1995 Pickup catalytic converter removal Q?

I would like to know if removing the original catalytic converter on a 1995 Chevrolet ext/cab 5.7 5-speed manual would have any effect on the way the computer controls the engine? Or does anyone have a 95 chevy witout a catalytic converter? If so does it drive fine?



Thanks
-Matt

no, unless theres a sensor in the cat or after it, even then i think it would be ok but im not positive

but on mine it doesnt look like theres a sensor. ive seen a few people driving 1500s without cats just dont expect to pass emmisions

I have a 94 sierra ext cab 5.7 auto with intentions of taking off the cat. There are a few things you have to know about with doing this. The O2 sensors and how it will affect your engine. I have heard of it helping backfire and better gas mileage and what not. You will probably get a reading about the 02 in your gauges or the check engine. Unless you notice something yourself, with these older model trucks there are no real gauges to detect it, yet the engine will still notice it. A friend of mine did this to his truck and if your looking for the bad*** ROAR this is the way to go... good luck trying to find someone to do it though, it is highly illegal tampering with a functional catalytic converter and fines can be steep.

removing the cat will affect your milage. for sure you will lose about 2 mpg. i did and then i put mine back on. as for the sound, if you dont have a muffler or mufflers, i think it sounds like a boat out of water. if you do/are planning on mufflers, it sound ok. my truck has the stock cat and no mufflers, (cat-back) duals. i love it, have had nothing but compliments.
as for the milage thing, with out the cat, your 02 sensor reads that the exaust temp is low, therefor the computer thinks the motor is "cold", sending the message to send more fuel and less air. hence the loss in milage. when i had my cat off, i actually noticed a loss in torque and hp.

You should read the other post out there about straight pipes and what not. If you’re oxygen sensor is in your manifold you should be ok, if it’s in your Y-Pipe or in the area it may affect your engine. Don’t forget that if you take it off you WILL loose low-end torque.

First of all, no internal combustion engine needs backpressure. Any work the engine has to do to push exhaust out is work against the engine. However, in today's computerized world engines are designed to work with the pressure and won't operate properly without it unless you recalibrate things, if you know how. That's the beauty of older vehicles. If the O2 sensor is in the headers as is my '88, the engine doesn't know the difference other than breathing easier. The two most noteable difference with my bone stock 350 were increasing the gas mileage on road trips from 19 to 21 (that's a 4X4, mind you) and chirping the tires on the 1-2 shift on dry pavement. Now she already had full length headers and got true duals (2 1/4" is optimal for best torque, bigger duals slow the flow and cost you. This is the mistake most 4-bangers make with sewer pipes) with two chamber Flowmasters with the deal.
BUT, in the end, unless you want to experiment with moving the O2 sensor, recalibrating the engine, and risking a heavy fine ($10,000 in North Carolina) it just isn't worth it. To top is off, it's irresponsible as hobbists and it's not something I'm proud of. A pair of high flow Catco cats tuned the sound from obnoxious to a respectable rumble that won't be mistaken for a tuner.

[QUOTE=67malibu]First of all, no internal combustion engine needs backpressure. Any work the engine has to do to push exhaust out is work against the engine... Now she already had full length headers and got true duals (2 1/4" is optimal for best torque, bigger duals slow the flow and cost you. This is the mistake most 4-bangers make with sewer pipes) with two chamber Flowmasters with the deal.QUOTE]
This is untrue. you need at least some backpressure to keep your low end. And you proved this in your own statement above. You said the less work the engine has to do to push exhaust out, the better, right? Now, would you agree that it takes less work to move slow than fast? If you had to RUN a mile you would be more tired than if you walked right? You also said that its best to run 2 1/4" pipes over 3" because the 2 1/4" moves the gases faster. The faster the engine pushes the gases the more work it is doing, Therefore, the engine has back pressure. You just proved in your own statement that the engine needs backpressure to keep low end torque.

We're talking basic physics here. There is an optimal size for a piece of pipe to maintain the highest flow with a given volume of gas or liquid traveling through it. You can calculate this just as engineers do every day that design everything from water pipe systems to racing exhaust. Why don't mustangs, corvettes and even vipers have sewer pipes? It would be an easy way to get more horsepower. Why don't the vast majority of racers use exhaust systems instead of straight headers? Wouldn't they be gaining torque?
You're thinking the engine has to further accelerate the gases which it would if you necked the line down. Keeping dual lines the same size as the collectors maintains the same flow rate. Some collector actually neck the exhaust down a bit with a venturi-like design to better scavenge the gases. But when you neck the line up, the gas slows as it enters the larger pipe. This decease in velocity causes pressure backward from that point as the gases 'stack up' due to the slowdown.
Now, the length of the pipe also factors in because of the drag created. The longer the pipes, the more friction the gases encounter. This is why racing systems are short as practical. If you port out the sides as in Nascar or Prostreeters, you use sewer pipes because a shorter pipe lends to less friction and you're producing alot more gas from burning way more fuel than a street vehicle. Think about it, have you ever seen a factory, aftermarket or racing system that necks the pipes up (for duals) after the collectors? There's a good reason. I'm an industrial scientist, man, I know physics doesn't always make sense but it is what it is. Best system you can do: put the cats and mufflers as close to the headers as possible then dump it.
Keep in mind this is all for engines designed for optimal performance, not the production vehicles designed and calibrated to operate with back pressure. Loss of back pressure on an engine built and tuned to have it can easily cause a lack of performance without retuning. Sorry for the long post. As far as running/walking a mile, don't confuse work with energy. Whether you ran a 4 minute mile or took an hour long walk, the same amount of work was done.

A simple test would be to blow through a straw and then blow through a piece of 1" pipe, and see which one is easier to blow through. You said that the smaller 2 ¼” pipe is better than the 3” pipe. That is because the 2 ¼ “ pipe has more backpressure than the than the 3”. You need at least some backpressure for best fuel mileage and torque. At least this is what we were taught at Wyotech.

. We're talking about maintaining the flow that is exiting the collectors. Stick with the diameter of your collectors to keep from slowing it down. Slowing the flow = loss of scavenging effect. As far as 2.25/2.5 versus 3 inch pipe, take 12 to 20 feet of said pipe providing friction to slow things down and run the calculus or the dyno and there is a balance to maintaining flow versus pressure build up. It's been done and reported in various articles as well (no, I don't keep them so I don't have a particular ariticle.) This is of course for your average small block. Fire breathers and big blocks produce more gases and need larger lines.
. As far as engines needing backpressure, I again point to my statement about an engine whose cam profile, air/fuel mixtures, timing curves, etc (modern production vehicles) have been optimized to operate with said pressure. Change the optimized conditions (remove pressure) and the engine is no longer optimized. Change some of the other factors to compensate and you get better performance. Again, as I said before, look at any high performance non-emission engines (racing, prostreet, etc) to see if what they think of backpressure. Any work the engine the has to do to expel exhaust gases is work against the engine. It is true that shorter duration cams (i.e. most cams found in stock trucks) can develop a little more torque with a small amount of back pressure but this is a compromise to get lower emissions with the overall setup and not performance.
. After freeing up the exhaust and intake and adding a bigger TBI on my 350 (a less computer controlled and monitored OBD I engine) I advanced the timing to 4 degrees BTC. Gas mileage did suffer about 1.5 mpg (and limits to running high test only) but the power increase in the seat-of-the-pants-ometer is unmistakeable. The newer the vehicle, the harder to make changes without screwing up things. The same changes on non-computer hindered engines (i.e. my 64 impala 283 and 67 chevelle 327) lent themselves to both increases in gas mileage and power (automatics, so they are set at 8 degrees BTC.) In a 4000+ lb impala, I'm getting 22 mpg on road trips with the powerglide (on my list to chunk one day.)

So your saying it doesn’t pay to have anything bigger than your collectors. That would make sense because it’s only going to flow as much as your headers will allow it to. You do loose some fuel mileage and your torque curve shifts higher up the RPM band, which would be my guess as to why racers use open exhaust. This wouldn’t make much sense for a truck. I’m not trying to start anything here, I’m just probing you for as much info as I can get.