A little cylinder porting advice please....

[scootertrog]

Hello all,
I've aquired a ruined cylinder from a friend that I am playing with before putting my good cylinder under the grinder. I have read A. Grahm Bells' book and understand the cylinder porting section, well most of it, lol, but I still had a couple of questions that I hope can be answered here.
First, is there anything to be gained from the exhaust opening at the flange to be larger than the opening at the pipe? I know that you do not want the exhaust opening smaller than the pipe.

Second, is there anything to be gained from smoothing out the lips, or edges, of the area leading into the cylinder vanes like I did at the inlet boost port entry?

I do not want to alter the port timing or raise the total rpms, I'm more interested in gaining bottom-end power.
Thanks!

scootertrog

 

[tiba_karotsu]

actually it's the other way around, you don't want the exhaust port outlet bigger than the inside diameter of the pipe flange.

 

[Zmod]

Well a basic cylinder porting is very easy. Just make the surface as smooth as possible. Like the boost port seems to be very smooth do the same on the transfer ports and also the surface of the exhaust port.

And yes the cylinder skirts side is a part of the transfer port so smooth it out!

 

[scootertrog]

actually it's the other way around, you don't want the exhaust port outlet bigger than the inside diameter of the pipe flange.

Yes, I think we were saying the same thing. Right now, the exhaust outlet at the flange is just a little smaller than the ID of the header pipe at the flange. So you are confirming that you do not want it to be larger than the header ID, right?
Thanks for the responses guys. Do you think this little bit of "clean-up" actually makes a noticable difference on the arse-dyno?
Zmod, I did the Inlet boost port, it was like the transfer vane inlet before. I found a cutting drill bit (1/8" shank) for a Dremel and it removes the alum really easy and controllable. I just did not know if I needed to do the transfer vane area or not.

scootertrog

 

[adas]

Aloha, I am not too thrilled with how the grinding work is already done on the transfer ports openings and center web divider. You need to match them to the carters and fix the irregular shapes and do not smooth out the sandcasting bumps, but only the ridges as you have circled. You can smooth out the exhaust and EXACTLY match the opening to the pipe diameter as well as the exhaust gasket, not smaller, not bigger. If your exhaust port is starting a taper then you should continue this taper into the pipe. Make the part where the pipe meets the cylinder "invisable" to the exhaust gas. frank

 

[scootertrog]

Aloha, I am not too thrilled with how the grinding work is already done on the transfer ports openings and center web divider. You need to match them to the carters and fix the irregular shapes and do not smooth out the sandcasting bumps, but only the ridges as you have circled. You can smooth out the exhaust and EXACTLY match the opening to the pipe diameter as well as the exhaust gasket, not smaller, not bigger. If your exhaust port is starting a taper then you should continue this taper into the pipe. Make the part where the pipe meets the cylinder "invisable" to the exhaust gas. frank

Adas,
I hear what you are saying. Please keep in mind that this is my first attempt and I know it probably will not be pretty. This is just a practice jug anyway, the cylinder wall has a bad scratch in it. I do appreciate the feedback from you guys that have experience with this - thanks.

scootertrog

 

[Big B NRG]

The things you want to do to your cylinder is not gonna give you any more power.

That bump on the foot is for centering the cylinder. Don't remove it.
Just remove all casting flaws and work the ports on the inside of the cylinder instead of the outside

 

[scootertrog]

The things you want to do to your cylinder is not gonna give you any more power.

That bump on the foot is for centering the cylinder. Don't remove it.
Just remove all casting flaws and work the ports on the inside of the cylinder instead of the outside

Centering the cylinder? I thought the studs and piston would pretty much align the cylinder. I do not think those ridges touch anything inside the carter.

scootertrog

 

[Big B NRG]

Mm maybe so, but removing them gives 0.0 effect.

 

[Browni]

Mm maybe so, but removing them gives 0.0 effect.

He don't want to remove it but surface it!!! Don't forget this is the the part of the transfer port!!! And also has an effect!

 

[scootertrog]

He don't want to remove it but surface it!!! Don't forget this is the the part of the transfer port!!! And also has an effect!

It is my understanding that any "steps", "ridges" or casting spru that is in the flow of the intake charge should be smoothed out. In theory, this all makes sense, just how much difference on the arse dyno might be another point entirely.
I've been told the greatest gains as far as for street riding is to work on the exhaust outlet at the flange, ensuring that it is the same diameter as the pipe ID. Remember that my end-goal is improving torque off the line.

scootertrog

 

[Big B NRG]

Just wider up the exhaustport then

@ Browni: Smoothing that, doesn't give noticable effect.

 

[Browni]

Just wider up the exhaustport then



Have you ever tune a thick cylinder skirt orig 50 cc cylinder! If you chamfer down the skirt (at three different points) has big effect, and if you smoothen the original casting, you gain some more rpm and some power too. Just put the cylinder to a flow bench machine you will see the different CF values!! You can see the positive effect with a thin skirt type cylinder too!! You guys ignore many fine tuning methods, that can lengthen the life of the parts, helps lubricating or can have any postivie effect. In many case even these stage 4-5-race, hyper race bla-bla tuning stages contains only base tuning (sure there are exceptions too) ! No offence meant, but this is a fact!

 

[Big B NRG]

Oke.

 

[Browni]

Oke.

Oke?

Tell me if you don't agree with me! :# I don't get shore!

 

[adas]

Aloha, every little bump removal helps!!!! Even though there may be no noticeable effect. frank

 

[scootertrog]

Yes, that is how A. Bell teaches, remove any bump in the air flow. A tiny improvement here, a tiny improvement there, it eventually all adds up to some improvement.
This is a great subject and again, I appreciate everyone's contributions.

scootertrog

 

[Big B NRG]

Oke?

Tell me if you don't agree with me! :# I don't get shore!

No you are right, tripple the bling, tripple the effect

and Frank, how can something help if you don't notice it. What's the point of doing it then?

I know, also the eye wants to be pleased, however I would go for more drastic measures.

 

[Big B NRG]

Yes, that is how A. Bell teaches, remove any bump in the air flow. A tiny improvement here, a tiny improvement there, it eventually all adds up to some improvement.
This is a great subject and again, I appreciate everyone's contributions.

scootertrog

Yes, mr. Bell was right, but don't forget that the Bell book is old. Back then they had cylinders with 2 transfers + simpel exhaust + crappy TA etc

Then removing a small bump gives 1 hp power gain. Nowadays those bumps don't matter, because the flowing etc makes up.

But don't let me stop you from removing. It's also never said it would be bad.