#1  
Old 03-11-2017, 02:52 PM
fairwayhit fairwayhit is offline
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Default 1st time porting attempt

Be gentle,

Decideded to try porting. I got Jim Hand's book and made the 1.63, 1.66, 1.72 templates out of old valves. Got the die grinder out and went to town.

Turns out this is a little more difficult that I thought. I may not have the speed set right on the grinder. It seems it wants to dig some ruts. I created more of an Octagon bowl than a nice circular bowl.

I also chewed up the seat because I didn't realize that the chuck was hitting it.

I was trying to bias the grinding toward the outside wall, but that didn't leave much meat below the seat on that side.

Did I ruin it?
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  #2  
Old 03-11-2017, 03:15 PM
694.1 694.1 is offline
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  #3  
Old 03-12-2017, 07:49 AM
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steve25 steve25 is offline
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From what it looks like you drove to town and then up on the sidewalk!

That seat will clean up with a valve job which should aways be part of a porting job on a stock head as the factory does not cut the seats to use the full OD of the valve.

You need to lay cut out strips of Duct tape on the valve seats so accidental mishaps like that are limited!

You should really cut your Teeth with porting work on a Mule head even if it's not a Pontiac.

Most auto Machine shops have a pile of cracked iron heads rusting away outside there location, go grab one even if you have to pay 10 bucks for it and develop your skills on that in regards to one or two ports atleast!

Also there is no need to grind that far down towards the valve guide in terms of the rear wall of the valve bowl.
That wall area just above the guide for about 3/8" is the thinnest in the whole head and a area where air flow gains will not be found!

How much additional Intake air flow over stock are you porting for?

  #4  
Old 03-12-2017, 11:35 AM
fairwayhit fairwayhit is offline
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Thanks Steve,

Mr Hand's book said that you should be able to drop the 1.66 template down to the top of the guide. I didn't want to take any material off of the short turn side, so that meant I had to grind the guide side wall down all the way to the guide. I'll try to do better on the next one.

I was trying to stay 1/8" below the seat with any grinding, but in order to get that 1.69 template to go down, I had to get pretty close to the seat. Again, that might be because I was shy of grinding anything on the short turn side of the bowl.

I am going to try to be a little more consistent going around the whole bowl and trying not to take too much off any one side. I am going to turn the speed down a little on the grinder too.

I'd like to get to approx 230cfm @.50 with the flow below .50 up 10-15cfm across the board. I'm thinking that would give me maybe +50HP. The cam I am planning on using only has between .46- .50 lift (depending on what rockers), so I think the flow at .30-.50 is going to be more important than the max flow number.

I don't really have any way to measure them, but it is just a daily driver and I am not really looking to win the NHRA title.

  #5  
Old 03-12-2017, 11:38 AM
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gtofreek gtofreek is offline
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Hold the grinder in a way that allows you to sweep back and forth, like you're spreading frosting on a cake. Don't hold the grinder in one spot. Sweep back and forth following the curvature of the bowl to keep it round. Use light pressure, and don't let the grinder get away from you. If you have an air die grinder, try wrapping a rag around the handle, and under the trigger, and around the air connection. This will give you more control of the throttle so it's not so abrupt to going full throttle. It also quiets the grinder down considerably. I grind with my right hand, and use the left to support and brace the grinder so it doesn't grab and walk across the seats, or anywhere else I don't want it going. I find that running the grinder at a slower speed, as opposed to full throttle, works better.

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  #6  
Old 03-12-2017, 11:42 AM
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The short turn is where the flow is. It needs to be widened out to the side walls, from the current "U" shape it has, if it's an earlier, pre-71 head. Short turn needs to be carefully rounded as it makes the turn into the bowl. Without doing anything there, the bowl work won't amount to much flow increase.

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  #7  
Old 03-12-2017, 02:56 PM
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Material needs to be removed evenly from the short turn side and the opposite wall until you've reached the diameter where you can get the template past the throat. As Paul says, you need to flatten it at the top to match the width of the port then carefully round it as it approaches the valve.

Here's a simple diagram that shows the goal for the port cross-section.

short_turn_diagram by Will Baker, on Flickr

As you can see, most of the work is in the short turn area. DO NOT lower the port floor above the short turn but you do need to lay it back a little to get the proper radius.

Here is an album of pictures of some head porting I've done. I'm just an amateur, but I've ported a couple sets of heads and had my results verified on a flow bench. Doing what you see in the pictures has resulted in ~245 cfm @ .550" with better flow than stock throughout the lift range.

https://flic.kr/s/aHskQGc7b9

Remember, you can always take off a little more metal, but putting it back on is really hard to do.

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Last edited by Will; 03-12-2017 at 03:10 PM.
  #8  
Old 03-12-2017, 06:04 PM
fairwayhit fairwayhit is offline
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Thank you for all of the help and replies.

I did better on the second intake bowl. I turned the grinder down to about half speed (electric makita), and kept it moving a little more uniformly. This bowl ended up a lot more circular and the duct tape trick helped a ton.

It definitely seems like the sides near the throat are the areas that have to be taken down the most.
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  #9  
Old 03-12-2017, 06:04 PM
fairwayhit fairwayhit is offline
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