matches. This puts the pipe's effective center closer to the most active area of gas flow, and the mis-alignment at the roof allows the highest-pressure gas an easier path away from the port; also adds some degree of anti-reversion."

This is interesting too; http://victorylibrary.com/mopar/ci-man-tech-c.htm

[Eddie]

I agree with Dave. The exhaust ports are under pressure and flow different than the intakes which are under a "vacum",(pressure differential actually), and musnt be 'hogged out' like the intakes. A lot of guys will port the exhaust ports and make them flow worse than the the stock ports. With your cam, I would keep the port matched intake as you have done and leave the exhaust side alone. A nice valve job, back cut valves or aftermarket, if you do any head work other than what you have done, a back cut valve, bowl cleanup but dont enlarge them past 85% of the seat opening in other words be conservative if removing any material other than the valve guide. Air likes a gentle radius or curvature no sharp edges and you'll be fine.

[Goldenblack440]

Thanks Dave and AFE. that info is gold- now i know the reason for it, where everyone was saying don't do it but couldn't tell me why! Hope you didn't mind me cutting and pasting your answers in to another (Aussie) forum- all helps spread the good word

All for now...steve