is porting a bike any good?

Ive got a friend that has driled the ports on the side of his piston out, so that they are bigger than normal, is this a good thing or will it eventually nacker his bike? Ive got a derestricted derbi senda which pulls about 60mph, would drilling out the ports do anything for the performance of my bike? Is there anything else for me to do to it to get the performance up?

Re: is porting a bike any good?

if you have a moped that goes 60mph, don't do anything else to speed it up. you will kill yourself when your brakes disintegrate at a stop. seriously, mopeds really shouldn't go much faster than 30mph (40 max).

but i have no idea what drilling holes in the side of the piston itself would do. though i don't think it would do anything.

Re: is porting a bike any good?

SteelToad /

With gravity fed fuel, tiny intake length, and small displacement, I don't think

porting would make enough difference to notice.

Re: is porting a bike any good?

Chris Robertson /

Making ports bigger can just as easily make your moped less powerful. In a two cycle engine a port's location in the cylinder is analagous to when a valve opens in a four cycle engine. A port's height is analagous to how long a valve stays open in a four cycle. The angle and shape of the port is also important.

Porting engines is an entire field of engine science that I admit I know only the very basics about. I do know that if you want to experiment, you'd better have more than one engine to play with. This is definitely something where you need somebody that knows EXACTLY what they're doing before you try to modify your engine!

Be careful what you wish for! The suspension, brakes, and frame of a 50cc moped (or your Senda motorcycle) are not designed to handle high speeds. Brake fade when you've still got 50mph to lose before you cross yon busy intersection is never happy fun time!

For your reference, try these web pages:

<a href="">Intro to Two Stroke Engines</a>

<a href="">Basic Two Stroke Engine Porting</a>


Re: is porting a bike any good?

Chris is right. There is more to speed than fast. These engines are designed for economy. Trying to make them something they are not isn't worth the effort.

A small motorcycle would be the logical step up. But too much is never enough. That's why I have an old Harley FLH. My Vespa Grande has it's place in the lower horsepower category and that's fine with me.


what's shakin' in CA?

gimmejimmie /

Hi Jim,

What year Harley ya got? Mine is a 64 Panhead.


Re: is porting a bike any good?

Although these bikes were'nt designed to go quite fast, there is no problem going over, as the brakes and suspesions are great. I'd get a speed kit, this is probably the best up-grade. Porting is not for the saturday-afternoon rider...

Re: is porting a bike any good?

what is a speed kit? i have never heard of one. I do agrre with you thought that the frame suspension and brakes are all good enough on some mopeds to withstand a lot of speed, for instance, a friend of mine has a Gilera runner dd, 50cc modified, it now does around 80mph with amazing take off speed.

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