TOPIC:

I've read a bit about them, I'm thinking about fabricating some to try in my custom headers. Does anybody have any experience with them? The theory seems to make sense for an engine with the same valve port diameter as the header. Here is what I'm considering for my KZ750 twin.

when i was at mondello's head porting school we spent a lil time on anti-reversion theory.
Joe was a believer and therefore he made the rest of us believers

it can be as simple as the exhaust tube being slightly larger in diameter than the port.
or,
having "torque cones" installed



or built in the way you describe.

it keeps those spent gases from creeping back up the outside walls and back into the chamber contaminating the charge.

let us know if you do it.

leon

Wouldn't a 2-1 exhaust do the same thing?

That looks simple enough. Is there any advantage in slipping some into a 4/1 at the head?
Steve

Leon- thats a great photo, and super cool you went to head porting school; I didn't even know those existed. Also good to hear a guy that teaches head porting theory is a believer in these. I didn't want to go bigger in diameter on the header because it would lower the exhaust velocity, but I have read that having an oversized header is an effective way to achieve the same thing. In retrospect I think I would have gone for a tapered primary, starting off oversized then going down in size to maintain velocity, but since i already have the flanges turned I thought I'd stick with them,

KidKawie- I'm planning on doing a 2>1 to help with scavenging, its free power and less weight and a smart move for sure. From my understanding the inserts are most effective in "road race" scenarios where you go from wide open to closed throttle and then back on the gas. The snapping shut causes a vacuum that pulls exhaust back into the chamber contaminating the charge making the engine hesitate when you give it gas again. Its not something that can be realistically tested on a dyno, so there appears to be some naysayers out there.

Swest - they would only be worth it if your head port is larger or the same size as the header diameter. if your header is bigger than they are not necessary.

I've been doing a bit more reading and seems that there is some concensues that even with antireversion chambers the header primary need to be bigger than the exhaust port. Perhaps I could go bigger for the first primary bend then taper down at the next straight section.

maybe this is overthinking a header for a stock motor, but i figure if i'm gonna do it I might as well do it right.

Used them on some big block Chevy's year's ago the A/R cone's work to stop sound wave's from
pushing exh. gas's back into the combustion chamber when using big cams and large tube header's.
Unless you're building a full on race motor I don't think you would see a benefit from them.
If I remember right Hooker made a few type's that had them built in.

That fits with the picture I am starting to form. They are best used on engines with a lot of cam overlap, or in headers that are too big for the exhaust port. I'm starting to think they may not be worth the trouble.

Well it was worth the learning lesson if nothing else.

I think with my large tube sidewinder header they might help
with lower to mid. range power but the way I modded it to fit it's more like
a step header so is having some what the same affect as the A/r cone's.
A 650/750 header primary tube is a slip fit inside my primary tube's

If AR chambers made any difference of measurable significance on a street motor the aftermarket exhaust manufacturers would be all over it as the latest leap in bolt on power and even the factories with their high revving sports bikes would have patented various versions of the same thing to improve performance and sales
Micron did this with their Ricardo wave software assisted Serpent header design which claims to improve scavenging as well as reducing negative flow (reversion) and whilst showing some improvement over stock they actually showed no more and some times less power gains than the equivalent mainstream big bore system which is why you don't see any other exhaust manufacturer or major bike factory capitalising on the idea,
Good luck with your experiment though.
It's always good to find out first hand whether something works or not rather than just take everyone's word for it.
You never know, you may have a breakthrough and come up with a workable design worth millions.
I can almost visualise the TV ads for the Doctorot developed AR performance exhaust system as I type

HA! now there's something i wish would happen.