August 10, 2011

Technical Enquiries #1, Surface texture

Hi mate,
Hope youre well. Perhaps you could help me this time...

When porting a 2t engine/ barrel what sort of fibish are you looking for... Some say polished, some say dull like the golf ball effect? Does the surface fibiah really matter as long as you have removed casting defects?
Also do you know anything about the AR fuel solenoids?


Cheers
Shaun.

Hi Shaun.
You are right, some people prefer a polished look while others a rough finish.
I dare to say that both are incorrect!
Though, this really depends on the engine and how someone tunes it.

In my opinion. this depends heavily on primary CR and this is the compression of the crankcase.

It seems like engines with high primary compression may seem to like a rough finish and more modern engines with lower CR and more transfer ports may like a mirror finish but this is not the best you can have.
In any case, avoid a literally mirror finish.
I've seen cylinders where the owners really polished them to a mirror finish look.
This is a no no and never works well... regarding the other example of the golf effect, this is a nice example but is the usual mistake that people do. You do not throw mixture into the engine, the engine draws the mixture in it... Not to mention that the golf ball has mass, the fuel mixture does not... well, not really accurate here but I'm sure you get the point.

In my opinion. you just need to keep smooth passages,
not rough as well as not mirror like but something in between. 
The mirror finish will only help on the exhaust side of the cylinder and the cylinder head.
It will NOT give better performance but only help with less carbon build up overtime so it's a good thing for street bikes that are rarely stripped...
So, just remove any casting flaws and radius all the corners. 
Take a look through the cases, reed valve openings etc and imagine the flow of the fuel, you will find that some things interrupt the flow and may benefit from some alterations here and there.
While you are at it, avoid knife edging the transfer port dividers.
They will sure look nice but this is all they do, they do nothing to help flow.
Some people make a knife-edge, some people lower them etc. after many cylinders I came to a conclusion that this is not the best option, especially on a more modern tuning conception.
In my opinion, the best option is to make a radius in there.
A small curve that will allow an even flow and will not disrupt and split the incoming mixture like a knife edge will do.

Check the lower part of your nose and how the air enters the nostrils, wise lessons from mother nature... there is not a sharp edge over there.

As a general rule, sharp, rough, mirror finishes and anything unrelated to nature rarely gives the best performance -if at all-. That said, you might see some more power over stock even if you used all of the above mistakes but I'm sure you've changed more things while you were at it that may have made a bigger difference... and after all, you could have gained more.

Regarding the fuel solenoids, I take it that you mean the usual air jet solenoids that you can find on most two stroke engines. They are just plain air valves that are electronically activated by the ECU. They just let the flow of more air on the air & needle jet of the carb as to better atomize the fuel at certain revs. Nothing to worry about as they are simple, rarely go wrong and essential for street use.

Let me know if I can be of more help.
Nick

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