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did a little bit of digging perhaps you'll find something Posted by vvack0matic [Email]  (#1443) [Profile/Gallery]
(more from vvack0matic) on Mon, 28 Aug 2006 19:27:21
In Reply to: Re: I think I've got engine knock at boost.. I'm stumped!, vvack0matic [Profile/Gallery]
, Mon, 28 Aug 2006 11:08:20
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lets just take a step back a moment and have a look at your set up, taking into account that the over all motor is fine, starting with just the volvo inner-cooler, im sure you know about it`s the size that matters but ill say it anyway in upgrading the intercooler only install one thats larger, if it is the same size as the old one, the only thing that would be different is the outside would be cleaner, the reason for it is to cool the compressed air to further increase its density and to increase resistance to detonation. after passing through the intake manifold, the air enters the engine’s cylinders. since the air is at elevated density, each cylinder can draw in an increased mass flow rate of air. higher air mass flow rate allows a higher fuel flow rate. combusting more fuel results in more power being produced.
now where dose knock play in here and what exactly is it ...
its deterioration of the motor
knock is a dangerous condition caused by uncontrolled combustion of the air/fuel mixture. This abnormal combustion causes rapid spikes in cylinder pressure which can result in engine damage.
three primary factors that influence engine knock-
-knock resistance characteristics (knock limit) of the engine: Design features such as combustion chamber geometry, spark plug location, bore size and compression ratio all affect the knock characteristics of an engine.
-ambient air conditions: both ambient air conditions and engine inlet conditions affect maximum boost. Hot air and high cylinder pressure increases the tendency of an engine to knock. henc smaller inercooler more knock when an engine is boosted, the intake air temperature increases, thus increasing the tendency to knock. (e.g. an intercooler) addresses concerns by cooling the compressed air produced by the turbocharger.
-octane rating of the fuel being used: octane is a measure of a fuel's ability to resist knock. The octane rating for pump gas ranges from 85 to 94, while racing fuel would be well above 100. The higher the octane rating of the fuel, the more resistant to knock, and how to get more octane with octane booster, since knock can be damaging to an engine, it is important to use fuel of sufficient octane for the application. generally speaking, the more boost run, the higher the octane requirement.
This cannot be overstated: engine calibration of fuel and spark plays an enormous role in dictating knock behavior of an engine.
aft = air fuel ratio
the turbocharger increases the density of the air resulting in a denser mixture. The denser mixture raises the peak cylinder pressure, therefore increasing the probability of knock. As the AFR is leaned out, the temperature of the burning gases increases, which also increases the probability of knock. This is why it is imperative to run richer AFR on a boosted engine at full load. Doing so will reduce the likelihood of knock, and will also keep temperatures under control.
try adding a bottle of boost to your gas and if the volvo intercooler is smaller than stock 900 get rid of it, and perhaps run this by the performance bb.
posted by 24.249.3...
, Mon, 28 Aug 2006 11:30:05, Mon, 28 Aug 2006 11:08:20, Mon, 28 Aug 2006 19:27:21 <-- Viewing This Message
, Mon, 28 Aug 2006 06:37:56
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