Anybody ever ported a Polini Contesta?

[coppah37]

Got my Polini 72cc big bore kit installed on my elite the other day. Pretty happy with the power considering i cheaped out and went with the contesta instead of the corsa. Im running a 24mm OKO and stock exhaust. My brother's elite, which is the same exact year and model, has a corsa bore but has all the same mods including the carb. Virtually identical except the bore. However his has a much better pick up and powerband than mine does which im assuming is because of the porting on the corsa.

I always read people saying you can port a contesta to make it more like the corsa but never see any pictures or technical info.

When you port it do you change the exhaust timing? How much?
How much wider do you make the port?

Any help would be good especially pictures. Im going to at least clean up the exhaust port a little bit but I'd like to get closer to the corsa's performance.

[veedubh20]

porting is your own risk...

[bakaracer]

copy your brothers bore. take the measurements from his bore

[coppah37]

I'd hate to take apart 2 motors to work on 1. I think I'll end up just cleaning up the exhaust port and smoothing it over.

[JJ Joseph]

Im running a 24mm OKO and stock exhaust.

The stock exhaust will strangle all your hard work. I'd add an aftermarket exhaust. Watch the exhaust pipe diameter since there's several choices.

[coppah37]

Yeah a new pipe is on the list definitely. At the moment both mine and my brothers elite are at the exact same mod list (except his is corsa mine is contesta) and his has a very noticeable advantage. Just trying to level the playing field a little.

[coppah37]

So I finished porting my ports last weekend and learned a couple things. On the exhaust side I raised the port timing by 2 piston ring widths. I kept the width of the port pretty close to original. Then i went ahead and smoothed everything out and polishing.


I started out thinking i was only going to do the exhaust port. I reassembled everything and ran it. I noticed about a 2 mph gain with this setup but my CHT went up 30 degrees at WOT. I tried going up to a 110 jet from a 107 and it dropped temps a little but hurt speed.

So after doing some thinking i took the jug back off to do some intake port work. I decided that because one port was opened and not the others that was my problem. So on the transfer ports i noticed theres supports that go across the port itself. I ended up knife edging those and smoothing the ports slightly and reassembled.

THE RESULT =

Keep in mind I'm still on stock gears and exhaust pipe.

I returned to the 107 main jet and saw that my CHT was back down to where i like it at 300-310. My top speed went from about 42 mph to 46 mph with a much more noticeable top end power curve. I also saw my flat ground RPM limit go up from 8000 to about 8600 rpm. Downhill it pulls like crazy up to 9500 with no spikes in temp.

I ordered a PG short exhaust that should be delivered in a few days. Hoping to really see an increase after that is installed

[deuce217]

viewtopic.php?f=4&t=25899

I had a very similar question before. Traffic came through follow this link and read his post. He gives instruction for where you can find more info.

Have fun.

[coppah37]

Hey thanks for that link! I tried finding that info before but couldn't. Wish i had the measurements before i ported. Oh well next time I got some time I guess I know what I'll be doing.....

[deuce217]

Hey thanks for that link! I tried finding that info before but couldn't. Wish i had the measurements before i ported. Oh well next time I got some time I guess I know what I'll be doing.....

No problemo

[kingkamehameha]

You need a 90 degree dental dremel to port the transfers correctly.

[kingkamehameha]

You need a 90 degree dental dremel to port the transfers correctly.

[deuce217]

Bought one of those! Cant wait to use it, and a bunch of stones, flapper wheels(sand paper type w/ 1/8'' shaft). About 170.00 will get you a nice CP or Sioux brand if you find a good deal.