Teach me a bit about porting.

[Honda 250r 001]

I figure im never gonna learn if i dont just try on a cylinder. So i have mapped out the transfer and exaust port on this cylinder i have. I would like this to be a agressive shear top end performance cylinder. So can you guys tell me what i need to do somewhat and i will grind away and make a new map and see what you think.

What i know right now is that i need to raise the exhaust port to make a more top end powerband. The question is, how much and what else needs changed?

I know you guys use degrees to tell when the ports open and stuff but how do i tell what degree it is in the cylinder? I dont have any software just maps and my brain.

If you need measurement off the map i have, tell me where to measure and what unit and i will get it posted.

Tools:
What do you guys use? I have a dremel and a right angle grinder. What cutting heads should i use?

Thanks

Link to the map.

http://s804.photobucket.com/albums/yy330/hedberg345/?action=view&current=100_3722.jpg

[1promodfan]

Just my 2cents..........I wouldn't try it!!!! I don't think (could be wrong) that its just something you pick up and do. You start grinding on that cylinder and you'll probably ruin it.

[Honda 250r 001]

well theres not many other ways to do it. I figure its worth a cheap 20 dollar cylinder to try it out.

its either i get someone to show me a little or i do what i think is best, put it together and blow it up and try again.

[8686]

Originally posted by Honda 250r 001
well theres not many other ways to do it. I figure its worth a cheap 20 dollar cylinder to try it out.

its either i get someone to show me a little or i do what i think is best, put it together and blow it up and try again.

That should get expensive real quick.

[SuperSherman]

Don't listen to anyone who says you can't do it. Listen to the people who say you'll likely ruin it. I have invested a LOT of time, money and ruined cylinders to learn how to cut a port and make power out of it. Your right angle grinder will not work, unless it's tiny and takes a 1/8 shank. Use lots of oil on your bit, take your time! Get a degree wheel, set it up right, and mark your ports, Good luck!

[Honda 250r 001]

Also i would like to know a little about blow down if someone could explain that to me.

[Ruf Racing]

“using no way as a way, using no limitations as a limitation.”

Bruce Lee

"You know the conseqences" This ones mine. lol
Good luck.

[Buttermilk]

You'll need to measure your port map from the top of the cylinder down to the top of the ports (highest point of the port) for both exhaust and transfers.

You can also measure down to the bottom of the port to confirm where the port floors are at currently.

Next time you make a port map, make sure to "map" the top of the cylinder all the way accross the same span as the ports. You'll need to take your measurements from the scribed line to measure port heights.

If you are adept at using Excel, I can send you a spread sheet that will calculate the port timings for you based off your measurements (takes away the hassle of a degree wheel).

I've got a port map posted on here somewhere you can eyeball for some information. It's a mid-top port.

Regards,

Rog

[Honda 250r 001]

hey man send that spread sheet to hedberg345@hotmail.com. Thanks for the info man

Ill do another port map later today and mark the top of the cylinder wall too.

[79vwrabbit]

It's important to design the whole engine to make power where you want. The carburetor, head shape, and pipe are also VERY important considerations to making serious power. If you just clean up the ports, the butt-o-meter will feel a difference though.

I use the Motion Pro degree wheel to map out ports. The degree wheel makes finding port timing very easy. A piston stop is easy to make too to dial in the wheel. But I’ve found that you have to pull off the flywheel to degree accurately with this method. (A flywheel puller makes this job take like 2 minutes.) You can also make a wheel yourself or print one off the Internet and cut it out and tape it to cardboard. Having a degree wheel is not a big deal, but it really helps in building engines.

Blowdown is the time after the exhaust port has opened until the transfer ports open. The hot air pushing on the piston has pretty much finished its business by then and is rushing out into the exhaust pipe. The blowdown allows the high pressure in the cylinder to “blow down” through the exhaust port so that the important process of cylinder filling through the transfers can begin. Shoot for 30-35 degrees of blowdown when porting. As far as cutting ports, it’s easier to raise them a little and then experiment. It’s better to have the ports lower than higher. Higher ports make peakier engines and not very much fun to ride. I like a nice broad powerband so I only run 188* exhaust and 122* transfer on my 250R. I cut my exhaust port REALLY wide to gain time/area. The key to making good power down low is high compression.

If you’re serious about porting engines, C.C. Specialty in Tennessee sold me my #10 kit. Wise man once said “the man with the tools rules.” And theirs are THE BEST hand porting tools you can buy.

If you’re serious about learning how to build engines that are competitive and/or a lot of fun to ride (sounds like you are), head on over to macdizzy.com. There’s some great info for free, but if you just pay the $20 to get into the forums, it will be 100,000 times better than trashing a $20 cylinder for nothing.

[Honda 250r 001]

Originally posted by 79vwrabbit
It's important to design the whole engine to make power where you want. The carburetor, head shape, and pipe are also VERY important considerations to making serious power. If you just clean up the ports, the butt-o-meter will feel a difference though.

I use the Motion Pro degree wheel to map out ports. The degree wheel makes finding port timing very easy. A piston stop is easy to make too to dial in the wheel. But I’ve found that you have to pull off the flywheel to degree accurately with this method. (A flywheel puller makes this job take like 2 minutes.) You can also make a wheel yourself or print one off the Internet and cut it out and tape it to cardboard. Having a degree wheel is not a big deal, but it really helps in building engines.

Blowdown is the time after the exhaust port has opened until the transfer ports open. The hot air pushing on the piston has pretty much finished its business by then and is rushing out into the exhaust pipe. The blowdown allows the high pressure in the cylinder to “blow down” through the exhaust port so that the important process of cylinder filling through the transfers can begin. Shoot for 30-35 degrees of blowdown when porting. As far as cutting ports, it’s easier to raise them a little and then experiment. It’s better to have the ports lower than higher. Higher ports make peakier engines and not very much fun to ride. I like a nice broad powerband so I only run 188* exhaust and 122* transfer on my 250R. I cut my exhaust port REALLY wide to gain time/area. The key to making good power down low is high compression.

If you’re serious about porting engines, C.C. Specialty in Tennessee sold me my #10 kit. Wise man once said “the man with the tools rules.” And theirs are THE BEST hand porting tools you can buy.

If you’re serious about learning how to build engines that are competitive and/or a lot of fun to ride (sounds like you are), head on over to macdizzy.com. There’s some great info for free, but if you just pay the $20 to get into the forums, it will be 100,000 times better than trashing a $20 cylinder for nothing.

Ohh!!! i get it, you put the degree wheel on the crank i see. Im thinking about dishing out some money and getting some good tools.

Thanks for the numbers, i will try to get my cylinder close to that.

Thanks

[Swiper77]

Check out mac dizzys website he used to have tons of porting knowledge on there for reference.

[fulltiltrider]

Originally posted by 79vwrabbit
It's important to design the whole engine to make power where you want. The carburetor, head shape, and pipe are also VERY important considerations to making serious power. If you just clean up the ports, the butt-o-meter will feel a difference though.

I use the Motion Pro degree wheel to map out ports. The degree wheel makes finding port timing very easy. A piston stop is easy to make too to dial in the wheel. But I’ve found that you have to pull off the flywheel to degree accurately with this method. (A flywheel puller makes this job take like 2 minutes.) You can also make a wheel yourself or print one off the Internet and cut it out and tape it to cardboard. Having a degree wheel is not a big deal, but it really helps in building engines.

Blowdown is the time after the exhaust port has opened until the transfer ports open. The hot air pushing on the piston has pretty much finished its business by then and is rushing out into the exhaust pipe. The blowdown allows the high pressure in the cylinder to “blow down” through the exhaust port so that the important process of cylinder filling through the transfers can begin. Shoot for 30-35 degrees of blowdown when porting. As far as cutting ports, it’s easier to raise them a little and then experiment. It’s better to have the ports lower than higher. Higher ports make peakier engines and not very much fun to ride. I like a nice broad powerband so I only run 188* exhaust and 122* transfer on my 250R. I cut my exhaust port REALLY wide to gain time/area. The key to making good power down low is high compression.

If you’re serious about porting engines, C.C. Specialty in Tennessee sold me my #10 kit. Wise man once said “the man with the tools rules.” And theirs are THE BEST hand porting tools you can buy.

If you’re serious about learning how to build engines that are competitive and/or a lot of fun to ride (sounds like you are), head on over to macdizzy.com. There’s some great info for free, but if you just pay the $20 to get into the forums, it will be 100,000 times better than trashing a $20 cylinder for nothing. Listen to this guy, lots of good advise in that statement. Im more into the drag racing end of porting so I like my blowdown in the 33-35 range and a little more timing like 194*, 128* for the hondas. Maybe a little more on a oem jug but not on the prox jugs. They just dont seem to like real high timing #'s like other drag setups. Once you get past 192* on a honda they tend to get high strung pretty quick and are pretty much useless for anything but sand and drags. If that matters to ya at all.

[fulltiltrider]

Originally posted by Swiper77
Check out mac dizzys website he used to have tons of porting knowledge on there for reference.

Well the best thing about MacDizzy now is, Rick doesnt work on engines anymore and will now release even more good info than he did before. He spends alot of time on the boards and answers any questions, its nice to talk to someone with so much knowledge, anyone who can get 60 hp out of an oem jug that pulls like a freight train is a good person to talk to.

[All250R]

In my opinion pick up some books and articles first. There are so many different combinations and ideas and theories even between books and between accomplished builders. The amount of information and testing that can be toyed with is staggering. Realize too then that no one knows it all. However don't underestimate the job either. 2strokes are mechanically simple and this leads newbies to think they're simple to tune. They're not. People use software to model 2 dimensional models of the fluid mechanics all the way from the air filter to the exhaust tip, and the math behind it is not something someone simply pulls down off a website. Here it helps to have a natural knack and curiosity for physical science so you can grasp the concepts easier. I'm no math genius by any means, but in college this was an area I didn't have to apply myself real hard to do well in. That kind of curiosity helps keep you motivated through the theory and actually enjoy it.

Beyond the theory software can help get you closer to a target but even then it's tough to model all the abstract things going on inside a two stroke engine and you ultimately wind up with some of your own theories and likes and dislikes, hopefully backed by repeatable and controlled testing, but honestly sometimes tuners have a basket of "I think this is the cause of x" that they like to employ. You'll also discover that everyone has some sort of opinion. People sometimes keep things to themselves for that reason. That seems to be the state of the art in my understanding of it today anyway.

But again at the core it helps to have some fundamentals that make things easier and steer you away from basic mistakes. With so much to potentially understand and gain experience at, you really want to study for a while to feel like you have a rudder in your ship. Then you can go out and feel like you'll make a positive impact on the engine even if you make some mistakes or wish later you'd done something different.

Once you have what you feel is a comfortable level of theory under your belt and you're off to the bench it might take a little time to develop methodology with just the hand tools. I'm good with understanding what the cutter is doing and how to get it to do what I want. You can't let your mind wander if you want a purposefully cut tunnel. You want to be aware continually of what you're doing. It gets tedious honestly too. However, the cutter can take a good design and dull the results if you're not careful what you're doing..

But by all means give it a shot! It's fun. I absolutely love these engines. It fills the cracks in my thinking daily. Good luck with the journey!