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Unread 07-05-2010, 08:51 PM   #31
troy32323
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Just using less back pressure does not equal an increase in horsepower. The cotton ball example is just silly. Try taking off your exhaust and running open headers. It will not run well at all and you will lose power. Engines need a certain amount of back pressure. The amount will depend on many things such as compression, duration of the came etc etc. In many cases adding performance exhaust will add little or no extra horsepower. I am not familiar about how mufflers effect the HP on jeeps but on bikes I am. Generally the stock pipes work better than slip ons. Some lose HP with aftermarket exhaust. The manufacturers always show dyno charts with huge gains but I have never seen them replicated in real life. They are better becasue they are louder and safer. To be fair there are gains to be had on some vehicles but it can not be automatically assumed.

The diesel example is very true. Huge gains to made by just exhaust. But that is only because you are removing emmissions. We are discussing cat back.

After market exhaust is generally going to show benefits once the intake system and motor work is done.

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Unread 07-06-2010, 06:01 AM   #32
daggo66
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Quote:
Originally Posted by TheDustMan View Post
I drive my Jeep over 4000 RPM all the time. Stop trolling, daggo.
You might hit it briefly, but you maintain over 4K RPM? If I'm cruising at 70mph, I'm at 2300 in 6th with 3.73 gears. This is on a 3.8.
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Unread 07-06-2010, 11:06 AM   #33
hwill
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Didn't mean to start a Crap Storm with a simple question.

Alot of misconseptions about exhaust in here though.
I built many exhaust for my cars.
Backpressure is bad and doesn't make power no matter what you think. It is simply thrown around by those that don't know it is exhaust velocity and scavagging that makes power and torque.

I start a dyno at 2000rpms, really no point in starting earlier as peak power will be made much higher in the powerband. But it doesn't matter if the peak hp/tq is at 4K or higher....what matters is the gain over the entire powerband! Doesn't matter if you cruise at 2300 in 6th at 70mph, getting on an on ramp you will most likely hit 4000rpms or where ever the peak power is.....and this is where you will need it.

I have had vehicles that didn't benefit from a cat-back exhaust powerwise and that was because the restrictions was in the headers and cats. Not to mention the mufflers were not that bad.
On the Jeep is it hard to believe there will be no power gains because of the huge muffler. Been my experience that replacement of this with a much better one will produce some gains.

If you think the manufactures left nothing on the plate as far as performance you are sadly mistaken.

There are a few dynos of intake/exhaust and tuner for the jk on the net. I asked only because they showed gains and there was a response that they didn't. Having tested many parts from various cars on the dyno I would NEVER trust the manufacters dyno claims as many are way off.
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Unread 07-06-2010, 11:21 AM   #34
TheDustMan
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Quote:
Originally Posted by daggo66 View Post
You might hit it briefly, but you maintain over 4K RPM? If I'm cruising at 70mph, I'm at 2300 in 6th with 3.73 gears. This is on a 3.8.
I was just trolling back I've hit over 4k a few times... accidentally. But never actually maintained it on purpose, that would be absurd. The little 3.8 sounds like it's getting ready to stroke out if you crank it over 4k.
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Unread 07-06-2010, 12:40 PM   #35
daggo66
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Quote:
Originally Posted by hwill View Post
But it doesn't matter if the peak hp/tq is at 4K or higher....what matters is the gain over the entire powerband! Doesn't matter if you cruise at 2300 in 6th at 70mph, getting on an on ramp you will most likely hit 4000rpms or where ever the peak power is.....and this is where you will need it.
I added bold to the important part of your statement. Getting a boost of hp AT 4K when you are only going to just hit it, is useless. You need the power at the lower range, not the peak range. I'm not sure if you drive a JK or not, but 4k is the high end of a normal shift point. Normal would be in the 2500 to 3500 range.
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Unread 07-06-2010, 03:55 PM   #36
hwill
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Quote:
Originally Posted by daggo66 View Post
I added bold to the important part of your statement. Getting a boost of hp AT 4K when you are only going to just hit it, is useless. You need the power at the lower range, not the peak range. I'm not sure if you drive a JK or not, but 4k is the high end of a normal shift point. Normal would be in the 2500 to 3500 range.
From your post it seems you have never been into adding performance parts and knowing how they work.
Yes the gains through out the powerband is important but it is highly unlikely for there to be peak gains without other gains throughout.

And having your shift points where you make peak power is just as important.
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Unread 07-06-2010, 04:51 PM   #37
OneLoud
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It still amazes me how some people can come in here and rip on everyone else and demand proof of gains and yet never come forward with a single piece of evidance for there side of the argument.
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Unread 07-06-2010, 05:13 PM   #38
Charles
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Quote:
Originally Posted by owtdorz View Post
No warranty problems just throwing $$ away for an obnoxious noise maker.
No REAL performance gain.
My MBRP is not noisy. It sounds nice and confident. They also posted dyno results that show a gain in performance. Additionally, RIPP Superchargers backs them up as the only exhaust that they see real gains on.
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Unread 07-06-2010, 08:19 PM   #39
daggo66
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Quote:
Originally Posted by OneLoud View Post
It still amazes me how some people can come in here and rip on everyone else and demand proof of gains and yet never come forward with a single piece of evidance for there side of the argument.

wow you just don't get it do you? I haven't "rip on" anyone and I certainly haven't "demanded" anything. My "side of the argument" is very simple and requires no "evidence" because I am not making any claims. You so called performance parts guys are making the claims.
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Unread 07-06-2010, 08:26 PM   #40
daggo66
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Quote:
Originally Posted by hwill View Post
From your post it seems you have never been into adding performance parts and knowing how they work..
I've never been into adding USELESS "performance" parts. Window tint, fart cans, and stickers are not performance parts.


Quote:
Originally Posted by hwill View Post
Yes the gains through out the powerband is important but it is highly unlikely for there to be peak gains without other gains throughout.

And having your shift points where you make peak power is just as important.
That is EXACTLY what they obviously want you to believe! They show a chart with gains that begin at 4K RPM and want you to believe that there must be gains below 4k even if there aren't any! Why do I need to gain 2 or 3 hp at the shift point? I need that gain BEFORE the shift point.
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Unread 07-06-2010, 08:27 PM   #41
daggo66
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Quote:
Originally Posted by cbloyer81 View Post
My MBRP is not noisy. It sounds nice and confident. They also posted dyno results that show a gain in performance.
A gain after 4K rpm. How often do you run your JK in that range?
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Unread 07-06-2010, 08:46 PM   #42
Warlord2
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depends on the offroading you do... I have hit 4k-5k for fairly long streches on the sand dunes and the engine has no problem handling that. The only way adding a exaust is cost effective from my point of view is that it can remove that huge muffler and clears up room for other more useful things or better clearance. Some have even reported better gas mileage and response times wich doesnt mean more HP

Troy has hit the nail on the head with his post. Some engines can effectively gain a consider amount of power, however I dont believe the 3.8L is one of them. Currently its very hard to change the A/F/ timing mixture to compensate for the less restrictive exaust. Some manufactorers will allow changes, such as Subaru who has open source code not all locked up and very easy to change with a programmer.
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Unread 07-06-2010, 09:22 PM   #43
fernjack
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I have to admit that I do quite often exceed the 4000rpm mark though not for extended periods . However it would be nice to hear the rumble ....even if it is from the week little six . Power gain ..... I don't think it would be noticeable for me but I will change my muffler just for tone ....I'm thinking a cherry bomb .....why not ??? I won't be gaining practicle power but resonance ....sound and that's pretty much what we will gain with this enemic little mill ........ Deal with it
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Unread 07-07-2010, 01:07 AM   #44
hwill
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Quote:
Originally Posted by daggo66 View Post
I've never been into adding USELESS "performance" parts. Window tint, fart cans, and stickers are not performance parts.




That is EXACTLY what they obviously want you to believe! They show a chart with gains that begin at 4K RPM and want you to believe that there must be gains below 4k even if there aren't any! Why do I need to gain 2 or 3 hp at the shift point? I need that gain BEFORE the shift point.

No! This is from personal experience. I have never seen an exhaust give ONLY peak gains, same with an intake. If there are gains to be had they will be throughout the powerband.
While you might just be looking at the 4k peak there will be other gains through out the powerband.
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Unread 07-07-2010, 05:23 AM   #45
daggo66
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Quote:
Originally Posted by hwill View Post
No! This is from personal experience. I have never seen an exhaust give ONLY peak gains, same with an intake. If there are gains to be had they will be throughout the powerband.
While you might just be looking at the 4k peak there will be other gains through out the powerband.
That's the information I would love to see! The chart that was posted only showed gains above 4k for the 3.8. Sound and clearance are both valid reasons for changing. The stock 3.8 is definitely too quiet.
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