Lets play guess that porting

[BombThreat]

:Banane01: Here's a couple pics from a 61x thats been ported. Is it racing or freestyle porting?

 

[MADMAT]

Thats a good pic. I think I could make a friggin template from that.

I say race.

 

[BombThreat]

If ya need anymore let me know! Ill take extra shots while Ive got it open.

 

[Matt_E]

Thats a good pic. I think I could make a friggin template from that.

I say race.

It's impossible to say. THe exhaust port shape is good for ring life.
Other than that, without actual numbers, it's hard to say what RPM it was ported for.

Additionally, the exhaust port is only part of the whole package. To give you more accurate information, post pictures of the bottom of the cylinder, and detailed shots of the transfer port windows.

 

[douglee25]

The other thing that may tell you something is to measure the exhaust port height. If it's raised, more than likely it was used for racing.

Doug

 

[#ZERO]

Yeah... measure the height of the exhaust to the top of the cylinder in mm.

Race porting on the exhaust is usually straighter on the sides and at the top it will be flusher with the piston surface for faster release of burnt gases. Freestyle porting is more oval looking; like your photograph. Also take a picture of the bottom of the cylinder so we can see if the sleeves have been modified.

 

[BombThreat]

I cant take pictures of the bottom, its mounted on the engine still. Ill get a measurement too.

I'd like to note that I know the boat this engine came from was built for mod racing but that was back in 1994 or 1995. In my little mind and what the guy was telling me people were JUST starting to figure out what parts to use to make the SJ's scream... Im thinking maybe people werent sure yet exactly what kind of porting to do and could have been experimenting a little bit? The porting was done by Scott Pratt, a friend and shop owner (BP Racing) of the previous owner. He said this guy was a racer himself and went to the world finals. Anyone hear of that guy?

This motor/ski was built back then and ever since its gotten very little runtime and no racing. Just been in storage.

 

[SUPERTUNE]

Race porting on the exhaust is usually straighter on the sides and at the top it will be flusher with the piston surface for faster release of burnt gases. Freestyle porting is more oval looking; like your photograph. Also take a picture of the bottom of the cylinder so we can see if the sleeves have been modified.

Chris, NOT IN MY OPINION! My freestyle exhaust ports are NOT oval! Race porting for high RPM motors are mostly oval to prevent ring snag and promote ring seal and less wear with the added rpms. Did you note that the way Yamaha ports are mostly square from the factory? (61X/62T cylinders)
The total correlation between the ports are also very important, (it's called blowdown and/or port stagger) as you would run a race motor and freestyle motor totally different in port mapping.
Port heights play a major roll as to where the mean target RPM's are designed for.

 

[Flash-FX]

I cant take pictures of the bottom, its mounted on the engine still. Ill get a measurement too.

I'd like to note that I know the boat this engine came from was built for mod racing but that was back in 1994 or 1995. In my little mind and what the guy was telling me people were JUST starting to figure out what parts to use to make the SJ's scream... Im thinking maybe people werent sure yet exactly what kind of porting to do and could have been experimenting a little bit? The porting was done by Scott Pratt, a friend and shop owner (BP Racing) of the previous owner. He said this guy was a racer himself and went to the world finals. Anyone hear of that guy?

This motor/ski was built back then and ever since its gotten very little runtime and no racing. Just been in storage.

#18 with the holeshot

http://www.x-h2o.com/gallery/displayimage.php?pos=-7041

 

[dbrutherford]

Yeah I would like to see the underneath of the cylinder and the transfer ports as well. A cylinder I had ported once had the transfers shaped on an angle where the fuel/air mix would be on the right angle into the cylinder. Yours don't look like they have been touched much. Then again, I am a Kawasaki guy.

DBR

 

[waxhead]

im with chuckie on that one
you run flat ports on a race engine and you get to replace pistons alot
but the flat port makes power at the exp of ring life
this is not an issue on a free ride engine because its not hitting the rpm for such a sustained time as a race engine

I voted race porting because of that
but as every one says let see some measurements so you can really tell

 

[BombThreat]

Alright I finnally got those measurements. The ported cylinder has 35.5mm and I took a measurement of a stock 61x ive got laying here. That's 40mm.

So if this in fact a racing ported cylinder would it be advicable to switch to a stock ported cylinder which I have readly avalible here with matching pistons (all new and fresh bore 81.5mm). But would that create problems with the fact this has a 5mm stroker with custom cut domes for clearances? (squish height?)

 

[douglee25]

I'm assuming those numbers are from the top of the deck? Just to be sure the deck hasn't been cut, is the overall measurement the same on both cylinders as well?

Doug

 

[BombThreat]

Yeah thats to the deck,

I measured both the stock cylinder and the ported. Stock reads right about 120mm from bottom to top and the ported one read about a 1mm longer... But that one was more difficult to measure since its still attached to the cases. Id imagaine they are both the same.

So would it do any good to switch to stock cylinder or should I leave it alone?

 

[Half flip95]

curious as well

 

[BruceSki]

a 6 year old thread? really?

 

[TheBuzzard]

my guess is that thing is in davey jones' locker by now

 

[Half flip95]

google can find anything

 

[BombThreat]

Lol still have that cylinder but rest of that motor is in NJ somewhere