[MarkS57]

This is a great thread. I've often wondered why a 428 SD wasn't considered in 69. Using the 69 RAIV heads and a forged version of the 428 dish piston. Would have necessitated forged rods of course but that was a given with the RAV anyway. I guess they were sticking to the RAV game plan and that was that. Pity. All this 428 talk is making me want to pull out the 428 block & crank from my shed and get started!!

[Skip Fix]

Ran into a guy a few years ago with a 69 Firebird Gay Pontiac built a RAV headed 428 for. I think he said it was one of the Gay's personal cars initially.

[Formulajones]

Originally Posted by Will

Wanna have some fun? Put a 428 crank in a 455 block with some light pistons and longer rods, good flowing heads and a nice cam and get ready for power out to 7000+ RPM.

I did the opposite about 22 years ago and put a 428 crank in a .030" 400 block, turned down the mains. Basically a small main 433 CI engine. I ran the snot out of that for years. I liked the combo for the most part.

[67GP428]

I miss driving my 428 GP. It ran very strong. The 428 was a unheard motor outside the Pontiac world.

[PontiacJim1959]

Originally Posted by Schurkey

No catalyst before model-year 1975. I think you mean "Thermal Reactors".

Essentially after-burning exhaust manifolds fed with fresh air from the AIR pump or the Pulse Air system. The added oxygen allowed the overly-rich mixture to continue to oxidize.

Ah, you are an automotive engineer - I say that with no disrespect. So here is the complete info I got this from as the word "catalytic" caught my attention. The topic is headed AFTERBURNERS. My book source is published 1968 and specific to automotive emissions systems of all the US manufacturers and the diagnosing, troubleshooting, calibrating, and repair of the systems.

"The two types of afterburners that have received extensive development work to date are the catalytic and the flame type. The catalytic afterburner is designed to consume the discharged hydrocarbons by means of heat developed through a chemical reaction. The units may be positioned at the muffler or in the exhaust manifold. Chemically coated pellets are arranged so that the flow of hot gases activates them; the pellets then promote oxidization of the unburned hydrocarbons. The flow of gases also must agitate the pellets in order to reduce carbon build up in the catalytic bed. Temperatures required to maintain this chemical reaction range from 400 degrees to 1,300 degrees."

So, as you can read, it is exhaust heat activating chemically treated pellets - not air injection.

However, the same section also describes another system - a flame-type afterburner:

"The flame-type afterburner consumes unburned hydrocarbons by means of an open flame. This system requires the adjustment of the carburetor and distributor to produce, as fuel for the flame, a controlled concentration of the unburned material in the exhaust stream. The exhaust must be kept rich enough or the afterburner will "flame out." If the exhaust is too rich, the unit will burn out from excess heat. Also, the extra gasoline needed to keep the burner going exacts a 3-7 percent fuel consumption penalty."

So both devices/concepts use heat and I fail to see in the description of either anything about injecting air?

The type system you describe has nothing to do with a catalytic system as described above, but the Air Injection Reaction System (A.I.R) is what you reference. For your recollection, and the others who may have never even seen one of these nifty units, I will clarify and describe some basic operations of the system.

"The AIR system consists of an air pump (belt driven) that constantly forces air into each exhaust port immediately after the exhaust valve. Since the exhaust gases at this point are above kindling temperature and have an excess of hydrocarbons, the infusion of oxygen starts the mixture burning and so consumes the hydrocarbons that normally would be expelled into the atmosphere.
The AIR system pump draws air from the air cleaner/air filter canister and forces it through two outlet hoses (one for each side on a V8 engine) through a check valve and into an air manifold, where it is delivered to each cylinder through stainless steel nozzles that project into the exhaust port."

I won't get into the fine points as the system has many features in the event of backfires, pressure changes, high speed pumping, and the like.

[PontiacJim1959]

Originally Posted by steve25

Low power and crappy mileage came about due to the drop in compression that just so happened to come along with the open chamber, but it does not have to be that way!

And you have something way the heck wrong, as closed chamber heads require more timing then open chamber heads to make max power, its just that the open chamber heads can be more prone to ping and knock if compression ratios your looking at are are kept equal.

Anyway have we gone off the rails in regards to the OPs original question here, sorry about that!

We haven't really gone off topic as in a sense emissions requirements did shape engine sizes with the lowering of compressions.

Your statement about low power and crappy mileage came about due to the drop in compression that coincided with the open chamber heads is a bit off.

Open chambers were introduced to Pontiac in 1968. Are you saying that the 360HP 400CI or 370HP RAIV engine with open chamber heads had low power?

Crappy mileage? What do you think these cars got for mileage back in the day? The GTO's, depending on engine option, transmission, and gear ratio got crappy mileage from the start. 10-13 MPG's for many if you ordered one that has some snap to it. Now if you ordered one with an automatic and 3.08 gear, you got a little more. Keep in mind these were 55MPH speed limits back then. Many of these cars would have suffered going 70 MPH.

Open chambers can make the same compression as closed chamber heads. It is all about the chamber cc's, and Pontiac did use different thickness head gaskets as well. So you could get an 8.0 compression or 10.75.

The closed chambers used less initial timing, total timing was in much earlier, and seemed to handle more total timing.The open chambers, as compression dropped through the years, used more initial timing, and total timing comes in much later up the RPM scale with factory set-up cars. The Royal Bobcat treatment on open chamber heads dialed in the factory timing much tighter, more closer to a closed chamber head but the best Sunoco 260 had to be used to prevent detonation. Too low of an octane for any head/high compression combination, closed or open chamber, will get it to ping/knock. Keep in mind things like cam choice (ie cylinder pressure), engine heat, grade of gas, distributor advance curve, type of trans, gear ratio, weight of the car, etc. also has bearing on timing. So singling out the open chamber as using more/less timing as compared to a closed chamber head has to also takes in other factors than just the chamber type. I don't think any of the aftermarket aluminum heads are of closed chamber design?

I will agree that the open chamber may contribute to additional heat. Guess what, goes back to emissions again. The open chamber burns better; more complete and efficient burning of the air/fuel lowers emissions out the pipe. Most here probably understand the "squish/quench" area found between the top of the piston and bottom of the head. Having a tight squish/quench is what many try to shoot for, right? However, those good old test engineers trying to reduce hydrocarbons studied the quench areas of a cylinder. It was found that when the air/fuel mixture was ignited by the spark plug, it traveled out towards the cylinder walls, and the cooler cylinder wall (ie cooler than the ignited gas mixture) acted as a quench area and snuffed out the flame and left a minute quantity of the unburned mixture to be sent out into the atmosphere through the exhaust.

If you know what a closed chamber head looks like, then you will understand that a good portion of the head has a flat area hanging over the top of the piston which acts as a quench. This was bad news to the emissions police.

So what did their findings reveal? You guessed it, open chamber designs to reduce the cooling effects of quench. Pontiac was not the only manufacturer to go with open chambers.

Head gaskets were also designed to follow the contours of the cylinder. Pontiac used scallops in the top of the block for valve unshrouding. It would have been easy to just cut a round diameter gasket the size of the bore as measured by the outside edge of the scallop and be done with it. But the round gasket would have been seen as oversized and left a small gap between the mating surfaces of the head and cylinder bore along the top of the cylinder bore. This small area not covered by the head gasket was considered a quench area. So head gaskets were designed to follow the general size of the cylinder's bore, and then incorporate the needed shape to follow the contour of the valve scallop - and why head gaskets can be specific to its engine.

So open chambers do promote more heat due to design of the open chamber and minimize the cooling effect of a good quench area. For us engine builders, we actually shoot for a good tight squish on those quench areas (any flat portion of the head above the piston) to take advantage of the cooling properties of the quench area and force the mixture into the chamber in an effort to minimize detonation.

I suspect the engineers also learned a lesson in detonation and why compressions were lowered and premium fuel was required so as to have the higher octane to prevent detonation - even with mild cams/engines in the family sedan.

[70 bird]

I think many have a more favorable opinion of the 428 because if you drove one they all had decent compression. 455... many were 8-1 or lower . Give a 455 some compression and things improve.

Didn't the Olds engines have those great windowed mains?

[Schurkey]

Originally Posted by PontiacJim1959

Ah, you are an automotive engineer - I say that with no disrespect.

Nope. Former mechanic, long-ago retired.

Originally Posted by PontiacJim1959

So here is the complete info I got this from as the word "catalytic" caught my attention. The topic is headed AFTERBURNERS. My book source is published 1968 and specific to automotive emissions systems of all the US manufacturers and the diagnosing, troubleshooting, calibrating, and repair of the systems.

"The two types of afterburners that have received extensive development work to date are the catalytic and the flame type...
...So, as you can read, it is exhaust heat activating chemically treated pellets - not air injection.

But catalysts were NOT installed on a production vehicle until model year 1975. Everything prior to that was "extensive DEVELOPMENT work". NO cars came with catalytic converters in '68.

As for AIR vs. thermal reactors, your text explains the mixture in the cylinder has to be overly-rich to support the post-cylinder burn in the exhaust system. If the mixture in the cylinder is overly-rich by design, you'd HAVE to add oxygen to continue the burn "downstream". The air added to the exhaust system goes without saying; you can't burn something without enough oxygen.

Originally Posted by PontiacJim1959

Your statement about low power and crappy mileage came about due to the drop in compression that coincided with the open chamber heads is a bit off.

Yes, it's a bit off. Low power, crappy mileage, lower compression and open chambers are all interrelated. But not necessarily in the simplistic way folks expect as presented in this thread.

Originally Posted by PontiacJim1959

I don't think any of the aftermarket aluminum heads are of closed chamber design?

I'm thinking just the opposite. Virtually all aftermarket heads have a quench pad, some have more than one.

Originally Posted by PontiacJim1959

I will agree that the open chamber may contribute to additional heat. Guess what, goes back to emissions again. The open chamber burns better; more complete and efficient burning of the air/fuel lowers emissions out the pipe.

"Additional heat"? Leaving aside the issues of higher-rated thermostats that drive operating temps higher, yes, the open-chamber head will tend to push more heat into the coolant. This is less a matter of "more-complete, more-efficient combustion" and more a matter of SLOW, LAZY burn, so that the heat is absorbed by the combustion chamber and then goes out the exhaust port instead of doing something useful like pushing the piston down. The exhaust port, along with the greater surface area of the combustion chamber increases the BTUs that have to be carried away by the cooling system.

Originally Posted by PontiacJim1959

If you know what a closed chamber head looks like, then you will understand that a good portion of the head has a flat area hanging over the top of the piston which acts as a quench. This was bad news to the emissions police.

Yes, that was the belief at the time. Turns out, it was a mistake in logic. Open-chamber heads were a dead-end technology. Solved immediate problems, was "rushed" into production; then dropped like a broken rubber when the REAL solutions were identified.

Originally Posted by PontiacJim1959

So what did their findings reveal? You guessed it, open chamber designs to reduce the cooling effects of quench. Pontiac was not the only manufacturer to go with open chambers.

Which got many manufacturers past the immediate crisis. Later research brought back the quench pads and higher compression. The real problem was not the quench pads per se, it was the horse-sh!t machining practices where the quench distance was too great to be beneficial, but too small to promote full combustion--combined with poor control over fuel mixtures, poor control over spark timing, poor combustion chamber and port design in general, etc.

Originally Posted by PontiacJim1959

For us engine builders, we actually shoot for a good tight squish on those quench areas (any flat portion of the head above the piston) to take advantage of the cooling properties of the quench area and force the mixture into the chamber in an effort to minimize detonation.

The "cooling properties" are a side effect. The real bonus is the in-cylinder turbulence that proper quench provides.

Originally Posted by PontiacJim1959

I suspect the engineers also learned a lesson in detonation and why compressions were lowered and premium fuel was required so as to have the higher octane to prevent detonation - even with mild cams/engines in the family sedan.

Detonation became a problem because Detroit foolishly gave up the faster combustion of a properly-done quench pad in favor of a slow, lazy burn that left the chamber and piston-top hotter. This did reduce hydrocarbon emissions, but vastly decreased efficiency and therefore power and fuel economy.

Look at the new engine designs: Mopar Hemi: Double quench pads, two spark plugs leading to fast combustion. GM LS: quench pads, high in-cylinder turbulence, fast combustion. GM "performance aftermarket" heads are called the "Fast Burn" heads. GM's TBI Swirl-port heads and the 7.4L "Vortec" heads have ski-jumps cast into the intake ports to promote in-cylinder mixture motion leading to...you guessed it...speedy combustion. Fast, controlled combustion leaves less time for the combustion chamber to be exposed to heat. The combustion starts later, is DONE before the exhaust valve opens, so temperature of the exhaust gas is already dropping by the time the port is exposed to the exhaust gas stream. In short, more power, less wasted heat.

Open-chamber heads tend to be turds. Garlits found out in the '50s that the only way to make a (First-Generation) Hemi provide power for racing was to advance the timing beyond all reason: They burn so slow! They also retain heat in the combustion chamber, so you need high-octane gasoline, or alcohol fuel to avoid detonation.

My point is, it's not "just" the drop in compression that made the mid-'70s engines so pathetic. It's also the WAY they dropped compression, which compounded the power/fuel economy problem The open-chamber head proved to be a short-term fix, and has all but been abandoned since then.

[242177P]

Originally Posted by PontiacJim1959

Open chambers were introduced to Pontiac in 1968.

Actually, the 061 head in 1967 has that distinction. But yeah, in 1968 the open chambers were used across the board.

[steve25]

The problem with original Hemi heads heads in relation to timing needs is the total lack of squish.

And if you do get the piston dome near enough to the chamber walls to generate some turbulence then the flame travel goes to Hell in the Hemi head faster then the added timing can make up for!

Just go look at the power improvements in the aftermarket Harley heads designed for squish.

[dataway]

Tight squeeze.

[Formulajones]

Originally Posted by dataway

Tight squeeze.

Yeah....I think they work pretty well They've been in the record books since the 50's and still continue to be the mainstay in top fuel and funny car. Just look how competitive they are in Pure Stock and FAST classes.

[mgarblik]

Originally Posted by steve25

The problem with original Hemi heads heads in relation to timing needs is the total lack of squish.

And if you do get the piston dome near enough to the chamber walls to generate some turbulence then the flame travel goes to Hell in the Hemi head faster then the added timing can make up for!

Just go look at the power improvements in the aftermarket Harley heads designed for squish.

Dead on target and the reason the hemi heads work so well in racing and not so great in low RPM, street engines with emission requirements. Racing engines: High RPM, high flow, low turbulence, hemi is perfect. Especially true on nitro where squish and quench=explosion and severe detonation. Usually, when I say this, a Mopar nut will say, "then explain the modern hemi" The modern hemi is a "Hemi" in name only. It is really a 2 valve pent roof chamber. It has both a quish and quench pad. Small, but they are there, unlike the original Chrysler Hemi design. They are needed for mixture motion, turbulence, low speed driveability, emission control, primarily, HC emissions from the dead space created by the hemi shape.

[Region Warrior]

Blew the doors off a 70-455 GTO with a 69-428 in my brothers 68FB back in the 70's.

[MarkS57]

Originally Posted by MarkS57

This is a great thread. I've often wondered why a 428 SD wasn't considered in 69. Using the 69 RAIV heads and a forged version of the 428 dish piston. Would have necessitated forged rods of course but that was a given with the RAV anyway. I guess they were sticking to the RAV game plan and that was that. Pity. All this 428 talk is making me want to pull out the 428 block & crank from my shed and get started!!

So I'm thinking a 428 SD might be a "retirement engine build" for me. I will collect the additional items during my last few years in the rat race. I bought a set of GM Pontiac 4 bolt caps to go with the 428 block, not because they were absolutely necessary but because I'm certain if such an engine was produced it would have been fitted with the 4 bolt caps and besides, the block is already drilled for the 4 bolt caps. Running down a set of 722 RAIV heads will be the most expensive item.

[Formulajones]

Originally Posted by mgarblik

Dead on target and the reason the hemi heads work so well in racing and not so great in low RPM, street engines with emission requirements. Racing engines: High RPM, high flow, low turbulence, hemi is perfect. Especially true on nitro where squish and quench=explosion and severe detonation. Usually, when I say this, a Mopar nut will say, "then explain the modern hemi" The modern hemi is a "Hemi" in name only. It is really a 2 valve pent roof chamber. It has both a quish and quench pad. Small, but they are there, unlike the original Chrysler Hemi design. They are needed for mixture motion, turbulence, low speed driveability, emission control, primarily, HC emissions from the dead space created by the hemi shape.

Who's worried about low rpm street manors in the street section?

[dataway]

They need to add a "Freakin Stock Pontiacs" section

[steve25]

Sub title that "The reality street section"!

[Skip Fix]

I have a 4" stroke 400 block plan using my RAIV heads for my 65 GTO project.

[MarkS57]

Originally Posted by Skip Fix

I have a 4" stroke 400 block plan using my RAIV heads for my 65 GTO project.

I figured I would put these on my 65 after the 428 build, not a 421 but it will be 4" stroke engine. From the Full Size Ames catalog 65 model year