Exhaust Idea
08-21-2012, 08:50 AM
#1
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Exhaust Idea I've definitely wanted to do something about the sound of an LS(x). Not that I have something against a big V8, but I don't think it matches what I have it in. I currently have a 6.2L that is going in the back of an SLC (check picture below). I was thinking about doing 180 degree headers but wondering if anyone has tried something similar to what I propose below
. I have a thought on a header design,, but not sure if it would be rubbish or not, but here is the concept.
What gives V8's it's "rumble" is the double pulses combined with a long pause between firing pulses. Here is the breakdown.
An LS(x) firing order is 1,8,7,2,6,5,4,3
The (*) represent pauses between the pulses
L Bank 1*7**5*31*7**5*3
R Bank 8*26*4**8*26*4*
Now what if you lengthened runners 1 & 7 on the left bank,, and 6 & 4 on the right. They would be considerably longer to compensate for the short exhaust pulse timing between (3 and 1) and (2 and 6). Pretty much trying to make pulses show up at the collector more evenly.
Think about 4 cars showing up at an intersection. Two of them always leave early, so to get them there "on time" you make the road to the intersection a little longer for the early goers, so they all show up properly staggered.
My "guess" would be that (1 & 7) and (6 & 4), would have to have an extra length that would increase the volume of the runners to that of half of the cylinder volume. Another question would be the pros & cons (theorizing here)
Cons:
Header length may not be optimal for all runners to take advantage of the "pulse" scavenging per cylinder cycles.
Pros:
Increase scavenging at the collector because the pulses will arrive more evenly
This is actually mine in the garage just after it arrived. It's going to be a while before I get to actually work on it (I'm overseas)
. I have a thought on a header design,, but not sure if it would be rubbish or not, but here is the concept.
What gives V8's it's "rumble" is the double pulses combined with a long pause between firing pulses. Here is the breakdown.
An LS(x) firing order is 1,8,7,2,6,5,4,3
The (*) represent pauses between the pulses
L Bank 1*7**5*31*7**5*3
R Bank 8*26*4**8*26*4*
Now what if you lengthened runners 1 & 7 on the left bank,, and 6 & 4 on the right. They would be considerably longer to compensate for the short exhaust pulse timing between (3 and 1) and (2 and 6). Pretty much trying to make pulses show up at the collector more evenly.
Think about 4 cars showing up at an intersection. Two of them always leave early, so to get them there "on time" you make the road to the intersection a little longer for the early goers, so they all show up properly staggered.
My "guess" would be that (1 & 7) and (6 & 4), would have to have an extra length that would increase the volume of the runners to that of half of the cylinder volume. Another question would be the pros & cons (theorizing here)
Cons:
Header length may not be optimal for all runners to take advantage of the "pulse" scavenging per cylinder cycles.
Pros:
Increase scavenging at the collector because the pulses will arrive more evenly
This is actually mine in the garage just after it arrived. It's going to be a while before I get to actually work on it (I'm overseas)
08-21-2012, 12:04 PM
#2
If the pulses arrive at the same time you will effectively get interference. You get better scavenging if they come out inline and can foolow in the others "wake" so to speak. That is why X-pipes are so popular. They allow both sides to see more low pressure zones.
08-21-2012, 12:26 PM
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I think you might have misread. The goal was not to get the pulses to arrive at the same time. It was to "delay" the 2nd pulse of the double pulse.
The left bank you would delay pulse 1 & 7 so that they arrive later than usual
One the right bank you would delay 6 & 4
Instead of this
L Bank 1*7**5*31*7**5*3
R Bank 8*26*4**8*26*4*
It would look more like this
L Bank 1*7*5*3#1#7*5*3
R Bank 8*2#6#4*8*6*4
The (*) represents the normal space between pules
The (#) represents the added delay due to extra piping
I think it would even the firing up quite a bit.
The left bank you would delay pulse 1 & 7 so that they arrive later than usual
One the right bank you would delay 6 & 4
Instead of this
L Bank 1*7**5*31*7**5*3
R Bank 8*26*4**8*26*4*
It would look more like this
L Bank 1*7*5*3#1#7*5*3
R Bank 8*2#6#4*8*6*4
The (*) represents the normal space between pules
The (#) represents the added delay due to extra piping
I think it would even the firing up quite a bit.
08-21-2012, 12:44 PM
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Flat Plane crank would work, but I don't think it would be desirable nor economic to say the least
1) Flat plane crank has 1.44x the vibration of a 4 cylinder of the same stroke and piston weight. Unless you used exotic materials or destroked the heck out of it, it would vibrate itself apart
2) If you destroked it, you would have to make up the power somewhere. Since horsepower is a product of torque x RPM, and you are losing torque, you have to make up for it with RPM. On a pushrod engine that is not easy, and you will spend a ton to get 8500-9000 rpm reliably.
3) Vibration on a flat plane causes a lot of wear on the bearings. You would certainly not get much over 100k miles on it, if you are lucky.
The cost of a billet crank and cam isn't too bad. If that was the only extra cost, I wouldn't mind spending an extra $1K-$2K for a more exotic sound, but I don't think you could have a 6.8L stroked flat plane crank without the think shaking itself apart like a weed wacker.
1) Flat plane crank has 1.44x the vibration of a 4 cylinder of the same stroke and piston weight. Unless you used exotic materials or destroked the heck out of it, it would vibrate itself apart
2) If you destroked it, you would have to make up the power somewhere. Since horsepower is a product of torque x RPM, and you are losing torque, you have to make up for it with RPM. On a pushrod engine that is not easy, and you will spend a ton to get 8500-9000 rpm reliably.
3) Vibration on a flat plane causes a lot of wear on the bearings. You would certainly not get much over 100k miles on it, if you are lucky.
The cost of a billet crank and cam isn't too bad. If that was the only extra cost, I wouldn't mind spending an extra $1K-$2K for a more exotic sound, but I don't think you could have a 6.8L stroked flat plane crank without the think shaking itself apart like a weed wacker.
08-21-2012, 10:54 PM
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If you look at an LS(x), or any large V8 for that matter, you will see that the crank throws are 90 degrees from another. If you looked straight down a crossplane crank, you would look like a cross (+),,
A crossplane crank is balanced in the first order. Meaning the up and down vibration cause by pistons traveling at different speeds does not exist. However, it is not balanced end to end, so there is a need for heavy counterweights to fix this. Also, the firing order of any crossplane crank (due to design) has an uneven firing order and cannot be changed to an even (L,R,L,R,R,L,R,L). So you get a double pulse and a big gap somewhere in the firing order on each bank
A flatplane crank looks just like a 4 cylinder crank. So if you were to look at a flatplane crank engine without the heads on. You would see pistons (1 & 7), or (2 & 8), or (3 & 5) or (4 & 6) at the top at the same time. It's actually a simpler design than a crossplane crank.
The advantages of a flatplane crank are:
-Lighter - No need for heavy counterweights
- Better exhaust scavenging because the firing order is even
- Sound (that is a preference), because it will sound like 2 4 cylinders running in parallel. A more Italian exotic engine sound. But would sound odd on in a 69 Camaro.
Hope that clears it up. If you follow the link above posted by hookemdevil. You will see physically how they look different.
A crossplane crank is balanced in the first order. Meaning the up and down vibration cause by pistons traveling at different speeds does not exist. However, it is not balanced end to end, so there is a need for heavy counterweights to fix this. Also, the firing order of any crossplane crank (due to design) has an uneven firing order and cannot be changed to an even (L,R,L,R,R,L,R,L). So you get a double pulse and a big gap somewhere in the firing order on each bank
A flatplane crank looks just like a 4 cylinder crank. So if you were to look at a flatplane crank engine without the heads on. You would see pistons (1 & 7), or (2 & 8), or (3 & 5) or (4 & 6) at the top at the same time. It's actually a simpler design than a crossplane crank.
The advantages of a flatplane crank are:
-Lighter - No need for heavy counterweights
- Better exhaust scavenging because the firing order is even
- Sound (that is a preference), because it will sound like 2 4 cylinders running in parallel. A more Italian exotic engine sound. But would sound odd on in a 69 Camaro.
Hope that clears it up. If you follow the link above posted by hookemdevil. You will see physically how they look different.
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08-22-2012, 10:06 AM
#8
Thanks, I did take a look at his link.
My interest is in performance, is there a performance advatage and if so what is it? I can see how less weight would make me think higher rpms, but you mentioned vibration, so does this limit you?
Not to be a smart ****, but I do understand what you are talking about on orders of vibration. I am a vibration analysist at present. I run a Windrock 6320 Vibration Analyzer and all I do all day long is trap and process this type of data on iarge industrial machines. I have wanted to utilize this equipment on our engines for quite some time but I cannot because of the changing rpm. The engine has to be at a steady rpm to trap good quality data for processing.
Besides a one off custom build does anyone know if these shafts are being produced for the LS by someone?
Why does the OEM not utilize the flatplane design?
My interest is in performance, is there a performance advatage and if so what is it? I can see how less weight would make me think higher rpms, but you mentioned vibration, so does this limit you?
Not to be a smart ****, but I do understand what you are talking about on orders of vibration. I am a vibration analysist at present. I run a Windrock 6320 Vibration Analyzer and all I do all day long is trap and process this type of data on iarge industrial machines. I have wanted to utilize this equipment on our engines for quite some time but I cannot because of the changing rpm. The engine has to be at a steady rpm to trap good quality data for processing.
Besides a one off custom build does anyone know if these shafts are being produced for the LS by someone?
Why does the OEM not utilize the flatplane design?
08-22-2012, 11:48 AM
#9
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I didn't take that as you being a smart ****.
But one of the main reason it is not OEM in most cars is because the crank, rods and pistons would have to be extremely light weight and expensive.
Yes, RPM is limited because the faster the pistons are moving, the worse the vibration. If you have noticed, it too Ferrari 60 years to come up with a flat plane crank V8, and it's still only a 4.5L and has a stroke of only 81mm.
I think if you were going to go through the trouble of a flat plane crank, you might as well do it on a DOHC engine, such as (you might cringe on this one), a Coyote 5.0 engine. The valvetrain has already been tested to over 8000rpm (I believe 8700rpm). The the much lighter crank I am betting it would be nearly the same weight as an LS(x), but I am not positive.
GM nor anyone else will really mass produce this because the engines would vibrate themselves to pieces, so there is no durability in it.
I think the only really advantage you could get is in drag racing, where a few passes is all you need. Then you can blast a long stroked flat plane to 9000rpm down the strip, an the next day rebuild it. The light weight of the crank would allow more HP to the wheels, and the even firing would mean greater HP from scavenging.
Trust me, if anyone did this I would jump on it. Right now I'm stuck between 180 degree headers, and X-Pipe (last alternative) and maybe my crazy header idea.
But one of the main reason it is not OEM in most cars is because the crank, rods and pistons would have to be extremely light weight and expensive.
Yes, RPM is limited because the faster the pistons are moving, the worse the vibration. If you have noticed, it too Ferrari 60 years to come up with a flat plane crank V8, and it's still only a 4.5L and has a stroke of only 81mm.
I think if you were going to go through the trouble of a flat plane crank, you might as well do it on a DOHC engine, such as (you might cringe on this one), a Coyote 5.0 engine. The valvetrain has already been tested to over 8000rpm (I believe 8700rpm). The the much lighter crank I am betting it would be nearly the same weight as an LS(x), but I am not positive.
GM nor anyone else will really mass produce this because the engines would vibrate themselves to pieces, so there is no durability in it.
I think the only really advantage you could get is in drag racing, where a few passes is all you need. Then you can blast a long stroked flat plane to 9000rpm down the strip, an the next day rebuild it. The light weight of the crank would allow more HP to the wheels, and the even firing would mean greater HP from scavenging.
Trust me, if anyone did this I would jump on it. Right now I'm stuck between 180 degree headers, and X-Pipe (last alternative) and maybe my crazy header idea.
08-22-2012, 12:21 PM
#10
All that makes sense.
If your looking for the sound I would think the three exhaust ideas you have are going to be the best economical sulutions. I would think you could get there with the unequal length headers pretty easily. Sounds like something Kooks could handle for you. They might need the car in hand to do it though.
As for your car. Can you give some more details on it? It is one sick looking ride. I would love to pick something like that up. Is it a "kit" type car? Where do they sell them? Have any other pictures of it? Any and all details of it would be nice please.
Keep us up to date on your build. Love the car.
If your looking for the sound I would think the three exhaust ideas you have are going to be the best economical sulutions. I would think you could get there with the unequal length headers pretty easily. Sounds like something Kooks could handle for you. They might need the car in hand to do it though.
As for your car. Can you give some more details on it? It is one sick looking ride. I would love to pick something like that up. Is it a "kit" type car? Where do they sell them? Have any other pictures of it? Any and all details of it would be nice please.
Keep us up to date on your build. Love the car.
08-23-2012, 05:30 PM
#14
180* headers are the answer to your problem.
Flat plane and 180 headers have been discussed extensively here and elsewhere. There are lots of practical reasons to stay away from a flat plane crank. Since you have a mid/rear engine car, you should have room for 180 headers and it will give you the Ferrari exotic sound you're looking for.
Keep in mind everything in the flow path will affect the sound, including the intake design. ITBs, DTB, STB - all will affect how the car sounds. Search around on some of the replica building sites and I'm sure you'll find healthy discussion on this subject.
Flat plane and 180 headers have been discussed extensively here and elsewhere. There are lots of practical reasons to stay away from a flat plane crank. Since you have a mid/rear engine car, you should have room for 180 headers and it will give you the Ferrari exotic sound you're looking for.
Keep in mind everything in the flow path will affect the sound, including the intake design. ITBs, DTB, STB - all will affect how the car sounds. Search around on some of the replica building sites and I'm sure you'll find healthy discussion on this subject.
08-26-2012, 03:23 AM
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All that makes sense.
If your looking for the sound I would think the three exhaust ideas you have are going to be the best economical sulutions. I would think you could get there with the unequal length headers pretty easily. Sounds like something Kooks could handle for you. They might need the car in hand to do it though.
As for your car. Can you give some more details on it? It is one sick looking ride. I would love to pick something like that up. Is it a "kit" type car? Where do they sell them? Have any other pictures of it? Any and all details of it would be nice please.
Keep us up to date on your build. Love the car.
If your looking for the sound I would think the three exhaust ideas you have are going to be the best economical sulutions. I would think you could get there with the unequal length headers pretty easily. Sounds like something Kooks could handle for you. They might need the car in hand to do it though.
As for your car. Can you give some more details on it? It is one sick looking ride. I would love to pick something like that up. Is it a "kit" type car? Where do they sell them? Have any other pictures of it? Any and all details of it would be nice please.
Keep us up to date on your build. Love the car.
There are a lot of details on the superlite site. Crazy thing is, I have yet to see it in person. It's at my builders, but I've been overseas for the past 2 years, and plan on doing another year. In fact, I'm debating on just selling it (builder hasn't had time to do anything to it), and just order another one in about 8 months. That way it will be ready when I get home, and not have this one sitting in a garage for a year.
My builder's (well, was my builder) exact words were "no picture can do this car justice" and that's just sitting there as a rolling chassis. I plan on painting the wheels if I keep this one.
08-26-2012, 10:21 PM
#17
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Clint, I'm gonna have to disagree with you, with all due respect, on the sound issue. I raced NASCAR late models for many years. We tried all kinds of exhaust systems, from many different manufacturers, in an effort to move our powerband, due to different tracks, and tires, and I can say that using 180* headers never changed the sound of our engines, but simply moved our powerband around. We ran crossover style systems, with the exhaust exiting the car out through the right side door. This was of course dry sump, high compression sbc engines. The 180* headers made a slightly different pitch in sound around 8000 rpm or so, but never sounded anything like an exotic automobile, with a flat crank. If you were never around these cars much, you wouldn't even notice the exhaust note difference.
08-29-2012, 03:12 AM
#18
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Yes, the drawing is horrible, but it's done in Paint, but at least gives a visual of the concept. You will notice on the left bank how 1 and 7 are much longer than 3 and 5.
Though I would have to find out how the volume and exhaust speed to determine the right length so that runner 7 gets to the merge point exactly in the middle between the pulses of 3 (instead of arriving early as it usually would ).
Though I would have to find out how the volume and exhaust speed to determine the right length so that runner 7 gets to the merge point exactly in the middle between the pulses of 3 (instead of arriving early as it usually would ).
08-29-2012, 09:56 PM
#19
Scott, I am on board with your experience but want to elaborate a bit on my point. Getting an exotic sound without a flat crank will take much more than just 180 degree headers. Even pulses into the collector at all engine speeds is only part of the equation. There has to be a holistic effort from the intake all the way through to the tailpipe if you want to come close to replicating the exotic sound. You're not going to get it from an LS single plenum intake, typical LS-optimized cam timing, or conventional exhaust connections. I don't know how close you can get to it given the longer primary length needed to achieve a 180 header, the cylinder head design, or the bore/stroke compared to the exotic. But I do think the closest practical solution will involve 180 headers.