Home Porting

[Matt_E]

Home Porting - now with case porting info

I authored the Sport Port thread on PWCToday - unfortunately, with the demise of the Tech FAQ you have to really search for that thread to find it.
So, I am trying to get all the information and pictures from that thread ported to this forum.

I would like to thank Paul Lehr, the man behind Jr Magoos, for the many times he's helped me out with this porting work. He was always willing to help me and offer advice, both written and verbal on the phone.
THANKS PAUL!!!

Bear with me, as it may take me a couple of days to finish this thread.
____________________________________________________________________

A majority of the porting described by me is centered around the Sport Port templates that are available for purchase from www.racelogic.com
They sell templates for all kinds of two-stroke engines, but the one I used is for Yamaha Twin Cylinders 650-760.

The template is good for widening the exhaust ports, which is what a freestyle port job should include. The template also alters the intake side of the sleeve bottoms.
There are several ways to modify these intake sleeve areas, I'll try to describe them.

I also worked on my transfer ports - this is not part of the Sport Port Template. Stock Yamaha port matchup is reprehensible at best - there is power to be gained with some cleanup work. Basically, the idea is to match the ports in the cylinder casting to the ports in the steel sleeves. This maximizes port area, which improves power.
It makes me wonder whether Yamaha's Horsepower figures for their engines are based on that poor port matchup or on how they should match up.

First of all, the tools and equipment needed:
You should have a Sport Port template.
I used a Dremel rotary tool, with flex shaft and also the right-angle attachment.
For bits, sanding drums work, and cutting stones work. For some more radical work to the sleeves where massive material removal is needed, a cutting disk can be utilized.
Really, the pros in this business will use specialized air tools with good quality cutting stones. One major drawback to using a Dremel is access: It's not easy to work on the transfer ports, for example, with something as clunky as a dremel. I think that if you want to do the work with a Dremel, use the attachments I specified.
Also, have some porting wax available. I used candle wax. Coat your cutting stones with it frequently - it keeps the stone free of aluminum deposits and keeps it cutting well.
You will also need one or two metal scribes to transfer the template layout onto the cylinder walls.
Lastly, it's a good idea to wear safety glasses and at least a face mask - lots of metal particles, dust, and rotating equipment make for a potentially hazardous work environment.
Here are a couple of pictures to get started: First, an example of poor port matchup on a 701 cylinder.
Next, the templates and tools I used.

 

[Matt_E]

Of course, you need to have your motor disassembled. The only part on your work bench should be the bare cylinder.

First, you need to mark the area around the exhaust port with some dye. Ideally, use Prussian Blue for this. I used a Sharpie, and that worked fine.

Next, you'll need to apply the template to the exhaust port. The template is made of flexible magnet strip, so it sticks to the metal sleeve, can be moved around, etc.
You'll want to line up the top of the template with the top of the cylinder, as illustrated.
Center the exhaust port in the hole in the template for it - you want an equal amount of sleeve showing on each side.
Once you're happy with the alignment, use your scribe to mark the new outline of the exhaust port (marked by the template). Hold the template steady for this - you don't want it to move.
You'll likely have to scribe it a couple of times to get an outline that you can see readily.
The three pictures show the process.

 

[Matt_E]

Next, I used the Dremel with Flex shaft attachment and large sanding drum with rough grit to remove material. Don't try to go all the way to the scribe line yet, you'll want use finer grit, or a finer stone for that finer detail removal.

 

[Matt_E]

Finally, the exhaust ports should end up looking something like what's shown in the pictures.

I believe the ideal exhaust port size is something like 68%-70% (Thanks Ebrig!) of bore diameter.
If you're working on a 760, the exhaust port should probably be larger than what the template suggests.
Personally, I have recently had to bore up to 83mm, and I increased the exhaust port size a bit.

 

[Matt_E]

On to the bottom of the sleeves. You'll want to work on the narrow side - it protrudes into the intake area of the cases.

The proper way to apply the template is shown in the first and second picture.
I initially did this the wrong way and lined up the top of the template with the top (or bottom) of the sleeve. See pictures 3 and 4.

Either way works fine. If you do it the way Racelogic intended (Pics 1 and 2) you end up with more mid and top range. This part of the sleeve forms the backwall to the boost port. If you cut it as suggested in picture 1 and 2, you end up shortening the boost port length.
But you also have less sleeve hanging into the intake area of the cases. See a picture comparison between both lengths in the next post.

If you leave the sleeve longer there (and just notch it), as shown in pictures 3 and 4, you have more obstruction in the intake tract of the cases, but a longer boost port channel, which promotes low end power.
Again, see the next post for a picture comparison, and some more info from Paul, Racelogic, and Geek.

 

[Matt_E]

More on the intake side of the sleeves.
The first picture shows two port jobs done by HPT and TLR - SuperJETT posted those in the original thread.
Neither one has the sleeve shortened.

when I had my cylinder, I didn't do anything to the intake side.
this was at the same time as smitty had his 701 cylinder with the sport-port template.
our motors were almost identical (stock 38's, 180 psi head, limited 'b' pipes...)
his had WAY more midrange and rolled higher.
mine had way bigger bottom end and better monkey jumps.

Racelogic themselves showed up at the original thread and posted!

I'm not much of a forum poster (tend to walk on my own words). Everyone seems to question, notch or no/notch on the intake. The rear boost channel has a velocity sweet spot for the air/fuel mix (this is true for all models). A longer channel of the same dimension will reach this spot sooner (bottom end power) but it cannot move as much volume. When you cut the notch you will have shortened the channel. You now will have your spot (air speed) up in the rpm range with more volume. This is better for midrange and peak hp numbers.

Cutting off the bottom of the sleeve is a kinda nobrainer. Get it the he** out of the way of the f/a mix. You just can't go too far and sacrifice piston wear.

The SportPort kit give very good gains everywhere in the band. Using the notch or no/notch will tweak it a bit. Another tweak is putting the same notch from the template on the intake side of the piston.

I'd be happy to talk to anyone with questions on the phone
great posts and pictures

John
Race Logic

And here is Paul's opinion (Jrmagoos):

Kudo's to all who are watching this & doing your homework. This is a great thread.

I , Like Art said belives every tuner has their likes & dislikes. What some do works for their style & abilities, while others don't. I do primarily freestyle/freeride porting. I stay away from race style porting.
Race logic is completely correct on the sweet spot of the rear transfer. The leangth has a lot to do with where the powerband startes & ends.
When I do a port job for a customer, I tend to ask a lot of questions as to the riders likes & style. I do slightly differant cuts to try to give those results. Cutting the bottom of the intake skirt is one of them. Some of you, that have my 760 FS cyl mod, will have yours cut. This help that cyl work a little better.

For those of you trying the templates to do your own work. Congradulations ! This is a very frustrating, nerve wracking experiance.
But, when you are finished & run the boat. You have a great feeling of accomplishment. Stick with it, & most of all, be patient!


ski ya, Paul

The second and third picture show the very obvious difference in both setups.

Pictures 4 and 5 show a bit of the grinding itself.

 

[egbrig]

Matt,
70% is the general excepted max width, although pure race engines have gone futher with wear rates highly increased. An 83mm bore should have no wider than a 58.1 mm ex. port width. Measured accross the cord.

 

[#ZERO]

When grinding the exhaust port with the Race-Logic Sport Port the width comes out to be 67% on the stock 81mm bore. Going wider on the larger bore sizes would probably be the right choice up to 70%, any larger than that would be trouble. An exhaust width of 58.1mm on a 83mm bore equals 70%.

 

[romack991]

I'll add my pics of the same sportport template. Cylinder bore is 81.5.

I used an electric die grinder on the exhaust ports and 90° air grinder for the transfers. Used carbide bits lubricated w/ WD40 to keep them from clogging up with AL. Becareful with using stones on aluminum as they will clog up fast.

 

[romack991]

last two, exits matched to manifold

 

[Freestyleriverrat]

Hey romack991, have you run you ski after doing the porting?

 

[aqua]

here are some more pics/ideas or whatever. used the sport port template also but did my own thing on the intake side of the sleeve....ground it off using a drill with stone bit to where the template recommended but instead of cutting notch for boost port i just rounded off the edge of the sleeve. i measured the case and where the rounding off starts is where the sleeve sits beyond the case edge...if that makes sense. i was hoping that this would allow easy flow into the case without shortening the boost port too much. also sharpened transfer bridges and sharpened the bottoms of the sleeves a little bit where the transfer ports run along side. after grinding the exhaust ports down with a dremel i then polished them up. but do not polish the transfers and make sure there are chamfers around the exhaust ports similiar to the chamfers on the other ports...otherwise a ring could catch or cause bad wear.

 

[eel]

I'll add my pics. Becareful with using stones on aluminum as they will clog up fast.

Never use a mounted stone on aluminium. Use a burr or abrasives.

 

[romack991]

Hey romack991, have you run you ski after doing the porting?

not yet, its still sitting on the bench to be assembled. actually still need to chamfer everything since i got it bored. will be going by april/may.

 

[Matt_E]

Now to the transfer ports. As mentioned, the idea is to match the ports in the sleeves to the ports in the casting. You need to be very careful here - don't change the roof angle of the ports, and keep in mind that the roof of those ports is what seperates the inside of the engine from the waterjacket above.
Don't go crazy!
This is really fairly simple, just take your time.

 

[Matt_E]

Finally, pictures after boring & honing.

At this point it is very critical to chamfer all the ports! All horizontal edges need a chamfer so as not to catch and/or damage the piston rings. Vertical edges need chamfering as well, but not as much.
Do this right, and take your time! The lifespan of your topend is determined here!

Lastly, some pics of the cylinder installed, with pistons

 

[Matt_E]

I did the original port work described in this thread last Summer, and bored up my cylinders to an 82.5mm bore.
In December I seized it - a very dumb mistake on my part experimenting with hand warmers.
Anyhow, I opened up the exhaust ports a bit more at that time.
I also reshaped the walls seperating transfer tunnels, and shortened them a bit as well.
Sleeve removal in that area is optional - I tried it, we'll see where it leads.
The cylinder is now up to an 83mm bore.
I hope to be putting the ski and engine back together before too long and post results.
Overall, the porting was very much worth my while - a big increase in power.
Is it for everyone? No. You should be comfortable taking abrasive power tools to the internals of your engine.
If not, pay a pro.

Next up, some info on case porting.

 

[Freestyleriverrat]

Looking good.......man the 61x cylinder is really bad when it comes to the transfer ports matching up. Can you post your jetting specs when done? Nice build up thread.

 

[aqua]

Matt....how far do you think you raised your transfer port roofs....was it hard to keep the same angle that was presently there and how close to going through to the water side were you. i know you used a 90 degree attachment to get to them but did you also use a flex shaft. that is the only part i have left to do.....i cleaned them up a bit but being that i was restricted by the dremel tool i couldnt do much to the roofs of the ports. also...how would a handwarmer sieze a cylinder?? thanks for your posts on this subject here and on pwctoday....you were my inspiration man!!! :biggthumpup:

 

[orange flattop freestyler]

Excellent thread guys, well done Matt :biggrin:

Shame i never took any pics when i did my cases and built the ramps etc.

Nevermind :biggrin: