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Old 01-23-2012, 07:43 PM
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pontiac engines

Bought a Pontiac motor, I'm pretty sure it has a 350 block with #46 heads. I believe this head castings are from a 69 400/428, is this correct? If correct these heads should be 72 cc with 1.96" intake and 1.66" exhaust. I would like to put these heads on a 400. Is this a good combination? Can the bigger valves be machined into these heads (2.11"intake and 1.77"exhaust) ? Is it worth rebuilding these heads?

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Old 01-23-2012, 07:53 PM
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Number 46 heads were used in 73. They also used the same number to designate the earlier 428 heads.Check the date codes on them.That will be the determining factor. If the block is a 350, most likely it is a 73 and the heads will be too. Check the date codes to be sure.
I just ran across the same thing at a salvage yard when looking at a poncho motor that had been around for a long time. I got excited at first, then I checked the date codes......
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Old 01-24-2012, 06:47 AM
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Correct. The "early" 46 was used on 428 360 HP "grocery-getters". Joe Roberts' '69 Catalina wagon is so-equipped. Decent mileage, good low-end and mid-range power. Usually around 76-80 CC chambers.

The '74 46 was the head used on GTO 350s. One can easily spot the difference by looking for "screw-in" studs (the early one had pressed studs) and the "cavity" above the exhaust crossover for post-'71 "EGR" heads. Usually 92-96 CC chambers.

The early head is a paper weight unless you're restoring a car with them "original". The late head is a decent performance head on larger displacement engines. As it has "small" valves (1.96 in. and 1.66 ex), it is an excellent candidate for "large" valves (2.11/1.77). The ports are cast virtually the same in all the "d-port" heads. By opening the seats up for larger valves, one can take advantage of the situation and use modern cutters to re-profile the seat to flow MUCH better than the original Pontiac approach. We've learned a LOT about flow and valve jobs since the 1960s!

Once porting begins, d-ports are all pretty much the same.

FWIW

Jim
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Old 01-24-2012, 08:34 AM
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The intake seat would stay 30 degrees, wouldn't it? What angles above and below the seat do you recommend for a street/strip Pontiac?
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Old 01-24-2012, 11:38 AM
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The intake seat will have a 30 deg angle, yes. This should only be changed if high-lift flow is called for. Low- and mid-lift flow are far better with the shallower angle. There is no "top" angle, as the 30 deg. seat will make the transition to the chamber better, the "further" the seat goes "out". The throat angle is 70 deg. There's a slight 45 in between.

The exhaust side is the "key" to Pontiac performance. The intake port is very efficient and flows quite well for the cross-section. The exhaust has an horrendous 135 deg. "turn" in the port, seriously confusing the sound wave. By enlarging to the 1.77" valve, that is helped (not "cured"). A very thin 15 deg. top angle, 45 deg. seat and 70 deg. throat all "help". We use a profiled "radius" cutter to rough "in" the exhaust, then after grinding the seat to size, some mild "blending" is done.

These changes work well on their own, but offer a dramatically better "starting point" for a good port job. Our d-ports tend to flow as well as others at high lift (over .500), but generally dwarf the theirs regarding low- and mid-lift flow. Contrary to what advertisers want you to think, "peak numbers" aren't nearly as significant to overall power production as the "average" of flow. More low-lift tends to increase torque production across the RPM range. We've actually changed "lift rule" small blocks to 30 deg. intake seat in circle track engines where the modification is legal under the rules. If it can't open the valve more than .410", who cares what the heads flow at .500...

Jim
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