Exhaust design and anti-reversion

[RobT]

Been reading around exhaust design recently and come across some interesting info about anti-reversion - that is elements of the exhaust manifold design that stop exhaust gas going back into the cylinder when the engine is in its induction stroke.

Some of these 'devices' are simply a step in the exhaust tract - often the manifold flange being slightly bigger by approx 1mm than the exhaust port

http://i31.photobucket.com/albums/c356/remoer/exhaust/portmatch.jpg

http://www.team-integra.net/forum/14-performance/57159-jdm-type-r-header-vs-dc-jdm-header.html

Sometimes however anti-reversion cones are used in the head end of the primary pipe

http://i611.photobucket.com/albums/tt196/383man_70/anti-reversionplate2.jpg

http://i611.photobucket.com/albums/tt196/383man_70/anti-reversion-cones.jpg

and sometimes people go even further and fit these devices

http://www.hytechexhaust.com/images/whowe/reversion01.jpg

http://h7.abload.de/img/archamber022ngy.jpg

http://motoiq.smugmug.com/photos/590426941_cJrje-M.jpg

Do they work? seem to

http://www.team-integra.net/forum/14-performance/57178-anti-reversion-headers.html

[RobT]

http://bugattimanifolds.com/types-of-exhaust-manifolds

Explains why modern touring car-types use 4-2-1 design manifolds, and not 4-1s as you would expect following theory that a 4-1 is the optimum design for a full on race manifold

http://i32.photobucket.com/albums/d15/RobT1/vwtourerexhaust.jpg

also a bit on anti-reversion at the end

[RobT]

Optimum pipe diameter for primary pipes

http://www.pumaracing.co.uk/manifold.htm

[RobT]

exhaust system pipe sizes

http://www.pumaracing.co.uk/exhaust.htm

[m0rk]

That makes sense. Is there room on yours to modify and add these in?

[RobT]

Probaby yes.

[Slimy]

Here's a question for you, with a 4-2-1 manifold what makes up the -2- pairings? Is it simply cylinders 1+2 and 3+4? Or is there some other better combination?

I'd hazard a guess that having cylinders with opposing exhaust strokes would work better, so with a 1-3-4-2 engine sequence would 1+4 and 2+3 be the optimum?

I can't really see how that BTCC exhaust is laid out, then again I don't know the firing order either.

[RobT]

The vw mani above is 1-4 and 2-3 pairing so that opposite cycle phase cylinders are paired. This is so that the negative pressure pulse from exhaust stroke on one cyl acts to draw air into the cyl for the intake stroke of its pair