Raise the exhaust port?

[patthesoundguy]

Now that my spree is working quite nicely, and I don't feel like tearing into it right now, Im picking away at my Honda express. I have a spare cylinder that I've fixed all of the casting flaws and cleaned up all of the ports, I opened up the exhaust port from rectangle to round to match the pipe. Now when porting a cylinder I've been told and heard about raising the exhaust port. What are the pros and cons of doing it say a few milimeteres or so or 1 ring thickness in a scooter cylinder. I know the effects are supposed to be positive, but Id really like to know what the deal is on raising the exhaust port. I've done the process on a gas trimmer a week or so ago just to get the feel for doing and of course I had no problem, so all I need to do is go grab my dremel and do it.
Opinions please everyone.

[kingkamehameha]

You should read jennings articles and use the search

[Bear45-70]

Look in Wikispreedia like you should before asking questions like this.

http://hondaspree.net/wiki/index.php5?t ... st_-_Spree

[patthesoundguy]

Look in Wikispreedia like you should before asking questions like this.

http://hondaspree.net/wiki/index.php5?t ... st_-_Spree

I have read that many times, thanks for the link though. I'm just looking for some wisdom, experiences and opinions on the subject.

[fastplastic]

You should read jennings articles and use the search

you need to under stand what is going on before you start changing things.... Jennings will open your eyes....

[ottoman]

Since no one will answer your question. Yes raise it a MM.. 2 MM max. Follow the shape of the stock port. Widen it a MM on each side. If you have a steady hand and do a nice job you will be rewarded with better performance but you will probably have to play with the carb jetting. Dont forget to chamfer the port edges!
Worst result will be you grind poorly and wreck the cyl or it runs like crap
If you do mess it up I probably have a few nice express cyls laying around you can have.

[patthesoundguy]

Since no one will answer your question. Yes raise it a MM.. 2 MM max. Follow the shape of the stock port. Widen it a MM on each side. If you have a steady hand and do a nice job you will be rewarded with better performance but you will probably have to play with the carb jetting. Dont forget to chamfer the port edges!
Worst result will be you grind poorly and wreck the cyl or it runs like crap
If you do mess it up I probably have a few nice express cyls laying around you can have.

Wow thanks for the info, much apreciated. The cyl Im working on was one that I had bored out 0.25 over and have a new piston and rings for. That cylinder was the one that came on the bike when I got it 14 years ago. never ran it. So Im picking away at it every time I walk past the bench. Playing with the burr tool on various things over the past couple weeks has been paying of now that I have the feel for how the tool cuts Im feeling very confident about not wrecking the cyl. Your info is just what I needed to finish the job Thanks so much. The stock express motor works quite well with a pocket bike chamber I put on over the last two days, it was maxing out at 40km/hour even on the down hill and now on the downhill I get 60km and maybe more but I run out of road. But I can really feel how the thing needs to breathe better and the thing will come alive. I really see a new carb in that bikes near futre though, something that has actual jets I can swap out.

[Bear45-70]

Downhill speeds mean nothing and are irrelevant.

[patthesoundguy]

Downhill speeds mean nothing and are irrelevant.

yes you are right if you are doing official speed trials but... if the bike will only go 40km/hour on the flats and 40km/hour down the hill and then you make a change and it will do 50km/hour on the flats and 60+ Km/down down the same hill in the same conditions (without seizing the motor), I don't really call that irrelevant. All that seemed like valuable data in the search for more go out of my bike. And I live on a half mile of hill and the only way to get anywhere (like any flat ground) is up, the other end of the street is a dead end 100 yards away. I take all speeds and how the motor responds up and down the hill and on the flats into account because every where in this part of Nova Scotia is on a hill. It's definitely relevant here when the main road to go to anywhere is 70km/hour and all hills.

[Bear45-70]

With gravity boosting your speed down hill is not telling you anything about performance increase. On the flat yes, down hill NO!