Quote:
Originally Posted by Bonestock
It just depends on if the engine can benefit from the changes ie allows the exhaust gases to exit more efficiently. And increasing efficiency is called improving the engines VOLUMETRIC EFFICIENCY. I can not see how the addition of a resonator can have any effect on the engines performance providing it does not change flow +/- by any significant degree. I guess I should also note that when referring to exhaust back pressure its really a misnomer since we are really talking about maintaining exhaust velocity (to aid in expelling the burnt mixture as well as help draw the air and fuel into the combustion chamber ie scavenging like I mentioned before).
I may only have one SVX but I have been in the automotive world on both personal and professional level for quite some time now.
Oh and I guess I should throw in the obligatory hugs and kisses so no one takes offense.  |
That’s OK mate.
This is right, the gas plug that is released when the exhaust valve opens, has a pressure of about 65psi. This gas pressure has to push the gas in the pipe in front of it. So the gas plug has a pressure front. As this plug travels away from the cylinder, it pulls a low pressure behind it that is maintained till the inlet valve opens, to start the inlet gas moving into the cylinder. It is equally important to reduce this gas plug pressure in the pipe as soon as its usefulness is over, we can’t wait till it reaches the end of the exhaust pipe, so we fit the Resonate chamber where the gas plug can expand to reduce the gas pressure, just like it reached the end of the pipe.
This is the gas inertia being used, to increase the Volume Efficiency of the engine, as you say. The US have lagged behind the others by producing larger capacity engines that produce good torque at low engine speeds. So they have not had used the resonate theory like the Japanese or Europeans, to produce the torque at higher engine speeds.
This has been used on engines that produce the Torque under 4500rpm. It loses it usefulness after that speed, as the gas plug only has a speed of about 300ft per sec. So as the engine revs faster, the low pressure it the cylinder, cannot be maintained till the inlet valve opens. It is occurring earlier, when the piston in rising on the exhaust stroke, so we lose the benefit of its help in increasing the VE.
The SVX uses this gas plug to lower the cylinder pressure as the piston is reaching its maximum speed at about 80* ABDC. Reducing the pressure here reduces the power loss, by the piston having to push against a pressure. To get the low pressure in the cylinder that we need to start the inlet flow, we use sound waves (and just for Trevor) or acoustic waves.
When the exhaust valve opens besides the gas pressure, a positive sound wave is released to travel down the pipe, at about 1600 ft per sec. When this reaches the end of the pipe, it expands into the atmosphere, to be replaced with a negative wave that travels back up the pipe, to reach the cylinder as the inlet valve opens. It then travels up the inlet tract to start the inlet sequence.
As the length of the pipe affects when the negative pressure will arrive back at the cylinder, we can’t just use the end of the pipe so we use the resonator to do the same job for the sound waves, as it does for the gas plug, imitate the end of the pipe.
So the SVX design uses the inertia theory to reduce pumping losses and the resonate theory to raise the VE.
Best of both worlds.
Harvey.