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  #1225  
Old 11-13-2014, 09:02 AM
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Originally Posted by Alex47er View Post
He still has them on he said you canstill feel the gains
I still feel it in mine some 3 years later. That mid range tho!

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  #1226  
Old 12-02-2014, 08:00 AM
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Re: 3.7l performance love

Well I have had a few questions recently on what backpressure is in regards to a performance exhaust or basically any exhaust for that matter. So ill do my best to disprove the biggest misconception about exhaust systems...

Basic exhaust theory:
The exhaust system is designed to remove the exhaust gasses from the engine as efficiently and in the most cost effective way. However, this doesn't always mean "best performing" or most efficient. The exhaust operates as a series of pulses with each engine producing a pulse for each cylinder. so a 4 cyl. will make 4 pulses and a 6 will make 6 and so on. The more pulses an engine makes, the more continuous and consistent the flow will be.

"So what is backpressure?"

Well it can be defined as a resistance to flow or as turbulence in the exhaust stream.

"Well wait a minute. I put on a freer exhaust with larger pipes. Why am I losing power?"

This is a little bit harder to explain then defining what backpressure is. Since back pressure is a Myth and resistance in the exhaust is bad what do we have left?
It comes down to pipe size and exhaust velocity. A lot of people believe that a larger pipe will flow better and they are right...well sort of. While its true that a larger pipe does in fact have a higher flow capacity the a smaller one, the thing most people forget is velocity and that's what you want. when designing a exhaust system you need to balance your flow capacity with exhaust velocity. This mean that you need the largest pipe possible while still keeping a high exhaust velocity.

So while the larger pipe has a high flow cap. then a smaller pipe will, the loss of power is attributed to a loss in velocity. Remember, the exhaust's job is to remove the exhaust gasses as fast as possible.

So lets say we have two pulses of the same volume but with two different sized pipes. A 3in and a 2in. The 3in pipe can flow more but because of the size in comparison to the pulse, that pulse will be slower. The opposite is true with the 2inch. Yeah it cant flow as much as the 3in, but the pulse is dramatically faster.

OH and the powerband is dependent on pipe size and RPM. How you ask? Simple. A small pipe will flow better at a lower RPM then a larger pipe. this means better low end. unfortunately, this hurts top end flow. Likewise a larger pipe will make better power up top from the higher flow capacity but losses too much velocity down low. Hence the loss of power. the trick here is to have the right sized pipe for your application. For the 3.7 liter V6, I found that a good balanced size is 2.5 inch in single form and 2.5 in dual. Just note that the dual will have a higher flow rate but a slightly less velocity.

well its getting late so ill finish up this little "class" tomarow with headers and exhaust scavenging.
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  #1227  
Old 12-02-2014, 04:24 PM
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Re: 3.7l performance love

I won't pretend I know about exhaust, and it's not my intent to take anything away from what Jeff said. I only hope to clarify.

But, from the physics side, it's a sound wave. It'll only travel so far before dissipation. Pulse one needs pulse two to help push out pulse one. If the exhaust is too big, pulse three can't push pulse two. Two can't push one far enough (b/c the exhaust is too big), and the wave/pulse "dies").

It's kinda like when you throw a rock (far enough out) in the water. It makes multiple ripples. The second pushes the first; the third the second and so on -as Jeff said. Eventually the ripples die. They never reach the shore because there isn't enough "energy" generated by the rock. The bigger the rock (engine), the more ripples (exhaust).
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  #1228  
Old 12-02-2014, 04:50 PM
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Re: 3.7l performance love

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Originally Posted by Truck.Norris View Post
I won't pretend I know about exhaust, and it's not my intent to take anything away from what Jeff said. I only hope to clarify.

But, from the physics side, it's a sound wave. It'll only travel so far before dissipation. Pulse one needs pulse two to help push out pulse one. If the exhaust is too big, pulse three can't push pulse two. Two can't push one far enough (b/c the exhaust is too big), and the wave/pulse "dies").

It's kinda like when you throw a rock (far enough out) in the water. It makes multiple ripples. The second pushes the first; the third the second and so on -as Jeff said. Eventually the ripples die. They never reach the shore because there isn't enough "energy" generated by the rock. The bigger the rock (engine), the more ripples (exhaust).
Well said
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  #1229  
Old 12-02-2014, 05:02 PM
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Re: 3.7l performance love

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Originally Posted by BlackN'Blue View Post
Well said
Thanks, Nick, but I think Jeff said it best. I just offered up an example I remembered from physics class. . One has to find the "happy medium" between pipe diameter and low end/high end RPM HP gain (and consequent loss of power). Both results are mutually exclusive: you can't have your cake and eat it too -as the saying goes.
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  #1230  
Old 12-02-2014, 09:53 PM
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Re: 3.7l performance love

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Originally Posted by Truck.Norris View Post
Thanks, Nick, but I think Jeff said it best. I just offered up an example I remembered from physics class. . One has to find the "happy medium" between pipe diameter and low end/high end RPM HP gain (and consequent loss of power). Both results are mutually exclusive: you can't have your cake and eat it too -as the saying goes.
exactly bro. if size and velocity didn't matter id have 3in pipes all the way back lol.
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Old 12-02-2014, 10:19 PM
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Re: 3.7l performance love

one more thing....ill get into how the turbo is affected by exhaust size. this is where the mind blow comes from and it contradicts how the exhaust works for a N/A motor
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  #1232  
Old 12-03-2014, 04:13 AM
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Re: 3.7l performance love

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Originally Posted by Strongjeff View Post
well its getting late so ill finish up this little "class" tomarow with headers and exhaust scavenging.
Well her it is. Part 2. Headers and scavenging:

Headers or extractors as they can be referred as are essentially a manifold designed for performance. they promote the scavenging effect.

"What is scavenging?"

Put simply, scavenging is the vacuum effect created when the exhaust pulse from one cylinder helps "pull" exhaust gasses out from another cylinder during valve overlap. (That brief amount of time in which both the exhaust and intake valves are open. when the exhaust valve is closing the intake is opening) this also applies for a cross pipe like an x pipe or an h pipe. The effect is minimal in a y pipe setup. the reason behind that is because you are merging the 2 exhaust streams (V type motors or H type) causing the pulses to slow down.

What makes headers special over a stock "Log" style manifold is that instead of dumping the exhaust into one common tube, each cylinder has its own tube. inside a stock manifold there is a lot of sharp 90* turns the pulses have to make. this slows down the pulse and created turbulence in the exhaust stream. there is also the possibility for the exhaust pulses to travel backwards.

aftermarket headers come in 3 flavors. Long tubes, which produce the best overall gains and the most torque. Mid-length, which is a compromise between a long tube and short tube, it shares many advantages of both and some disadvantages as well. and lastly short tubes. short tubes don't make the power that a long tube does but still inherently increases it from improving the scavenging effect. short tubes are also the most easily installed as they are a direct fit to stock mid pipes. shorties also tend to make there power higher in the rpms. Mid-length headers have a broader power band then short tubes but may require new mid pipes and possibly a tune. long tubes will require tuning and new mids but make the best and widest power gains.

having longer tubes allows more time for the gasses to fully escape the chambers and increases the speed of the pulse. long tubes have a greater scavenging effect. however, you can buy headers with tubes too big and not make the power that ones with a slightly smaller tube could make. so to make the best power at the rpms you want, you need a properly sized header. this goes back to Size vs Velocity again. another advantage to headers is that they prevent revision, the effect of the exhaust pulse traveling backwards.

But as a recap as to why velocity is so important, tho I really haven't touched on it is this. A fast moving pulse creates a low pressure area behind it. this vacuum effect (scavenging) will speed up the pulses that are behind it. think of how nascar does drafting. the car behind is faster then the lead car, but a train of cars is faster the one car on its own.
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  #1233  
Old 12-04-2014, 06:24 AM
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Re: 3.7l performance love

just foolin around lol...intitial design of my upcoming intake project I have planned for next year. to reduce production cost it will be a Carbon and fiberglass construction and will be reinforced

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Old 12-16-2014, 12:19 PM
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Re: 3.7l performance love

alternative to Fastman throttle body - "Viper" throttle body for 3.7L - JeepForum.com
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  #1235  
Old 12-16-2014, 03:48 PM
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Originally Posted by whhjr73 View Post
alternative to Fastman throttle body - "Viper" throttle body for 3.7L - JeepForum.com
you dont need it that big. Plus the 3.7 couldnt process all that extra air anyways so its just gonna be a waste
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Old 12-16-2014, 04:25 PM
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Re: 3.7l performance love

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Originally Posted by Strongjeff View Post
you dont need it that big. Plus the 3.7 couldnt process all that extra air anyways so its just gonna be a waste
Did you read the whole thread? what's the difference between buying a 4.7 Tb and one from fastman (besides price)? they didn't have any issues after putting it on. i ordered one and will let you know how it performs.
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