help pontiac head porting

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Len
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Post by Len » Mon Feb 25, 2008 8:00 am

Kieth
that is exactly what I have but I think the radius may be a little too abrupt so I am going to make a template for a 3/4 radius to check it.
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Re: help pontiac head porting

Post by 65mustang393 » Tue Feb 21, 2017 1:58 pm

Len,

I know this post is almost a decade old but I wanted to share what I did on a set of Pontiac #62 castings that seemed to help it get up to 270 at 0.8"

1. Used a sonic tester and opened the pinch to .030" on the thinnest curved wall. Due to casting shift, some curved walls had less meat than the others. Once I got that measurement, I ground the other curved walls to match the thinnest one. Then I dug out the combined wall enough to make the width from port to port. I think it ended up being 1.030" wide. I then raised the roof until the area around the pinch was .060" thick (the inner walls have less meat than the outer walls because of the valve cover rail bolt boss. I think the height was around 2.125" at the pinch.
2. I cut the intake seat with a 35/45/60/75/82 seat cutter and blended the ridges. The diameter at the bottom of the seat cut ended up being around 1.82"
3. I opened up the bowls from 1.55" to about 1.78". I took as much off the straight wall as I could and the rest off the curved wall. On port 2 and 4 there is a thin spot on the straight wall that limited me.
4. I laid back the short turn, using a piece of solder for a template, to about a 1.67" radius. I ended up pushing the turn back quite a bit. I also cut back the guide that was over the turn and also raised the turn to about 1.68" tall.
5. After the above work, I was reaching 275 at .55 and then dropping at .6 to about 258. After that, I took off the ridge in the combustion chamber on the intake side of the valve and that allowed it to get to 270 with no drop off in the flow curve. The flow at .5 did drop to about 260 but the chamber work really smoothed out the flow curve all the way up. Below is the flow curve I saw.

0.2- 144
0.3- 208
0.4- 248
0.5- 260
.55- 263
0.6- 263
.65- 265
0.7- 267
.75- 267
0.8- 270

Airspeed at .640" was about 275 in the pinch, 300 over the center of the turn, 315 over the straight wall portion of the turn and about 295 over the curved wall portion of the turn.

Later, I'll flow the head w/the valve upside down and see if the chamber needs more work.

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Re: help pontiac head porting

Post by Geoff2 » Wed Feb 22, 2017 4:17 am

Do you have the exh flow #s?

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Re: help pontiac head porting

Post by 65mustang393 » Wed Feb 22, 2017 10:34 am

Geoff2 wrote:Do you have the exh flow #s?
Numbers for a stock exh port only.
-1mm 45* seat, 40* top cut and radius throat cut
-exh crossover filled with splash zone and a top layer of high temp chimney/stove mortar.

Below are stock numbers on a Brzezinski 4.250 plate sitting on a 4.155 bore with the stock 30* int and 45* exh valves.

0.2- 152 / 119
0.3- 194 / 142
0.4- 201 / 160
.45- 205
0.5- 208 / 172
.55- 212
0.6- 212 / 178
.65- 212
0.7- 212 / 182

The ported intake was initially flowed on a 4.100 acrylic stand and when I re-flowed it on the Brzezinski stand the numbers were about 3 cfm lower across the board.

Once I finally finish an intake and exhaust port I'll post the results.

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Re: help pontiac head porting

Post by jarmoyp » Thu Feb 23, 2017 1:44 am

Throat and seat has valve stem inside the port or have you stemles valve :D

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Re: help pontiac head porting

Post by 65mustang393 » Thu Feb 23, 2017 7:41 am

jarmoyp wrote:Throat and seat has valve stem inside the port or have you stemles valve :D
Not exactly sure what you're asking... I flowed the head with the intake valve flipped upside down and it looked like the port moves about 275-278 cfm...

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Re: help pontiac head porting

Post by jarmoyp » Thu Feb 23, 2017 11:19 am

I have made this calculation the wrong way, I calculate valve stem in too but it is not wright. It has nothing to do with curtain area ☺

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Re: help pontiac head porting

Post by 65mustang393 » Thu Feb 23, 2017 4:02 pm

jarmoyp wrote:I have made this calculation the wrong way, I calculate valve stem in too but it is not wright. It has nothing to do with curtain area ☺
The main reason I do it is just to see if the chamber needs more unshrouding. If the port moves roughly the same cfm with the valve upside down, then I'm satisfied that the chamber is unshrouded enough. Within 10 cfm is close enough for me and keeps the chamber volume smaller... less to mill off afterwards to get the desired chamber size.

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Re: help pontiac head porting

Post by JoePorting » Thu Mar 02, 2017 12:22 pm

Your intake flow appears to be dying after .500". I'd spend more time cutting back the ssr. Try an incremental approach to the ssr of cut/test, cut/test. If the flow numbers continue to rise, continue cutting. When the flow numbers start to go down, stop.
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Re: help pontiac head porting

Post by 65mustang393 » Fri Mar 03, 2017 9:12 am

JoePorting wrote:Your intake flow appears to be dying after .500". I'd spend more time cutting back the ssr. Try an incremental approach to the ssr of cut/test, cut/test. If the flow numbers continue to rise, continue cutting. When the flow numbers start to go down, stop.
0.25 x 2.11 valve = .5275" and that's where the flow is starting to die off... so I think you're spot on about the ssr not having enough area between the turn and the back of the bowl to support more.
I cut back the ssr some more last night and I'll try to find time this weekend to flow it again.

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Re: help pontiac head porting

Post by mag2555 » Thu Jun 15, 2017 8:48 am

I just got finished with a guide port on a 6X - 4 head and here are some shots.

Currently its topping 280 cfm at .700" lift with 30 degree seat.

I have topped 290 cfm on a number 62 casting with a 45 degree seat, but the 1.850" Throat diameter and it's resultant need for a minimum 5.80" port circumference can only be done on D port type heads with little core shift and a sonic wall thickness check out.

Shot 1 is the start of the whole porting work and why knowing how much core shift the Head has to allow metal removal to this level, (i.e.) going from 205 cfm to over 280.

Shot 2 is a 1.77" template down in the window area of the port.
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Re: help pontiac head porting

Post by PackardV8 » Thu Jun 15, 2017 4:21 pm

What would be the going rate these days for porting a max effort pair of iron heads? Just porting, no milling, seat and guide work.
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Re: help pontiac head porting

Post by mag2555 » Fri Jun 16, 2017 6:27 am

Is that question for me Jack?

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Re: help pontiac head porting

Post by RAS » Sun Oct 22, 2017 7:36 pm

I've been a closet Pontiac fan for over 50 years. What I do know is that for every cfm that a Pontiac head does flow, they seem to make better power than any other head out there. Flow doesn't always mean power. The quality and speed of the air through the port is what's critical. Pontiac had a valve angle and port floor height that just flat out worked. It's not a screamer or a giant killer. With the small bore space (small valves) I'm still wondering how this deal makes power. Had Pontiac done a 4.900" block with that deck height the entire supercar era would have way different. The Pontiac Engineers got a lot right and were ahead of their time.
I'd just buy a set of Kauffman raised ports and let that sucker eat. 330 cfm out of the box is 650-700HP capable. Have fun!

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Re: help pontiac head porting

Post by mag2555 » Wed Oct 25, 2017 12:52 pm

Once Pontiac changed fully over to the open chamber in mid 1967 they had a wedge Head that had better emissions and made greater TQ with less timing then anything production wise the other brands/ makes would come up with for many years!

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