[Sox]

Originally Posted by STINKY NINJA

Theres a lot of chatter about pacies vs hurricane etc,inch and a half vs inch and 5/8 primary size making a lot of difference to low end torque,would it even be noticeable?

Absolutely it's noticeable.
However, many times people are looking in the wrong places, that is, peak power.

Peak numbers are only a tiny part of the story, and the least important.
Power under the curve, and part throttle response are much more important as that's where the vast majority of our driving is spent.
The area between (say) 5000rpm and 6000rpm is only a tiny portion of the engines range we use, and for the least amount of time.
Yet these are the numbers most seem to focus on. Bragging rights. Go figure.

Has anyone ever done back to back tests or does anybody have dyno results to prove this,id love to see them.

Sure, but not much is documented.
There are a few articles showing pipe diameter differences, they are very informative, and an eye opener to bigger is better crowd.

Originally Posted by STINKY NINJA

Pacie has bigger primary and secondary but a 2 1/4 collector,hurricane has smaller primary and secondary but a 2.5 inch collector,you would need some decent hp to be making use of a 2 1/2 collector on a 5.0 but tbh how would one be better than the other,one has slightly faster gas speed leaving the head and slowing down at the big collector the other the total opposite,how can the hurricanes be better?

Because what happens immediately after the port is the most important.
Secondary's and then collectors are important, but not as.
Pipe length is also very crucial, of both primary and secondary.

A 2.5" collector is ok for a 5L, particularly at that point, where the exhaust gasses merge and are hot.
So long as it steps down to 2.25" at some point where it's cooler to keep velocity high.
Exhaust gas shrinks as it cools.

A lot of exhausts on high hp cars ive seen has a step down after the collectors,is this to speed up exhaust flow?

My pursuit has headers made like this, the primary pipe exits the port at 1 5/8 for around 200mm, then steps back to 1 1/2" for another 200mm.
Then into looong 2" secondaries, and onto 2.5" collector.
This then steps down again to 2.25" at the diff.
Gas velocity remains high from port to tip.

Is exhaust gas speed more critical to making torque as its leaving the head or nearing the collector?

From the port is most important, but it all plays a part.
Like all parts of an engine, it's only as strong as the weakest link.

Pipe diameters should remain as small as possible to cause minimal restriction at the engines highest RPM.
This keeps velocity at it's highest.

A 5% loss at 6000rpm is more than acceptable for a gain of 15% in the midrange, yet time an time again systems which are too big are fitted.
It happens more than you can imagine, and plenty of exhaust places won't acknowledge it because you've just outlaid $3000 on that big bore system.

Most people seem to think that everything from the race track will work on the road. It doesn't.