Mr Gadgets

Hi Dennis,
I have been doing some reading.. oh oh trouble. I am wondering what the characteristics of a fast burn combustion chamber are. I mean, how would you identify if a head that had such a chamber. I know some of the newer heads are classifed as "Fast Burn" from the factories, but what about aftermarket heads, AFR, Dart, Dart Big Chief, Merlin, Brodix, etc.
Are there any heads that will bolt to the BBC and be considered "Fast Burn"??

Any info would be appreciated..

Dick

Dennis Moore

I really like the large oval port heads on the L29 Vortech 454. They have a fast burn combustion chamber and ports that have swirl technology. They also have the good D shaped exhaust ports. They can only be used with flat top pistons though. They would be my choice for a head on a nice running big block (Gen V or Gen VI) in a family boat running at 5,000 rpm or less.
Sincerely
Dennis Moore

Mr Gadgets

So what makes this chamber fast burn? and How do they introduce the swirl effect. Any idea of pics of this head?
I am looking at more cubic inches, 565, and higher rpms maybe 6k.
Can you determine what makes these fast burn and apply the characterisitics to identify other heads? Or is it more complicated than that? Do we need an engineer to make the statement that this head or that head is fast burn??

Thanks
Dick

blown1500

There really is no Fast Burn head, except by name. Some heads have better flame travel than others with a given piston configuration. Heart shaped usually does better, but any head with good flame propogation could be called "fast burn". AFR and TFS have very good chambers. I have had the best luck with AFR for the best performance, followed by TFS and Dart. Each application has it's differences and the same head is not always the right answer. Be carefull about too big a head. Blowers add a different factor to the mix.

Dennis Moore

In simple terms a fast burn head moves the flame front across the combustion chamber very fast. A fast burn head can usually be determined by the amount of ignition advance that the engine requires. If the engine will make as much horsepower at 28 degrees advance as it does at 34 degrees advance than you could assume that the flame front is moving faster across the combustion chamber than an engine that makes maximum power at 34 degrees advance. Usually this is accomplished by relocating the spark plug farther into the combustion chamber and redirecting the air/fuel mixture towards the plug.
The swirl ports I was talking about have a vane inside the port bowl to spin the mixture.
If you are building a large engine for high rpm you will need aftermarket rectangle port heads not the Vortechs.
Sincerely
Dennis Moore

WETTE VETTE

Other things that affect flame burn rate are the finish of the combustion chamber and the piston dome height and design. A polished combustion chamber speeds up the flame a bit as do flat pistons. Cylinder pressure and fuel type are other things that affect flame speed. When pressures are raised temperatures are also raised and burn occurs more quickly. Large piston domes get in the way of the flame so timing has to be advanced in order to get max pressure at the right time. One thing head manufacturers are doing in max effort drag racing is designing heads with very small combustion chambers so high compression can be had without domed pistons. This creates a fast unobstructed burn. As for "fast burn" heads I thought they are just a marketing name for some of the new small block chevy heads.

Mr Gadgets

Blown1500,
Your analogy is correct, I guess I am looking for a head with a better flame travel, or faster burn rate than another. To put it another way, I dont want to buy a set of heads and find out that I need 40 degrees of timing to make them work. I am familiar with the AFR, and Dart, but not the TFS? Of course as soon as you mention the full name I will go.. OH Yeah.. those.,
My present combination is NA, with flat top pistons and a 116 cc chamber puts me at 9.85:1. I am also running a very "long" rod to help with dwell time at TDC. I am looking for a set of heads with great flow, high velocity and the best possible burn rate without having to be ported to the point of paper thin walls. Of course isnt everyone!! And pump gas is a requirement, soon that will be the too expensive to run and we will all look at fuel oil motors for our boats.
I have looked at one set of heads that use 3 valves and a very small chamber, but the valve train was very complex. I am looking for info on the Big Chief 14 degree head with oval ports, as a possible solution. I am not sure if the ports are too big and the chambers are too small.

I do appreciate everyone's input. It seems that the newer heads are obtaining better flame travel, I was just wondering if one stood out above all the rest. I like the AFR numbers, but as always, I want to make sure I didnt miss anything. I have spent a lot of money on heads over the years with some good and some tragic results..

Thanks

Dick