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jkclns
Dodge Dakota
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4/17/2003
14:49:56
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 Subject: 4.7 Single or Dual Exhaust
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Got a problem, I am stuck between getting a true dual system for my 4.7 with headers or staying with a single and then running it 2.5in all the way from the headers. Has anybody had expreriences with either? thanks
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01Motorsport
Dodge Dakota
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4/17/2003
15:29:30
|  RE: 4.7 Single or Dual Exhaust
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The stock 4.7 manifolds flow within 2% of headers from the factory. The easiest setup is a pre-fab cat-back (single), or cop a Flowmaster with a single entry and two exits and hook up 2.5 duals on back. On mild street motors, if you lose too much backpressure, you can hurt performance. If you're racing and have the mods, open 'er up.
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gfdssd
Dodge Dakota
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4/18/2003
13:49:25
| RE: 4.7 Single or Dual Exhaust
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I think there is a guy on this board who has true duals on his 4.7. That would be awesome but if you don't run true duals then I would reccomend a single exit. I would stay away from the single in dual out muffler. I've tried those and I think I lost power throughout the power band.
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farout
Dodge Dakota
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4/18/2003
22:55:27
|  RE: 4.7 Single or Dual Exhaust
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Just a note of caution, ANY change before the Cat. converter VOIDS Dodge's wareente. At least it's worth thinking if you want to risk it.
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franlofter
Dodge Dakota
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4/19/2003
00:07:27
| RE: 4.7 Single or Dual Exhaust
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I would like to put true duals on my 4.7 I know they will sound better I dont think that could be argued but price and backpresure loss are my reasons not to.
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philburnmaui
Dodge Dakota
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4/19/2003
05:21:30
|  RE: 4.7 Single or Dual Exhaust
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I put gibson headers and gibson exhaust (catback)
on my 2001 4.7 slt 4X4. I also put a high flow
air cleaner . The cat back is 3.0" and sounds
really mean. I increased the HP and love the
overall effect. GO FOR IT!!
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jkclns
Dodge Dakota
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4/22/2003
13:42:49
|  RE: 4.7 Single or Dual Exhaust
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Thanks for the responses. Has anybody done the headers and single out, and if so, how did it run, as goes for the true duals with headers. thanks guys
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common sense
Dodge Dakota
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4/22/2003
14:28:56
| RE: 4.7 Single or Dual Exhaust
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backpressure is NEVER good for horsepower. people get this idea because backpressure is often associated with exhaust gas velocity. higher velocity is better. i don't know the specifics so i'm not going to make myself sound like an ass but if you do some real research you will find that this is true.
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nobody
Dodge Dakota
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4/22/2003
18:30:07
| RE: 4.7 Single or Dual Exhaust
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sorry "common sense", but it's NOT always good to get rid of backpressure on a stock motor. And the reason is because there is overlap in cam profiles where the exhaust valve and intake valve are both open AT THE SAME TIME for a brief period at the end of the exhaust stroke and the beginning of the next intake stroke. Too high of an exhaust velocity causes some of the incoming intake charge to escape out the still open exhaust valve, resulting in power loss at low rpm. Every dyno chart ever posted on this site shows loss of low rpm torque and HP if just a larger diameter low restriction exhaust is installed, especially on the 4.7l motor. Bigger exhaust only benefits if there is a major increase in intake flow as well, such as adding the HO cams and intake or adding forced induction like a turbo or supercharger.
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Texas Todd
Dodge Dakota
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4/23/2003
08:34:30
| RE: 4.7 Single or Dual Exhaust
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cool, posts from 'nobody', using 'common sense'
it's just 'farout'!
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01Motorsport
Dodge Dakota
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4/23/2003
10:05:54
| RE: 4.7 Single or Dual Exhaust
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I've owned 7 Mopars over the years, 4 V-8s and 3 4-cyl. The common performance deal with all of them was that they all liked more air in and more air out, even when the rest of the motor remained stock. I only tried headers once. Free flowing cat-back exhaust yielded a better result, performance-wise.
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KJW
Dodge Dakota
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4/23/2003
17:19:46
| RE: 4.7 Single or Dual Exhaust
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The back pressure issue is valid for the reasons common sense has already stated. Street smog motors need to have some back pressure on them due to the way they are designed.
The question is.... How Much? I don't know that answer either but I just talked with a guy here in SoCal that does some of the exhaust work for Dependable Dodge. He installed a cat back 3" system on one of there 4.7 Dakotas and it allegedly really made quite a difference. He felt it was one of the better performance increases he has seen from just exhaust work.
Does anyone really have some technical data on doing this?
Could you counter the loss of HP that comes with taller tires by putting a 3" system behind the existing cat?
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common sense
Dodge Dakota
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4/23/2003
17:42:47
| RE: 4.7 Single or Dual Exhaust
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anyone who thinks that i am a dick and enjoys having their head so far up their ass that they can't see the light of day shouldn't read this. but, if you think that what i said had just a tiny little bit of sense to it or you want to actually learn how this really works then you really, really, need to read this article.
http://www.burnsstainless.com/TechArticles/Theory/theory.html
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common sense
Dodge Dakota
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4/23/2003
17:50:21
| RE: 4.7 Single or Dual Exhaust
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sorry for making two posts in a row.
nobody,
you don't seem to understand that big pipes cause low velocity and small pipes cause high velocity. and yes big pipes cause loss of low rpm power. small pipes aren't better at low rpm because they cause backpressure, it's because they cause high gas velocity. there is a comprimise made in every header for a high or low rpm powerband. some of you people make it sound like clamping the end of your pipes shut would make more low end power because it would cause back pressure.
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wertew
Dodge Dakota
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4/24/2003
13:30:52
| RE: 4.7 Single or Dual Exhaust
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agree with common sense. Bottom line is larger diameter = lower velocity, higher volume, loss on low end, gain on top end. Smaller diameter = higher velocity, lower volume,gain on low end, loss on top end. It's always a tradeoff.
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Texas Todd
Dodge Dakota
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4/24/2003
15:58:46
| RE: 4.7 Single or Dual Exhaust
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KJW....
SHOW ME THE DYNO SHEET!!
From the dynos I've seen, your exhaust tech is full of it! Maybe he wants to sell you one also?
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farout
Dodge Dakota
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4/24/2003
16:23:52
|  RE: 4.7 Single or Dual Exhaust
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Texas Todd: Why you brought me into you note is beyond me. But I guess that's part of being a Texas boy. Now up north when a Texan dies we give them an enma and burry then in a shoe box. I don't think you will understand that but think on it. I dont care if you run a 4.7 with no exhaust, do as you want, pardner?
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jkclns
Dodge Dakota
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4/24/2003
20:02:40
| RE: 4.7 Single or Dual Exhaust
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alright farout, that was F*** stupid about what you said about Texans. Nobodyever said anything and you Yanks, so just stick to the post or get the hell out with you your stupid info.
P.S.
Houston , TX
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KJW
Dodge Dakota
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4/24/2003
21:24:04
| RE: 4.7 Single or Dual Exhaust
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Todd......
1. I don't have a dyno sheet and if you read the post it asks if anyone does have technical info...that is all the post said.
2. He is not my exhaust guy he is just a muffler guy who has done a Dakota for a dealership and offered up an opinion when asked. Again that is all the post said.
3.RELAX!!
All we are discussing here is if there is a way for all of us to do a better job then MOPAR did on the exhaust systems of our trucks.
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philburnmaui
Dodge Dakota
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4/25/2003
05:26:15
| RE: 4.7 Single or Dual Exhaust
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Such hostile responses. It makes perfect sense to
increase the diameter of BOTH the air and exhaust.
Its common knowledge that manufacturers of combustion engine have to run their engines very lean and restrict the exhaust. so... open it up
and let the computer make the adjustments. I have
a very good set up with the high flow intake, headers and a catback. I did not void my warranty,
and increased power and mileage. (not at the same time!!I keep leaving rubber on the road :(...)
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Demon Dakota
DakotaEnthusiast
4/25/2003
12:11:55
| RE: 4.7 Single or Dual Exhaust
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You won't lose anything going with true duals "if" you have the other mods that are pretty much required (common sense stuff). More air in and more air out combined with more fuel = more power. It's not as difficult as folks make it out to be.
K&N Drop in AF (CAI during summer months)
True Dual exhaust and removed third cat
HO Cams & HO Intake
FASTMAN 70mm TB
Autolite 3923 Plugs
TPS @ .76 VDC
IAT Adjuster Mod
14.52@94.2 MPH at Silver Dollar Raceway
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Mr.H
Dodge Dakota
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4/27/2003
16:06:00
| RE: 4.7 Single or Dual Exhaust
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Well,
I've heard that to optimize the exhaust-pulse pressure you need to do an X or H pipe with true duals, and the downside can be totally defeated with single exit exhaust.
Also, when going too big of an exhaust diameter, the gases cool too quickly and actually INCREASE back pressure due to the weight difference of cold/hot gases.
This quick-cooling is why most people relate "less back-pressure to power loss" because of the actual increase related to over-sized exhaust tubing setups.
To solve this at the track, build a custom dump just past the y-junction of the collectors , and Ta-Da, free flowing exhaust good for a considerable gain.
Unless you're going for looks alone, the single exit is the way to go, assuming you're not using the factory collectors and cats, and keep it to 3". That should be good for around 600+ rwhp. And with the dump removed, your only real restriction is from your headers and Hi-flo cats, I'll be running 2.5" collectors behind headers with 2.5" CATCO's both into a 3" single collector.
I'll be sure to post how effective the setup works with the custom dump/wingnut cover setup.
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Demon Dakota
DakotaEnthusiast
4/28/2003
11:34:45
| RE: 4.7 Single or Dual Exhaust
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Mr. H, you're exactly right on the X pipe (I'm not sure H's work that well with true duals). To get the correct pulse flow pattern, you need an x pipe. It will help both HP and TQ.
K&N Drop in AF (CAI during summer months)
True Dual exhaust and removed third cat
HO Cams & HO Intake
FASTMAN 70mm TB
Autolite 3923 Plugs
TPS @ .76 VDC
IAT Adjuster Mod
14.52@94.2 MPH at Silver Dollar Raceway
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blackbeauty
GenIII
5/01/2003
05:45:29
| RE: 4.7 Single or Dual Exhaust
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Message:
COMMON SENSE,
Use some of your name, first of all, from what I read, the author was talking about high performance race engines. I think that others were talking about optimizing their mostly stock Mopar engines with some sort of highly engineered aftermarket products.
Second, how many times did I just read the word "theory" That word gets old after a while. If you want to make a statement, bring something else other that someone's 'theory'. Do you know what goes into designing an engine for a major automaker? Millions and millions of dollars can be gained or lossed just because of a single change in design. Everything is the way it is because of money. That's what aftermarket is for. That's why people test aftermarket products, and yes, they test them on dynos.
clean&shiny is good, mud&dirt is better
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dodgetomahawk
Dodge Dakota
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5/01/2003
10:28:40
| RE: 4.7 Single or Dual Exhaust
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Do I need an exhaust system? I've heard that you always need "some back pressure." Anyone who says you need "some back pressure" to make power needs "some re-education." Aftermarket exhaust systems help on some vehicles and make "0" HP on others. Check out the Kenne Bell "Tech Tips" and "Dyno Tests" for specific vehicles. We cut off the entire exhaust system in back of the cat and test it with no exhaust to determine if there is any exhaust restriction (back pressure).
The above taken from kennebell web site.
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