Extractor tuning - Anti-Reversion Headers

[Radar]

Ok so i've been playing with an engine analyzer program for the past few weeks, trying to get the most out of my manifolds to suit my cam.
After quite a few days, I'd found that I if placed an expansion chamber, in the correct place I could raise my torque very early in the RPM range and keep it flat until peak RPM.
It also allowed for over 100%VE from 3600+rpm.
Has anyone:
A)Heard of this being done to 4stroke engines?
B)Seen it been done before?
C)Actually currently using this style setup?

This is just the dyno sheet the program has spat out:

3T with 13:1CR

[mattysshop]

i see alot of designs, and my mate discussed them with me (specialises in extractor and manifold design and has improved on his own version of a 'burns collector design')

most of the torque increases seen in extractors, are due to merge collector design, the angle and length of the merge, and it's outward path..

in real life driving it's sometimes hard to actually pick the difference, but most of the time you can feel a difference low down.. after fitting a set of pacemakers with 'bash collectors' to my old 3.5L v6 mitsubishi i was somewhat dissapointed still... so we played with the 2-1 transition we made a 15 deg merge reducing to 2 1/4" then expanding to 2.5" (rest of the system)...

this made an instant increase in low down torque... honestly you could really feel the increase especially as it was automatic...


so yes.. if your talking taper/expansion at the merge collector... been done, tried, tested, almost garunteed to work for torque, even on a set of average off the shelf extractors...

normally his customers see massive differences with his tuned extractors/merge collectors... but were talking 7-800hp aspirated windsor, clevo, SBC etc...

[Radar]

I agree about the merge collector, but no not quite what I mean.
The idea i'm going off is: 18"@1.42"ID->25"@1.7"ID->54"@1.44"ID. (ID = inner dia.)
The 25"@1.7" being the expansion chamber.
It brang the exhaust velocity right up early and left me with about 390ft/sec exhaust velocity at 8000rpm.

I was reading about a set of extractors to suit a 4age that were similar to this but I cannot find them.

[trdee]

cusco powerballs maybe?

[jeffro ra28]

Look at late model Motorcross 4 stroke aftermarket pipes and the like. 250F's 450F's etc.

[Radar]

The fmf powerbomb is exactly what I mean!

[Talasas]

I was under the impression expansion chambers were for 2 stroke because of the lack of exhaust valves. Interesting thought, in a way creating a plenum to achieve the opposite of an intake plenum.

[Billzilla]

I agree about the merge collector, but no not quite what I mean.
The idea i'm going off is: 18"@1.42"ID->25"@1.7"ID->54"@1.44"ID.

Just out of curiosity, try making the exhaust 18" long @ 1.42" for the primaries then add an 18" long collector.
See what the power does.

[Radar]

Do you mean make the merge collector 18"?

[mattysshop]

2463mm odd of primaries?? then add at least another 250-260 for a merge collector

keen to see pics!

[Billzilla]

Do you mean make the merge collector 18"?

Yep.
(10ch)

[xa-mont]

2463mm odd of primaries??

That's what i was thinking... you would be rocking primaries to half way down your car!

[Radar]

Gained 1nm and lost 1hp changing the collector length... 193ft-lb (265nm) with 291hp

[gixer]

These are some stepped pipe diam headers we whipped up for a 20v in a buggy, worked really good, nice gains everywhere compared to std exhaust on right.

[Radar]

I found what I've been trying to describe! They are called anti reversion headers... Here is a perfect example of what im talking about!
"Another design exception is the Anti-Reversion header. Whether Anti-Reversion headers work or not is a controversial subject. Some engine builders say that highly tuned race engines with big overlap camshafts prefer anti-reversion headers. These have a chambered primary tube. In other words, the primary tube increases in diameter by about a quarter of an inch, a few inches from the head flange for about 2". The chamber is believed to prevent reversion of the exhaust gases during the overlap period by trapping the reversion back pulse that can contaminate the cylinder with exhaust gas, creating a wider powerband and more torque. " With 83degree's of overlap no wonder I've been seeing an increase in power.... Talk about stumbling across something by accident!!