Planet Minis

sweetjeep

I am in the process of porting out my stock head.

In my case I am planning to match the exhaust to my 2bros pipe at about 28mm at the tip. I don't know how far back I can get it at that width, but I'll find out.

On the intake 36mm would be optimum, but there just isn't enough material, so I'll be taking what I can get. 30-32mm looks pretty reasonable. I might egg shape it a bit to help with more area.


Either way, my real question is whether or not anyone has bothered to unshroud the valves on the stock head? They sit in a fairly deep pocket with a moderate lip. So it appears it's worthwhile to uncover them a bit, I am jsut curious if anyone else has spent the effort.

Oh.. and the piston is a 136cc Tak kit with a 24mm Mikuni carb.

cyclerider57

What size valves?

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

2wheeltyson

do you have a flowbench or are you just thinking to go as big as possible. because bigger isn't always better.

sweetjeep

The valves are stock (21 and 23mm I think) and in both cases my desired dimensions will only be the the diameter at the very entrance/exit of the port.

I assume I'll only be able to get in a certain distance and when I get to the actual valve it won't be as massive an increase, but I won't know until I get in there.

sweetjeep

Oh, and for the flowbench question: I have a homemade one, so I don't know actual flow numbers only if there is an increase or decrease in performance.

It's basically a set of electric fans blowing through the assembly and pushing a ball up a tube. If I looked up the specs on the fans I could probably figure the CFM, but that's not really important.

turboglenn

one tip is to make the port cone shaped if you're going witha big opening... air traveling doena funnel shaped path (larger to smaller) picks up air speed and can deliver a denser charge ( one of bernoulis pricipal of airflow) but don't just make the whole port huge or you'll lose power.. i forget the rule on bowl size, and i'm in a hurry to get ready for a masonic lodge officer installation i have to be at so hopefully some one can chime in with bowl area dimensions and volume/size

sweetjeep

Thanks Glenn. That's more or less what I am curious about. Reporting the port diameter was as much as background information as anything else. That I'm fairly confident on (and the principles thereof) it's the combustion chamber details I am unsure on.

cyclerider57

Your ports are going to be way to big. Plus, what carb would you match up to a 32mm port? A bigger hole flows more on a flow bench but in no way does that equal performance. If I were you I wouldn't go bigger than the valve sizes. Also a set into the exhaust is not a bad thing always. It traps the slow moving gases from moving back into the combustion chamber. Search through some of my other posts for info.

__________________
The wise understand by themselves; fools follow the reports of others. Goodness speaks in a whisper, evil shouts. -Tibetan Proverb

sweetjeep

Yeah.. you know, that's what I failed to think through. THAT'S why I posted the other information that I didn't think I needed to report. Because I often forget some of the neccessary details.

I was thinking about a 30mm intake port to keep the ratio with the exhaust. Optimal, based on the exhaust, would be 36mm (for the intake). Which simply can't be done. But I forgot to realize that the exit bell of the carb is only 28mm and going larger than that would be a waste of time and probably pretty detremental.

My thought on the valve inset wasn't to get them flush but more to simply uncover them a bit. The walls of their pocket are pretty steep and have a sharp lip. My thinking was to soften the lip but leave the overall pocket. The valves seem to be set in the pocket about 1.25mm, call it 1mm. That seems a bit deep.