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post #1 of 92 (permalink) Old 12-27-2004 Thread Starter
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Question Questions on port timing...

What is involved in aquiring the optimum port timing for a 2 stroke motor?
How do you determine what is best?
How do you alter the stroke/head/ports to achieve the sweet spot?
I know you can alter the compression by using gaskets or sealer but looks like you would need a removable head such as the torquer from BAT to change the timing.
With the torquer I assume you can get your port timing set by using base gaskets to get the jug where you want it set and then cut the top off the head to optimize your compression and use the dome to set the squish.
Does porting come into play here also?
Not sure if I'm going in the right direction here so I'd appreciate the people in the know shareing the knowledge.
Thanks

BTW...I read the answers that Ritchey and bart provided me a couple of months ago but I need a little more info.
Is there any sites and/or books that I could get on the subject?

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Last edited by caferacer; 12-27-2004 at 09:44 PM.
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post #2 of 92 (permalink) Old 12-27-2004
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When the piston is at bdc you want the edge of the piston to be even with the floor of the exhaust port. With a 2mm spacer and a gasket it is usually at this point. For a 39cc motor you widen the inner portion of the exhaust port to 28mm and raise the roof about 2-3mm
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Quote:
Originally Posted by badazztoyz.com
When the piston is at bdc you want the edge of the piston to be even with the floor of the exhaust port. With a 2mm spacer and a gasket it is usually at this point. For a 39cc motor you widen the inner portion of the exhaust port to 28mm and raise the roof about 2-3mm
Thanks Chris.
Now exactly what do these changes do?
Widening the inner portion of the exhaust does what?
Raising the roof does what?

I really asking for the info more or less for my knowledge on 2 strokes.
I think you have your kit set-up really well I just need more info about port timing and how it works.

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post #4 of 92 (permalink) Old 12-27-2004
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Theres a book by someone bell that blah and ritchey know about that goes more in depth on porting, and how it benefits a two stroke.
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post #5 of 92 (permalink) Old 12-27-2004
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Quote:
Originally Posted by badazztoyz.com
Theres a book by someone bell that blah and ritchey know about that goes more in depth on porting, and how it benefits a two stroke.
The latest edition has a more tech about modern engines than this edition.

Hmm, if they had 5 Port 50cc engines back in 1964 and boosted306 has been porting for only 10 years and claims to have "the original 5 port" then it must only be 1974?, so this edition is well ahead of the times.

I wonder who will flame me first?
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post #6 of 92 (permalink) Old 12-27-2004
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Quote:
Originally Posted by caferacer
Thanks Chris.
Now exactly what do these changes do?
Widening the inner portion of the exhaust does what?
Raising the roof does what?

I really asking for the info more or less for my knowledge on 2 strokes.
I think you have your kit set-up really well I just need more info about port timing and how it works.
Think of the engine as an air pump. You're increasing the transfer area. This allows more gas/air in and out of the engine = more efficient engine = higher rpms = more power. This is why boost ports increase rpms.

To do this without a head kit:
1.Remove your base gasket if possible to achieve tighter squish = more compression.
2. Raise the roof of the transfer ports between 1mm to 3mm depending on what kind of results you want. 1mm for slight rpm increase, 3mm for large rpm increase. Don't change the angle just the height.
3. Raise the exhaust port the same dimension as the transfers. You can lower the very middle of the floor so it is flush with the crown of the piston. This will create a "D" shaped e-port.

This will not only increase rpms, but it will move the engines powerband higher up in the rpm range. Meaning if your powerband kicked in at 5,000 rpms stock, it may kick in at 9,000 rpms now. This means you will loose low and mid power unless you have an adj clutch or you increase the compression by adding a head kit. This is a very basic description and you should start by making very small incremental changes if you have not done this before. Hope this heads you in the right direction though.

The book is called "Two-Stroke Performance Tuning" by A. Graham Bell. By far the best 2 stroke tuning book available. Be warned it is dense in calculations and theory, but all have been proven and have shaped todays HP 2 strokes. Check it out here and click it and read the 1st chapter and be amazed! lol. http://www.amazon.com/exec/obidos/tg...glance&s=books

**** you Blah, you beat me to it again! LOL.
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wow that bike is awesome blah, do they only sell them down under

i was first to flame?
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post #8 of 92 (permalink) Old 12-27-2004
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Quote:
Originally Posted by badazztoyz.com
wow that bike is awesome blah, do they only sell them down under

i was first to flame?
Sonic, Australia is a nation crawling with taipans, red-belied black snakes and funnel-web spiders, and surrounded by bastard sharks, massive crocks, box jelly fish and 50cc scooters.

Does that answer the question?
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post #9 of 92 (permalink) Old 12-27-2004
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Usually if you take out the base gasket on a stock motor, the piston at BDC will be higher than the floor of the exhaust port. You'll have higher compression due to a tighter squish, but to compensate for the piston sitting higher than the floor of the piston, is to do what Ritchey said, and that's to raise the roof of the exhaust port. Also, I agree in raising the transfer ports 1-3mm. I wouldn't lower the exhaust port floor though.

Just my .02.

Quote:
Originally Posted by Ritchey79
Think of the engine as an air pump. You're increasing the transfer area. This allows more gas/air in and out of the engine = more efficient engine = higher rpms = more power. This is why boost ports increase rpms.

To do this without a head kit:
1.Remove your base gasket if possible to achieve tighter squish = more compression.
2. Raise the roof of the transfer ports between 1mm to 3mm depending on what kind of results you want. 1mm for slight rpm increase, 3mm for large rpm increase. Don't change the angle just the height.
3. Raise the exhaust port the same dimension as the transfers. You can lower the very middle of the floor so it is flush with the crown of the piston. This will create a "D" shaped e-port.

This will not only increase rpms, but it will move the engines powerband higher up in the rpm range. Meaning if your powerband kicked in at 5,000 rpms stock, it may kick in at 9,000 rpms now. This means you will loose low and mid power unless you have an adj clutch or you increase the compression by adding a head kit. This is a very basic description and you should start by making very small incremental changes if you have not done this before. Hope this heads you in the right direction though.

The book is called "Two-Stroke Performance Tuning" by A. Graham Bell. By far the best 2 stroke tuning book available. Be warned it is dense in calculations and theory, but all have been proven and have shaped todays HP 2 strokes. Check it out here and click it and read the 1st chapter and be amazed! lol. http://www.amazon.com/exec/obidos/tg...glance&s=books

**** you Blah, you beat me to it again! LOL.
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Quote:
Originally Posted by Ritchey79
Think of the engine as an air pump. You're increasing the transfer area. This allows more gas/air in and out of the engine = more efficient engine = higher rpms = more power. This is why boost ports increase rpms.

To do this without a head kit:
1.Remove your base gasket if possible to achieve tighter squish = more compression.
2. Raise the roof of the transfer ports between 1mm to 3mm depending on what kind of results you want. 1mm for slight rpm increase, 3mm for large rpm increase. Don't change the angle just the height.
3. Raise the exhaust port the same dimension as the transfers. You can lower the very middle of the floor so it is flush with the crown of the piston. This will create a "D" shaped e-port.

This will not only increase rpms, but it will move the engines powerband higher up in the rpm range. Meaning if your powerband kicked in at 5,000 rpms stock, it may kick in at 9,000 rpms now. This means you will loose low and mid power unless you have an adj clutch or you increase the compression by adding a head kit. This is a very basic description and you should start by making very small incremental changes if you have not done this before. Hope this heads you in the right direction though.

The book is called "Two-Stroke Performance Tuning" by A. Graham Bell. By far the best 2 stroke tuning book available. Be warned it is dense in calculations and theory, but all have been proven and have shaped todays HP 2 strokes. Check it out here and click it and read the 1st chapter and be amazed! lol. http://www.amazon.com/exec/obidos/tg...glance&s=books

**** you Blah, you beat me to it again! LOL.
Thanks Ritchey and blah...exactly what I was looking for.

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Yeah if the e-port is below the piston crown is at BDC don't lower it. Depending on the engine it may or may not be.

_____
no problem bro!

Last edited by Ritchey79; 12-27-2004 at 11:58 PM.
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Ritchey

Do you recommend doing anything else if people run into this problem?

What I've done, is raise the roof of the e port the same amount it would take the piston to reach the top of the floor. I also port the transfers top by the same amoun that I ported the top of the e port. Just wanted to know if you do anything extra.

-E

Quote:
Originally Posted by Ritchey79
Yeah if the e-port is below the piston crown is at BDC don't lower it. Depending on the engine it may or may not be.

_____
no problem bro!
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i hate messing with transfers so i raise roof to compensate for the piston at bdc and then raise the boost ports above the transfers
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If the port floor is low it really won't rut much, not much you can do to fix it. Main problem is it's slowing velocity. If you raise the e-port just enough to get back to flush with the piston you're not really increasing much over stock b/c the bottom of the e-port is blocked off with the piston.

Quote:
Originally Posted by snowboardgeek1
Ritchey

Do you recommend doing anything else if people run into this problem?

What I've done, is raise the roof of the e port the same amount it would take the piston to reach the top of the floor. I also port the transfers top by the same amoun that I ported the top of the e port. Just wanted to know if you do anything extra. I keep the ratio of the transfer height to e-port height the same. So if I raise the transfers 3mm then I also raise the e-port roof 3mm. This way your percentages are increased proportionally. You don't want the transfers to close at the same time as the e-port does.

-E
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post #15 of 92 (permalink) Old 12-28-2004 Thread Starter
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When you are talking about porting do you mean the inner portion of the e-port towards the cyclinder?
Can this be done with a dremel?
If so I have many attachments...can you tell me which one I need to use?
I have a spare head that I will be practicing on.

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True, so I assume you go even higher on the roof, maybe 2-3mm higher. Makes sense.

Quote:
Originally Posted by Ritchey79
If the port floor is low it really won't rut much, not much you can do to fix it. Main problem is it's slowing velocity. If you raise the e-port just enough to get back to flush with the piston you're not really increasing much over stock b/c the bottom of the e-port is blocked off with the piston.
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i only do the inner portion I do it from the outside at an angle as to only hit the inner part then use a emery bit from inside to make sure theres no rough edges. Go to my site and under tools etc i have a carbide cutter that will last forever. Ive used one on like 10 heads so far
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Like Badazz said if you have a carbide cutter use that, just becareful b/c it removes alot of material fast. If you don't have a carbide cutter, use the sanding drums. They are the only other dremel bit that will cut through the NicaSil easily, and they remove material smooth and consistenly. They're perfect for boost ports! *hint*hint* The transfer roofs are alittle harder to reach and if you're going big like 3mm you're gonna need to change the roof angle due to lack of material. You'll have to experiment with some different bits here, maybe a carbide ball cutter or a diamond tip bit, or different shaped grinding stone bits. Anybody have an easir way without using a mill?
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i think the best way to correct port timing is to custom cut the head for the crank that is being used and use a spacer on the base of the head to correct the port timing! then when assembling the head kit make sure that you can get the squish real close to .5mm with out using excess gaskets! this is one of the only ways you can correct the port timing with the stroker crank and a head kit!
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Pcp...

Quote:
Originally Posted by blah
The latest edition has a more tech about modern engines than this edition.

Hmm, if they had 5 Port 50cc engines back in 1964 and boosted306 has been porting for only 10 years and claims to have "the original 5 port" then it must only be 1974?, so this edition is well ahead of the times.

I wonder who will flame me first?
Blah, Don't make me change my signature (PCP) ported chinese potmetal!

HA! You guys are great!!

The original 5 port head!
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