Anti reversion cones

Gents,

Has anyone tried fitting anti reversion cones to a Commando exhaust?

Just type 'anti reversion cone' into google if you're not familiar. They're kinda like a velocity stack that goes in the exhaust, clamped in the gasket face.

A cruder alternative could even be a large washer clamped in this place!

The anti reversion port is noted as one of the advantages of the Fullauto head. Could this be a way of gaining similar benefits?

I recall reading of D-ports / pulse-reversion mods in the 1980's in a Phil Irving book/article or it could have been in the book by A. Graham Bell "Performance Tuning in Theory and Practice: Four Strokes". I lent mine years ago but it never came home. A sketch I made in the back of my Chiltons manual shows different approaches dicussed in that era e.g. pipe mismatch/offset, inverted cuts and backfill, etc.
Ta.

needing said:

I recall reading of D-ports / pulse-reversion mods in the 1980's in a Phil Irving book/article or it could have been in the book by A. Graham Bell "Performance Tuning in Theory and Practice: Four Strokes". I lent mine years ago but it never came home. A sketch I made in the back of my Chiltons manual shows different approaches dicussed in that era.
Ta.

Click to expand...

Based on your notes and learned reading, dya reckon there's any gain to be had playing in that area with a Commando?

Fast Eddie said:

needing said:

I recall reading of D-ports / pulse-reversion mods in the 1980's in a Phil Irving book/article or it could have been in the book by A. Graham Bell "Performance Tuning in Theory and Practice: Four Strokes". I lent mine years ago but it never came home. A sketch I made in the back of my Chiltons manual shows different approaches dicussed in that era.
Ta.

Click to expand...

Based on your notes and learned reading, dya reckon there's any gain to be had playing in that area with a Commando?

Click to expand...

A question best directed to Fullauto as he has put the theory into a Commando head design.
Ta.

Hi Fast Eddie
This patent is from the '90s.
http://www.google.com/patents/US5165231
Seems there are a few number in this area of research.
My muffler internals are styled on this concept.
Ta.

I like the idea of something that clamps in the exhaust gasket face of the head, its the best place for it, its easy to experiment with and its removable.

My interest is sparked by the fact that the megaphone's I tried on mine clearly give a boost over 5k but is awful below 4k. I'm thinking a reversion cone set up may cure / minimise the megaphonitis.

needing said:

Hi Fast Eddie
This patent is from the '90s.
http://www.google.com/patents/US5165231
Seems there are a few number in this area of research.
My muffler internals are styled on this concept.
Ta.

Click to expand...

A bout a year and a half back, Norman White told me that the later works Norton exhaust headers went 2" into the mega, rather as shown in this drawing......which explained to me why he said the lengths should be 30 inch and I though was 28" (based on external measurements!)

Nigel.....its much 'easier' just to get a FullAuto :wink:

needing said:

Fast Eddie said:

needing said:

I recall reading of D-ports / pulse-reversion mods in the 1980's in a Phil Irving book/article or it could have been in the book by A. Graham Bell "Performance Tuning in Theory and Practice: Four Strokes". I lent mine years ago but it never came home. A sketch I made in the back of my Chiltons manual shows different approaches dicussed in that era.
Ta.

Click to expand...

Based on your notes and learned reading, dya reckon there's any gain to be had playing in that area with a Commando?

Click to expand...

A question best directed to Fullauto as he has put the theory into a Commando head design.
Ta.

Click to expand...

I think he will tell you that Jim Comstock designed that head.

Glen

worntorn said:

I think he will tell you that Jim Comstock designed that head.

Glen

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I know I am being pedantic Glen,and you are right to some degree, but I think he will tell you:

The head 'design' is straight from the Norton drawings as supplied by Mick Hemmings, with a port design provided by Jim Comstock (which works very nicely thanks).

Casting, machining and finishing by FAT selected suppliers to FAT requirements.

Ms Peel picked up some spunk by too big an intake lip into small port head but it was the 2-1-Mega very similar to the exhaust photo above, w/o the baffle packing that gave her suddently scary acceleration. Reversion cones references say they mostly help IF there is a cross over bewteen headers of multi cylinder engines. Anywho whole system needs tuning - and there is some rocket science to apply in the last few inches of megaphone exit - not shown above. Off to work now but dwell on Tesla valve to make restless. Also look into stepped headers which I am going to apply to my lawn mower as well as next Peel.

What diameter exhaust pipe gives the best result with the anti-reversion mod ? My feeling is that the ID of the header pipes on a two into one exhaust should exactly match the ID of the stub in the head, and the tail pipe should be large enough in ID to offer no restriction. In my experience fitting a megaphone to a race bike which is to be used on a short circuit simply makes the power delivery harsh, kills of any torque under the cam spot and makes the bike much more difficult to ride fast. I had the experience where the point at where the power came in on my short stroke Triton at 5000 RPM on a circuit where you could not possible get around the corners pulling those revs in first gear of the CR box. It meant the motor would always drop off the bottom of the power band, then you had to decide whether to slip the clutch and go sideways while doing about 60 MPH in a corner or go slower and wait until you had the bike upright and let the power come back on by itself. I still get anxiety even thinking about those days.

Dang it Alan thats some butt tightening experiences and decision points. I love it when we survive this and even better if best compromise obtained. i think all mc will tend to crank in sharper on far lean and hi thrust helps rear swing around to aim thrust better for desired line of travel. Once in a while in just right places I can get equal side and thrust loads on both patches in normal counter steer so essentially the stuck on rails sense on THE Gravel, usually in a well banked bowl like sharpish turn I just slightly increase throttle to keep rear spun some while holding-dampening forks to keep same angle to onset a deliciously easy two tire slide that does not tip more bike lean angle down into ground nor swing rear out much that snags a hi side. This does two things at once w/o loss of much momentum, the side slide bleeds entry direction speed w/o brakes and slowly swing bike around its CoG to face well for exit power hook up which is also the point the rear actually does sling out enough to snag a hi side but only enough to pop upright for best power hook up out of there. more or less as THE Gravel is never ever mastered.

The trouble on tarmac doing this is the traction levels can exceed frame and fork and supsension tolerance so ocsilations build up to splash together. On The Gravel its too obvious that counter steering severely adds to risk of rear spin out trip down but on tarmac its not really sensed till some frame snap backs add little jerks to forks. When modern or antiques tend to sudden hi side out the blue what happening is the bike mass auto correction snapping in some straight steer which can put a little or a LOT of shudder through frame. The amount of straight steer auto snapped is not neccessary ful real straight steer like Peel does but more or less reduces the amount of counter steer pilot put in to get the lean and radius going,
WHICH>>>
because when front tire turned this induces some drag to straight forward motion while rear thrust shoving so tends to work the dual hinge fromed by the stem and axle lines, so counter steer tends to fold bike stem downward while straight steer tends to fold hinge upward. This is a big factors of forks helping induce or risist leans which angles rear patch to actually turn the cycle in powered assisted turning. Power assisted turning is what we are concerned most with limiting our fun. You can corner sharper better on power than w/o, same in parking lots, easier if slight throttle or slight rear drag. Supermotards and flat trackers will rear brake as extreme example of parking lot or gymkana steering.

My SuVeeTwin on heated race tires will surprise me in chicanes and bowl like intersections but either the rear skip out trip down or the front tire sliding almost dropping me but going fast enough there is some recovery space time, not like on THE Gravel, all errors instantly crash usually too fast to know what went wrong so much never get spirtited on it or must face more crashes and injury till its sinks in what not to do even though all survival intincts screaming NOOOOOO. So when nothing to loose but your teeth and frame ya tend to go bezerk.

Another manhood tester is decision if going out of control is to leap off while easy landing or fight it down with risk of horrific hi side &or impact &or slide under oncoming truck.

I eventually was forced to force myself to sort of crash into turns and spend rest of the turn trying to recover by suddenly lightened load of throttle lean and fork angle in the least states of traction. If done right bike kind of falls down out of control with rear swinging out/down but forks resisting by straight steer so hooks back at right time to pop back up just right to toddle on into next toes nail curler. I have to keep alert to tire wear and pressure and humidity and temp level to get this right for fun rather than fear but if I do not stay semi in panic practice then may react wrong with deer or limbs or mud etc.

Steve, the point about the bike going sideways on a bitumen surface is that you usually end up going slower even if you don't crash. I don't know the theory behind the anti reversion mods, however I think that if you were not using the large diameter exhaust pipes they would simply offer a restriction that might knock the top end off the power band.
I think Eddie's idea of a bolt-on mod is a good one. I just find it difficult to imagine one which would not rotate in the port and end up pointing in the wrong direction. I guess it could be pegged. Are there any photos of the inside of the Fullauto exhaust port ?

acotrel said:

Are there any photos of the inside of the Fullauto exhaust port ?

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Comnoz provided the picture below of the Fullauto EX port in a previous AN thread - "Head Flow Testing".



The Harley XR EX port is another example of a "stepped" port that might be relevant to the discussion so images of the port and a casting thereof are also included. Even with the stepped port, a fuel cloud can sill be visualized in the carb throat during out-of-phase operation, but quickly disappears as EX pulses come into phase. Although an XR won't make huge power when running in the reversion regime, it does pull through smoothly without rich stutter or blubber.

XR Ex Port


Casting of XR EX Port Step


In addition to the previously cited patents, an additional patent on anti-reversion cones is the 1980 James Feuling patent, US 4,206,600, which expired long ago and is now open art.

http://www.google.com/patents/US4206600
click the small page of images to see the images at larger scale

The subject patent teaches the critical parameters and equations required to optimize the cone configuration, thereby minimizing the effects of out-of-phase waves and accompanying reversion. Drag Specialties either licensed or purchased the Feuling technology and offered anti-reversion cones for OHV HD applications in the past, where individual straight pipes were commonly employed.

Another approach to circumvent the stuttering/blubbering behavior accompanying reversion is to fit a ThunderJet kit to a carburetor to add another circuit.

http://www.zippersperformance.com/all-p ... carbs.html

For example, in the case of a Mikuni VM, the ThunderJet would be fit upstream of the venturi (toward the horn end of the carb) to provide a new high speed circuit, that based on installation orientation (3 o'clock, 12 o'clock, etc) allows one to vary when the ThunderJet circuit is recruited. The conventional main circuit of the carb is modified by fitting a larger air correction jet, thus simultaneously delaying recruitment of the main jet and leaning it, and the main jet itself is reduced in size such that the traditional main circuit of the carb now functions as an intermediate circuit only, and the ThunderJet circuit becomes the new main circuit. By leaning the mid-range in this manner, reversion is minimized as the out-of-phase pulse can no longer pull large excesses of fuel from the main jet that cause stuttering/blubbering, and progression through the reversion regime is smooth.

In a best case scenario anti-reversion cones or the ThunderJet circuit modification provide means of smoothly transitioning through the reversion regime, much like a fuel injected engine would smoothly pull through this regime (essentially unaffected by the double pulse the carb is susceptible to). However, IMHO, the engine is not going to make much power in the out-of-phase regime relative to in-phase operation, so perhaps the best we can hope for is to smoothly transition through, without having to nurse it through a stuttering/blubbering period to "get on the pipe". My $0.02.

And of course all the foregoing relates to carbureted cammed-up engines having significant valve overlap and modified exhaust, e.g., straight pipes, megaphones, etc. When Comnoz returns to the forum I'm sure he'll be smirking as he extols the virtues of fuel injection and how, relative to carburetors, he is essentially unaffected by reversion phenomena (at least as far as rich stutter/blubber goes).

I have found some type of anti-reversion to be helpful with any engine, even with fuel injection. It fills in the flat spot just below the peak power.

Where is is really valuable is with a race engine running a cam with a lot of overlap and megaphones on a tuned exhaust. It really helps make them easier to jet properly when the megaphonitis is reduced.

The raised floor of the Fullauto head also stops the tumbling in the exhaust port when the valve is over .400 lift. That tumble will reduce the flow considerably. Jim

Here yer go, prototype anti reversion accessory from Fast Eddies Speed Shop...

Is it a flat disc?

The old Norton tuner Bill Stuart made up inserts to fit between the exhaust pipe and the port on Charlie Luck's Manx Norton engined sprinter.
The inserts were in the form of a short sleeve that was inserted into the header pipe, and was tapered so that it formed a converging cone shape to the out going gasses, but presented a sharp step to any reverse pressure waves.

I never heard that Bill ever proved the worth of this insert on a dyno, but he was adament thet it was beneficial to Charlie's sprinting sucesses.

D- shaped parts are not anti-reversion cones &or chambers. D-ports are planned ahead to construct to help expel exhaust and stifle sound compression echos reaching into chamber. The cones are cheap after thought in attempt to stifle back wash and sound wave reaching chamber during over lap interval. Stepped headers are supposed to help reflect sound waves in rpm stages to reflect sound wave back to keep intake from rushing out exhaust during over lap.

I agree Steve. My dyno testing of my anti reversion device proved beyond any doubt that it was NOT and anti reversion device!

It needs a tad more thought and effort putting into it than I did I feel!