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Old April 26th, 2016, 10:07 AM   #1
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Arrow DIY porting cylinder head and valve lapping

http://www.affordablegokarts.com/Sta...%20Porting.pdf

http://www.affordablegokarts.com/valve-lapping.php
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Old April 26th, 2016, 12:38 PM   #2
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I would like to see some build threads where some head work was done on the 250/300 engines. Just never really seen it documented or the results.
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Old April 26th, 2016, 01:18 PM   #3
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Multiple people did headwork on ninjettes.
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Old April 26th, 2016, 01:23 PM   #4
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Quote:
Originally Posted by Motofool View Post
http://web.archive.org/web/200812021...m/diyport.aspx is a copy of the original page that PDF was made from, if you'd rather get it from the source. It had larger versions of the pics, but it looks like they didn't get archived.
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Old April 26th, 2016, 02:34 PM   #5
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Lol! Sad how my poor old brain doesn't work like it used to: I read the title as: "DYI poor cylinder head and valve lapping"
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Old April 27th, 2016, 08:01 AM   #6
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I'm a complete n00b when it comes to porting. I'm curious as to others' thoughts on something...

Power News 18 - Think Fast: Understanding Intake Porting
Power News 19 - Homework: How To "Hi Velocity Port" Your Own Cylinder Head
Power News 20 - The 2007 Superbike!
Power News 21 - Super Sonic Nozzle
Power News 22 - Success Stories & Exhaust Porting
Power News 23 - Future Horsepower
(I apologize for the horrible old website.)

The gist of what he's saying is that simply making the holes bigger doesn't necessarily result in better output. His strategy is actually to make the ports smaller, which results in higher velocity, which overall does a better job of filling the cylinders. Simply sucking air through something on a flowbench won't necessarily show how well the whole system works together to rhythmically flow air into and out of an engine.

He does mention that making a port too small will restrict airflow and hurt peak numbers. As with a lot of things, it seems to be a balance of getting the most out of the overall system instead of focusing on one single thing.

Despite doing things "the wrong way" he seems to have the results to back it up. There's not a lot of detail though. I'd love to see back-to-back dyno runs of the same engine with stock/ported heads compared to his for a direct comparison. He even points out that little things like the exhaust exit can have an effect on how gases leave, and therefore create differences between a dyno setup and actual racing. But if you're claiming something will have an effect of 4-5%, that should be visible on a dyno test too.


I just wanted to point out that dynamic air flow is complex, and simply hogging out every hole you see won't necessarily make everything better, before everyone with a grinder starts hacking away at stuff.
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Old April 27th, 2016, 08:11 AM   #7
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Quote:
Originally Posted by InvisiBill View Post
I'm a complete n00b when it comes to porting. I'm curious as to others' thoughts on something...

Power News 18 - Think Fast: Understanding Intake Porting
Power News 19 - Homework: How To "Hi Velocity Port" Your Own Cylinder Head
Power News 20 - The 2007 Superbike!
Power News 21 - Super Sonic Nozzle
Power News 22 - Success Stories & Exhaust Porting
Power News 23 - Future Horsepower
(I apologize for the horrible old website.)

The gist of what he's saying is that simply making the holes bigger doesn't necessarily result in better output. His strategy is actually to make the ports smaller, which results in higher velocity, which overall does a better job of filling the cylinders. Simply sucking air through something on a flowbench won't necessarily show how well the whole system works together to rhythmically flow air into and out of an engine.

He does mention that making a port too small will restrict airflow and hurt peak numbers. As with a lot of things, it seems to be a balance of getting the most out of the overall system instead of focusing on one single thing.

Despite doing things "the wrong way" he seems to have the results to back it up. There's not a lot of detail though. I'd love to see back-to-back dyno runs of the same engine with stock/ported heads compared to his for a direct comparison. He even points out that little things like the exhaust exit can have an effect on how gases leave, and therefore create differences between a dyno setup and actual racing. But if you're claiming something will have an effect of 4-5%, that should be visible on a dyno test too.


I just wanted to point out that dynamic air flow is complex, and simply hogging out every hole you see won't necessarily make everything better, before everyone with a grinder starts hacking away at stuff.
I generally try to just make the straightest smoothest path into and out of the engine. You also need to think about the path the air is taking, where it will want to go, and if what you are doing will create turbulence. A smaller port will have higher velocity and run better at lower rpms, but it will also be a restriction at higher rpm, however, if it is a good flowing port keeping the velocity up is a great thing. If you hog the port out it might have proper velocity at high rpm, however it will run like garbage below that.

The last thing I have to say about porting is think about what has been done to the motor. A stock motor will not want the same size valves and ports as a bored stroked high compression motor with a free flowing exhaust.
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Old April 27th, 2016, 09:15 AM   #8
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Quote:
Originally Posted by HoneyBadgerRy View Post
Multiple people did headwork on ninjettes.
I'm sure they did, I have not however seen empirical results from such headwork . It would interest me to do so lol .
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Old April 27th, 2016, 09:20 AM   #9
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Quote:
Originally Posted by HoneyBadgerRy View Post
The last thing I have to say about porting is think about what has been done to the motor. A stock motor will not want the same size valves and ports as a bored stroked high compression motor with a free flowing exhaust.
This is key really. Most OEM heads will benefit from a little bit of clean up. Things like smoothing, port matching, minor clean up does little to change the airflow profile in terms of volume and velocity but rather removes little inefficiencies within that profile.

Major port reshaping and reconfiguration is a different animal and in many cases are going to need to be considered in conjunction with cam profiles, valve sizing, and intake and exhaust size, length, and shape.
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