I am wanting to hear from the guys who basically run open headers. I have the loudmouth cat back and i am planning on long tubes with and off road y-pipe. the problem i am worried about and the reason that i will probaly not go with that set up is the lack of backpressure. I dont want to float any valves and i was wanting to hear from the guys who run that setup mentioned earlier, to see if they have had any porblem? my other concern was sound because i know that set-up will be to much for a daily driver. I had a worked 94 silverado before the bird and i had cut outs on that. That was only for the track becaseu i wouldnt be be to handle that everyday, and i know the bird will be just as loud.



Thanks in advance.


----Jack

 

I have lts+ory+lm. Just installed it and it sounds horrible, very raspy and lots of drone. Also about the backpressure i dont know if its because of that but i was running 1/4 times about like yours and now im running 13.5-7s. Maybe its my tune but i dont see how a tune cant make u run that bad. I mean to run basically a second slower which would put me at 12.5-7 would take like 100hp.

 

Backpressure if a horrible word to sue. backpressure is bad period....

What you really need to be worrying about is exhaust scavenging which is not going to be a problem with the setup you listed. The main thing that causes problems that a lot of people think is because there is not enough backpressure is have something really restrictive upstream and then giving it some large piping down stream to expand out into where it looses lots of heat and velocity which = less power.........


Sorry for the quick run through, but it is late......

 

back pressure, well i ran opened headers for a month, no problems. But the rasp and the sound of a headache was really bad. With pipping that far, you should not have to worry about that. A muffler will not give you much, its the cats that will give you the most back pressure. You could just stick up another bullet muffler???

 

Backpressure will not be an issue...

I ran 1 7/8 headers to a 2 7/8's-3" Offroad-Y to a 3" cutout, on a stock internals car. It went 11.54 @ 115

Currently it runs 10.92 @ 122 with same setup with Heads and a Cam.

Car was my only transportation for 2 years and now it's driven in all but the worst weather to work and the occational blast down the track.

 

It would be correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." The idea of backpressure is not entirely true. However, there is a small amount of truth to this. 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. The other reason why people say backpressure is good, is because they hear that cars running open collector would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred, because 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 to 1 part of gasoline. This is referred to as a Stoichiometric (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. 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. 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. Carbureted cars can not adjust because of the way that backpressure causes air to flow backwards through the carburetor after the air already gets loaded down with fuel, and causes 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.


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Taken from Mike Kojima’s article.

backpressure = TORQUE?
An old hot-rodder's tall tale: Engines need some backpressure to work properly and make torque. That is not true. What engines need is low backpressure, but high exhaust stream velocity. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust valve as it opens. This vacuum helps scavenge the cylinder of exhaust gas faster and more thoroughly with less pumping losses. An exhaust pipe that is too big in diameter has low backpressure but lower velocity. The low velocity reduces the effectiveness of this scavenging effect, which has the greatest impact on low-end torque.

Low backpressure and high exhaust stream velocity can be achieved by running straight-through free-flowing mufflers and small pipe diameters. The only two exceptions to this are turbocharged engines and engines optimized for large amounts of nitrous oxide. Both of these devices vastly increase the exhaust gas volume and simply need larger pipes to get rid of it all.

Some stock mufflers and exhaust systems have up to 18psi of choking, power-robbing backpressure. In direct contrast, a well-designed, high-performance street exhaust system typically has about 2 to 6 psi of backpressure. For an interesting comparison, an un-muffled straight pipe on a real racecar usually has 1 to 3 psi of backpressure.

To get the least amount of backpressure, most of the good, high-performance mufflers available today have what is called a straight-through design. These mufflers quiet the exhaust by absorbing high-frequency vibrations in heat-resistant packing, usually consisting of stainless-steel mesh and heat-resistant ceramic fibers.

It is best to avoid straight-through mufflers that have a louvered core. Many old-school glass packs suffer from this design. Some spiffy polished stainless and big tip mufflers on the market also have these. The louvers generate quite a bit of backpressure because they stick into the exhaust stream and create considerable turbulence. Even though these mufflers are a straight-through design, they can have more backpressure than a stock muffler.

When buying a straight-through muffler, look for one with a perforated core if you are interested in producing more power. A good, properly sized, perforated-core straight-through muffler will add only about 1 to 2 psi of backpressure to your exhaust system

Remember that maintaining velocity is just as important as reducing backpressure.

 

I know i can not stand mine i have not had it tuned either but it lost power on the dyno plus it feels sluggish now. I use to be able to hit WOT at any point and get the overdrive to kickdown and kick *** but now the only time i get any power is at WOT on the initial take off everyone has told me tune too but i as well do not see how all that $$$ can result into a loss of power. I have LM+Jet Hot L/T, and ORY

 

i have LT headers, 3" y pipe, SLP LM Resinator, and no cats. all i can say is it is LOUD. turns a lot of heads, but is a bit too raspy. also, you'll have to deal w/ the occasional backfire that sounds like a gunshot thinking about installing a high flow cat.

 

Im sorry that u have this problem but its good to knw im not the only one to lose power. I installed the this setup and lost a lot down low.