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Straight Pipe

7K views 43 replies 15 participants last post by  BenReardon 
#1 ·
So, today after work I am going down the my local muffler shop and having them drop the muffler and run a straight pipe with the stock resonator. I was quoted $125.00. I am getting the mount plates welded on either side, so if I don't like it I can easily put the muffler back in myself. I am not going for a few hours, I will have pics as well as a video posted by the end of the day. Its snowy up here in MA, and once I get them up I don't want to hear any bull about how dirty my Jeep is right now. I am not all that happy about it, waiting til Tuesday for $5 washes, I go once a week. I hate the salt and sand all over the place.

Ben
 
#4 ·
cant wati to hear it bro! Dont worry about the backpressure thing...you got plenty of fresh, cool air coming in the front with your CAI.
 
#6 ·
Some say that.......an engine needs backpressure to work correctly. Is this true?

No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.

The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Modern vehicles don't have to worry about the effects described above, because the PCM ( computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the PCM's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached.
 
#7 ·
Soooo......This was an ok idea? This video is hilarious, it is 6 degrees outside and ice is everywhere, and I'm no Scorsese. The camera got blown away, glad it didnt break. It sounds pretty good, but I havent gotten a good pull yet cause its sooooooo icccyyy. Cant wait to get it cleaned up and situated. I will do in cabins too for all you sound haters! Music is meant to be heard a loud.

http://s911.photobucket.com/albums/ac320/BenReardon/?action=view&current=MOV00795.flv
 
#11 ·
I love it.
 
#13 ·
I had to run to Blockbuster this AM to return some movies. FYI Cloudy with a chance of Meatballs was great! Figured it was a good time to get some in cabin videos. First and second ones are just off a red light and I forgot to turn off the radio for the first. Had someone in front of me, just in town driving, last one I was able to open it up a little bit. Roads are still salty/sandy, cant wait for clean pavement. Breathes a lot better from 3000-5500 RPM's.

http://s911.photobucket.com/albums/ac320/BenReardon/?action=view&current=MOV00796.flv

http://s911.photobucket.com/albums/ac320/BenReardon/?action=view&current=MOV00797.flv

http://s911.photobucket.com/albums/ac320/BenReardon/?action=view&current=MOV00798.flv

I am interested in all opinions. Thanks guys.
 
#19 ·
Ive been preaching it for 8 months....you guys are wasting your money on mufflers. Chop the stock out and stay with the stock resonator. No drone and a good sound---
 
#20 ·
i like this a lot. I was going to get a borla cat back... i think you have changed my mind...good vids
 
#21 ·
I will try to do a few more videos with drive by's for you guys. I am gonig to try to get some pics of the pipe up as well, its just too cold to climb underneath today. After driving almost all day, it really isnt that loud or have any drone because the resonator does do its job. I drove down to Hartford ladst night for dinner and the ride was fine. EVEN MY GIRLFRIEND LIKED IT! It sounds mean, I am very happy with the way it turned out. The guys that did it did a great job. It lets that exhaust just flow out, doesnt hurt my jeep, will pass emissions, and with the stock resonator right at the end it'll pass inspection. It is only loud when you lay on it, which is when I want to hear her scream. If you want a super luxury ride, dont do this, get a Borla, but if you want to hear that HEMI roar, definately do this mod. It feels like I am driving a Tan Dragon.
 
#29 · (Edited)
so bordam got the best of me today... I went down to the muffler shop, and chopped the stock muffler off... its loud and sounds good. but when I floor it and it shifts it sounds like a glass pack...kinda raspy, that the only down side. Besides that Bad a$$!! really deep rumble. 100$ cant really beat that... will post vids tomorrow
 
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