FIX for loss of torque and MPG from dual exhaust
02-17-2009, 06:00 AM
#21
JK Junkie
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There are scavenging effects which clear exhaust gases from the cylinders that will absolutely create a loss of power when proper exhaust velocity isn't maintained. It doesn't just change rpm power bands as we are dealing with a finite set of power produced by the engine. There is no additional power to be made by anything more than a 2.5" exhaust without some sort of forced air.
Conversely, a smaller diameter pipe will change the torque and hp curves, but will also limit high rpm power. All too often it is discussed as a matter of adding back pressure, while it's really a matter of exhaust gas speed. There is a ceiling on how much exhaust gas you can get through the pipe, and with a 2" pipe you won't make much if any additional power over 3500 rpm.
Conversely, a smaller diameter pipe will change the torque and hp curves, but will also limit high rpm power. All too often it is discussed as a matter of adding back pressure, while it's really a matter of exhaust gas speed. There is a ceiling on how much exhaust gas you can get through the pipe, and with a 2" pipe you won't make much if any additional power over 3500 rpm.
02-17-2009, 12:40 PM
#23
JK Enthusiast
Thread Starter
For what it is worth - I have regained my lost torque at low RPMs and I have plenty of power at higher RPMS. The acceleration is must better than stock.
I am on my second tank of gas since installing the venturi and I am averaging over 16 mpg in the city and close to 20 on the highway (20.7 to be exact).
I am on my second tank of gas since installing the venturi and I am averaging over 16 mpg in the city and close to 20 on the highway (20.7 to be exact).
There are scavenging effects which clear exhaust gases from the cylinders that will absolutely create a loss of power when proper exhaust velocity isn't maintained. It doesn't just change rpm power bands as we are dealing with a finite set of power produced by the engine. There is no additional power to be made by anything more than a 2.5" exhaust without some sort of forced air.
Conversely, a smaller diameter pipe will change the torque and hp curves, but will also limit high rpm power. All too often it is discussed as a matter of adding back pressure, while it's really a matter of exhaust gas speed. There is a ceiling on how much exhaust gas you can get through the pipe, and with a 2" pipe you won't make much if any additional power over 3500 rpm.
Conversely, a smaller diameter pipe will change the torque and hp curves, but will also limit high rpm power. All too often it is discussed as a matter of adding back pressure, while it's really a matter of exhaust gas speed. There is a ceiling on how much exhaust gas you can get through the pipe, and with a 2" pipe you won't make much if any additional power over 3500 rpm.
02-17-2009, 12:43 PM
#24
JK Enthusiast
Thread Starter
02-17-2009, 01:00 PM
#26
JK Junkie
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Having a pinch point or squeezing the tube diameter for a few inches is quite different than running narrower pipe the length of the exhaust. What it does is increases velocity though that section pushes through a portion of the dead spot in the exhaust. Kind of like putting your thumb at the end of the hose to increase speed, and the scavenging effect of the venturi serves scavenging purposes on the other side.
02-17-2009, 01:31 PM
#28
JK Enthusiast
Thread Starter
JPop,
You may be right....but it seems to be working
You may be right....but it seems to be working
Having a pinch point or squeezing the tube diameter for a few inches is quite different than running narrower pipe the length of the exhaust. What it does is increases velocity though that section pushes through a portion of the dead spot in the exhaust. Kind of like putting your thumb at the end of the hose to increase speed, and the scavenging effect of the venturi serves scavenging purposes on the other side.
02-17-2009, 01:59 PM
#29
JK Junkie
I am using the Unichip on 87 pump and I am already getting 16 in town and 20 on the highway on 35's. But the unichip was tuned for the exhaust and intake. I wonder if I did this could I squeeze a bit more out of it... For 15 bucks it sure would seem worth a shot.
