Two Stroke Porting
12 posts
• Page 1 of 1
by pee wee » Thu Feb 05, 2004 10:26 am
I'm wondering if any of you have experiece with 2 strokes(port & polish) as I've had alot of customers asking. Been sort of hesitant at doing for fear of messing up. How does 2 stroke porting compare to 4 stroke porting? I realize that the crankcase must come into play, and right angled die grinders, etc. are a must. Any feedback would be appreciated.
"Where aer yea bee let the wind blow free."
- pee wee
- Posts: 5
- Joined: Tue Feb 03, 2004 11:45 am
- Location: Nova Scotia
by willeng » Fri Feb 13, 2004 4:08 am
pee wee
When porting two strokes --be carefull
For get the polish, this can cause you no end of head aches---just a smooth mat finish will do nicely.
You don't want to open the transfer ports to much or you can make the volume to large & hurt performance.
Until you can test your porting techniques it is better to just debur the transfer ports & at the entry just gently radius them so the air flow can make the entry easier with no sharp edges etc, use a file if you cannot reach areas that may have sharp edges.
They make files of all different shapes, bends etc.
Dip them in trans fluid when filing, this helps them from clogging up.
Check all the radiused turns & remove anything that will impede or upset the flow.
Make sure you debur everything once you finish.
Check the intake port & give it the same debur etc same with the exhaust port.
The exhaust port opening or openings---in the barrel can be slightly radiused if they have sharp edges--work carefull though.
The crankcase volume can be made smaller, you have to look where this can be done safely, with aluminium epoxy fill.
You have to rough the area's & drill small shallow opposed direction holes in the cases to make sure the epoxy stays put.
Once it is filled & cured you can shape it etc etc. Avoid thin sections.
Make sure you wash the area's with acetone & let it dry before using the epoxy.
When porting two strokes --be carefull
For get the polish, this can cause you no end of head aches---just a smooth mat finish will do nicely.
You don't want to open the transfer ports to much or you can make the volume to large & hurt performance.
Until you can test your porting techniques it is better to just debur the transfer ports & at the entry just gently radius them so the air flow can make the entry easier with no sharp edges etc, use a file if you cannot reach areas that may have sharp edges.
They make files of all different shapes, bends etc.
Dip them in trans fluid when filing, this helps them from clogging up.
Check all the radiused turns & remove anything that will impede or upset the flow.
Make sure you debur everything once you finish.
Check the intake port & give it the same debur etc same with the exhaust port.
The exhaust port opening or openings---in the barrel can be slightly radiused if they have sharp edges--work carefull though.
The crankcase volume can be made smaller, you have to look where this can be done safely, with aluminium epoxy fill.
You have to rough the area's & drill small shallow opposed direction holes in the cases to make sure the epoxy stays put.
Once it is filled & cured you can shape it etc etc. Avoid thin sections.
Make sure you wash the area's with acetone & let it dry before using the epoxy.
- willeng
- Posts: 14
- Joined: Fri Feb 13, 2004 1:59 am
by pee wee » Fri Feb 13, 2004 3:43 pm
Wow excellant info Willeng, have been very leary of wondering into those ports. Have polished a few surfaces along time ago on motoX bikes but after seeing the changes that manufactures came up with each year, said that maybe I'd just get egg thrown in my face. How are the ports flown on the bench, are they tested on exhaust mode(blowing) with a velocity probe,etc? Also with all the jet skis and motox bikes and sleds(this is where the latest technology in porting has to be going) just my opinion of course. Thanks again for your insite on this subject. Dave PS hoping to tackle some of those drag sled ports in the near future 
"Where aer yea bee let the wind blow free."
- pee wee
- Posts: 5
- Joined: Tue Feb 03, 2004 11:45 am
- Location: Nova Scotia
by willeng » Fri Feb 13, 2004 11:47 pm
pee wee:
Two strokes are quite easy to test on the a flow bench, you just have to make the appropriate adapters.
Make them out of wood because there are going to be many different shapes & styles you need to test.
Wood is easy to turn & shape quickly, name them so you know what they are , soak them in a timber preserver they use for boats, this also makes them alot harder once dried. It sets like epoxy, they will last forever if looked after correctly.
I used to cast aluminium adapters for what i needed but first you have to make the patterns out of wood anyway.
I can tell you how to make a small cheap furnace for under 50 bucks if you want to do it more proffesionally-saves a lot of machine work!
I can tell you how to cast also.
Firstly in the top of the flow bench have the hole bigger than anything you wan't to test , place one of your wooden fittings into this, it needs to fit just tight enough so it won't come loose & seal it with some grease to make it air tight.
The inlet side should be tested by placing the barrel into an appropriately sized adapter.
The top of the bore will need a plate or anything placed on top, sealed with a smear grease again.The transfer ports & the exhaust ports need to be blocked off, i used modeling clay for this, it's quick & easy & reuseable.
Make sure it won't get sucked out though.
It's only a matter of drawing the air through the bottom of the barrel-- this will test your intake.
Make sure you test with everything in place, carb, airbox, filters whatever, this way you can quickly verify your work the way it will be run.
Test different filters etc etc etc you'll be amazed how bad somethings are.
For the transfer ports make a fitting that fits your hole once again but this time the top of it has it has to resemble the crankcase fitting where the barrel is mounted originally. It takes a bit of time to make this particular piece but once you have it you can reuse it for life.
You block the bottom of the barrel & fit it into the fitting you've made.
The pieces i made for blocking the barrels where the same as the bore dia on the bottom snug fit with grease & tapered to a rounded point at the top high enough so the air coming out of the transfer ports in the bore was directed out of the top of the barell.
You blow out of the bench, through the bottom of the fitting & this will test your transfer ports.
The exhaust ports you test with the same fitting as the intake one, put the head on with a couple of bolts to hold it, dont forget to put the spark plug in ,block the inlet & the transfer ports & blow through the bottom of the barrel.
Do not fit the expansion chamber, just the open port for two strokes.
Remember that is good air flow with good velocity you are chasing.
You don't want heaps of flow with no velocity.
Basically make minor changes that improve the flow & you will be on track.
Hope this helps out.
Two strokes are quite easy to test on the a flow bench, you just have to make the appropriate adapters.
Make them out of wood because there are going to be many different shapes & styles you need to test.
Wood is easy to turn & shape quickly, name them so you know what they are , soak them in a timber preserver they use for boats, this also makes them alot harder once dried. It sets like epoxy, they will last forever if looked after correctly.
I used to cast aluminium adapters for what i needed but first you have to make the patterns out of wood anyway.
I can tell you how to make a small cheap furnace for under 50 bucks if you want to do it more proffesionally-saves a lot of machine work!
I can tell you how to cast also.
Firstly in the top of the flow bench have the hole bigger than anything you wan't to test , place one of your wooden fittings into this, it needs to fit just tight enough so it won't come loose & seal it with some grease to make it air tight.
The inlet side should be tested by placing the barrel into an appropriately sized adapter.
The top of the bore will need a plate or anything placed on top, sealed with a smear grease again.The transfer ports & the exhaust ports need to be blocked off, i used modeling clay for this, it's quick & easy & reuseable.
Make sure it won't get sucked out though.
It's only a matter of drawing the air through the bottom of the barrel-- this will test your intake.
Make sure you test with everything in place, carb, airbox, filters whatever, this way you can quickly verify your work the way it will be run.
Test different filters etc etc etc you'll be amazed how bad somethings are.
For the transfer ports make a fitting that fits your hole once again but this time the top of it has it has to resemble the crankcase fitting where the barrel is mounted originally. It takes a bit of time to make this particular piece but once you have it you can reuse it for life.
You block the bottom of the barrel & fit it into the fitting you've made.
The pieces i made for blocking the barrels where the same as the bore dia on the bottom snug fit with grease & tapered to a rounded point at the top high enough so the air coming out of the transfer ports in the bore was directed out of the top of the barell.
You blow out of the bench, through the bottom of the fitting & this will test your transfer ports.
The exhaust ports you test with the same fitting as the intake one, put the head on with a couple of bolts to hold it, dont forget to put the spark plug in ,block the inlet & the transfer ports & blow through the bottom of the barrel.
Do not fit the expansion chamber, just the open port for two strokes.
Remember that is good air flow with good velocity you are chasing.
You don't want heaps of flow with no velocity.
Basically make minor changes that improve the flow & you will be on track.
Hope this helps out.
- willeng
- Posts: 14
- Joined: Fri Feb 13, 2004 1:59 am
by MIKE » Fri Mar 26, 2004 6:02 pm
Hi, Gordon Jennings' TWOSTRIKE TUNERS HANDBOOK is the bible of this subject. It is currently out of print, but you may find one at the library. I would suggest great care in modifying port openings as the shape also defines the open duration. Without the formulas you are shooting in the dark. Experimention is great but when you read the book you will be amazed at what there is to know and what can be done. Gordon Jennings is my and many others hero for his work and sharing in this field. Good luck, Mike.
- MIKE
by jukk » Fri Apr 16, 2004 8:20 am
Be aware that Gordon Jennings' TWOSTROKE TUNERS HANDBOOK deals with old school thinking. The technology has developed a bit since the 60's and 70's. Although keeping this in mind, reading newer litterature also, it will make a good book for the beginner. Good modern litterature is A. G. Bell's Two-Stroke Performance Tuning and John Robinson's Motorcycle Tuning Two-Stroke. These books deal with modern engines.
I can give one example why you should read some of these newer books also. Mr Willeng above suggested making the crankcase smaller by stuffing it. This is exactly what was done in the 60's and 70's. If you are dealing with a modern engine this is NOT the way to go. Modern engines work on another principle. Read the books!
I can give one example why you should read some of these newer books also. Mr Willeng above suggested making the crankcase smaller by stuffing it. This is exactly what was done in the 60's and 70's. If you are dealing with a modern engine this is NOT the way to go. Modern engines work on another principle. Read the books!
- jukk
by bnelson » Fri Apr 16, 2004 11:08 am
Forgot to mention the title: Design and Simulation of 2-stroke engines. Lots of good stuff on Compression and Expansion waves........the waves that make expansion chambers work.......sometimes called finite amplitude waves.
- bnelson
- Posts: 25
- Joined: Thu Apr 08, 2004 11:35 pm
by L Lowman » Sat Apr 24, 2004 12:24 am
Theres a couple more books that are in print Bell's Two Stroke Tuning and John Robinson's Two Stroke Tuning.
One thing about 2 strokes is port timing. Its the relation between crank angle and when the piston just uncovers an exhaust port or intake transfer. Its like cam duration and lift only different.
One thing about 2 strokes is port timing. Its the relation between crank angle and when the piston just uncovers an exhaust port or intake transfer. Its like cam duration and lift only different.
- L Lowman
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