Porting - are you actually taking advantage of it?

DuctTapedGoat

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Dec 20, 2010
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I hear people talking about porting all the time. I see pictures of ported motors - and they're using stock exhaust and stock intakes.

If you're going to port, wouldn't you need to use a modified exhaust and intake that actually matched the head porting?

I plan to first modify my exhaust to match the original intake port, then modify the intake to match the intake port, noting performance increase from each.
 

Tohri

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Aug 28, 2010
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In my personal case, and I've heard this a lot of other places, The 'porting' I did to my HT motor was mainly corrective. In it's stock setup, There was almost a 1/4" difference in BDC piston height vs the floor of the exhaust port. And at the other end of the stroke, the piston skirt was covering almost half my intake port.
On top of that, the transfer cutouts on the piston didn't match the cylinder cutouts at all, The transfers had massive amounts of slag and plating flaws in their ceilings, the exhaust port had a bad ridge on the ceiling, the intake was slagged up, and there was no bevel on ANY of the ports.
After correcting all of that and enlarging the intake and exhaust manifold throats, I've gone from a motor that's adequite in the low and mid ranges, and anemic at the top end (In some cases, nearly dead approaching top end) to a motor that needs help getting up to speed but has a power band that feels like it's never going to end.

This is with the stock pipe and a modified stock carb. Had to fabricate an aluminum spacer for the bottom end and copper gaskets all around. I have a puch HiHi 50cc moped head coming in from treatland that I'm going to experiment with next, and work my way up from there. My trike needs to be dismantled, and I could theoretically snag the Dellorto clone carb and tuned exhaust off that.

Long story way short: Porting and cleanup on these motors should be done even if you're using stock parts. Heh. Especially if you're using stock parts. I've noticed a dramatic increase in usable power and this is the first motor I've ever ported. My belief now is that the bottleneck lies not with the carb or exhaust, but with the sloppy castings and Zero finish work these engines receive.

The additude that performance comes from expensive aftermarket parts has always puzzled me. I'll rack it up to the aftermarket stuff being shinier.
 

DaveC

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I call it "The Barbie Doll Effect". Barbie dolls by them selves, nekked, are not all that expensive. It's when you start buying the accessory outfits it starts to cost big money. When it's $85 shipped for a new 49cc nekked you can see my point. I've got waaaay more into bolt-ons than the motor costs. I'd list them all out but I'm afraid at how much it would be, enough for a pretty good Morini motor new. Which all the add-ons do not equal.. It would be like getting a Barbie with 3 outfits, day, night and beach wear ;) Costs more but all the good stuff is there ;)
 

bairdco

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Aug 18, 2009
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the best thing you can do with a stock motor, even if you do nothing else, is to match the intake manifold and the exhaust pipe flange to the motor ports.

it's simple, can be done with a dremel, a drill, or even (eventually) with a file.

any idiot... i mean... person with no mechanical know-how can do it and it only takes a half-hour or so.

the only thing to look out for is trying to grind too much and compromising the strength. most of the time you can't match the ports exactly 'cause there's not enough metal on the intake or exhaust, but opening them up as much as you can can make a sluggish motor come alive.
 
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JdubMotorMan

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the best thing you can do with a stock motor, even if you do nothing else, is to match the intake manifold and the exhaust pipe flange to the motor ports.

it's simple, can be done with a dremel, a drill, or even (eventually) with a file.

any idiot... i mean... person with no mechanical know-how can do it and it only takes a half-hour or so.

the only thing to look out for is trying to grind too much and compromising the strength. most of the time you can't match the ports exactly 'cause there's not enough metal on the intake or exhaust, but opening them up as much as you can can make a sluggish motor come alive.
hey Bairdco is it ok to port a motor that is already in use or does that have to be done with a brand new motor?
 

DuctTapedGoat

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It doesn't have to be a brand new motor, though honestly, just as the cost of a jug is only 12 -20 bucks, I would get a new jug, port it and then swap it out, so you can take your time matching it and not be on a time constraint and not be able to ride in the meantime.

Many people port day one of getting it, but those people also ported their first motors after in use.

Since you're pulling the jug off anyways, be sure to polish your piston, head and cylinder, there's a lot of performance to be gained there.
 
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Skarrd

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i trimmed my piston skirt and also experimenting on the exhaust with using gasket maker rather than the cheap graphite gasket.

trimming the skirt did a big improvement on it, the exhaust gasket was already close to the size it needed to be, getting rid of it just made it better (SBP expansion pipe flange is already shaped to the port how it should be)
 

Lubo25

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Dec 22, 2009
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porting should not be attempted without the proper tooling and definitely without the proper knowledge

example: a quality degree wheel(for port duration, blowdown, etc.), a means for measuring volumes before/after porting to establish the correct pressure ratios based off volume and also determining desired compression(cylinder/crankcase compression), a high quality grinder with diamond bits for around the ports and carbide for the aluminum, and these are just the starter tools

I have intrinsic knowledge with RC nitro engines which are extremely precise and sensitive motors when it comes to calculating power output and porting which I consider myself to be quite adept when it comes to this type of work, and besides these Chinese motors will not benefit from any porting as the motors themselves are not built for power, but for economy, do not waste time porting and blowing parts up

the exhaust port is responsible for your final rpm and some people go crazy with its size and wonder why the engine blew up, leave these engines alone, because they are fine for modest gains with a cylinder head compression boost and really good carburetor needle tuning with a decent tuned pipe setup

look towards a gilardoni 75cc hybrid set up and have some safe fun there
 

Tohri

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Lubo, I'm going to disagree with you there.

RC nitro engines are one thing, and a High quality motor won't see anything but improvement from anyone who's done their research and knows how to use a dremel. I'm from the paintball world, and the basic premise with these little HT engines is the same as trying to wrench more performance from a Spyder or an old Autococker: Flow is key.
Bring up the hydrodynamics of the motor, you're halfway there. Then it's just about knowing what you're after. The first step is just smoothing everything out so it looks halfway decent. My motor had plating slag and casting flaws in all the ports, but the transfers were the worst. Uneven, slagged up, and mismatched transfer windows all needed fixing.
Of course I read up on Macdizzy, Bell's book and on this forum as to how to port, what to port, and how far you can go. I put a Puch hi comp head for extra cooling, and reamed out the carb. I'm getting fantastical performance, but I'm probably going to need a balanced crank, the vibration at Higher RPMs is unacceptable.
 

DuctTapedGoat

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porting should not be attempted without the proper tooling and definitely without the proper knowledge...
This is a very valid disclaimer - but...

I have intrinsic knowledge with RC nitro engines which are extremely precise and sensitive motors when it comes to calculating power output and porting...
This is true when working on an RC car - as when you're at 1:16 scale, small changes make a large amount of difference. Kudos to you for having a calm enough hand to be able to! I know that I don't. But, china girls are FAR from 1:16 scale.

...these Chinese motors will not benefit from any porting as the motors themselves are not built for power, but for economy, do not waste time porting and blowing parts up
Actually china girls respond to porting very well - but when it's done right, which is the purpose of this thread. Sure you can match the ports - but without matching the intake and exhaust to the ports, there won't be any noticeable gain (when in comparison to matching intake and exhaust). There is a reason that you can get a 150 dollar chinese motor around 50 MPH - and that's not because they "will not benefit". When you see a motor that blows up, it's usually operator error in that it wasn't maintained properly. Ask anyone who has blown a china girl recently who did do everything right, and odds are they'll say they were just redlining it at 60-70:1 oil and that they're entirely to fault. Next up is manufacturer defect, followed in the end by ill maintenance.

the exhaust port is responsible for your final rpm...
This is true to a point - your exhaust is the equivalent of a turbo charger when set up properly. But depending on where you want to tune it to - you would need to port it out and match to place your power curve where you want it.

...leave these engines alone, because they are fine for modest gains with a cylinder head compression boost and really good carburetor needle tuning with a decent tuned pipe setup
When you're tuning something like these china blocks, you want to start at square one. It's just like a piece of music. When you write a song, you have to choose what key it's in. When you hard tune your motor, you're selecting that key. From then on out it's fine tuning between the carb and exhaust to fit the "key" you chose for your motor, just as when tuning a guitar you will go back and forth retuning strings multiple times until it produces the sound you want to have.


It might be a stupid analogy, but it's late, incredibly accurate in comparison, and I'm sticking to it. :D
 

sketchman

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Mar 23, 2011
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Something that annoyed me was when I looked at the intake port and compared it to the intake manifold. Wouldn't it have been simpler to do a circular port that made the intake tract uniform all the way from crankcase to carb instead of the huge slowdown abruptly after the intake manifold flange?

Seems like one could gain a fair bit from just running a new intake manifold from carb to crankcase that's just big enough to flow what the carb can do. Or maybe I don't understand how it works.
 

darkhawk22

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Maybe it might be a good business for someone who gets it all set up, to sell ported/matched heads with proper gaskets etc.. Something for the swap and shop maybe or from one of the vendors on here, pirate cycles or sbp
 

Lubo25

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Dec 22, 2009
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thank you plentifully guys, but my main point was to just enjoy the bolt on action and fuel efficiency of these china girls, because these are not engines we should be spending time and money on porting, flowing the individual ports on the head, measuring volume differences before porting and after several times throughout at least, establishing pressure ratios, etc., with the list that keeps on going, trust me, after 7 years with nitro engine 2 stroke theory and performance modifications while making 5 hp out of almost 8cc's, these engines will never come close to that power to weight level

my stock exhaust port I raised with base gaskets, with no need for raising the roof, the width and so on, and by doing so I achieved a higher rpm by 600 rpm! it now revs to almost 8000 rpm without attacking it with the dreadful dremel grinder, pencil grinders are king when it comes to porting, I almost always warn people with dremel grinders

I am not trying to steer anyone away from porting, but this is an exact science, and if you do not want to go all of the way, then do not touch the port walls and just fiddle with the base gaskets, and besides it is the CR and squish band that need to be modified on these engines more so for I find the ports to be satisfactory to about 70%
 

DuctTapedGoat

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thank you plentifully guys, but my main point was to just enjoy the bolt on action and fuel efficiency of these china girls, because these are not engines we should be spending time and money on...
Porting is standard practice, I'm not saying you yourself have to, but I am saying there is enough people with positive results to where it's an incredibly valid mod to do - especially when you're just port matching, it's not as exact as you're making it out to be. Yes - with a 600 dollar 16:1 RC car, it is exact, but you're not at that scale with these motors, it's not so exact a science.


Anyways, the initial point of this thread isn't to discuss whether or not porting makes a difference - it's that if you do, then you need to match your exhaust flange and intake pipe.

The second reason is that without porting, I plan to note the difference between just matching the intake tube to the intake port, and matching my exhaust - there's not any porting that will be going on, and nobody has listed yet the benefits from simply matching without porting.


The last thing I want is a "To port or not to port" controversy thread.

I would love to hear from some of the builders I've seen who spend the time to port but don't match their pipes to it - and hear their justification. As well, I'd love to hear from someone who already has done intake matching without porting, and hear what the improvements are.
 

bairdco

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i said it earlier, match porting the intake and exhaust flanges will give you a big increase in performance. or at least, in drive-ability.

i've matched transfer ports, and cleaned up burrs on engines, but i haven't gone as far as trimming piston skirts, or other internal mods. i'm not afraid to, i just haven't had to. there's simple mods you can do, and you don't even have to finesse it with special tools. i mean, i use a dewalt cordless drill and some grinder bits for everything. i don't even trace out the amount of meat i have to grind off an intake anymore, i just go at it with the drill.

like DTG said, these ain't RC motors with high tolerances. they're 1900's technology, stolen by the russians, then copied by the chinese. it's an (at least) 3rd bastardized generation stump puller motor. and it's cheap. don't be afraid to experiment with it.

i build, ride, and race, the fastest 2 stroke china dolls around right now, and it really ain't that easy to make it go fast, last a long time, and exceed all your expectations.

and, for the record, the only major mods on my race bike is reversing the jug, so the carb's in front and the exhaust is out back,, then matching the ports, and "blueprinting" it all. i still have the NT carb and the stock exhaust. yeah, i tweaked everything a bit, but i lapped everyone at the deathrace with their shift kits, expansion chambers, etc...

and i'm just getting started. wait till the willow springs race...:)
 
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decoherence

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i'm just an average joe. i only have experience w/my first 2 stroke.
i have just slightly better than average mechanic skills. i'm use to working on all kinds of 4 stroke engines. i find 2 strokes as mystifying as women. there are no perfect answers.

i have never taken my jug off. i didn't see any flash on the intake or exhaust ports.
i have 3 different intakes. but i use the maniac mechanic billet.

i did have to work on the grubee style expansion chamber.
i had my engine about 2 weeks before i received my bike so i worked on the intake side of the chamber. i found the flange work easy to match. it was how the chamber was welded to the flange that i had to work on. it was off center so i just worked it a little to preserve integrity.

i always had problems w/4stroking @ 30mph. even w/ 2 different carbs.
when i had to retap my exhaust, i decided to try working on that chamber again.
the difference was night & day. no more for stroking @ 30mph. in fact i'm kind of afraid to drive it faster.
it has more power all the way up.
all this from between an 1/16 to 1/8 or an inch of material BEHIND the flange. since i already matched the flange to the port before
i'm still kind of miffed because the is material missing behind the flange from keeping it smooth that wasn't removed by me. it was welded off center.

maybe i will buy a jug to work on when i get me a billet head.

i do like the prior suggestion of somebody selling pre matched engine parts.

**** i would be interested in a china girl that was matched up. i won't say blue print since the chinas are not made w/ precision.
 
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decoherence

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i use the term "blueprinting" loosely. since there's no actual specs to follow, it's impossible to actually blueprint it. but i can clean up the mess the chinese castings and poor quality control leaves behind.
i agree with this.



i'm really surprised i don't see any engines sold that have that pre done & charge a little more for it.

i know i would throw down on an engine that was "onced over"
or "probuilt".
 

sketchman

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I would think the problem with that is the cost difference between American and Chinese labor.

You'd be paying for American parts and labor to go into something that's still junk in the grand scheme of things. I mean, I put upgraded bolts into mine before I ever ran the thing, and 1st time they were too loose and I lost one. Second time the threads gave way in the engine and so I may as well have never bothered. I'm very careful. I didn't over torque anything. My head studs come loose all the time, the clutch pucks are garbage, quality control is garbage, etc.

I see now why people get away from these things so often.

My next "play motor" will be one of these. At least I see real hex bolt heads in the pic.
Pocket Bike Motor Engine Carburetor 47cc 49cc 47 49 cc | eBay
 

decoherence

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the pocket bikes are nice but i like being able to bump start & having a clutch.
i had a cop follow me over two miles through a residential neighbourhood the other day.
he pulled up aside me & started chatting. i think he really appreciated that when i came up to an ice cream truck & i went from motor to pedalling around the truck . then back to motor w/o skipping a beat.
 
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