Back pressure for torque? doubt it... ive read somewhere that backpressure=torque is a myth. torque is mostly produced by volumetric efficiency, ie the more air you can cram into the cylinder the more air there is to be expanded in the resulting explosion thus creating more push down on the crankshaft. so bigger intake valves and increased bore are the torque producers, and bore/stroke determine at what rpm the torque is at.

although i think i know what you mean about flow... with the exhaust valve open, and the piston rising, this forces out the waste gases. so if the pipe on the header is bigger than the exhaust port the gas as it is being pushed out by the piston is moving into a larger volume area and slowing down. once the valve shuts there is only the ready momentum of the gas and expansion to power it along its way until the next pulse of gas from the same cylinder.

therefore shouldnt the primaries be matched or maybe a bit smaller than the exhaust port to keep flow at a good rate? what size is the stock falcon exhaust port? and the exhaust valve?

I think pacemaker would have done their research though.

make the port flow high number by making it bigger is the wrong to go about it. the port will loose velocity and it will make the engine 'peaky'.
loss of velocity means a loss of cylinder scavenging, resulting in residual gasses in the chamber.
gaining flow by make the port shape better while using the a smaller port will keep velocity up and create power over a broader RPM range.

the exhaust ports on the I6 heads already flow well, and very little work will result in big gains, the intake port is the problem and time and money are better spent there

thanks for that mate, much apreciated, I love the s**t you can pick up on here.

just wondering how much residual gas can be left in the chamber? how much room is left in the head after the piston reaches tdc? if the valve is still slightly open after tdc then I can see some gas being withdrawn back into the chamber, but that would be a cam timing issue wouldnt it?

obviously theres and optimum point for ex valve/port size on an i6, as you go too small, and the amount of energy required to push the gas out the hole would rob power off the other cylinders firing in order for the exhaust stroke on that cylinder to occur?! maybe ford should have swirled the exhaust port to increase velocity? you could take parts of the exhaust port out in a swirl patern.. if your good with a grinder. increase in size would be little, but shape would be improved for flow speed.

Im just drinking and chuckin ideas that hit my head... im no mechanic... not even close.

The reason the 4480 extractors are far better is that they have dyno tested them for the sallon race cars. The 4480 pacemakers are tuned length extractors (some length tubes). The reason why they are smaller in one section is that they will create a vacuum type suction affect to scavage all the gasesout of the engine which makes them work not just look good.

ever checked the pipe lengths on the 4480s?

and there one reason the primary pipes are the lenght that are, and it nothing to with any dyno testing.

cylinders 1 and 6 run into the same collector, these pipes are as short as they can be given the distance between the two exhaust ports.

shorter would be better, but you just can't do it. you'll also find that most of the saloon cars run a custom header anyway. as it's one of the few things they are alowed to change.

No i haven't. What i posted i got told by pacemaker.
I've got the 4480 on my car. I will measure them for self satisfaction.

well I know bruce heinrich uses and helped develpe them. If it works for bruce in his all conquering falc i6, its good enough for me. what a champ.

also helps to note that cyliner 1 and 6 fire to help balance each other so stands to reason that their tuned length primaries are similar.

I have to admit they work so well.
I have the 4480 pacemakers, high flow 2.5 magnaflow cat, lukey ultra flow staight through 2.5 middle muffler & a 2.5 lukey hotdog rear muffler.
I felt gains right through the rev range.
If any one is to buy a set of exctrators the 4480 PACEMAKERS is the way to go.

don't get me wrong guys, they are good thing.
i bought a set when they first came out for my XR6,
all i'm saying is they are a mass produced product, perfect design still has to make way for what will fit and what is cost effective to make.