Dual pipe
#2
03-08-2006, 07:05 PM
RE: Dual pipe
Dual straights (or dual with mufflers) will sound like two 3 cylinder motors. Won't sounds as bad with a x-over pipe, but still won't sound good. Sized correctly, it would offer decent performance, but 2 catalytic converters would be required if the vehicle was factory equiped with a cat.
a single 3" is still WAY too large for the motor. You shouldn't need any more than 2-3/4" pipe on the CAT back (assuming you have a cat on there - you didn't specify the year). No muffler shop in their right mind will remove the factory cat and they shouldn't assemble an exhaust system on a vehicle without catalytic converter seeing as how they can get fined just the same as you if caught.
With that said, the best gains can be found with a set of headers and a custom y-pipe and possibly an aftermarket higher flowing cat & muffler. The stock exhaust pipe size after the cat isn't the restriction.
If you go too big, you'll lose so much torque down low that you would run slower in the 1/4 because the lower restriction up high in the rpm band wouldn't gain enough to make up for the slower start.
a single 3" is still WAY too large for the motor. You shouldn't need any more than 2-3/4" pipe on the CAT back (assuming you have a cat on there - you didn't specify the year). No muffler shop in their right mind will remove the factory cat and they shouldn't assemble an exhaust system on a vehicle without catalytic converter seeing as how they can get fined just the same as you if caught.
With that said, the best gains can be found with a set of headers and a custom y-pipe and possibly an aftermarket higher flowing cat & muffler. The stock exhaust pipe size after the cat isn't the restriction.
If you go too big, you'll lose so much torque down low that you would run slower in the 1/4 because the lower restriction up high in the rpm band wouldn't gain enough to make up for the slower start.
#3
03-08-2006, 07:21 PM
RE: Dual pipe
Well its a 1999 4 door blazer nothing really done to it just stock... they said something about taking the bolts from the converter and welding from there an Y-ing out the pipes... and it is suppose to be straight pipes no mufflers.. thanks for the reply i really dont want to do this the wrong way...
#4
03-08-2006, 08:11 PM
RE: Dual pipe
Ok, well, I just had to add that tid-bit in about the cat because there are strict penalties if caught without a catalytic converter.
To me straight pipes would be from the headers back, but that sounded good on v8s due to 4 cylinders firing per pipe LOL. 3 just sounds weird. Since that's not what you were looking to do, no problem.
Anyway, dual straight pipes from the cat back wouldn't net you much over the same thing with high flowing mufflers. The straight pipes would tend to sound raspy and would probably crackle down from a higher rpm. I personally hate the sound of open exhaust in anything other than acceleration. Also, if not done properly, the tone would probably drone when cruising at highway speeds.
Others here have gone with aftermarket cat back systems. Most have just put it on and either liked the tone or haven't, but they thought it helped them out (ie made the truck faster). Another member here bought an aftermarket kit, installed it, and lost time in the 1/4 mile due to the loss in low end torque that I spoke of earlier.
There are a few good explainations of exhaust theories available on the intenet. It is a highly technical field. A good explaination of header design can be found HERE and the main theories extend all the way to the exhaust tip. Another good summary is listed below and was found HERE.
[quote]Exhaust System Diameter and Engine Horsepower- A popular idea is to select/size the exhaust system components to the engine's horsepower output. This idea typically attributes a header diameter or an exhaust system diameter to a particular horsepower level. To resolve this, look at how an engine operates and consider one cylinder. The cylinder will move a volume of air based on its crankshaft geometry, rpm, and sealing capability. The amount of air that can enter the cylinder is dependant on the intake flow capability, crank geometry, rpm, and valve timing as a minimum consideration. Likewise, the amount of air that exits the cylinder is dependent on the same characteristics.
An engine's output is usually thought of in terms of horsepower. Actually, an engine produces torque, and the horsepower is calculated through a units conversion. The amount of torque an engine can produce is directly related to the amount of cylinder pressure generated. This is all affected by the same previous characteristics (intake and exhaust capability, crank geometry, rpm, valvetiming, etc). So basically an engine's power output is about air exchange capability. Using this line of thinking, look at the exhaust path again. The exhaust system is more reflective of the engine's ability to move air, as opposed to horsepower numbers. Engine output does not address the breathing aspects of the engine and is probably not a good rule to use for exhaust sizing.
There is a very good reason that tuners/engineers/specialist have attempted to assign exhaust to intake relationships around 70-80% for a typical natural aspirated set-up. In non-detailed terms, it is a range that offers a good balance for power capability. Other relationships, such as 1:1, are used and they work very well, but these methods have to be applied and tuned for very specific circumstances. This relationship does not stop on the flow bench, it goes all the way from the intake path opening to the exhaust system termination. In short, try to maintain exhaust sizes that are inline with the intake capability. Also, do not stop your analysis at the intake and exhaust paths. If the engine already has the camshaft, look at the valve events. If the specs favor a restricted exhaust (indicated by early and wider exhaust openings with wider lobe separation angles), then size it accordingly by using exhaust components with smaller cross-sections. If the valve timing specs favor the intake, the
To me straight pipes would be from the headers back, but that sounded good on v8s due to 4 cylinders firing per pipe LOL. 3 just sounds weird. Since that's not what you were looking to do, no problem.
Anyway, dual straight pipes from the cat back wouldn't net you much over the same thing with high flowing mufflers. The straight pipes would tend to sound raspy and would probably crackle down from a higher rpm. I personally hate the sound of open exhaust in anything other than acceleration. Also, if not done properly, the tone would probably drone when cruising at highway speeds.
Others here have gone with aftermarket cat back systems. Most have just put it on and either liked the tone or haven't, but they thought it helped them out (ie made the truck faster). Another member here bought an aftermarket kit, installed it, and lost time in the 1/4 mile due to the loss in low end torque that I spoke of earlier.
There are a few good explainations of exhaust theories available on the intenet. It is a highly technical field. A good explaination of header design can be found HERE and the main theories extend all the way to the exhaust tip. Another good summary is listed below and was found HERE.
[quote]Exhaust System Diameter and Engine Horsepower- A popular idea is to select/size the exhaust system components to the engine's horsepower output. This idea typically attributes a header diameter or an exhaust system diameter to a particular horsepower level. To resolve this, look at how an engine operates and consider one cylinder. The cylinder will move a volume of air based on its crankshaft geometry, rpm, and sealing capability. The amount of air that can enter the cylinder is dependant on the intake flow capability, crank geometry, rpm, and valve timing as a minimum consideration. Likewise, the amount of air that exits the cylinder is dependent on the same characteristics.
An engine's output is usually thought of in terms of horsepower. Actually, an engine produces torque, and the horsepower is calculated through a units conversion. The amount of torque an engine can produce is directly related to the amount of cylinder pressure generated. This is all affected by the same previous characteristics (intake and exhaust capability, crank geometry, rpm, valvetiming, etc). So basically an engine's power output is about air exchange capability. Using this line of thinking, look at the exhaust path again. The exhaust system is more reflective of the engine's ability to move air, as opposed to horsepower numbers. Engine output does not address the breathing aspects of the engine and is probably not a good rule to use for exhaust sizing.
There is a very good reason that tuners/engineers/specialist have attempted to assign exhaust to intake relationships around 70-80% for a typical natural aspirated set-up. In non-detailed terms, it is a range that offers a good balance for power capability. Other relationships, such as 1:1, are used and they work very well, but these methods have to be applied and tuned for very specific circumstances. This relationship does not stop on the flow bench, it goes all the way from the intake path opening to the exhaust system termination. In short, try to maintain exhaust sizes that are inline with the intake capability. Also, do not stop your analysis at the intake and exhaust paths. If the engine already has the camshaft, look at the valve events. If the specs favor a restricted exhaust (indicated by early and wider exhaust openings with wider lobe separation angles), then size it accordingly by using exhaust components with smaller cross-sections. If the valve timing specs favor the intake, the
#7
07-04-2006, 06:08 PM
RE: Dual pipe
have flowmaster 40 series single into dual 3" straight out the back and it runs and sounds good at idle but runs and sounds like a pinto with an exhaust leak down the highway...not happy and going back to stock really soon
#8
07-05-2006, 12:34 PM
RE: Dual pipe
a quick little side note - i was thinking of a similar setup for the 92 4.3L TBI, i was going to slip after the cat to twin 2 inch pipes out the back. would that keep up performance and add a nice rumble out the back?
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