Guinea Jay

After welding up one of my 85's mufflers once I decided to pull em off. I was just gonna get some pipe bent and bolt it on in their place but my friend says pull out the cats too. Might as well I say.

They're not bad, no actual stink, just figure I'll get a bit more power and sound. Anyone done something like this? Any problems or suggestions?
I Just got it inspected so that's not a worry and I don't have the cash for a new exhaust.

c-4 lhozwalte

might want to check out youtube there are quit a few c-4s with "muffler elims" on there.if your looking for real loud your on the right track.to me it has the sound of low performance,kinda like daddys ol lond bed farm truck.

WW7

Pulling the mufflers is one thing but if you pull the 2 cats off its going to sound like a piece of junk going down the road, and you had better have a supply of aspirin for the headache your going to get from the noise...WW

BrianCunningham

Mine's an LT1, but I'm currently not running mufflers

Meloyelo90

For what it's worth -

I'm running my 95 without mufflers - sounds great to me. It was a little loud at the beginning but now I'm used to it and love the sound.

c4cruiser

You may lose some low-end torque with straight exhaust. The L98 likes some back pressure at low RPM.

You can remove the pre-cats but leave the O2 sensor in the same spot. There are high-flow main cats available that are a bolt in. Then you can run a good performance muffler for better sound. You can weld in short pieces of pipe in place of the pre-cats.

My 87 is pretty much a dedicated autocross car and I run true duals with Dynomax Ultra-Flo oval race mufflers. It's still licensed for street use and the sound is not that bad at low RPM cruising. Very little interior resonance even with no carpeting in the car. But WOT is a different story. They are pretty loud at that point.

c-4 lhozwalte

damn that does sound good.no cats,no muffs,and no resonator?

BrianCunningham

I still have cats & resonator

ggrassmid

I gutted the CAT on ym 85; think it was orginal; I also have those targa type mufflers from ecklers, I think they are glass packed. I really like the sound, I've taken many long distance trips with it and I have no problems with the sound bothering me. i dont know if I'd like the sound of true straighs all the time, for track use I think ti would be fine, but driving around and cruising... all your choice though.

pearlvett

Im running straight pipes with only moroso spiral flow mufflers and i think it sounds great! It sounds really good at idle with my cam and all

WW7

Its ok to remove the cats, its ok to remove the mufflers, but if you remove both at the same time that baby is going to be way to loud for the average person to handle, and if your on the street you wont get 2 blocks before a cop has you .Ask me how I know..Ive finally just settled on leaving the cats and removing the mufflers and using muffler eliminators and it sounds great..Just my 2 cents..WW

M.J.L.

I run true dual straight pipes with flowmaster 40 series. I set off car alarms....

RC000E

This is one of the MOST classic false statements ever made. NO motor likes backpressure. I feel like typing, and since I do an easy 80wpm with no mistakes...lemme explain a little for those willing to read.

First, lets be sure we all understand backpressure. Backpressure is "backing up" residual gasses from the combustion process in the exhaust.

Fact---- torque curve VERY closely follows volumetric efficiency curve. This means that torque production, especially at lower rpm, is going to be the result of port velocity and cylinder fill. That means bringing in the largest fresh charge of fuel and air, for the highest resulting brake mean effective pressure possible (via combustion), which acts upon the piston and turns the crank, creating rotational force.

Volumetric Efficiency, simply put, is the percentage of fuel and air that is drawn into the cylinder through induction, versus the true volume of the cylinder under static conditions. In other words, your 5.7 liter is a 5.7 liter when measured in a static condition, but when running at low rpm its like your Corvette has a 4 banger! I'm just kiddin...I like messin with you V8 guys sometimes. Literally though, most OEM motors never achieve 100% volumetric efficiency, maybe 85% at best, but the concepts being discussed here, when optimized, are responsible for exceeding 100%...without a turbo or supercharger! If you've ever heard the term static compression and dynamic compression, volumetric efficiency is directly related. Static compression may be 10:1, though when running your compression is commonly much lower.

So, now to the statement that a motor WANTS backpressure to create torque. We know that torque is the result of better cylinder fill, so how can backed up spent combustion byproduct in the cylinder lead to more fuel/air mixture to burn and thereby create more torque? It can't.

So then many say, well then why do motors make less torque when changing exhaust to a larger diameter, or removing "backpressure" creating devices like cats, etc? It's because when you alter an exhaust in any way, you alter the scavenging characteristics of the exhaust to remove byproduct from the cylinders.

To explain this simple, isn't really easy, because exhaust science is pretty complicated, as anyone who's truly studied it knows. The best example I can use to visualize whats happening in your exhaust is with a bucket of water. Imagine dropping a pebble or even another drop of water in the center of the bucket of filled water. You'll see waves initiate from where the drop broke the surface and they will travel outward, hitting the outside of the bucket, then return towards the center, hit the center and return to the outside. Alter the diameter of the bucket and this happens at a different speed, etc.

Exhaust waves happen very similar to this and inside the header tubes it creates waves of varying pressure (peaks being higher pressure, troughs being low pressure). This frequency is altered by the diameter of the tube, the temperature, shapes in your exhaust that create blockage, etc and effect the speed and frequency of how those waves bounce back and forth of the face of the exhaust valves.

Now, the way this helps your motor make torque is the timing of those pressure waves in relation to when the exhaust valve is opening. The rpm of your motor dictates the intervals between the opening of your exhaust valves (low rpm=longer intervals, high rpm=shorter). Just the same, at various rpms your exhaust system, with pressure pulses (using simple language here) bouncing back and forth, will present varying pressures at the exhaust valve depending on rpm. If the pressure is higher than ambient pressure when the exhaust valve opens, then some residual exhaust gasses will backflow into the cylinder and if the pressure is lower than ambient the cylinder will evacuate into the exhaust more efficiently, creating the potential for more cylinder fill on the intake stroke.

(SIDENOTE) I should mention, this is very much where cam overlap also comes into play, where the intake valve opens just before the exhaust valve closes to use intake valve fill to "push" residual gasses out. Pressure waves in the intake then come into play also...but that'll just scramble your brain worse if your new to this.(END)

So, it's not backpressure that's creating the torque, its the conditions within the exhaust, which peaks at varying rpms based on its design that's helping the motor to produce torque. This is why you see headers designed with varying lengths, diameters, stepped tubes, varying angled collectors, and many more design nuances that exhaust systems have.

Like I said, the factors that come into play are many (cam science, compression, intake design, etc), but I tried to explain this as simple as possible. Having studied exhaust and intake science and design for many years through my business and the custom headers and manifolds I've built (avatar), its been a many year journey and I still could learn a ton I'm sure. I've got a lot of material from various authors, as well as a large journal of combustion experiments done at MIT many years ago...though your calculus should be up to snuff to go through some of it. Luckily, I read the bulk of it while I was taking calc, so it helped my understanding. Rewriting or regurgitating it is tough though. So, if anyone is interested in some material suggestions, I can give you many authors and books to buy.

I hope this at least dispells the myth that backpressure creates torque for a few here. That or everyone is gonna start arguing....which is pretty common too cause it's a pretty long standing myth/statement people have made...lol.

WW7

Dude, your fingers are going to be worn out by the time you get 4 stars.....WW

RC000E

Shoot...this is 10 years of forums and countless website articles still goin strong...lol.

M.J.L.