dual exhaust for hemi
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10-06-2004 | 01:38 AM
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dual exhaust for hemi
I have some newbie questions about exhaust systems. I am not a mechanic or an engineer, so my questions may seem off the wall. But I'm trying to understand the reason behind something rather than just getting the plain facts which you all already know.
I've been reading posts on this forum and other places on the internet about negative effects of installing dual exhaust on a hemi. (I have an 04 quad cab with a hemi.) Most posts that state this say a couple of things.
1. "You will lose torque." Does this mean torque is lower at low RPMs? I think that (tell me if I'm wrong please!) torque at higher rpm's means higher horsepower. So does this mean that the dual exhaust will cause lower torque at low rpm's while torque is higher at high rpm's? Why is this? Is there some kind of vacuum/siphoning effect of properly sizing the exhaust system to more efficiently clear out the exhaust?
2. "If you want to go with dual exhausts, go with 2.25" or 2.5" pipes." I did some arithmetic to figure out the difference in volume. For every 1" in pipe, you get the following volumes in cubic inches of air/exhaust gas. I did this with pi * radius squared where radius = half of diameter and pi is 3.1416.
2.25” pipe = 3.976087
dual 2.25” pipe = 7.952175
2.5” pipe = 4.90875
dual 2.5” pipe = 9.8175
3” pipe 7.0686
dual 3” pipes = 14.1372
So 3" pipes almost give you double the output of 2.25's, and more than 50% more than 2.5's.
How is this related to what is going on in the engine? Is there a formula to use, or a way to measure the volume of exhaust gasses at given RPM's? Also, with the hemispherical combustion chamber that makes the hemi a Hemi, the intake and exhaust are already supposed to be more efficient than cylinders.
And another possibly random item... I remember reading or seeing on tv something about a dual exhaust system that uses a pipe between the two branches to equalize flow or pressure. Would this help in the case of the hemi?
Sorry if I sound like I am way out there. Well all right, I am way out there. :-D But I am really interested in finding out the "why" behind this conclusion that everybody accepts for fact.
I've been reading posts on this forum and other places on the internet about negative effects of installing dual exhaust on a hemi. (I have an 04 quad cab with a hemi.) Most posts that state this say a couple of things.
1. "You will lose torque." Does this mean torque is lower at low RPMs? I think that (tell me if I'm wrong please!) torque at higher rpm's means higher horsepower. So does this mean that the dual exhaust will cause lower torque at low rpm's while torque is higher at high rpm's? Why is this? Is there some kind of vacuum/siphoning effect of properly sizing the exhaust system to more efficiently clear out the exhaust?
2. "If you want to go with dual exhausts, go with 2.25" or 2.5" pipes." I did some arithmetic to figure out the difference in volume. For every 1" in pipe, you get the following volumes in cubic inches of air/exhaust gas. I did this with pi * radius squared where radius = half of diameter and pi is 3.1416.
2.25” pipe = 3.976087
dual 2.25” pipe = 7.952175
2.5” pipe = 4.90875
dual 2.5” pipe = 9.8175
3” pipe 7.0686
dual 3” pipes = 14.1372
So 3" pipes almost give you double the output of 2.25's, and more than 50% more than 2.5's.
How is this related to what is going on in the engine? Is there a formula to use, or a way to measure the volume of exhaust gasses at given RPM's? Also, with the hemispherical combustion chamber that makes the hemi a Hemi, the intake and exhaust are already supposed to be more efficient than cylinders.
And another possibly random item... I remember reading or seeing on tv something about a dual exhaust system that uses a pipe between the two branches to equalize flow or pressure. Would this help in the case of the hemi?
Sorry if I sound like I am way out there. Well all right, I am way out there. :-D But I am really interested in finding out the "why" behind this conclusion that everybody accepts for fact.