LG vs Dynatech cat converter placement
Thread Starter
Pro
Joined: Oct 2004
Posts: 514
Likes: 2
LG vs Dynatech cat converter placement
With the header war raging again, I was reminded of a question that I never got answered while doing my own research.
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe. With the Dynatech, the cats are prior to the crossover, immediately after the header collector.
I am no techie, but it seems like this must have an impact. Just prior to picking up my Corvette, I had an 01 Camaro, and was doing header research. I found that those long tube systems which were street legal, were those that had the cats close up to the header. Those that couldn't get the street legal stamp of approval, had the cats located too far back - that's what I was told anyway, by one manufacturer.
Legality aside though, it would seem that the benefit of the x-pipe would be impacted if it were located after the cats(Dynatech style), since the cats provide some kind of flow impedence. Isn't the whole idea behind the x-pipe, that it lends to a flow situation that better 'pulls' the exhaust out? If this is correct, then the cats would seem to negate that effect. I own the Dynatech, by the way.
I could be way off, and I am hoping some people with the know will chime in.
greg
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe. With the Dynatech, the cats are prior to the crossover, immediately after the header collector.
I am no techie, but it seems like this must have an impact. Just prior to picking up my Corvette, I had an 01 Camaro, and was doing header research. I found that those long tube systems which were street legal, were those that had the cats close up to the header. Those that couldn't get the street legal stamp of approval, had the cats located too far back - that's what I was told anyway, by one manufacturer.
Legality aside though, it would seem that the benefit of the x-pipe would be impacted if it were located after the cats(Dynatech style), since the cats provide some kind of flow impedence. Isn't the whole idea behind the x-pipe, that it lends to a flow situation that better 'pulls' the exhaust out? If this is correct, then the cats would seem to negate that effect. I own the Dynatech, by the way.
I could be way off, and I am hoping some people with the know will chime in.
greg
Burning Brakes
Joined: Feb 2004
Posts: 831
Likes: 0
From: Country Boys Can Survive.
Originally Posted by greg_nate
With the header war raging again, I was reminded of a question that I never got answered while doing my own research.
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe. With the Dynatech, the cats are prior to the crossover, immediately after the header collector.
I am no techie, but it seems like this must have an impact. Just prior to picking up my Corvette, I had an 01 Camaro, and was doing header research. I found that those long tube systems which were street legal, were those that had the cats close up to the header. Those that couldn't get the street legal stamp of approval, had the cats located too far back - that's what I was told anyway, by one manufacturer.
Legality aside though, it would seem that the benefit of the x-pipe would be impacted if it were located after the cats(Dynatech style), since the cats provide some kind of flow impedence. Isn't the whole idea behind the x-pipe, that it lends to a flow situation that better 'pulls' the exhaust out? If this is correct, then the cats would seem to negate that effect. I own the Dynatech, by the way.
I could be way off, and I am hoping some people with the know will chime in.
greg
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe. With the Dynatech, the cats are prior to the crossover, immediately after the header collector.
I am no techie, but it seems like this must have an impact. Just prior to picking up my Corvette, I had an 01 Camaro, and was doing header research. I found that those long tube systems which were street legal, were those that had the cats close up to the header. Those that couldn't get the street legal stamp of approval, had the cats located too far back - that's what I was told anyway, by one manufacturer.
Legality aside though, it would seem that the benefit of the x-pipe would be impacted if it were located after the cats(Dynatech style), since the cats provide some kind of flow impedence. Isn't the whole idea behind the x-pipe, that it lends to a flow situation that better 'pulls' the exhaust out? If this is correct, then the cats would seem to negate that effect. I own the Dynatech, by the way.
I could be way off, and I am hoping some people with the know will chime in.
greg
Le Mans Master
Joined: Mar 2004
Posts: 5,562
Likes: 5
From: South East coast Florida
Below is a post from an ongoing "discussion" on headers titled call Pro' and Cons....
Theory, theory, theory.....
--------------------------------------------------------------------------------
Quote:
Originally Posted by C5XTASY
Ed, I read a very informative article on X-pipes awhile ago. The bottom line was, the closer you can mount an X-pipe to the headers, without anything between the two, the greater the scavenging action. Plugging a cat in, between the headers and X-pipe, will greatly reduce that action. The article tested the car with straight duals, H-pipe and X-pipe. As I recall, it used both dyno runs and 1/4 performance testing as benchmarks. It was really interesting. There was a significant difference in the three setups. As I recall, the X-pipe, with mufflers, outperformed the other two setups without mufflers. I'll post the thing if I can find it.
Ed
Credit for the following response goes to Topcat:
You have to be careful when speaking of exhaust systems and tests of that nature. A lot depends on the cam and the inherent valve timing. An engine can run better with a muffler and tailpipe versus running an open header if the cam isn't suited to an open header/open exhaust system (proven in tests documented in "The Theory of Intake and Header Design").
The theory behind an x-pipe and its location is that, when installed as part of an exhaust system, it can help model the length of a header collector on open headers. It's easier to find the optimum length of collectors with open headers. Just start out long and cut the collector where the highest heat results, i.e. where the paint burns. With systems and x-pipes it's a little more difficult. You can go with programs that estimate the collector length needed for open headers, say 14 inches for example, and use that figure to get close.....but experimentation is key, and selection of cam is important to match the backpressure created by the entire system.
But back to x-pipe theory. Find out how long the collector is supposed to be (run open headers until you get the right length?) and install an x-pipe of a diameter equal to the collector with the junction at the optimum collector length i.e., 14 inches from the collector reducer. The increase in area reflects the scavenge wave back up to the exhaust port at the optimum time (if collector length has been properly selected). I think for an LS-1 with typical bolt-ons and using 1-3/4" dia., 32" long primaries, the collector length should be around 14 to 16 inches, depending on where you want your HP peak. If you look at a catless LG system, you can see that they've designed theirs very close to that.
Cats before the x-pipe will break up the sound waves, like a muffler, and will impact the amplitude before the reflection point in the 'x' and then mess with it again as it travels back to the exhaust port (if it even makes it).
Now - tailpipe theory.
For street-strip applications, the combined cross-sectional area of tailpipes should not exceed the combined cross-sectional area of the header primaries. The ratio should be, by theory,no more than 60%, i.e., for 4 primaries of 1-3/4" (.066813 ft^2) you should use a collector size of 2.75" (0.04125ft^2) to get @ 62% ratio. Street performance should be (by theory) @ 50%, i.e., 2.5" collector. FYI, a 3" collector is a 73.5% ratio. I wonder why the LG's do so well.....unconventional. If i only had a dyno, unlimited time, and a million dollars to settle all of this........
Theory, theory, theory.....
--------------------------------------------------------------------------------
Quote:
Originally Posted by C5XTASY
Ed, I read a very informative article on X-pipes awhile ago. The bottom line was, the closer you can mount an X-pipe to the headers, without anything between the two, the greater the scavenging action. Plugging a cat in, between the headers and X-pipe, will greatly reduce that action. The article tested the car with straight duals, H-pipe and X-pipe. As I recall, it used both dyno runs and 1/4 performance testing as benchmarks. It was really interesting. There was a significant difference in the three setups. As I recall, the X-pipe, with mufflers, outperformed the other two setups without mufflers. I'll post the thing if I can find it.
Ed
Credit for the following response goes to Topcat:
You have to be careful when speaking of exhaust systems and tests of that nature. A lot depends on the cam and the inherent valve timing. An engine can run better with a muffler and tailpipe versus running an open header if the cam isn't suited to an open header/open exhaust system (proven in tests documented in "The Theory of Intake and Header Design").
The theory behind an x-pipe and its location is that, when installed as part of an exhaust system, it can help model the length of a header collector on open headers. It's easier to find the optimum length of collectors with open headers. Just start out long and cut the collector where the highest heat results, i.e. where the paint burns. With systems and x-pipes it's a little more difficult. You can go with programs that estimate the collector length needed for open headers, say 14 inches for example, and use that figure to get close.....but experimentation is key, and selection of cam is important to match the backpressure created by the entire system.
But back to x-pipe theory. Find out how long the collector is supposed to be (run open headers until you get the right length?) and install an x-pipe of a diameter equal to the collector with the junction at the optimum collector length i.e., 14 inches from the collector reducer. The increase in area reflects the scavenge wave back up to the exhaust port at the optimum time (if collector length has been properly selected). I think for an LS-1 with typical bolt-ons and using 1-3/4" dia., 32" long primaries, the collector length should be around 14 to 16 inches, depending on where you want your HP peak. If you look at a catless LG system, you can see that they've designed theirs very close to that.
Cats before the x-pipe will break up the sound waves, like a muffler, and will impact the amplitude before the reflection point in the 'x' and then mess with it again as it travels back to the exhaust port (if it even makes it).
Now - tailpipe theory.
For street-strip applications, the combined cross-sectional area of tailpipes should not exceed the combined cross-sectional area of the header primaries. The ratio should be, by theory,no more than 60%, i.e., for 4 primaries of 1-3/4" (.066813 ft^2) you should use a collector size of 2.75" (0.04125ft^2) to get @ 62% ratio. Street performance should be (by theory) @ 50%, i.e., 2.5" collector. FYI, a 3" collector is a 73.5% ratio. I wonder why the LG's do so well.....unconventional. If i only had a dyno, unlimited time, and a million dollars to settle all of this........
Last edited by mowton; Feb 26, 2005 at 08:21 PM.
Instructor
Joined: Mar 2002
Posts: 239
Likes: 0
From: Fredericksburg VA
There are no holds barred when designing a header exhaust system for a race application. But designing a street legal emissions header is a different story. I think you are aware of some of the differences.
This is from the instructions for the header program on the HeaderDesign site:
"9. Ceramic-coated headers will help minimize the light-off time of your catalytic converters. Locate catalytic converters as close as possible to the collector outlet, but on the downstream side of the H-Pipe, X-pipe, or Y-pipe."
I have had difficulty modelling the influence of the cat when it is placed midway down the collector. There is reflection of the blowdown wave that tends to cancel some of the scavenging wave, but the power output is still excellent with the high-flow cats. Nevertheless, I don't like designing with the cat in the collector.
I use the collector diameter, length and taper to shape the scavenging wave for the specific application. The entry into the X provides an important expansion to terminate the collector length. If the cat or cats are downstream of the X, I can accurately predict what is going on in the primaries and collector in low backpressure systems.
If the cat needs to be upstream of the X, I prefer to design the system as 4-2-1-cat. This type header has two collectors that expand into the pipe with the cat, and up the adjacent collector. But it doesn't mean that the cat will end up close enough to the head for emissions legality (although it may pass emission tests). The primaries for a 4-1 and 4-2-1 header will be similar in length, but the collectors for the 4-2-1 header can be smaller than for the 4-1. The 4-2-1 is also very useful for sidepipe applications, and in high RPM applications where the headers and collectors are too short to reach the X and maintain proper wave timing. It is also a natural for I-4 engines.
So as far as it goes with the cats, you might just have to live with the position in the collector. Fortunately cats flow really well these days.
To size the tailpipes you should be using a percentage of the tributary primary pipe INSIDE area as predicted BY THE PROGRAM on the HeaderDesign site. For race applications (or if you don't care about part-throttle performance) use tailpipes with about 70%-75% of the predicted tributary header primary area. The necessary muffler core diameter will help you make the decision as well.
This is from the instructions for the header program on the HeaderDesign site:
"9. Ceramic-coated headers will help minimize the light-off time of your catalytic converters. Locate catalytic converters as close as possible to the collector outlet, but on the downstream side of the H-Pipe, X-pipe, or Y-pipe."
I have had difficulty modelling the influence of the cat when it is placed midway down the collector. There is reflection of the blowdown wave that tends to cancel some of the scavenging wave, but the power output is still excellent with the high-flow cats. Nevertheless, I don't like designing with the cat in the collector.
I use the collector diameter, length and taper to shape the scavenging wave for the specific application. The entry into the X provides an important expansion to terminate the collector length. If the cat or cats are downstream of the X, I can accurately predict what is going on in the primaries and collector in low backpressure systems.
If the cat needs to be upstream of the X, I prefer to design the system as 4-2-1-cat. This type header has two collectors that expand into the pipe with the cat, and up the adjacent collector. But it doesn't mean that the cat will end up close enough to the head for emissions legality (although it may pass emission tests). The primaries for a 4-1 and 4-2-1 header will be similar in length, but the collectors for the 4-2-1 header can be smaller than for the 4-1. The 4-2-1 is also very useful for sidepipe applications, and in high RPM applications where the headers and collectors are too short to reach the X and maintain proper wave timing. It is also a natural for I-4 engines.
So as far as it goes with the cats, you might just have to live with the position in the collector. Fortunately cats flow really well these days.
To size the tailpipes you should be using a percentage of the tributary primary pipe INSIDE area as predicted BY THE PROGRAM on the HeaderDesign site. For race applications (or if you don't care about part-throttle performance) use tailpipes with about 70%-75% of the predicted tributary header primary area. The necessary muffler core diameter will help you make the decision as well.
Safety Car
Joined: Nov 2002
Posts: 4,394
Likes: 6
From: Melbourne FL
I'm no exhaust engineer either.
But, the theory behing moving the cats closer to the collectors is that it assists with bginging the cat temps up sooner so emission issues can be addressed sooner. The newer high flow cats really don't impede flow as much as older designs.
But, the theory behing moving the cats closer to the collectors is that it assists with bginging the cat temps up sooner so emission issues can be addressed sooner. The newer high flow cats really don't impede flow as much as older designs.
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Originally Posted by HeaderDesign.com
There are no holds barred when designing a header exhaust system for a race application. But designing a street legal emissions header is a different story. I think you are aware of some of the differences.
This is from the instructions for the header program on the HeaderDesign site:
"9. Ceramic-coated headers will help minimize the light-off time of your catalytic converters. Locate catalytic converters as close as possible to the collector outlet, but on the downstream side of the H-Pipe, X-pipe, or Y-pipe."
I have had difficulty modelling the influence of the cat when it is placed midway down the collector. There is reflection of the blowdown wave that tends to cancel some of the scavenging wave, but the power output is still excellent with the high-flow cats. Nevertheless, I don't like designing with the cat in the collector.
I use the collector diameter, length and taper to shape the scavenging wave for the specific application. The entry into the X provides an important expansion to terminate the collector length. If the cat or cats are downstream of the X, I can accurately predict what is going on in the primaries and collector in low backpressure systems.
If the cat needs to be upstream of the X, I prefer to design the system as 4-2-1-cat. This type header has two collectors that expand into the pipe with the cat, and up the adjacent collector. But it doesn't mean that the cat will end up close enough to the head for emissions legality (although it may pass emission tests). The primaries for a 4-1 and 4-2-1 header will be similar in length, but the collectors for the 4-2-1 header can be smaller than for the 4-1. The 4-2-1 is also very useful for sidepipe applications, and in high RPM applications where the headers and collectors are too short to reach the X and maintain proper wave timing. It is also a natural for I-4 engines.
So as far as it goes with the cats, you might just have to live with the position in the collector. Fortunately cats flow really well these days.
To size the tailpipes you should be using a percentage of the tributary primary pipe INSIDE area as predicted BY THE PROGRAM on the HeaderDesign site. For race applications (or if you don't care about part-throttle performance) use tailpipes with about 70%-75% of the predicted tributary header primary area. The necessary muffler core diameter will help you make the decision as well.
This is from the instructions for the header program on the HeaderDesign site:
"9. Ceramic-coated headers will help minimize the light-off time of your catalytic converters. Locate catalytic converters as close as possible to the collector outlet, but on the downstream side of the H-Pipe, X-pipe, or Y-pipe."
I have had difficulty modelling the influence of the cat when it is placed midway down the collector. There is reflection of the blowdown wave that tends to cancel some of the scavenging wave, but the power output is still excellent with the high-flow cats. Nevertheless, I don't like designing with the cat in the collector.
I use the collector diameter, length and taper to shape the scavenging wave for the specific application. The entry into the X provides an important expansion to terminate the collector length. If the cat or cats are downstream of the X, I can accurately predict what is going on in the primaries and collector in low backpressure systems.
If the cat needs to be upstream of the X, I prefer to design the system as 4-2-1-cat. This type header has two collectors that expand into the pipe with the cat, and up the adjacent collector. But it doesn't mean that the cat will end up close enough to the head for emissions legality (although it may pass emission tests). The primaries for a 4-1 and 4-2-1 header will be similar in length, but the collectors for the 4-2-1 header can be smaller than for the 4-1. The 4-2-1 is also very useful for sidepipe applications, and in high RPM applications where the headers and collectors are too short to reach the X and maintain proper wave timing. It is also a natural for I-4 engines.
So as far as it goes with the cats, you might just have to live with the position in the collector. Fortunately cats flow really well these days.
To size the tailpipes you should be using a percentage of the tributary primary pipe INSIDE area as predicted BY THE PROGRAM on the HeaderDesign site. For race applications (or if you don't care about part-throttle performance) use tailpipes with about 70%-75% of the predicted tributary header primary area. The necessary muffler core diameter will help you make the decision as well.
Rod, great post...thanks for the time to put all that in!
Ed
Last edited by C5XTASY; Feb 26, 2005 at 10:40 PM.
Le Mans Master
Joined: Mar 2004
Posts: 5,562
Likes: 5
From: South East coast Florida
I must say, this thread has much more technical content than the name calling one from 3 weeks ago. Interesting reading. As I have stated before, you must compare Apples to Apples to develop valid findings. The new LGM design does sound like it more replicates that of the Dynatechs and other "emmissions friendly" products.
Ed
Ed
Team Owner
Joined: Aug 2003
Posts: 38,314
Likes: 35
Originally Posted by greg_nate
With the header war raging again, I was reminded of a question that I never got answered while doing my own research.
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe....
The differences that aren't mentioned between the LG header system and the Dynatech header system is with the placement of the cats.
With the LG system, the cats are AFTER the crossover in the x-pipe....
http://ls1howto.com/howto/c5/lgheade...gm_headers.jpg
It will be interesting to see what, if any performance differences, such a relocation of the cats would produce.
Last edited by '06 Quicksilver Z06; Feb 26, 2005 at 11:35 PM.
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Pro
Joined: Feb 2005
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Putting the cats after the Xpipe will make a big difference in scavenging.
Cats (especially mettalic substrate) are really like high flow mufflers.
Having them after the Xpipe allows the Xpipe to function as it was designed.
Having them before the Xpipe affects it's ability to equalize pressure between the two banks.
This would likely be most evident in the amount midrange torque produced.
I believe having the X before the cats is illegal though in most areas.
Cats (especially mettalic substrate) are really like high flow mufflers.
Having them after the Xpipe allows the Xpipe to function as it was designed.
Having them before the Xpipe affects it's ability to equalize pressure between the two banks.
This would likely be most evident in the amount midrange torque produced.
I believe having the X before the cats is illegal though in most areas.
Thread Starter
Pro
Joined: Oct 2004
Posts: 514
Likes: 2
This brought up a few more questions:
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
2. Just to clarify: all around, not counting emissions, cats after the x-pipe are preferred. Correct or not correct?
3. The only pictures I could find of the LG header system showed the cats downstream from the x-pipe: did they change their design? Has their performance changed as a result? Any info on this? Hopefully Lou will chime on on this one himself.
Thanks again for all the good technical info. I really appreciate all the great feedback!
greg
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
2. Just to clarify: all around, not counting emissions, cats after the x-pipe are preferred. Correct or not correct?
3. The only pictures I could find of the LG header system showed the cats downstream from the x-pipe: did they change their design? Has their performance changed as a result? Any info on this? Hopefully Lou will chime on on this one himself.
Thanks again for all the good technical info. I really appreciate all the great feedback!
greg
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Originally Posted by greg_nate
This brought up a few more questions:
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
2. Just to clarify: all around, not counting emissions, cats after the x-pipe are preferred. Correct or not correct?
3. The only pictures I could find of the LG header system showed the cats downstream from the x-pipe: did they change their design? Has their performance changed as a result? Any info on this? Hopefully Lou will chime on on this one himself.
Thanks again for all the good technical info. I really appreciate all the great feedback!
greg
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
2. Just to clarify: all around, not counting emissions, cats after the x-pipe are preferred. Correct or not correct?
3. The only pictures I could find of the LG header system showed the cats downstream from the x-pipe: did they change their design? Has their performance changed as a result? Any info on this? Hopefully Lou will chime on on this one himself.
Thanks again for all the good technical info. I really appreciate all the great feedback!
greg
Originally Posted by nwdanner
Well, I received my set of LGs last week and will be having them installed here in the next couple of weeks. I'm very curious about the power differences regarding the placement of the cats; before/after the x-pipe. I asked Lou this question recently and he responded that there will be a "slight power increase" when placing the cats after the x-pipe. So, I'm going to do a base dyno on my car before the header install followed by two runs afterwards (with tuning of course). The last two runs will differ only by the location of the cats. I'll post the dyno graphs afterwards as I know you guys will be curious to see the results.
Moderator
Joined: Jun 2004
Posts: 22,780
Likes: 943
I have LG Pro Long tubes with cats and I put my cats ahead of the X-pipe. I dynoed yesterday @ LGM with no tune for the headers and got 382rwhp and 361 rwtq. TQ was 310 @ 2700 rpm and 360 by 4500 and didnt strat to fall until 5500rpm. Does anyone have a dyno of no cats or with cats after the x pipe?
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Originally Posted by greg_nate
This brought up a few more questions:
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
1. Scavenging helps torque and not power - or vice versa? I thought I understood his post, but after reading your response, I guess I didn't. My understanding of scavenging was that it created a negative pressure which helped "suck" the exhaust coming out of the cylinder - thus lettting the piston do less "pushing" of the exhaust gas out. Help me out here please!
I understand it. There are other benefits to an X-pipe, as far as "smoothing" the exhaust sound, but that's a different discussion, unless you want to get into how an X-pipe does that, relative to an H-pipe.
Ed
