how much torque will you lose if you do this? i heard a video clip on youtube of a guy with a straight pipe and it sounded pretty nice. will it be a noticeable loss?

 

The only thing you are going to lose is your hearing.

 

Straight pipe as in no cat and no muffler? That's ridiculous for a street car and you won't pass emissions if you have it. All states have sound laws as well I believe.

 

that depends one your cats are off you can buy a programmerthat willreport the O2 senors as working and at safe levels. at least at the newer DEQ's they just plug a computer into my dash and say pass or no pass. and no cats on a v6 sounds ok but again youll loose alot of trq for the best noise with powergo with good headers maybe cam it and or headsand a good flowmaster or borla.

 

Well, you have a '95 3.4L, and in states like IL there is no longer emissions testing for OBD-I cars (95 and older), so you can delete the cat, and will get some better sound...

I have not heard that a cat delete will reduce torque the only possible reason I can imagine is some backpressure needs? I assume the 3.4 & 3.8 have different needs in this respect, and should also depend on the size of exhaust pipes and if you get headers and an off-road Y-pipe, etc.

 

It is not the lack of back pressure that kills torque but the lack of exhaust scavenging. The slug of exhaust gas coming out of each cylinder needs to move fast enough to createa low pressure area behind it. This low pressure helps to extract the exhaust from the next cylinder on the firing order.If the exhaustheader plumbingis too large,the exhaust flow will slow down and there will be no scavenging action.Mufflers and cats act as restrictions and cause the exhaust flow to slow down, which in turn inhibits the scavenging action.

 

in other words, no backpressure "can" be bad for your valves. am i right?

 

If mufflers & cats inhibit scavenging, then freeing up either area should encourage scavenging if I understand what you wrote. If so, then assuming you didn't increase the exhaust pipe diameter and don't have headers that are wider than matched to the car, then replacing a cat with straight pipe should be a torque improvement, which is what I have noticed.

I assume the entire equation plays a part as well, i.e. a good CAI improves the type of changes you can make on exhaust without a torque performance hit. Some of these things would be impossible to measure without using a dyno or similar...

So a 3.4L with high-flow muffler, standard exhaust piping & manifold, straight pipe and CAI would amount to what effect relating to the cat delete?

 

i always assumed the bigger the pipe the faster and more air would flow? correct?

 

With the same amount of pressure , a larger pipe will move more air than a smaller pipe, so to move the same amount of gas using a smaller pipe the air speed will have to be higher. High exhaust gas velocity is needed in the manifold or headers to promote cylinder scavenging; however, once the exhaust is out of the header runners or exhaust manifold the scavenging work has been done, and now the larger the exhaust pipe diameter the less restrictive it is , and more power can be produced due to better breathing. If the engine uses log type exhaust manifolds with the typical 1 inch long runners then there is no exhaust tuning involved, and the best thing is to open up everything downstream.

The intake side works in a similar way, but intake velocity is much slower than on the exhaust side so runner length is much shorter.