More porting questions

Steeltoad /

I've been warned not to grind out the intake port on the cylinder, and it makes sense to me that it would affect the gas going in. Can somebody explain a little better what would happen if the port were elongated along the top or bottom edge.

I'm just curious and trying to learn a little more.

Re: More porting questions

You change the intake timing ( you'll let the intake charge that is commpressed in the bottom end of the engine out into the cylinder earlier ). My advice is, don't do it unless you've got a spare cylinder head to wreck, or you know someone with a flowbench and past experience with your engine who will check it for you after porting it and knows what will produce a screamer or a slug. Just a hint, if you decide to port a cylinder make sure you camfer the ports slightly so the rings don't hang up on them.

Re: More porting questions

I wouldn't do it either... if that motor doesn't have a reedvalve I think it it will only narrow the powerband (less low end).

I fthere is any port you are going to alter.

Then do the exhaust port.

raise the roof 1mm (the 'roof' being the edge closest to the spark plug)

and widen it 1mm on both sides

maintain the port contour as it is

Put it in a vise and use a file and make several small sharp cuts next to each other across the port roof and sides (1mm deep or less)... then use the broad surface of the file and take the entire port roof down till all your little cuts are smoothed away.

You will need about 2 or 3 files... a crescent shaped one for the corners.. and a flat one to do most of the 'hogging out".. and a sharp corner for the initial light "gouging".

File and look, file and look, file and look (so you don't get carried away)

When you are done with that use a strip of emery cloth and pull it back and forth over the new port edge to bevel the edge to keep it from catching the rings.

Then when you are done wash it thoroughly in hot soapy water or clean solvent.. then dry it and oil it and reassemble.

Should be worth 3 mph.

Might lose a leeetle low end.

If you screw up your cyl could be junk.

Re: More porting questions

Steeltoad /

Rest assured, I don't plan on changing the porting. I'm just smart enough to know that I'm not that smart. I did know that it can come out either really good or really bad. I was just wondering what effect elongating either the top or bottom edge would do.

I don't think I'll do anything to the exhaust port either. The idea of taking the engine apart, and hoping I dont screw anything up, just for 3 mph, doesnt sound that appealing.

Re: More porting questions

Yeah,but Steeltoad, 3mph is a 10% increase on a moped.And maybe a little better on hills since you could hit them at a little higher speed.HMMMM? I may just try it on an old Minarelli I've got laying around,you know? THANKS,FRED !! I printed that out.

Re: More porting questions

What you might notice more than the few mph.. might be harder acceleration from say 20mph to top speed... which might allow taller gearing.

Re: More porting questions

When you say harder,it's the same as saying more `punch',right? That alone would be worth tryin'.Thanks!

Re: More porting questions

Steeltoad /

Ok, now you've piqued my interest. a little more zip from 20mph up would be very usefull, and a bigger gear would be great. I'm running 27:22, and I can get a 30 tooth front to put in, but quite frankly the acceleration is about as low as I can take it now. If that would let me move up to the 30, it would be worth it.

BTW Don, 3 mph is only about 6% for me :-) (70cc)

I may just make that exhaust port a little bigger, thanx as always Fred.

Re: More porting questions

keep in mind that (usually) gains in top end (max speed) mean losses in bottom end (acceleration). so you might gain a few more mph, but then lose ability to climb hills or start quickly from a full stop.

i'm currently doing just above 40mph on my bianchi. but i have very little acceleration and have trouble going up hills.

Re: More porting questions

Steeltoad /

Luckily hills are not a problem, I live in Delaware, and going up somebody's driveway is the largest incline I have to deal with. I am seriously lacking at takeoff though. Top speed is about 55 (60 with the wind at my back on a good day) but taking off from the light is a nuissance.

Re: More porting questions

just passing through but wondered if this guy might be able to help with your porting problems. The persons name i sMick Abbey and he tunes all my teams engines for the moped mayhem series in the uk

you can check out his work by goingto my parts & tuning page at www.evolutionracing.co.uk then clicking on Mick Abbey professional Tuning

Hope this helps

Ps Our racing moped will hit 90MPH

he tunes engines as a hobby so give him a try

Re: More porting questions

SteelToad /

Thanx for the advice, sounds like I may wind up doing the exhaust afterall. I've got to paint the jug anyway. Just some followup questions if you dont mind...

You say changing the porting on the intake would lessen the low end, would hit help the top end ??

You said to keep the exhaust port coutour the same. I assume you mean the shape of the port. Aside from the obvious of matching the exhaust pipe, is there another reason to keep the shape the same ??

Does 1mm really make that much of a difference? Wow

thanx as always

Re: More porting questions

SteelToad /

It would be nice if it weren't in the UK :-)

What size/type of engine in that 90mph monster ?

Re: More porting questions

SteelToad wrote:

>

> Thanx for the advice, sounds like I may wind up doing the

> exhaust afterall. I've got to paint the jug anyway. Just

> some followup questions if you dont mind...

>

> You say changing the porting on the intake would lessen the

> low end, would hit help the top end ??

A > As far as the intake goes... the engines I am most familiar with (from my age) all had reed valves... so my knowledge of non reed valve behavior is limited.

Also... If you are going to do the exhaust... DON"T do the intake at the same time!

You will not know which caused what.

> You said to keep the exhaust port coutour the same. I assume

> you mean the shape of the port. Aside from the obvious of

> matching the exhaust pipe,

A> First of all the shape is not round.. so it doesn't match the exhaust pipe anyway.

> is there another reason to keep the shape the same ??

A>Yes... the shape is meant to be friendly to the rings

Make the little V cuts like 1/8th" apart (maybe 14 of them total?)

That is the simple way to maintain the shape of the 3 'sides'.

> Does 1mm really make that much of a difference? Wow

With a 1 tooth gearing change I am pretty sure you will get 3 mph... and maybe even without the gearing change it will get that.

(however.. the speed comes from RPM.. the gearing is to help save your motor)

And I am telling you 1mm... because by the time you are done.. the 1mm tends to become a little more than 1mm... like maybe 1.5mm (1/16th)

You can go for 1/16th... and it will tend to become a little more.

Just trying to prevent you overdoing it... you can always go back in and do it again.. it is an easy process.

You only have to file the port surface about 3/4 of an inch back from the 'piston face'... not all the way out to the exhaust pipe connection.

Re: More porting questions

Since you asked it's a honda MT5 engine air cooled and restricted to 50cc

just takes a lot of porting and a bit of messing about with pipes and timing

if you want to know what's been done check my site at www.evolutionracing.co.uk for the latest updates on the new bike for next year sholud be at least as fast

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