Building a 406.

Would  AFR 195 heads with  76 cc combustion chamber and SRP forged flattop piston be more suitable for street and burn better, or 64 cc with a dished piston

On getting file fit rings, which would be better plasma, moly, and cast or steel.

This is for a street driven engine in a 1/2 ton truck,  Will be running hyd roller cam from a 270 anywhere to a 282, havent'e decided, (and will I have any problems with detonation, I am really concerned with this ) using a scat steel crank and rods, Eld.  air gap intake

Thanks, you guys are good

If you look at the heads you will see a open area where the valves and spark plugs reside and a flat surface opposite the valve/sparkplug location which is call the quench or squish deck. The quench/squish deck is greatly important to designing-in resistance to detionation, this is often called mechanical octane. This feature is somewhat independent of compression. That's to say a low compression engine without an active quench/squish area will be more detonation prone than a high(er) compression engine with a very active quench/squish area., all other things being equal. Generally the closer you can close the piston to the quench/squish deck of the head, the greater will be the engine's resistance to detonation.

The OEM tends to use a full dish piston which results in a lazy quench/squish which translates into engines that tend to detonate or ping. The average person just doesn't push the engine hard enough for this to be a problem. But when you start to put a load on an engine either by hopping it up or using it ihard in a working truck, the lack of mechanical octane can become a problem. Most people throw a higher octane rated fuel at the problem and that will work to a point.

The better solution is to use pistons whose design allows the gap between the piston and the quench/squish deck to be minimized to .040 inch or a bit less (and yes that includes the gasket thickness). With this goal in mind, you can go at solving the problem in a couple ways and as long as you have enough compression ratio, either solution is valid and close to equal in terms of performance. For example, you could go with the 76 cc chamber and a flat top piston and lets say arrive at a static compression ratio of 9.5 to 1. This would have excellent quench/squish properties and the open combustion chamber allows space for mixture to flow in and exhaust out while the piston and chamber work well for flame propagation, ie Fast Burn. Another design solution is to use the smaller chamber head with a "D" dish piston. This keeps the dish under the combustion chamber and also allows a tight closure between the piston and the head's quench/squish deck. You probably sacrifice a little bit of gas ( gas as in air's components not gasoline, a liquid) flow in and out of the chamber at higher RPMs. Either of these solutions will maximize detonation resistance of the design and will be close on breathing performance.

My recommendation would depend on use. A high speed competition engine would probably have an edge with a larger combustion chamber in the head and flat top or slightly domed pistons to control the compression. A street engine that spends most of its time at or below its torque peak would probably benefit more from the smaller chamber with a "D" dish piston to flattop piston to control compression.

A 270 to 282 degree cam will reqire that you keep the static compression up around 9.5 or more. Aluminum heads let you push higher than cast iron, while aluminum may give up a small amount of thermal efficiency against cast iron, the cams you propose need compression recovery more than the thermal effeciency between cast iron and aluminum.

Hope this helps. Bogie 

Well it sure helped me!  

I've read John Lingenfelter's book on building small blocks.... it is/ was very informative, and I highly recommend it.

Now I want to know where I can get ahold of Bogie's book....

Now I want to know where I can get ahold of Bogie's book....

It is a work in progress and is not available as of yet, but excerpts are avialible here on the CHP Board.

(Bogie, you should think about a book deal) 

Thanks For the info Bogie, very helpful.  Also, on a carb, what are your suggestions.  I know it is going to drink some gas, and I was thinking about a 750 holley, but a guy at the local part store was trying to tell me that with the right Quadrajet and tuned right that it will perform just as good as the holley and get an extra mile or two per gallon, If so what kind, He said they are expensive.....]

P.S Hooking up a kill swith on a friends truck, what would be the correct way to do it...

Again thanks for letting me pick your brain