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Author Topic: porting/engine breathing  (Read 1298 times)

porting/engine breathing
« on: February 24, 2011, 01:27:48 PM »
Hello all .  Attached find a link about the art of porting which substantiates what ACE is saying.  It also underscores the potential limitations of CNC porting vs hand sculpted.  for those following some of the performance modification discussions this may be of interst.

http://en.wikipedia.org/wiki/Cylinder_head_porting

It seems that this both an art and a science.  The "wave" discussion I think addresses what ACE is discussing in terms of cam mods to slightly delay timing of intake closure so that the "pressure wave" hits the cylinder when the valve is still open.  Issue 237 of the Classic Bike Guide" p 24 also has an interesting editorial by Andrew Wilson discussing the mysteries of engine breathing and "valve overlap" (the phenomena of simultaneous intake and exhaust valves being open at one point in the cycle----just at the beginning of the intake cycle I think---  due to the necesssity for  gentle (hence slower)  opening and seating but t high valve thrst (hence fast)  in the middle of each valves travel)   All of this is governed by the "humble" pear shaped cam and its profile .  He likens this ballet of valves to the aerodynamics of a bumblebee....Shouldn't fly but it does.  And goes on to discuss the tradeoffs of valve overlap length, timing in the cycle and the effects of the viscosity of incoming air gas mix.

All interesting stuff.  Frankly I had no idea previously of the factors involved in even a very basic four stroke engine (read "large lawnmower" )  and I am duly impressed by the wizardry that makes these things work in the first place, and even more impressed by what can be done to them by tweaking the breathing like ACE does with the Fireball Bullet and hopefully will do with the "JUIICED UCE "  (ou can patent that one ACE)


HOLY SMOKE    I spell checked this and not a single error first draft.....must be the morning coffee    Nigel


ace.cafe

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Re: porting/engine breathing
« Reply #2 on: February 24, 2011, 02:38:40 PM »
Nice topic, Nigel !

Yes of course, it's a very complicated subject.

Here is what a very good intake port for a Bullet(by Mondello) looks like, as seen in the Fireball.
Viewed from the chamber with the valve out



And viewed from the other end at the manifold junction, with the valve in


You may notice a few rough or uneven spots remaining, but the aim is to flow best, and we worked with the original casting, and did minimal enlargement. So it was found that removing those areas resulted in poorer flow, so they were not removed. It flowed better with them there, than to smooth them down, because it would have changed the port shape too much, and reduced the desired results.

Also, note the concentric rings cut into the valve seat area. This is the most critical flow area, and every one of those angles that are cut, have specifically designed angles to improve the flow. They are not "standard angles". This set of seat angles was developed for this head, and a special seat cutter tool made for Mondello's Serdi valve machine, so that all the angles are machine-cut in a single pass, and are perfectly concentric, and have sharp transitions to effect fuel-shearing for improved atomization of the fuel as it enters the combustion chamber.
"Wet-flow" technicqus were used in this head design, which takes the wet fuel mixture into account, and not just the air. This can make radical improvements in combustion efficiency, because the fuel is better dispersed into the air, and burns more evenly and efficiently, resulting in better power and economy.

This is the rest of the intake system, showing the flow-matched connection of our custom hand-matched alloy manifold to the Mikuni TM32 flat-slide carburetor.


You can notice that the flange end of the manifold has holes drilled in it that match the holes drilled into the head, and it is pinned in place, and hand flow-matched to the port entry also. this creates minimum flow disturbance all the way thru the intake tract, and keeps the bulk flow rate even from beginning to end.


On the exhaust port with the valve out, you can see a similar treatment for the valve seat area here, and also the special Thermal Barrier ceramic coating inside the exhaust port to minimize heat transfer to the head, which helps prevent overheating of the head from the hot exhaust gases in the port, and speeds up exhaust flow.


All of these features are on every Fireball made. It is all standard practice on the Fireballs.

These are the kind of things that are needed to bring the power up to the levels that we get. Similar things would need to be done to the UCE, but done specifically for the individual needs of that engine, in order to bring it up to a similar higher power level.
« Last Edit: February 24, 2011, 03:37:12 PM by ace.cafe »
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

Please visit my new website:
http://groups.yahoo.com/neo/groups/AcePerformanceBullets/info

singhg5

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Re: porting/engine breathing
« Reply #3 on: February 24, 2011, 03:50:30 PM »
Nice topic, Nigel !

Yes of course, it's a very complicated subject.

Here is what a very good intake port for a Bullet(by Mondello) looks like, as seen in the Fireball.
Viewed from the chamber with the valve out

And viewed from the other end at the manifold junction, with the valve in

You may notice a few rough or uneven spots remaining, but the aim is to flow best, and we worked with the original casting, and did minimal enlargement. So it was found that removing those areas resulted in poorer flow, so they were not removed. It flowed better with them there, than to smooth them down, because it would have changed the port shape too much, and reduced the desired results.

Also, note the concentric rings cut into the valve seat area. This is the most critical flow area, and every one of those angles that are cut, have specifically designed angles to improve the flow. They are not "standard angles". This set of seat angles was developed for this head, and a special seat cutter tool made for Mondello's Serdi valve machine, so that all the angles are machine-cut in a single pass, and are perfectly concentric, and have sharp transitions to effect fuel-shearing for improved atomization of the fuel as it enters the combustion chamber.
"Wet-flow" technicqus were used in this head design, which takes the wet fuel mixture into account, and not just the air. This can make radical improvements in combustion efficiency, because the fuel is better dispersed into the air, and burns more evenly and efficiently, resulting in better power and economy.

This is the rest of the intake system, showing the flow-matched connection of our custom hand-matched alloy manifold to the Mikuni TM32 flat-slide carburetor.

You can notice that the flange end of the manifold has holes drilled in it that match the holes drilled into the head, and it is pinned in place, and hand flow-matched to the port entry also. this creates minimum flow disturbance all the way thru the intake tract, and keeps the bulk flow rate even from beginning to end.

On the exhaust port with the valve out, you can see a similar treatment for the valve seat area here, and also the special Thermal Barrier ceramic coating inside the exhaust port to minimize heat transfer to the head, which helps prevent overheating of the head from the hot exhaust gases in the port, and speeds up exhaust flow.

All of these features are on every Fireball made. It is all standard practice on the Fireballs.

These are the kind of things that are needed to bring the power up to the levels that we get. Similar things would need to be done to the UCE, but done specifically for the individual needs of that engine, in order to bring it up to a similar higher power level.

@ICE:

That is pure magic !  Thanks for beautiful explanation of this topic with great pictures.  Really enjoying reading it.
1970's Jawa /  Yezdi
2006 Honda Nighthawk
2009 Royal Enfield Black G5

Re: porting/engine breathing
« Reply #4 on: February 24, 2011, 05:32:56 PM »
A propos the debate  between size and finesse, (or brawn and brains)  (see the 1000 cc beast siingle on the 535 cc piston mod thread )   , I porpose a new rejoinder to the the those who disdain the Bullet for its modest size.:

To those who say;

 "There is no replacement for displacement"   we can answer

  "BUT IT'S THE FLOW THAT MAKES IT GO"


Enter chorus chanting
"JUICED  UCE, JUICED UCE, JUICED UCE..................."
Nigel