porting heads

[mo haggs]

i was reading a thread about porting heads and someone mentioned it actually looses power rather than gains it .

so i had a trawl and found this http://www.mototuneusa.com/think_fast.htm

i thought it was a good read with som interesting points.

[amaechizzle]

You CAN have a loss in power, depending on how you port it.

It all depends on how much air your getting in, in the first place.

What your trying to do is pump more air/fuel into the cylinder right?
If your fuel system isn't equipped to produce as much as is required by the porting it's useless.

Not to mention if you perform it incorrectly, , then you've completely ruined the velocity at which it enters the cylinder.
And funnily enough, if you have an increase in flow when the valve is slightly open that is equal to a decrease in flow at fully open, you will still have a slight gain as you spend more time at slightly open then fully open.

[uber pikey]

Top tip, don't fucking port it!

unless you know exactly what your doing then disaster is just one file stroke away.
You are not trying to PUMP more air into the engine at all, you are trying to make a smooth air resistant surface so that the air is less disturbed through the ports creating a better flow, again don't touch it and only give it to pro's full stop

[CMSMJ1]

nah - depends if you mean proper job porting (as per the great posts by G-force on here) or you are going to remove the casting flash from the heads?

Porting, for me, means altering the shape of the tracts themselves, whereas te DIY optoion is just to clean up the heads so that are better than they were and still the same shape.

I cleaned up my heads on the race bike and am going to do the same to the RVF heads I have to fit to no9.

The race bike is pretty rapid!

[Malc]

Top tip, don't fucking port it!

Bottom line. People don't charge hundreds of pounds for this kind of work because they are greedy bastards...

[Martin]

But if you fancy having a dabble and don't mind potentialy ballsing it up why not give it a go.

[mo haggs]

lol it had crossed my mind about getting it done ( im not brave enough to do it myself),
but im not going to bother as it is for a road bike so i cannot justify the work.

[duncan]

My old BMW was professionally ported and twin-plugged by a man who knew what he was doing and it made an enormous difference.It was not faster or more powerful,it just had a lot more torque,bottom end and midrange,or at least that was my impression because it was not dynoed before and afteri

[spanky]

I can see his point if the porting is just about making the ports bigger or smoother, but I wouldn't have thought that things like knife-edging would have an effect on flow going back up through the ports.

Maybe the most interesting point about that article is the talk of smaller ports equalling more power - the nc35 Vs nc30 carb argument.

According to Honda the nc35 carbs are better than nc30 carbs because they have a smoother straighter air flow. According to some tuners the nc30 carbs are better because, well, they're bigger. It would be interesting to know if anyone has done side-by-side comparisons of the two

james.

[spooky]

I heard that to make the ports smaller will increase the power as the mixture is speeded up as it goes through the ports, only about 15% smaller port size will give good results., from what I've read/heard anyway.