Port velocity

Have an interesting technique, tool or just anything related to porting? Post it here . . . please no bashing anyone for the model of engine they are working, we're here to share ideas . . .

Postby Little Rocket » Sun Jun 24, 2007 3:01 am

How fast is too fast? I have a 4 valve head that is flowing 420 fps at the short turn @.28" of water. Every thing I have read says 300 fps is fast. The ports stock average 320 fps (averaged from 24 locations) After a days work flow is up 25cfm and speed is up an additional 30 fps average in the port.

Should I consider opening the port up more to slow the air down? I don't think so but I thought I would throw it out there.
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Postby gofaster » Sun Jun 24, 2007 1:01 pm

Try adding clay to the floor ahead of the ssr, and to the roof above the ssr. Then try several tests, shaving off a little bit of clay at a time to see which direction this takes you. If removing clay steadily inproves things until it is all out of the port, then you will know where to start removing metal. If adding clay improves the port, then you need to build up the surfaces with weld or epoxy.
Or poke around with various sized flow balls to try to see what is causing the acceleration.
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Postby Thomas Vaught » Sun Jun 24, 2007 6:44 pm

Ford typically shoots for an AVERAGE port velocity of 300 ft/sec but a pitot tube will show that some parts of the port will be higher than others to get that average port velocity.

Tom V.
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Postby Little Rocket » Sun Jun 24, 2007 9:20 pm

Thomas Vaught wrote:Ford typically shoots for an AVERAGE port velocity of 300 ft/sec but a pitot tube will show that some parts of the port will be higher than others to get that average port velocity.

Tom V.

Interesting. Everywhere in the port is faster than 300 fps. The port opening is right at 300 fps all the way to the divider between the valves. When the air moves past the divider it picks up considerable speed~ 350 fps. Then the short turn on both valves is 420 fps. The middle of the port at the short turn is 350 and the roof is 320 fps.

Building up the floor should increase the floor and short turn speed no? I have a couple different clays and I can't seem to make any stick. It hangs on for a second then gets sucked into the port. What brand clay are you guys using?

FWIW this is a yamaha designed head making 120 crank h/p per litre stock. I will post up the flow data when I get back to the shop.

Thanks for your input. :p
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Postby larrycavan » Sun Jun 24, 2007 9:35 pm

Little Rocket wrote:How fast is too fast? I have a 4 valve head that is flowing 420 fps at the short turn @.28" of water. Every thing I have read says 300 fps is fast. The ports stock average 320 fps (averaged from 24 locations) After a days work flow is up 25cfm and speed is up an additional 30 fps average in the port.

Should I consider opening the port up more to slow the air down? I don't think so but I thought I would throw it out there.

That's not untypical of a modern 4V head to have local air speed over 400 FPS in that area and even upstream from the SSR if the runner pairs are small and the valves are large.

Look at how much air speed difference there is between the floor and the roof.

If you can, [motorcycle or atv] before you modify the port any further, mount the carb and retest the velocity. Try to get dead down the middle of each runner as you can get when you poke the pitot in there.

NOTE: We must have been posting at the same time!

I bought some cheap clay at the dollar store that is just great. Doesn't get hard when left out and sticks very well to the port.

Before you go trying to greatly increase the flow of the port, set about calculating the stock Volumetric efficiency of the engine and the stock peak HP RPM. Then look at what's realistic to achieve RPM wise and Ve wise. You need to look at your cam lift as well.

CAUTION - a lot of the modern heads are really hard to improve on when it comes to making power. You can increase the flow for sure.....pay close attention to Ve and peak HP RPM for the flow and cross sectional area.

Another consideration is the OEM CDI box. Can you get the RPM required with it......

Just pointing out some realistic criteria that should be evaluated......
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Postby 1960flh » Thu Jun 28, 2007 10:56 am

As for clay I have found the Green Electricians clay sold at Home Depot the brand is GB it is oil based, never dries out and is very sticky. Cleans up well with WD40. Comes in a 1x2x8 bar.

Rick
HP = Torque x RPM / 5252
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Postby jsa » Sat Jun 30, 2007 4:29 am

Cheers

John
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