Athena 170 porting
The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone..while it benefits from porting, lifting the whole lot 3mm is a bad idea...The Athena 170 cylinder is the same casting as the 125 but bored out to 65mm. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so has 125cc sized ports.
I opened them up to 170cc sized ports by widening the exhaust
5mm, and lifting the transfers 1mm using a 1mm base spacer
and 1mm skimmed of the top of cylinder. It is better raising the
cylinder rather than modify the transfer ports as the Nicasil
plating chips easily.
Double check the pv cable setting. On mine with the pulley
lined up with the mark, it was only about 3/4 open. Only when
I looked up the port did I spot why it felt so flat initially!
Initially the 170 kit felt awful, until I double checked the pv
setting and found it was about 3mm closed. Once that was
reset, it flew...
declan last edited by
@theportingmaster nice info thank you
MadGyver last edited by
@theportingmaster Reading your post is almost like reading my final calculations,little different numbers by +0.1mm,I did not skimmed the cylinder.
I did work on crankcases,transfers,exhaust,exhaust port,pv,cylinder head(compression,squish,volume) and custom gaskets.
Calum last edited by
If you're porting the 170 then the plating has to come off, which is really the only reason why I haven't done mine yet. I will do it, but after a season of riding it. Seems criminal to destroy good plating.
MadGyver last edited by MadGyver
@calum No destruction to the plating,everything was done very slow and carefully,the edges are very smooth.
Only sandpaper (dremel and hand) was used,it took A LOT of hours.If I used dremel carbide bits or sandstone it was faster but risky.
How much of a diffrence did the 5mm widening of the port make?
I've just completely rebuild my engine. (Gearbox, bearing, new piston) Already have 320km's on it and it's pretty solid. The 170 kit is a huge improvement over the 125. Is it worth messing with the ports?
MadGyver last edited by
@llldennis How much should the port for the 65mm bore,47mm wide (43 in chordal length).It's 42mm like the stock cylinder.
Worth messing,no and yes,what you after is the right question.