## Porting by Computer

Rule #1: There’s more or less a set amount of power available for you to manipulate. If you port for high RPM power then your low/mid-range power will suffer. You are robbing Peter to pay Paul.

Rule #2: You are pretty much stuck with the porting arrangement the factory put in your cylinder. If the exhaust port is single with no auxiliary ports then you are stuck with that. If your transfers have limited area then you can only widen them a little to the rear which won’t make any big difference in power.

Rule #3: Widening the exhaust port or making it more square at the top will shorten the lifespan of your rings. So when you gain something you lose something.

Rule #4: The expansion chamber controls the top RPM, not the porting. Porting can only move the power up or down in the powerband.

Rule #5: Blowdown degrees are only half of the equation. Avoid people that emphasize them without any mention of port size. True blowdown is the time it takes for the combustion pressure to fall to near zero so the intake charge can enter the cylinder freely. This is where computers come in. Depending on the piston speed (due to RPM and stroke) the time it takes can be calculated according to the open port area every millimeter down as the piston uncovers the port. This can show if you need more area/degrees between exhaust port opening and transfers opening. You can increase the area by widening the port or making the top half of it more squarish, or increase the degrees by raising the top of the exhaust port. And a computer can remove any guesswork on how much to do. Widening is preferable because raising the exhaust port reduces the trapped volume of the engine, effectively making it a smaller engine. Only the area above the exhaust port is the true engine size. For some fucked up reason the same formula for 4 strokes is used on 2 strokes for their engine size which is the volume the piston displaces from BDC to TDC. It’s totally wrong for 2 strokes. Here is a free spreadsheet that allows calculation of your engines trapped volume: www.dragonfly75.com/moto/various.html

Rule #6: The exhaust port location and size is only relevant in relation to the transfer ports. The transfers height/width control whether or not the power emphasis is for top RPM or for a broad powerband. The higher/wider they are, the more the emphasis is on high RPM power. If the exhaust port is too narrow or too low then at high RPM the pressure will still be present when the transfer of intake charge wants to happen. Delaying that transfer reduces top RPM power. A good porting calculator will help you figure out if anything needs to be done with the exhaust port according to the designated top RPM.

Rule #7: Porting is not the end all. Just as important is the jetting, the reed petal tension, the lack of air intake restriction, the squish velocity, quality of fuel and engine oil, the ignition timing, and the design of expansion chamber which can either emphasize a narrow powerband with high peak power, and a broad powerband with lower peak power.

To read more on this topic go to http://dragonfly75.com/moto/porting.html

## Re: Porting by Computer

Rule #2 is bullshit

## Re: Porting by Computer

Yeah rule #2 is not true, boost ports and aux ports can always be added

## Re: Porting by Computer

> Ľ̷̝̽͒i̶̛̼͑͠ȁ̸̧̛̽m̵̻̟̯̀̅ ̷͎̙̽̊F̶̲̺͑̓ F Wrote:

> -------------------------------------------------------

> Yeah rule #2 is not true, boost ports and aux ports can always be added

Absolutely, with good results too

## Re: Porting by Computer

yup ive done it re aux ex ports and ive just converted a piston port cylinder to reed valve and added a boost so ive now got 3 transfers instead of the original 2.

## Re: Porting by Computer

the higher rpm u hit the more hp is possible. its an increasing curve not linear and defintely not a dollar for dollar trade. keep thinking

## Re: Porting by Computer

This dude comes in here every once in awhile with his big authoritative statements.

But I've never seen anything he's done actually go fast.

Post what you have done.

## Re: Porting by Computer

Yes it is possible to add a boost port and/or auxiliary ports but it takes a very determined and skillful person to do such and they are never as good as those made by the factory. So this is the exception, not the rule. So generally speaking rule #2 is true.

## Re: Porting by Computer

Also;

If you want to increase top RPM you have to shorten the header of the expansion chamber. But only with a good expansion chamber calculator will you know how much to shorten it by.

If you want to port for more emphasis on high RPM power you don't know to raise the exhaust port, raise the transfer ports, or raise both. This is where a good porting calculator comes in. It will tell you if you have adequate separation between the exhaust and transfer ports with your current setup. If you have more than enough then you can just raise the transfers. If it is inadequate then you need to just raise the exhaust port. If it is just right then you need to raise both.

## Re: Porting by Computer

I am the least skillful porter with shaky hands and I was able to add boost ports to my Vespa cylinder. Only thing I measured was where the ring gap was, and how high the transfers were

## Re: Porting by Computer

OK, good for you. But I know most people won't attempt to do such. But for those who do maybe you should tell them how you did it and offer tips and advice. I'm all for going to extremes to better your ride.

## Re: Porting by Computer

I think you're mistaking this forum for a scooter forum. The performance section isn't about adding flush turn signals or deleting your mirrors. People on this forum know that your rule #2 is just plain wrong. Do 2 seconds of searching and you'll see over a decade of posts about modifying cylinders for gains.

## Re: Porting by Computer

michael care to tell us what speeds have some of your projects have attained?

i got halfway through one of your spreadsheets for making a pipe but then aborted and wondered if anyone has made a pipe with success from your spreadsheets?

when i looked again i think the spreadsheet cost money.

## Re: Porting by Computer

Alan the expansion chamber calculator took 7 years to finish. All during that time I offered it in its "unfinished" state for free. Now it is finished and costs \$25, a modest fee for it being the only decent program using a return wave simulator. People get good results using it now. Please go to my site to read more about it and see the testimonies: www.dragonfly75.com/moto/calculators.html

## Re: Porting by Computer

But what have you done/built? According to your profile you put a cheap 2 Stroke on a bicycle, and some 100cc motorcycle, so not one moped and no actual testing of pipes or port maps, etc. have you built a pipe?

## Re: Porting by Computer

Mike Boyd, I never said you couldn't "modify cylinders for gains". If I thought that then why would I make a porting calculator? What I was referring to is that we are mostly stuck with the # of transfer and exhaust ports they come with, the basic design. Yes a few people have drilled in exhaust auxiliary ports, a very very few people compared to everyone who has put a tool to their cylinder ports. And it is possible to grind out a very shallow boost port but its a whole lot of work on an iron sleeved cylinder. I've done it to a plated aluminum cylinder, no problem but still it was fairly shallow.

So I still think that, generally speaking, we are mostly confined to the # of ports it came with, not that it isn't possible to make shallow boost and auxiliary ports. It's just that you shouldn't take the exception to be the rule. I try to keep things in their proper perspective. But I am certainly all for someone wanting to give it a go. My statement was not meant to discourage anyone. But I'd be willing to bet that if all the ported cylinders from any city were gathered together and inspected that less than 5% of them will show such modifications.

So guys, can we not just leave it at that? It's not fucking important and was not the centerpiece of the article. jeesh, chill out dudes

## Re: Porting by Computer

Quote: ...to increase top RPM you have to shorten the header of the expansion chamber. But only with a good expansion chamber calculator will you know how much to shorten it by...

This is crap, too. A calculator will only get you the basics. You need to do real life testing to know how your pipe works.

You could plug all the input possible into a program and still have a crappy pipe.

And whatever rule number it was that said the x chamber controls max rpm, not porting.

That's a totally generalized statement. Everything needs to be in tune in order for your chamber to over rev to it's limit, and again, a calculator isn't gonna get you there.

I've seen the pipe(s?) you made. Not impressed at all. Wouldn't waste my money on your software.

## Re: Porting by Computer

You obviously have not a clue about how extensive and detailed my pipe software is. It always hits right on the head. You should be informed about something before making erroneous statements.

www.dragonfly75.com/motorbike/ECtheory.html

www.dragonfly75.com/moto/portsMS.html

You've "seen my pipes and aren't impressed". ha ha, what a hoot. I don't know shit about welding and I live in south america where these lazy fucking latinos can barely find their own ass let alone do a pretty welding job.

But how a pipe looks is how you judge what is happening on the inside of them. really? so retarded, my god. FY(dumbass)I a pipe doesn't function by good looks. Even shitty welding doesn't affect them. See this pipe? Notice anything strange about it? Look at the baffle. Special design for extra long powerband. Works great. No one taught me how to do that. I learned by playing around with my pipe calculator. It's a fantastic tool to learn everything about pipes and make some fantastic pipes. I had a Suzuki AX100 four speed and a normal design of expansion chamber didn't have a long enough powerband for it. Oh I forgot, I am talking to a retard so I need to explain every little thing. A 4 speed has a broader spread of RPM between shifts and if the pipe powerband isn't wide enough for it then when you upshift you are automatically out of the pipe powerband and you probably won't be able to accelerate. Only by use of my pipe calculator was I able to design a special pipe that worked great on it. www.dragonfly75.com/moto/AX100mods.html I could go on and on but the haters on this forum have clogged ears and they only hear what they want to.

## Re: Porting by Computer

> Michael Forrest Wrote:

> -------------------------------------------------------

> lazy fucking latinos

You can take your racism, and your shitty fucking tuning software, and pound fucking sand.

## Re: Porting by Computer

One thing I have noticed about haters on bike forums. Other than being negative, self-loving, asinine, corrupt, petty, totally lacking in logic (low IQ), they are always fucking

AMERICANS !

The Europeans have class and culture. Only americans are rednecked assholes. Your continuing fall from grace is cherished worldwide and we will mock your downfall.

It couldn't happen to a more deserving bunch of assholes.

## Re: Porting by Computer

Lazy latinos?

Here's a big ol fuck you for you

Ya piece of shit

## Re: Porting by Computer

I have a few rules about porting too!

RULE #1,

Don't take advice from racist South American porting instructor jag-off turd boi (edited)

## Re: Porting by Computer

well i bet this thread didnt turn out like he expected....

## Re: Porting by Computer

> Michael Forrest Wrote:

> -------------------------------------------------------

> One thing I have noticed about haters on bike forums. Other than being

> negative, self-loving, asinine, corrupt, petty, totally lacking in logic

> (low IQ), they are always fucking

>

> AMERICANS !

>

> The Europeans have class and culture. Only americans are rednecked

> assholes. Your continuing fall from grace is cherished worldwide and we

>

> It couldn't happen to a more deserving bunch of assholes.

LOL, YOU'RE FROM TEXAS.

And as post-script, I'm sorry you're single. This is obviously the woman's fault for being snobbish, and not yours for being a walking carbuncle. (edited)

## Re: Porting by Computer

wow, this thread has it all.

## Re: Porting by Computer

Hey douchebag. See this pipe? I built it myself using basic formulas from Graham Bell's book, and tweaking it to hit the powerband I wanted on the track. Hits at 6.5k and over revs to 11. You can feel the punch and it keeps on going.

And for your shitty motorized bike? I modified this KTM pipe for my old one, before I threw away all my Chinese motors. Notice how it doesn't have a useless, power robbing, sink-drain header pipe on it like yours. I also took this bike to the track with an adjustable header pipe and tuned it to hit where I wanted it to.

You can slap on any piece of shit pipe to a China bike motor and see an improvement over stock. but yours? Seriously. Not a good advertisement for pipe design software. Maybe the welds are so bad because you can't cut your cones to fit without having to fill the gaps. There's more weld than pipe on that abomination.

So fuck you and fuck your pipes.

## Re: Porting by Computer

Its baffling to me how dragonshit thinks it would be accepted to post racist shit and it would be ignored.

You dumb bro

Dumb as hell

## Re: Porting by Computer

Here's what you said "If you want to increase top RPM you have to shorten the header of the expansion chamber. But only with a good expansion chamber calculator will you know how much to shorten it by."