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Old 11-26-2006, 09:53 PM
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What Exactly is a "Fast Burn Head"?

I see mentions of "Fast Burn Heads" requiring less total ignition advance - less than 36*. I know GM has what they call "Fast Burn Heads", but my question is, are all or any of the aftermarket heads considered "Fast Burn"?

What determines "Fast Burn"? Chamber size, chamber shape or just HYPE? Who decides? There must be, maybe, some standard. Are my TF 23* heads considered "Fast Burn"?

Thanks,
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Old 11-26-2006, 10:27 PM
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Fast Burn is a name that GM came up with. It really is a great technology and really does work as well as it says. There are aftermarket fast burn heads, usually copied from GMs chambers.

The general idea is to shape the combustion chamber in such a way that the rising piston meets a specially shaped deck. It attempts to make optimum squish or quench, which is a fancy way of saying it squishes all the charge out into the combustion chamber making it turbulent. Turbulent = well mixed = fewer liquid droplets of fuel = fast flame front. All of that equals to better detonation resistance, less ignition lead, better economy, and more power. It hasn't solved all the worlds problems, but it has taken a significant leap forward in all of those parameters.
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Old 11-26-2006, 10:27 PM
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They generally have a smaller combustion chamber with the spark plug located closer to the center so the fire starts more centrally and burns out toward the edges. Older designs have the plug closer to one side, which makes the fire have to burn all the way across in one direction.

The theory is that detonation is encouraged by radiant heat causing fuel on the far side to ignite prematurely. By speeding up the burn, there's less time for the heat to build up.

The shape of ports and combustion chambers is also a factor. Modern shapes induce motion in the mixture, and the extra motion causes the fire to spread faster.

A faster burn also reduces ignition advance requirement, which means there's less force trying to stop the piston on its way up before top dead center, therefore more energy available to push it down.
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Old 11-26-2006, 10:28 PM
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^^ yeah, what he said
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Old 11-26-2006, 10:37 PM
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Here's a couple of examples, the combustion chambers are compact, the squish to bore ratios are maximized and the spark plug is more centrally located. All gear towards speeding up the combustion process in effort to lower detonation tendencies.

This allows higher compression ratios for greater efficiency. In addition reduced ignition advance requirements creates less pressure on the advancing piston resulting in reduced negative work.

Sounds like we are all saying the same thing. jimfulco talks about the port shape, this LT1 example has a twist in the intake port to enhance mixture movement.




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Old 02-25-2009, 03:23 PM
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I understand this is an archived thread, and I apologize.
But I googled into your site, so obviously others will too.
So I have a question on the subject.
Since combustion chamber design and centrally located plug are a few of the makings of a "Fast Burn" head, would an overhead cam head fall into this category, without the labeling of course?
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Old 02-25-2009, 04:31 PM
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Quote:
Originally Posted by Positive P
I understand this is an archived thread, and I apologize.
But I googled into your site, so obviously others will too.
So I have a question on the subject.
Since combustion chamber design and centrally located plug are a few of the makings of a "Fast Burn" head, would an overhead cam head fall into this category, without the labeling of course?
Sort of, hemi and pent chambers typical of OHC engines work a lot differently than wedge chambers using in-a-line valves.

Actually the so called Fast Burn head is a rediscovery of Sir Harry Ricardo's work starting in the 1920s and published in his volumes titled the "High Speed Internal Combustion Engine". He achieved knighthood based upon this research, just to show how fundamental to the modern industrial age and to national economies and defense this work was considered to be.

Ford incorporated his work into their flathead engine which kept it competitive in power and economy till the early 1950's. Ford's early OHV Y blocks for the Lincoln in 1952 thru 1955 and the smaller Ford Y block in 1954 and 55 used the same type head we see in today's Fast Burns that is a tight valve pocket, a spark plug as centrally located as possible that clears the valves, and beak that projects between the valves from a generous squish/quench deck. These type heads make use of a highly energetic vortex or swirl to fill the cylinder. Chevrolet used a very similar but somewhat simplified chamber up to the compression reductions of the SMOG era. Ford with the Y block engines simplified their chamber starting mid 1955 as well, since higher octane fuels were becoming available and they as well as the other OEMs could reduce manufacturing cost a few cents per unit by transferring the "octane" cost to the end user.

Federal emissions standards finally drove the manufacturers back to a re-evaluation of the situation in the 1980s where you start to see a return to Sir Harry's combustion chamber technology combined with electronic fuel injection.

The effect of the Ricardo Fast Burn technology is significant and measurable. The Chevrolet Vortec head is a good comparison because you have basically the same old Gen 1 engine under the head before and after. These heads will add anywhere from 20 to 40 horsepower, or more, to an earlier engine without any other changes.

Now overhead cammed engines tend to have hemi or pent combustion chambers. These use a tumble flow of intake charge into the cylinder which essentially is a vortex set on its side, so a lot of different things are happening compared to an inline valved wedge head. But there are combinations out there, one is the Yamaha V-Star motorcycle engine which uses an overhead cam with 2 valves canted as in a Hemi engine but placed in a pocket as it were a wedge. But generally hemi and pent headed engines didn't need as much fixing in the sense of improving burn efficiency as did the wedge engines. Using the Ricardo chamber allows the wedge to be much more competitive in terms of low emissions, low fuel burn and high power with hemi and pent chambers at significant production cost reduction, less weight, and in a smaller external volume.

Bogie
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Old 02-26-2009, 09:25 AM
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WOW, OldBogie. That was very helpful. Thank you for your reply!
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