- Location
- Mechanicsburg, PA
Out of curiosity, is there a rule of thumb for transfer port size / volume to overall cylinder bore (ie, 67% to 70% exhaust opening to cylinder bore)?
Transfer Port Sizes
- Thread starter x2skier
- Start date
There actually is a formula to figure out the required area and duration but you'll need to read up on it vs. trying to get an informed answer here. If your truely interested go to WATCON.com and get some books from Randy. David Simons "Jetski Bible" is geared toward watercraft as is his follow up writing. Turners "Two Stroke Tunning" is one of the best. I guarentee you will learn more from books than getting a reply from some one on this forum who used a dremal and a sport port. Also most of the members here ride freeride and therefore set up their engines for a specific task and don't have a wide range of setup experiance or knowledge.
x2 - I agree.
(And I am the guy that used to dremel & sport port)
Get some good books by reputable authorities on the subject and/or talk to pro engine builders.
Personally, I found that I didn't have the time or ambition to learn all of it myself. I resorted to paying someone to do it for me and have peace of mind.
(And I am the guy that used to dremel & sport port)
Get some good books by reputable authorities on the subject and/or talk to pro engine builders.
Personally, I found that I didn't have the time or ambition to learn all of it myself. I resorted to paying someone to do it for me and have peace of mind.
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Matt, I know you use a dremel but your posts also show you read, nothing wrong there. You seem to be one of the stable posters, you know the types I'm refering to. I like it when people discuss ideas and you can tell who knows what there talking about vs. someone who read a post and uses the term blowdown as their statement of technical knowlege. You can have the perfect port timings according to a program but if you don't know how to tune an engine it won't make one diff.
You will never get a jetski cylinder to have big enough transfers. Look at a 125 or 250cc dirt bike cylinder. Ports as big as a GPR1200 if not bigger.
As for widths at the piston openings? make them as big as feasible with a web that can support the ring without cracking. Cracking on OEM cylinders is the issue cheap cast iron. By the time you make the windows bigger if you really make them wide, you will not have a venturi from the bottom of the cylinder because there is not enough meat to grind out to match the piston window transfer area on all 5 ports. I still make them wider, mainly the mains and boost, because it helps distribute the charge over the piston better and in some cases helps more than it hurts. The transfers in the YAMAHA's and KAWASAKI twins started life in the 80's as transfers for low rpm 650 cc motors. Think of what we are pushing through them with 85mm bores and 78mm cranks? lot of velocity......
The book from WATCON does give a good build example in it and discusses transfer time/size relation to exhaust time/area. Lots to learn in those books for 99% of the riders out there.
As for widths at the piston openings? make them as big as feasible with a web that can support the ring without cracking. Cracking on OEM cylinders is the issue cheap cast iron. By the time you make the windows bigger if you really make them wide, you will not have a venturi from the bottom of the cylinder because there is not enough meat to grind out to match the piston window transfer area on all 5 ports. I still make them wider, mainly the mains and boost, because it helps distribute the charge over the piston better and in some cases helps more than it hurts. The transfers in the YAMAHA's and KAWASAKI twins started life in the 80's as transfers for low rpm 650 cc motors. Think of what we are pushing through them with 85mm bores and 78mm cranks? lot of velocity......
The book from WATCON does give a good build example in it and discusses transfer time/size relation to exhaust time/area. Lots to learn in those books for 99% of the riders out there.
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- Location
- Mechanicsburg, PA
I guess my question stems from the Group K write ups with the big bore options. For each option he states the OEM transfer port sizes do not lend themselves well to the larger bores (84mm +). I was just curious if there was a rule of them in terms of percent volume transfer compared to cylinder bore. Or, what are the cons, if any, with enlarging the overall volume of each transfer port and ultimately reducing the velocity of the charge?
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I believe the concern that you speak of leads back to the cylinder casting itself not being big enough to support the larger diameter sleeves required for bigger bores.
The bigger the sleeve gets, the more it cuts into the transfer tunnel area.
The bigger the sleeve gets, the more it cuts into the transfer tunnel area.
- Location
- Mechanicsburg, PA
Yeah, that's a big part of it but it's also recommended for boring the 62T to 84mm; no re-sleeving required for this so the transfer ports remain the same volume.
#ZERO
Beach Bum
- Location
- Florida - U.S.A.
There is a rule of thumb when setting your transfer port timing and time area but it gets complicated. If you're porting a cylinder and cleaning up the transfer area be sure to keep the same angles that Yamaha uses or your fuel mixture will end up going right out the exhaust. Also the roof angles along with the port height will determine where the power band hits along with a bunch of other factors. Read the some the books egbrig mentioned and you'll be doing yourself a big favor.
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- Location
- Mechanicsburg, PA
Nice post #.0.....you're always full of detailed info.
#ZERO
Beach Bum
- Location
- Florida - U.S.A.
Thanx!!!... send me your e-mail address and I'll send you the pdf 2-stroke performance book, along with some others, if you like reading this kind of stuff.
- Location
- Mechanicsburg, PA
- Location
- South Africa
Those pages are in my special file, helped me snap my 61X cylinder 8 years ago with with an ungirdled head
#ZERO
Beach Bum
- Location
- Florida - U.S.A.
You should have been using a girdled head, they've been out for a while now. :nutkick:
#ZERO
Beach Bum
- Location
- Florida - U.S.A.
Here's part of the tuners handbook by Gordon Jennings that has some good info too. http://www.datafan.com/TunersHandbook/2-strokefiltered.html
Mark44
Katie's Boss
- Location
- 100% one place
Very cool #0 thanks.
Mark44
Mark44
Then you need to get Blair's book on two-strokes. Its like a thermodynamics book with mixed in cool stuff. Blair's a professor and its like the old 1.5" books from school.
- Location
- South Africa
8 years ago I was a newbie to jetskis, dealer told me I wouldn't neeed a girdle unless I went big-bore/stroker, I also had a problem of domes cracking on me, a set of RIVA domes once lasted 3hrs.
You need the software to get the most out of the Blair book
You need the software to get the most out of the Blair book