Port Moding

QuinnO · 12-29-2009, 01:41 AM

I just ported & polished the exhaust ports on a new OEM 640 jug "644cc".
I'm looking to get the best mid and top end.

I will be using Wiseco forged graphite coated 76 mm pistons.
Dual dry tuned pipes, a total loss MSD, dual SBN 44 carb's.
I'm using the old Oil tank for VP C-12 race fuel to be injected with nitrous oxide "25-75" shot. Inline 15 PSI pump for the NOS kit.with a regulator and return.

I'm running a stock pitch impeller.

Knowing all that, should I raise the exhaust ports?
The ports are 41 mm round at the smallest point.

QuinnO · 12-29-2009, 01:58 AM

EX opens at 91* and has 276* open right now.

jetski9010 · 12-29-2009, 03:57 AM

where are you getting pipes to run on this thing?

jetski9010 · 12-29-2009, 04:12 AM

If I were you I wouldnt port anything too extreme unless you for sure know what your doing. You could always just do a mild port job. Widen the exhaust port to 70% of the width of the bore. You can match the sleeve like you were saying and then just sharpen the bottom of the transfers. I wouldnt go much more then that.

QuinnO · 12-29-2009, 04:47 AM

I can make a nice set, I'll use 2 Stroke Tuned Pipe Wizzard for specs. Easy, but time consuming. I have a lot of time porting heads for all kinds of stuff. I am going to raise the exhaust port to an aggressive 292* The ski is all high RPM use.

jetski9010 · 12-29-2009, 04:56 AM

If you mean the exhaust is going to open at 68 degrees maybe? If thats the case you are going for all out top end haha. Why are you going though all this work for a 640 motor? Whats the top speed your trying to get?

QuinnO · 12-29-2009, 05:03 AM

Just want to see how much I can get out of it. I like the old Tigersharks hull. I have a Montego 640 I ride and a Montecalo 640 I am testing things on. What I like go's on the Montego to stay.

Krispy · 01-20-2010, 11:45 AM

Do you guys know about MacDizzy? I have learned alot about 2 strokes from the site, I havn't gotten serious enough about it yet to join.

They discuss nitrious and 2 strokes on that site...aswell as port timing etc.

jetski9010 · 01-20-2010, 05:44 PM

Yea MacDizzy is a great site with a lot of good 2 stoke info. I want to make the jump and get a nice porting tool setup but havent got one yet.

QuinnO · 01-20-2010, 06:26 PM

Yea Krisp I have. Im a manic gear head and builder of strange things,sites like that are a must.