quench on boost?

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quench on boost?

Post  waypastcrazy on September 1st 2009, 10:15 pm

Is a tight quench needed on a boosted engine or can you have less quench to help lower compression by using thicker head gaskets and not decking block as much?thx
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Re: quench on boost?

Post  bruno on September 2nd 2009, 5:13 am

Remember this.. A tight quench is less important in a forced inducted application..

The purpose of a tight quench is to add turbulence to the combustion chamber.. By squeezing the a/f mixture toward the center of the chamber..

With forced induction a great amount of turbulence is already induced in the mix..

There is a debate amoung knowledgeable engine builder if a tight quench or a wide quench is more benificial on a force inducted motor..
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Re: quench on boost?

Post  bruno on September 2nd 2009, 5:15 am

Per "Maximum Boost" by Corky Bell-

Changing compression ratio: A variety of methods exist to change compression, Almost all are unacceptable. The crux of the matter is upsetting the "squish volume" around the chamber. Squish is perhaps the strongest deterrent to detonation designed into the system, as it tends to either eliminate end gas, or keep the charge turbulence high. Consider "squish" volume sacred and do not tamper. It is possible to err so badly in removing the squish that a resulting 7:1 CR may ping worse than a 9:1 with proper squish.>>>>>Approaches to lowering the CR that do not work are thicker head gaskets and shorter connecting rods.
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Re: quench on boost?

Post  bruno on September 2nd 2009, 5:16 am

There is the debate amoung experts..


Squish Band
This is defined as the area in the combustion chamber where the piston (at TDC) comes extremely close to the head. It's usually around the perimeter of the piston, and no mixture is expected to burn there. Physical contact is the only factor determining the 'height' of the squish band, so practically no mixture will be expected to be there as the flame front moves from the spark plug outwards.
Here's how it works: the upcoming piston squishes out that mixture, forcing it to blend with the rest around the plug. This action creates extra turbulence and homogenises the resultant mixture, which means that it burns cleaner and quicker, requiring less ignition advance. As a bonus, the outmost edges of the combustion chamber are closer to the plug tip, further reducing the need for extravagant ignition advance. All this leads to efficiency, especially in off-boost situations, where the mixture is not well homogenised (there are rich and lean spots within it)
Under boost, the role of squish takes the backseat. The compressed air is already agitated enough for the squish turbulence to make any major difference. Therefore race engines designed to run mainly on-boost don't have to pay much attention to it.
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Re: quench on boost?

Post  Northwest outlaw on September 2nd 2009, 10:20 am

thanks Nick sorry i have been working on the new fox and havent been on in a few.
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Re: quench on boost?

Post  moparman on September 2nd 2009, 11:33 pm

If it's a street car I recommend building the engine with the proper quench present. The street manners will be more mannerly and fuel economy will likely be better as well. On high boost engines the charge is so dense that it burns very quickly and quench is no longer necessary.
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