Maniac57 40mm intake 66cc porting thread.

[maniac57]

Here's the latest porting job.
I decided to go a bit more aggressive this time since the last turned out so well.
Raised exhaust port about 1-2mm, lowered intake same and trimmed piston skirt for full duration.
Widened intake 5mm and exhaust 6mm. Extensive transfer work to remove ridge and open entire length for better flow and aim. Notched piston for better transfer flow and aim.

 

[maniac57]

 

[maniac57]

 

[maniac57]

 

[Davezilla]

Those are some purdy looking ports you got there... that engine's gonna scream when you're done...

 

[maniac57]

If it turns out better than the current 66cc, I'll be thrilled! It should too since this jug started out with substantially better ports. I didn't go anywhere near as deep on notching the piston for transfer flow but I did do a LOT more work cleaning and opening the transfers. I concentrated on better aim like the last but more aggressively. I'm hoping it will work well with the raised exhaust and longer intake duration.
But I desperately need a real pipe. The current pocketbike pipe has too small a chamber and is the weak point now I think.

 

[Davezilla]

If you got a decent welder the small dirtbike pipes work really well, any of the 65cc pipes can put the power where you want it, and the KTM 50 pipe has a nice taper on the baffle cone for a wide powerband, that's what I'm using but I spliced in a 4" section of belly from a pocketbike to bring the powerband down to a more usable area, still strong on top but comes on a bit sooner so power is good by about 15 or 20 mph, but it pulls all the way to around 40. It takes off slowly from andead stop then it pulls smoothly until the pipe kicks in. A pipe similar to the SBP would hit a lot harder but the powerband is a bit more narrow because the baffle cone is at a much steeper angle.
The kx, rm, yz, or cr, 65 to 85cc pipes are plentiful on ebay as well as used FMF fatty pipes for a decent price ranging from about $30 for a used KTM 50 pipe to about $80 or so for a used fmf fatty, the stock kx or rm etc pipes can be had for around $45 on up, these will all work and can be tuned by adding header or belly length, and the type of powerband can be predicted by the shape of the baffle cone... long and smooth taper = wide powerband while a short more drastic taper will have a harder hitting narrower powerband and with more power when it hits so you can choose how you need it to run, then choose the pipe, then tune by lengthening or shortening the header and/or belly so the power is where you need it and so it fits the bike.

 

[YesImLDS]

Looks like she'll flow better! What's your address so I can send over my jug and have you port it! Haha just kidding, but seriously good looking stuff!

 

[brown]

I have to ask.

Are you just using a dremel with a long carbide bits?
Has anyone tried a 90 degree head on the dremel?

If so ..........did it fit and how did it work out?

 

[Davezilla]

I did most of my porting work with a pencil grinder and a regular sized 1/4" die grinder, the die grinder will do the bulk of the work, then the pencil grinder for the tight spots including the transfer tops with an extra long rotary file to get that casting ridge out.
Other tools I use are pneumatic files, sanding drums and rolls, carbide burrs, diamond burrs, needle files, and most important, a degree wheel, dial indicator,and depth micrometer to make sure I don't cut out too much.

As far as what you use to port your cylinder, the right tool is the one you can control and that works best for you for what you're doing. Dremels are great, I just use a pencil grinder because I can plug into my shop air which is more convenient than extension cords, different story when I'm doing the job at home... Then I'll prefer the dremel and my electric tools, but if you need to use a 90 degree extension and it works for you, by all means, use it... there's no wrong method.

 

[Theon]

I have the Dremel 90 deg head, It's crap!, Don't fit and no help at all.
A good variety of burrs is all you really need, sandng drums ect are also helpful.
As Dave suggested starting with a Die grinder and a steady hand!, saves a lot of time with the dremmel.

 

[brown]

I used to do some port work to my small block 406 cid Chevy back in my racing days. so I know of what you speak. Just been a while. Glad I didn't go buy a 90 degree head. Thanks for the info.

 

[Ron344]

I didn't want to say anything, but the size of the exhaust port looks questionable. To me it looks too wide and could cause the ring to hang up in the port. If not it's right on the edge. One more thing when you port this big you lose low end power.

 

[YesImLDS]

I didn't want to say anything, but the size of the exhaust port looks questionable. To me it looks too wide and could cause the ring to hang up in the port. If not it's right on the edge. One more thing when you port this big you lose low end power.

True, but if you are porting this big you should already have supporting mods which should counteract that. High compression etc etc

 

[Davezilla]

I didn't want to say anything, but the size of the exhaust port looks questionable. To me it looks too wide and could cause the ring to hang up in the port. If not it's right on the edge. One more thing when you port this big you lose low end power.

I agree... that port looks mega wide, but as long as he's following the 60% rule, keeping the openings as round as possible, and chamfering them really well it should be safe. Too bad these cylinders don't have a split design for the exhaust port to help support the ring when it goes over the widest point.

 

[Theon]

That's about how wide I go, measuring in the round, 29 - 30mm.
Not really looking for longativity, lol.
Looks to me there is a fair arch in the roof of the exhaust port, I've not had problems with ring snag, I aim for about 1/2 an inch of flat roof and floor on the port, with the rest radiused.

 

[Davezilla]

Same here, I'll go just a little higher at teh middle to continue the arch as far as I can get away with, then I take my time and get a nice even chamfer all the way around the port, strips of fine emery cloth work great for doing the finishing touches of the port chamfers, I just feed a strip about1/4" (6mm) to 3/8" (10mm) wide thru the port and out teh top or bottom then I can push/pull the emery cloth around the opening to even everything out and put a nice radius on the chamfer, one of the few parts of the porting job done best by hand.

 

[Theon]

I use to keep an arch to the roof, but read that a flatter roof will give a little more punch (and noise.)?
I've found these motors to rev well with fairly conservative exhaust duration, and the lower the top of the exhaust port, the more effective stroke, ect.
So I've been leaning towards getting the ports as wide as possible and not lifting anything too much, in fact thinnest base gasket possible, but I guess it all depends what your starting with.
If those wide inlet barrels are the same as what I'm getting, you don't need to do much at all in regards to lifting ports.

 

[maniac57]

I stayed conservative with raising the exhaust. Only went about 1mm higher, about what ramping the piston gives so it should be fine.
I'm not too worried about ring snags as it's well under the 60% rule.
And I deburred the ports extensively....
*crosses fingers*
But now that I look at the pics again, that port DOES look huge. Heh heh...

 

[CarpsCustoms]

Haa yeah i was thinking that exhaust port was huge too but i said to myself let me mind my business, lol.. So what do you plan on running to combat low-end power loss?? Reeds & a longer intake tract??