Low end torque loss with Magnaflow kits?
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Senior Member
Joined: Mar 2003
Posts: 530
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From: Northern IL
Altho I enjoy reading all the banter back and forth here, I will soon put this issue to rest, in my own opinion anyway. I ordered the system last Friday morning from hottexhaust and it came yesterday per the misses. Alas as I am currently in Motor City USA, about 400 miles from home, I will put the system on saturday and find out for myself if I can tell by the seat of my pants if I lost any low end torque. I don't give a s*** about mpg too much, if I did I wouldn't have bought this truck that I love so much. I simply would have gone and bought a Fusion or something and made sure I didn't ruffle my skirt getting in and out of it. So I hope soon I will be able to voice a biased opinion one way or the other. I am hoping it is no more than a three or four beer job to complete. I have to test drive it afterward right?
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Senior Member
Joined: Mar 2003
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From: Northern IL
OK so I put the 16523 Magnaflow system on today. First off, it went on pretty smooth, except as some others I have read, it was hitting the heat shield on the tire. I ended up bending the one hanger on the tailpipes so it didnt hit. It dropped the tips a little lower than I wanted but still looks clean. So after I fifnished I took a test drive. Sound is exactly what I wanted. Cruising I don't even really hear it. Step on it and you hear a nice low rumble. As for any low end torque loss, my seat of the pants dyno tells me I had no low end torque loss. Maybe mine needs to be calibrated or something? But I am happy with the system. Sounds good and looks good and I see no change in torque. Just what I wanted. I will post some pics when I get a chance to snap some. Truck is dirty anyway after my drive home from Auburn Hills. I give for the Magnaflow system.
for the Magnaflow system.
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Joined: Jun 2010
Posts: 510
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From: Holt, MO
Wow, this has been a spirited thread. I think the bottom line is he is happy with it for the money he spent? If he is, then I say great!
I have put true duals on 5 different pickups in the last 10 years. One 2002 Ford 4.6 and the rest GMs. Of all those, two were 8.1 Ltr Big Blocks and the others were 5.3s. I never dynoed these trucks, and as such can only tell you what I thought before and after. All of these trucks got true duals, with an H pipe and criss crossed tail pipes to equal the length of pipe on each side. This gives the most balanced system I could think of for both banks of cylinders.
Having said all that I cannot tell you that I gained one bit of power on the bottom end, which is where we all work these trucks. Maybe at 3500 to 4500 I gained a little, but I am so very seldom there. Where I run these trucks is in OD at 75 to 80 mph, and they run about 2,000 rpm, or less as the case with my new F-150.
I still have my 06 GMC 8.1 that I use to pull a gooseneck, and I don't think it pulls on bit better now than with stock exhaust. If anything, I would have to say it is a little worse, but I am not going to use my butt as a measuring device, because what does it know, it gets sat on all day long.
I am sure there are some engineers that specialize in flow dynamics that could really shed some light on this for us, but I don't know any. From what I have learned, my gut tells me that at 2000rpm, there is plenty of flow in a stock exhaust to remove what is being created by the engine. Now, is it enough at 3500, maybe not, but how many of us run these trucks at that RPM? Probably not many of us for very long.
The dyno charts that were posted on this thread show a Mustang GT500. Notice that the big difference was at the top end of the rpm band. Great for racing, which is what that car does, but if you look at the bottom of the chart, it really didn't make much difference at all, and the chart didn't even go down to where we run our trucks. You know why it didn't go down that low? Because it would have showed that there was not a difference, or a little loss of performance in the low end of the rpm band. So I don't put much stock in that chart. Show me a chart that starts at 1000 rpm and stops at 4000 and lets see what happens.
The other thing is backpressure. It is not always a bad thing. You need a little of it, to create a scavenging effect in the exhaust system. Without it, you loose that and create more work for the engine.
I used to think that they helped, and back in the days of 3 speed transmissions when we were turning 3000 to 3500 rpm cruise ranges, duals and the like made a bigger difference. Also, car company's have put more technology into the exhaust systems to try and get more mpg out of these beasts.
I put them on my trucks because I love the sound of a rumbling V-8. I realize that I am not gaining anything in performance, but it sure sounds good and it makes me smile when I fire up that 496 cubic inch big block and roars to life. Good Stuff.
I have put true duals on 5 different pickups in the last 10 years. One 2002 Ford 4.6 and the rest GMs. Of all those, two were 8.1 Ltr Big Blocks and the others were 5.3s. I never dynoed these trucks, and as such can only tell you what I thought before and after. All of these trucks got true duals, with an H pipe and criss crossed tail pipes to equal the length of pipe on each side. This gives the most balanced system I could think of for both banks of cylinders.
Having said all that I cannot tell you that I gained one bit of power on the bottom end, which is where we all work these trucks. Maybe at 3500 to 4500 I gained a little, but I am so very seldom there. Where I run these trucks is in OD at 75 to 80 mph, and they run about 2,000 rpm, or less as the case with my new F-150.
I still have my 06 GMC 8.1 that I use to pull a gooseneck, and I don't think it pulls on bit better now than with stock exhaust. If anything, I would have to say it is a little worse, but I am not going to use my butt as a measuring device, because what does it know, it gets sat on all day long.
I am sure there are some engineers that specialize in flow dynamics that could really shed some light on this for us, but I don't know any. From what I have learned, my gut tells me that at 2000rpm, there is plenty of flow in a stock exhaust to remove what is being created by the engine. Now, is it enough at 3500, maybe not, but how many of us run these trucks at that RPM? Probably not many of us for very long.
The dyno charts that were posted on this thread show a Mustang GT500. Notice that the big difference was at the top end of the rpm band. Great for racing, which is what that car does, but if you look at the bottom of the chart, it really didn't make much difference at all, and the chart didn't even go down to where we run our trucks. You know why it didn't go down that low? Because it would have showed that there was not a difference, or a little loss of performance in the low end of the rpm band. So I don't put much stock in that chart. Show me a chart that starts at 1000 rpm and stops at 4000 and lets see what happens.
The other thing is backpressure. It is not always a bad thing. You need a little of it, to create a scavenging effect in the exhaust system. Without it, you loose that and create more work for the engine.
I used to think that they helped, and back in the days of 3 speed transmissions when we were turning 3000 to 3500 rpm cruise ranges, duals and the like made a bigger difference. Also, car company's have put more technology into the exhaust systems to try and get more mpg out of these beasts.
I put them on my trucks because I love the sound of a rumbling V-8. I realize that I am not gaining anything in performance, but it sure sounds good and it makes me smile when I fire up that 496 cubic inch big block and roars to life. Good Stuff.
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Joined: Oct 2009
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From: Missouri
Get the physics of exhaust theory right so you don't make false accusations.
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Joined: Jun 2010
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From: Holt, MO
Okay Chief, give us the "physics of exhaust theroy".
Drag racers run open headers why? Because they want to build peak HP at high RPM. They are not concerned about torque created down in the lower rpm band, because they are never in the lower rpm band. They launch at4 to 5 grand and go from there.
I have seen many, many dyno charts where they ran an engine with open headers, and then put mufflers and pipes on it and ran it again. The difference was a drop in peak HP, and an increase in torque at a lower rpm. Now, why is that? There would have easily been more backpressure with a muffler setup.
And why does an engine with small valves, and a dual plane type intake, with longer smaller intake runners make more tq at a lower rpm band that an engine with large valves and a Victor Jr type intake on it? The big valve will rev much higher, but won't build low rpm torque, because at low rpm, there is not enough air speed going through the runners to get enough fuel to charge the cylinders. The smaller valve engine will have a lot higher speed of airflow at lower rpms. It will charge that cylinder more completely at low rpm. Won't rev as high because it will reach a point where it cannot physically draw any more air into it. That is the trade off.
The same idea is true on the exhaust side. If you get a system that is to big and or to free flowing, you loose your air speed at lower rpm, and thus you loose any scavenging effect. The key would be to find that balance where the exhaust was tuned very closely to your rpm band and that would optimize the flow. Thats the moving target we would all like to hit.
The point is that we are using these trucks from idle to about 4000 tops, with most of time they are 1700 to 3000 if even that high. The added flow you are gaining by the performance exhaust is not being utilized in this rpm range. I am sure they help in the higher rpm, but these trucks don't live up there.
I love the sound of performance mufflers, as I have done all but one of my trucks with true duals, but I am not expecting gains by it, I just like to hear it.
Drag racers run open headers why? Because they want to build peak HP at high RPM. They are not concerned about torque created down in the lower rpm band, because they are never in the lower rpm band. They launch at4 to 5 grand and go from there.
I have seen many, many dyno charts where they ran an engine with open headers, and then put mufflers and pipes on it and ran it again. The difference was a drop in peak HP, and an increase in torque at a lower rpm. Now, why is that? There would have easily been more backpressure with a muffler setup.
And why does an engine with small valves, and a dual plane type intake, with longer smaller intake runners make more tq at a lower rpm band that an engine with large valves and a Victor Jr type intake on it? The big valve will rev much higher, but won't build low rpm torque, because at low rpm, there is not enough air speed going through the runners to get enough fuel to charge the cylinders. The smaller valve engine will have a lot higher speed of airflow at lower rpms. It will charge that cylinder more completely at low rpm. Won't rev as high because it will reach a point where it cannot physically draw any more air into it. That is the trade off.
The same idea is true on the exhaust side. If you get a system that is to big and or to free flowing, you loose your air speed at lower rpm, and thus you loose any scavenging effect. The key would be to find that balance where the exhaust was tuned very closely to your rpm band and that would optimize the flow. Thats the moving target we would all like to hit.
The point is that we are using these trucks from idle to about 4000 tops, with most of time they are 1700 to 3000 if even that high. The added flow you are gaining by the performance exhaust is not being utilized in this rpm range. I am sure they help in the higher rpm, but these trucks don't live up there.
I love the sound of performance mufflers, as I have done all but one of my trucks with true duals, but I am not expecting gains by it, I just like to hear it.
Senior Member
Joined: Aug 2008
Posts: 4,778
Likes: 10
From: Douglasville GA
Back-pressure is a myth cooked up by rednecks that can't comprehend the concept of exhaust velocity.
"Ah shoot Billy Jack, I just put a 5" diameter muffler on my Honda, now it's slow as my math skills. It must have opened up my exhaust too much and these little Honda's need back-pressure to run properly."
There are many articles out there, just type in "back pressure myth" in google.
http://my.prostreetonline.com/forums...php?t-1639.htm
"Ah shoot Billy Jack, I just put a 5" diameter muffler on my Honda, now it's slow as my math skills. It must have opened up my exhaust too much and these little Honda's need back-pressure to run properly."
There are many articles out there, just type in "back pressure myth" in google.
http://my.prostreetonline.com/forums...php?t-1639.htm
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Joined: May 2007
Posts: 1,413
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From: Iowa
Oh boy...
The reason a lot of people feel they "lost low-end power" is because the powerband has changed. With nearly all changes to an exhaust system, the powerband moves (ever so slightly in some cases, but it still moves). Often times, switching to a free-flowing system moves the powerband into the higher end range, which is why people complain about a lose of low-end power. And manufacterer HP/TQ claims and dyno numbers are simply peak HP/TQ numbers at very high RPM levels... Which means nothing to your average joe that tows or daily drives with his truck. A dyno sheet with the stock and aftermarket HP/TQ curves are what you REALLY want to see...
The reason a lot of people feel they "lost low-end power" is because the powerband has changed. With nearly all changes to an exhaust system, the powerband moves (ever so slightly in some cases, but it still moves). Often times, switching to a free-flowing system moves the powerband into the higher end range, which is why people complain about a lose of low-end power. And manufacterer HP/TQ claims and dyno numbers are simply peak HP/TQ numbers at very high RPM levels... Which means nothing to your average joe that tows or daily drives with his truck. A dyno sheet with the stock and aftermarket HP/TQ curves are what you REALLY want to see...
Senior Member
Joined: Nov 2008
Posts: 511
Likes: 0
From: Schenectady, NY
Oh boy...
The reason a lot of people feel they "lost low-end power" is because the powerband has changed. With nearly all changes to an exhaust system, the powerband moves (ever so slightly in some cases, but it still moves). Often times, switching to a free-flowing system moves the powerband into the higher end range, which is why people complain about a lose of low-end power. And manufacterer HP/TQ claims and dyno numbers are simply peak HP/TQ numbers at very high RPM levels... Which means nothing to your average joe that tows or daily drives with his truck. A dyno sheet with the stock and aftermarket HP/TQ curves are what you REALLY want to see...
The reason a lot of people feel they "lost low-end power" is because the powerband has changed. With nearly all changes to an exhaust system, the powerband moves (ever so slightly in some cases, but it still moves). Often times, switching to a free-flowing system moves the powerband into the higher end range, which is why people complain about a lose of low-end power. And manufacterer HP/TQ claims and dyno numbers are simply peak HP/TQ numbers at very high RPM levels... Which means nothing to your average joe that tows or daily drives with his truck. A dyno sheet with the stock and aftermarket HP/TQ curves are what you REALLY want to see...