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  #11  
Old 30th November 2012
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Default D Port

Quote:
Originally Posted by simeli View Post
MrMom,

Why do you use a flat floor on the port, does it increase the flow or are you using it for a turbulence point for fuel air mixture?

Sorry another question, Do you polish the exhaust ports or leave them with a 120 finish?
I'll Let mrmom answer but I found this article interesting after receiving my heads back from the man..
http://www.nightrider.com/biketech/hdheads_ports.htm
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  #12  
Old 30th November 2012
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Originally Posted by mrmom9r View Post
1000 heads have WAY too much volume as cast for a stock size motor. By the time the shape is improved and cleaned up they're way Past too big.

The small port 900's can be made to provide better velocity with adequate airflow.

Check the port size on a 1200 Evo. it's smaller than a 1000 ironhead.

As to the OP's original question: I feel-none are better to put seats in, none are better for cutting spring pockets .

there are a few different castings. I feel some of the later rubberband castings don't center the seat to the port as well.
Thanks for the reply.
Yes I know what you are saying about the EVO port size and velocity.
I guess I should have asked what you didn't like about the 70 and 71 heads.
As far as I knew the only difference was the Int. Valve size and the 71's don't have the 3 fins.
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  #13  
Old 30th November 2012
simeli simeli is offline
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Quote:
Originally Posted by Monte03 View Post
I'll Let mrmom answer but I found this article interesting after receiving my heads back from the man..
http://www.nightrider.com/biketech/hdheads_ports.htm
Thank you Monte, The Branch heads I have were done with a flat floor and I never understood why, all we ever did before I got the branch heads was just to clean up the basic stock port. I haven't tried welding into the floor of any of my ports and I don't think I am going to start now.
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  #14  
Old 30th November 2012
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the D shape is used to Decrease turbulence in the port. the column of air is best thought of as a fluid ,because that's what it is.
The air must travel thru the port as undisturbed as possible yet it has to turn a corner.

Just like the wheels on your car, the air on the outside of the turn must travel faster than the air on the inside of the corner or shearing of the air column takes place creating lots of turbulence slowing the entire column.

Since we have no way to speed up the air on the outside of the turn, we slow down the air on the inside by increasing the area of the port walls on the short side of the port.

That creates the flat floor D shape.

When one side of the column encounters the greater area on one side of the port it expands which slows it down allowing it stay atattched to the air in the rest of the column which is still traveling fast around the outside of the turn.

In effect it slows to "wait up" for the rest of the column which has to travel faster around the outside of the turn so it can all arrive at the valve entry to the combustion chamber at the same time.

That's what a D shape does and it is why it is one of the most efficient port shapes.
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  #15  
Old 30th November 2012
simeli simeli is offline
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Quote:
Originally Posted by mrmom9r View Post
the D shape is used to Decrease turbulence in the port. the column of air is best thought of as a fluid ,because that's what it is.
The air must travel thru the port as undisturbed as possible yet it has to turn a corner.

Just like the wheels on your car, the air on the outside of the turn must travel faster than the air on the inside of the corner or shearing of the air column takes place creating lots of turbulence slowing the entire column.

Since we have no way to speed up the air on the outside of the turn, we slow down the air on the inside by increasing the area of the port walls on the short side of the port.

That creates the flat floor D shape.

When one side of the column encounters the greater area on one side of the port it expands which slows it down allowing it stay atattched to the air in the rest of the column which is still traveling fast around the outside of the turn.

In effect it slows to "wait up" for the rest of the column which has to travel faster around the outside of the turn so it can all arrive at the valve entry to the combustion chamber at the same time.

That's what a D shape does and it is why it is one of the most efficient port shapes.

Mr Mom,

Thank you for the reply and explanation, it makes perfect sense! Do you leave the intakes with a 220 finish or courser or a 120 finish and do you polish the exhaust ports or leave them at 120.
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  #16  
Old 30th November 2012
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Quote:
Originally Posted by simeli View Post
Mr Mom,

Thank you for the reply and explanation, it makes perfect sense! Do you leave the intakes with a 220 finish or courser or a 120 finish and do you polish the exhaust ports or leave them at 120.
I use a very fine finish on the exhaust and a fairly coarse one (100-120) on the intake for gasoline.

With Nitro ,because of the greater volume of fuel and higher specific gravity (denser), it's a very coarse finish on the intakes ,60-80.


Chevelle, the 70-71 have the 1.94 intakes. I like the smaller valve for the port I do, or I should say used to do. I haven't done a welded up max effort 900-1000cc set of heads since the late 70's. I did win my first drag race National (AHRA Motorcycle Division) using a set in 1974 though, so they did work.
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  #17  
Old 30th November 2012
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Default best head casting

Thank you...that´s great info...

but what happens when you increase compression and throw in some hot cams...

what happens then...?

What difference in port shape when you have a stroker ?

I´m planing something so i need more input....
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  #18  
Old 30th November 2012
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Default

Quote:
Originally Posted by simeli View Post
MrMom,

Why do you use a flat floor on the port, does it increase the flow or are you using it for a turbulence point for fuel air mixture?

Sorry another question, Do you polish the exhaust ports or leave them with a 120 finish?
The 427 SOHC Ford from 1965 was the first engine to use a 'D' shaped exhaust port and YES it did increase flow....a lot. Most engine builders I've know polish the exhaust but not the intake because too smooth a finish on the intake and fuel will liquify on the port wall.
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  #19  
Old 30th November 2012
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Quote:
Originally Posted by xlproject View Post
Thank you...that´s great info...

but what happens when you increase compression and throw in some hot cams...

what happens then...?

What difference in port shape when you have a stroker ?

I´m planing something so i need more input....
What are you planning? If you want details you have to give details.
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  #20  
Old 30th November 2012
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Monte03 Monte03 is offline
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mrmom,
We were hoping your were busy cashin in on that MO Powerball!!!
Lottsa Sportsta's There Man!
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