help pontiac head porting

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65mustang393
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Re: help pontiac head porting

Post by 65mustang393 » Wed Nov 08, 2017 5:36 pm

I couldn’t find a photo on my phone of the #62 casting I did but I do have a data sheet with the measurements I used.
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mag2555
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Re: help pontiac head porting

Post by mag2555 » Thu Nov 09, 2017 6:55 am

That's a big Throat size for that head if it's correct!
A Throat size like that calls for a big port circumference at the crown of the short turn of 5.87".
Your flow regression down to 264 cfm is due to your small port volume and the overall short turn arc that does not complement that Throat size.
A Pontiac port flowing over 270 cfm should be in 178 cc range when the port circumference and short turn have been reworked enough to negate that flow regression!
If the motor is for race use only you should have converted over to a 45 degree seat, as this makes gaining control of the short turn air velocity easier.

Tomorrow I will post up some pictures of what a 290 cfm port looks like by means of a 2.14" valve.

Thanks for posting your info none the less!

65mustang393
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Re: help pontiac head porting

Post by 65mustang393 » Thu Nov 09, 2017 3:45 pm

Thanks for the feedback. I used a 35/45/60/75/82 intake cutter and should’ve made sure the area over the turn could be made big enough to support the throat.

Definitely something I’ll look closer at next time.

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Re: help pontiac head porting

Post by mag2555 » Fri Nov 10, 2017 7:08 am

This a shit of how I start off my porting work.
I cut straight down until my cutter stops cutting meat out from the short turn.

It all so gives a good indication of what your dealing with for core shift!

In doing this I only use a 30/45/60 valve job.
My pictures I promised are coming, I just have to dig the head out.

Geoff2
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Re: help pontiac head porting

Post by Geoff2 » Sat Nov 11, 2017 2:36 am

Nobody commented on the high exh flow #s, 224 cfm, a 93% E/I flow ratio.

65mustang393
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Re: help pontiac head porting

Post by 65mustang393 » Sat Nov 11, 2017 6:00 am

Geoff2 wrote:
Sat Nov 11, 2017 2:36 am
Nobody commented on the high exh flow #s, 224 cfm, a 93% E/I flow ratio.
85% ratio (224/264) at 0.75 lift. The numbers are what they are

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Re: help pontiac head porting

Post by mag2555 » Sat Nov 11, 2017 7:33 am

Sorry, I don't know why my picture did not post, but here it is.
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Re: help pontiac head porting

Post by Geoff2 » Sun Nov 12, 2017 4:42 am

65,
You are correct 85%. Fat fingers on the calc. But even 85% is high; I have seen as high as 94% for ported Pontiac iron heads. Most average 70-80%.
Many people reckon the Pontiac has a poor exh port because it has a bend in it. The numbers say otherwise & I think it is actually beneficial because the transition into the header pipe is at a much reduced [ less sharp ] angle.

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Re: help pontiac head porting

Post by mag2555 » Mon Nov 13, 2017 6:43 am

Sorry for the delay, but here are some pictures and I will post the details of each shot.

Shot#1
The short turn arc at the center of the floor .
The area in the V is a flat area ground at the valve inclination angle of 14 degrees.
It does not show up as much in the shot, but none the less it's about 1/8" tall and runs around the width of the short turn.
If pictures could show 3 dimensions and I took a shot of the short turn you would see it right away.
This is what slows down the velocity of the air flow around the short turn and fools the air mass into thinking that the overall short turn is taller then it is!

Shot# 2

The arc of the floor at the crown of the short turn on the push rod wall.

Shot# 3

The arc of the short turn on the common wall side, note how straight that wall even thru the valve bowl and how rectangular the runner is up to the crown of the short turn.
The height of the port from the crown of the floor to the roof is 1.745".

Shot# 4
Note that raising the port roof the needed amount has ground fully into the rocker stud hole.

Shot# 5
This is a 1.850" temp plate with one side cut back to 94% of that 1.850" ( 1.740" ) and a bit rounded off at the transitions .
Note the gap between the temp plate at points and how much more D shaped and wide the accutal floor is.

Shot # 6
That same template with the flat side now on the common wall, and it's shoved all the way up to the crown of the short turn which you can't quite see in this shot.


Since your hitting 270+ cfm you have the air flow, you just need to regain control of it and the proper short turn is a big key part!

I hope this helps you next time or maybe somebody now!
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