Gutting a cat... with pics!
#16
Rennlist Member
#17
inline 4s can have various firing orders depending on the crank design, a typical 1-3-4-2 using a tri Y will pair 1-3 and 2-4 primaries,
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve
#19
Rennlist Member
inline 4s can have various firing orders depending on the crank design, a typical 1-3-4-2 using a tri Y will pair 1-3 and 2-4 primaries,
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve
Also, the Japanese version had a shorter CAT with only 1 element in the system while the USA version used 2 of the same elements in series, both in the same B pipe position. The car barely passed NOX in CA smog testing and had to be really hot to pass.
#21
I should have pointed out there there actually 2 different Tri Y configurations commonly used on inline 4s
The one I described above is called non-sequential, there is another called sequential where consecutive firing cylinders are paired, so one branch gets B-B-S-S then the other gets B-B-S-S then the 2 branches are later merged into BB-SS. This is a compromise between, the max torque spread of the first set up and the max hp at a specific rpm of a 4 into 1 collector. The consecutive B-B doesn't load the collector as in the V8 because the firing pulses are 180* crankshaft degrees apart in the 4 and only 90* apart in the V8, the flat 6 is blessed w/ 120* crankshaft degrees between firing cylinders so the typical collector only sees one firing every 240*
The one I described above is called non-sequential, there is another called sequential where consecutive firing cylinders are paired, so one branch gets B-B-S-S then the other gets B-B-S-S then the 2 branches are later merged into BB-SS. This is a compromise between, the max torque spread of the first set up and the max hp at a specific rpm of a 4 into 1 collector. The consecutive B-B doesn't load the collector as in the V8 because the firing pulses are 180* crankshaft degrees apart in the 4 and only 90* apart in the V8, the flat 6 is blessed w/ 120* crankshaft degrees between firing cylinders so the typical collector only sees one firing every 240*
#22
Rennlist Member
I went to Dansk muffler in Viborg, Denmark yesterday and found the factory, really called JP Group a/s a huge manufacturer of a lot of different auto parts. I was given a factory tour and pictures will follow later.
I ordered their Cat bypass pipe system, part number 93.400S, for track use shown below. It is all stainless steel and mandrel bent from one piece of tubing with one O2 probe bung for a '95 Bischoff exhaust system:
I ordered their Cat bypass pipe system, part number 93.400S, for track use shown below. It is all stainless steel and mandrel bent from one piece of tubing with one O2 probe bung for a '95 Bischoff exhaust system:
#24
I went to Dansk muffler in Viborg, Denmark yesterday and found the factory, really called JP Group a/s a huge manufacturer of a lot of different auto parts. I was given a factory tour and pictures will follow later.
I ordered their Cat bypass pipe system, part number 93.400S, for track use shown below. It is all stainless steel and mandrel bent from one piece of tubing with one O2 probe bung for a '95 Bischoff exhaust system:
I ordered their Cat bypass pipe system, part number 93.400S, for track use shown below. It is all stainless steel and mandrel bent from one piece of tubing with one O2 probe bung for a '95 Bischoff exhaust system:
#26
Rennlist Member
After all the discussion here of even firiring versus uneven firing engines, and noting that Porsche has never used a crossover system in any of their dedicated racing 911 cars, I figured an X pipe would probably do no good and may do harm.
#27
Rennlist Member
#28
Rennlist Member
Sort of, inline 4s often use a Tri-Y exhaust because it's easy to construct and package, the pairing of primaries depends on the firing order, 2 alternately firing cylinders will be paired on one section and the other 2 which are also alternately firing cylinders will be paired in another section, then the 2 sections will be merged, this is essentially what *** does only they pair the left alternate firing bank, pair the right alternately firing bank then merge the banks, the lengths of the primary and secondaries are carefully selected so that the gas flow and acoustics of one cylinder are used to enhance the flow of another paired cylinder, the goal is to spread and enhance the torque curve, as opposed to totally separate pipes or 4 into 1 collectors used on odd fire engines which generally are tuned for max hp but only over a very narrow rpm range, this design can also be used on V8s
inline 4s can have various firing orders depending on the crank design, a typical 1-3-4-2 using a tri Y will pair 1-3 and 2-4 primaries,
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve
inline 4s can have various firing orders depending on the crank design, a typical 1-3-4-2 using a tri Y will pair 1-3 and 2-4 primaries,
so they go B-S into the one collector then B-S into the other collector than the 2 collectors are merged, into a B-S-B-S what happens w/ these is that the acoustic signal that enhances exhaust port flow occurs at 2 separate rpm pts because of the 2 separate merges, this smears the enhanced torque curve over a wider range than a single stronger signal generated by a solitary collector which only affects a single narrow section of the rpm curve
That said, for a 4-cylinder, I do not believe that a 4-2-1 is better (from an exhaust standpoint) than a properly designed 4-1 system due to the even fire nature of the engine. Tri-Ys can be lighter, and as said, package nicely, particulary in FWD applications.
Who is ***?
BTW, is there a difference in the exhaust note between the Bischoff and Gillet exhaust?
#29
Rennlist Member
I should have pointed out there there actually 2 different Tri Y configurations commonly used on inline 4s
The one I described above is called non-sequential, there is another called sequential where consecutive firing cylinders are paired, so one branch gets B-B-S-S then the other gets B-B-S-S then the 2 branches are later merged into BB-SS. This is a compromise between, the max torque spread of the first set up and the max hp at a specific rpm of a 4 into 1 collector. The consecutive B-B doesn't load the collector as in the V8 because the firing pulses are 180* crankshaft degrees apart in the 4 and only 90* apart in the V8, the flat 6 is blessed w/ 120* crankshaft degrees between firing cylinders so the typical collector only sees one firing every 240*
The one I described above is called non-sequential, there is another called sequential where consecutive firing cylinders are paired, so one branch gets B-B-S-S then the other gets B-B-S-S then the 2 branches are later merged into BB-SS. This is a compromise between, the max torque spread of the first set up and the max hp at a specific rpm of a 4 into 1 collector. The consecutive B-B doesn't load the collector as in the V8 because the firing pulses are 180* crankshaft degrees apart in the 4 and only 90* apart in the V8, the flat 6 is blessed w/ 120* crankshaft degrees between firing cylinders so the typical collector only sees one firing every 240*
After all the discussion here of even firiring versus uneven firing engines, and noting that Porsche has never used a crossover system in any of their dedicated racing 911 cars, I figured an X pipe would probably do no good and may do harm.
#30
The correct pairing would be 1-4 and 3-2 to get the even firing pulses. I have never seen any other firing order in inline 4s that would have an alternative pairing. Flat 4s (VWs and 914 - like I said VWs ) require that cylinders be paired across banks and makes it difficult to build a properly paired tri-y header. I like 4-1s for these applications.
That said, for a 4-cylinder, I do not believe that a 4-2-1 is better (from an exhaust standpoint) than a properly designed 4-1 system due to the even fire nature of the engine. Tri-Ys can be lighter, and as said, package nicely, particulary in FWD applications.
Who is ***?
BTW, is there a difference in the exhaust note between the Bischoff and Gillet exhaust?
That said, for a 4-cylinder, I do not believe that a 4-2-1 is better (from an exhaust standpoint) than a properly designed 4-1 system due to the even fire nature of the engine. Tri-Ys can be lighter, and as said, package nicely, particulary in FWD applications.
Who is ***?
BTW, is there a difference in the exhaust note between the Bischoff and Gillet exhaust?
here is 1&2, 3&4 pairing
here 1&3, 2&4 pairing
here a 1&4, 2&3
Which you use depends on firing order and hoe you want to affect the torque curve
non sequential tri-y has the widest torque spread, 4 into 1 the narrowest but also the most peak hp, non sequential tri-y is in the middle
When I raced Honda MC we played around w/ this a lot, I see that current 4 cyl inline superbikes are also playing w/ crank variations to further alter the torque curves