Velocity porting vs. Oldschool porting

[BadBillyB]

Porting tips for the hardcore..........BadBillyb
http://216.77.188.54/coDataImages/p/...o1(Medium).JPG

[Nerobro]

That makes more sense. Isn't high velocity for torque though, and short runners for top end? He also talked about road racing applications. I'm building my motors now for high RPM's. I don't see why he'd worry about velocity with a motor that's gonna spend it's mojority of time skimming the rev limiter.

BTW, your sig? I want to know about your bike. I always like to see new GS's.

The funny thing is, for the very small fraction of horsepower you loose up top, you fatten the torque curve all over by incresing the velocity of the ports. So long as you don't break mach, the faster the air is passing through the port, the greater the ramming effect you get.

If you wanna see something really fun. check out last years and this years R6 torque curves...

[nastyjones]

I want to buy a copy of this book (performance tuning in theory and practice). Is this the complete & proper name of the book by A. Graham Bell? Do I need to make sure I get the copy that was printed in the early 1980's?
Better yet, does anyone have a copy to sell?
P.M. me if you do.

Paul

[BadBillyB]

I want to buy a copy of this book (performance tuning in theory and practice). Is this the complete & proper name of the book by A. Graham Bell? Do I need to make sure I get the copy that was printed in the early 1980's?
Better yet, does anyone have a copy to sell?
P.M. me if you do.

Paul

The second edition is easy to find. The first edition is what I have. I would recommend getting the first edition, and once you soak up all this info, get the second edition. They apparently have both here....BadBillyB http://www.fetchbook.info/Four_Strok...ce_Tuning.html

[robus]

Heres a page scan from A, Graham Bells book, complete with my own scribbling. The scribbling is on the right. It demonstrates how the gases flow in a cone around the valve head. Let me know if the image is crappy. I am learnin the ropes......BadBillyB

http://216.77.188.54/coDataImages/p/...rt(Medium).JPG

Hi, I'm new to the forum and not even a GS owner, however I'm very interested in this porting technique. This is a great thread. After having had negative results with another port job, I'm keen on trying this one.

I understand the concept and it makes total sense. What doesn't make sense, at least from the picture Billy posted (first diagram from the top), is enlarging the port prior to the seat, having a sort of pocket there. Doesn't that affect flow negatively? It seems to me that that would send the air mix in the wrong way inside the cylinder and thus lead to a non homogeneous burn and thus loss of power.

And about the epoxy 'hump': is there a rule of thumb, percentage wise, of how much to raise the floor of the port? 20% in its highest point is ok?

Thanks for your replies!

Roberto

[BadBillyB]

I understand the concept and it makes total sense. What doesn't make sense, at least from the picture Billy posted (first diagram from the top), is enlarging the port prior to the seat, having a sort of pocket there. Doesn't that affect flow negatively? It seems to me that that would send the air mix in the wrong way inside the cylinder and thus lead to a non homogeneous burn and thus loss of power.

And about the epoxy 'hump': is there a rule of thumb, percentage wise, of how much to raise the floor of the port? 20% in its highest point is ok?

Thanks for your replies!

Roberto

Actually, the pic you are talking about shows material added to the floor of the port (short side) just prior to the seat, to increase the radius and make it longer. Material is removed from the long side radius to make the long side shorter. Look at the other pic that I posted and you will see 3 places where you remove material just prior to the seat.....As far as a rule of thumb on raising the port floor, there just isn't one, theres just too much variation in port shapes and sizes. Focus more on obtaining a better radius.....BadBillyB

[robus]

Hi BadBillyB, thanks for clarifying, however the diagram I meant is this:



Where the book says 'port tapered to compensate for epoxy added'.
Isn't that right before the valve seat or am I misunderstanding it?

[BadBillyB]

Where the book says 'port tapered to compensate for epoxy added'.
Isn't that right before the valve seat or am I misunderstanding it?

Well the tapered area is shown in the middle of the port, in the same area the epoxy was put in. If you raise the floor (w/epoxy) 1/4 of an inch, you have in essence made the port smaller in that area. If you raised the roof 1/4 inch, the port size would remain the same. Problem is, you will grind into the lifter cavity first. So to keep the port size from being choked down, A. Bell is showing you to remove material from the walls....My race head has been ported into the lifter cavity and has custom aluminum spacers JB welded in the bottom of the lifter cavity. Valve spring base sits right on top. If you look at the other pic on the same page, you can see where I drew a line through this cavity planning my port shape.......BadBillyB

[robus]

Got it. Thanks! I plan to do the porting next month. Time to buy some a+b epoxy...

[Keith Winter]

Hey all,
If you guy's are talking about the Mototune guy that compared fuel flow to water on the surface of the car paint,, forget about it. That's the dumbest thing I have ever heard. There is NO doubt that if you make the intake tract as smooth as possible you will get more flow into the cylinder's, any Holley book on carb's and intake system's will give you all the reason's why! However, you can't ever have a gain in one area without a loss in another. The fuel has to stay atomized in the air as it flow's into the cylinder and in a normal from the factory intake the friction from the less than smooth intake tract cause's turbulance and heat that help's the fuel stay mixed with the air. At slow rpm this is good, at high rpm this is bad. So, by smoothing and opening up the tract you will get better flow at high rpm, but, as the velocity goes down with rpm the fuel will try to seperate from the air and because a shiny smooth intake has less friction it also has less heat and the fuel will condensate on the wall's of the intake tract. This will cause, hard starting, idle fuel mixture problems, and a need for higher idle speed's to get an even idle. I have built some very high revving outboard engines years ago and the intake tract's had to be as smooth as possible to get the 3000 rpm more than stock that was my goal. These engine's were only mildly ported, maybe equal to a really good valve job on the bike I'm not to sure, and of course these engine's would not idle very long without bumping the throttle up and down, but these thing's were what you had to live with to get the top end power. Also we must remember that thing's that apply to 4 valve engines allot of time don't apply to the 2 valve engines because the 4 valve already has slow rpm velocity issue's that a 2 valve engine does not have, and the reverse is true at high rpm. As far as fuel/ air heater's, I think with the heat from the engine almost boiling the gas in the tank on hot day's we don't need any more heat in the air or the fuel for power output. Find any book's from Holley about carb's and intake's and ALL the answer's are in there about this stuff.
Keith

[speedy400]

The fuel has to stay atomized in the air as it flow's into the cylinder and in a normal from the factory intake the friction from the less than smooth intake tract cause's turbulance and heat that help's the fuel stay mixed with the air. At slow rpm this is good, at high rpm this is bad. So, by smoothing and opening up the tract you will get better flow at high rpm, but, as the velocity goes down with rpm the fuel will try to seperate from the air and because a shiny smooth intake has less friction it also has less heat and the fuel will condensate on the wall's of the intake tract. This will cause, hard starting, idle fuel mixture problems, and a need for higher idle speed's to get an even idle....
...
As far as fuel/ air heater's, I think with the heat from the engine almost boiling the gas in the tank on hot day's we don't need any more heat in the air or the fuel for power output.
Keith

Didnt you just contredict yourself? If fuel/air heaters are not needed because the engine is so hot and heating the intake enough.. Dosnt that say whith a little less friction in the intake isnt a bad thing? Just pointing out, awesome thread goin btw, really learning a lot-darren
PS- plus wouldnt 2-strokes act much diffrent than 4 stroke motorcycle engines/ports? I'd assume since its intake is moving cold air in twice as much as 4-strokes, the intake system as a whole, would get much more cold vs a 4-stroke. And the friction and atomization would be 2x of a factor.

[rosco15]

The only real downside to putting epoxy into the port is having it come out. My understanding is that it's just a matter of time. A friend had a pro-stock bike he used to run in pro-star and bring it out locally once in a while for testing. He had the epoxy come loose one day and get sucked into the valve. Made a nasty mess.

[RobGS850L]

Didnt you just contredict yourself? If fuel/air heaters are not needed because the engine is so hot and heating the intake enough.. Dosnt that say whith a little less friction in the intake isnt a bad thing? Just pointing out, awesome thread goin btw, really learning a lot-darren
PS- plus wouldnt 2-strokes act much diffrent than 4 stroke motorcycle engines/ports? I'd assume since its intake is moving cold air in twice as much as 4-strokes, the intake system as a whole, would get much more cold vs a 4-stroke. And the friction and atomization would be 2x of a factor.

Manifold heat is good on low end engines and cool smooth intakes are good on higher revving engines such as a small engine like on our bikes. It just depends on what your build requires. Streetability you want heat and on race types you don't care about the driveability issues because you want top end POWER. Sometimes that can be off but as a rule of thumb this is how it has worked in most cases.

[Keith Winter]

Hi,
It does sound like a contradiction,but as Rob pointed out, for streetability you need some turbulance/ heat to keep things right. I guess I didn't explain it right. The trade off for an easy to ride street bike that works well in typical street operation is top end power. Old, low tech, carb bike's like our's can be made to turn higher rpm and have more top end power, but, the trade off will be low end streetabily. As far as the 2 stroke air flow thing, it's not as easy as you may think. First, with no valve's or cam's you are very limited with the intake and exhaust timing. The ports are BOTH open very near TDC, so there is no room for mistake's when porting a outboard. Also the ports are in the side of the cylinder wall so removing to much to enlarge the ports will result in pistons that don't stay in the cylinders, I have seen this happen and it's not a pretty sight! Also the intake charge is drawn into the crankcase while the piston is going up, it then has to hang out in that hot crankcase till the piston come's down and pushes it through a hot transfer passage and into the cylinder. If everything works right the fresh fuel charge stops just short of the open exhaust port after pushing out the last of the hot exhaust gas. To get this all to happen at 9000 rpm with the most power doesn't make for a very slow rpm user freindly engine. In allot of ways it's easier to do on our old bike's. We can change intake and exhaust timing and our intake fuel/air mix doesn't have to wait in a hot crankcase, it just goes right in.
Keith

[speedy400]

I hear ya, my last 4-wheeler was a yamaha banshee( 350 2-stroke twin) I did a mild top end port job on that and since have ported a few other banshees with good successes. I hate to get off subject but I really miss that ol thing. I had clamp on k&n's, ported, bored to 364, and a set of dg pipes, man did that thing rip with it hit the powerband, too bad the reliability wasnt much to speak of on it. Now I'm stuck with a beastly modded 400ex thumper:-D .-darren