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Old 11-04-2012, 09:03 AM   #1
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Default Debuting on engine port mods

Grindings!
I always was interested on how these small engines work and the art of tailoring an engine powerband to conditions.We all know tuned pipes do that,but how about unleashing more power?
That leads me to engine timings and all the complications.There's really much to read and understand but the tip is Port area x time and this is where it gets too deep for me.First I'm showing my test subject,a SH PT12R02SXT.Standard engine like a NS12T1,not much power but from my measurements has so-so timings.Will be adding more pics and measurements today.Disclaimer,I'm not responsible for any damage you do on your engines.It's just my experience through what is available on various threads.

Specs: 13.8mm bore X 14.0 stroke 1.35hp @ 34000rpm slide carb standard plug.25mm rod with 4.0mm big end and 3.0mm smaller end.

Sleeve timing:
Exhaust 82.5 for a 5.1mm port height;
Inlet 61.6 for a 2.9mm port height.
Port width:
-inlet around 9.00mm
-exhaust 11.70mm widest part
-boost 7.05mm.

Crank timing:
Not measured yet,should be 29 open ABDC to 61.5 closed from TDC
7mm inner bore,non turbo.
Outer diameter:10.00mm
Inner diameter:6.75mm(BTW 7.00mm is maximum by rules)
Length:
-total 66.20mm
-bearing to bearing around 26.90mm
Crank pin length 4.57mm

Carb:
Neck diameter:10.00mm
Neck height:8.90mm
Intake bore 5.45mm

Sources:
http://www.rctech.net/forum/onroad-n...t-balance.html
http://www.prestwich.ndirect.co.uk/tunedpipetheory.htm
http://www.euronet.nl/users/tooms/timings/timings.htm
http://macdizzy.com/cyl_primer.htm
http://nitrokb.netne.net/engines/reading.html
http://www.rctech.net/forum/onroad-n...placement.html
http://edj.net/2stroke/jennings/
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Debuting on port modding-dsc00007.jpg  
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Last edited by 30Tooth; 11-09-2012 at 06:29 PM.
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Old 11-07-2012, 05:54 PM   #2
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First I'll start by blueprinting.As you can see there's still room for increasing timing on the exhaust port before enlarging the exhaust exit on the block/crankcase,and yes one side is ok the left side could be a little more enlarged.The bottom of the exhaust port and the right side are 100% fit on the block just bad angle for taking pictures I guess.Sorry for the bad focus.
The crank intake wasn't 100% wide open at max intake so took a little from that lip.DOH!Didn't take account the carb to crank passage before grinding so it's likely that the crank was fine.
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Debuting on port modding-dsc00034.jpg   Debuting on port modding-dsc00037.jpg   Debuting on port modding-dsc00038.jpg  
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Last edited by 30Tooth; 11-08-2012 at 05:17 PM.
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Old 01-21-2013, 02:30 AM   #3
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Quote:
Originally Posted by 30Tooth View Post
First I'll start by blueprinting.As you can see there's still room for increasing timing on the exhaust port before enlarging the exhaust exit on the block/crankcase,and yes one side is ok the left side could be a little more enlarged.The bottom of the exhaust port and the right side are 100% fit on the block just bad angle for taking pictures I guess.Sorry for the bad focus.
The crank intake wasn't 100% wide open at max intake so took a little from that lip.DOH!Didn't take account the carb to crank passage before grinding so it's likely that the crank was fine.
Hey buddy.. how this engine is running after the mods?
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Old 01-21-2013, 04:52 AM   #4
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Hey buddy.Engine is still unassembled,I have been running off road so this project was delayed.
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