super loud

[dennis ss]

I was going to the track Friday night and decided to run an open exhaust. I just pulled off the y-pipe and ran it wide open. Loud as hell and picked up almost 2 mph. Someone stated I could ruin my engine buy running open without the y-pipe, is that true? I have stock manifolds for now but with it open the ls1 revved quickly and pulled hard.

[Smittro]

IIRC, you guys need a little scavanging effect. But with logs on it i don't see it as hurting it too much. I just would'nt do that alot imho.

[dennis ss]

So some back pressure is good then. Maybe getting a cutout instead of removing the y would be better then. Thanks for the info. I was gonna pro charge it but I'm getting a new Z06 next year so I don't want to put to much into it.

[c5z28]

You should be more worried about the o2's being that close to the open air.

[dennis ss]

You should be more worried about the o2's being that close to the open air.

My rear 02 sensors are cancelled out from having the cats removed

[Too Fast]

I was going to the track Friday night and decided to run an open exhaust. I just pulled off the y-pipe and ran it wide open. Loud as hell and picked up almost 2 mph. Someone stated I could ruin my engine buy running open without the y-pipe, is that true? I have stock manifolds for now but with it open the ls1 revved quickly and pulled hard.

Not necessarily true. IF you run it open manifolds, all the time, there is a small chance a valve could bend, by running her hard then shutting off the engine. Hot valve + cold air = possibility of warping a valve.

Sounded great open manifolds, eh?

With LTs, bending a valve has not happened AFAIK, since the LT makes it harder for cold air to get to the valves. Think about all those drag racers who run open headers with no issues....

Also, since you gained some MPH, this also proves that there is something to be gained with a massively free flowing exhaust. Yeah, you *may* lose a bit of low RPM torque, but usually the high RPM HP gains offset that. Especially since you gained some MPH. However, that could be attained by different weather conditions. A lot of people lamented the loss of low RPM torque with the demise of the LT1, but that was quickly overcome when they found out the 1/4 mile times with the "torqueless LS1" were so much faster/quicker.

[my95z28]

There aren't any issues running like this when WOT. The problem is cause when you are idling or at low rpm. There is a very small amount of exhaust present, and fresh air can actually enter the open end of the header and contacting your o2 sensor. This causes the engine to see what it thinks is fresh air, dumping massive amounts of fuel. Therein lies the danger.

[Too Fast]

^^^But not really a danger to the engine, unless it is so rich with the excess fuel that the oil gets contaminated/too thin with fuel contamination that it ruins the bearings.

Other than that, you are right since the engine will run too rich due to a false lean condition being reported by the O2 sensors, but that is a safer way to run an engine than being too lean.

[Z28_Driver]

I have been running my 400 chevy powered truck with long tubes and 14 inch downtubes for 7 years without any problem, most of it in the winter. Not sure I understand how cold air is going up the headers with the engine running. I just let it idle for a minute after driving. No problems yet.
No cats or o2 sensors of course.

[c5z28]

My rear 02 sensors are cancelled out from having the cats removed

If you removed the y-pipe that just leaves your fronts then

[sjgreen6]

Given your set-up I wouldn't worry so much about engine damage but you might want to make up a couple of extension tubes 12-18 inches to see if adding a little pipe gets you any more speed.

[my95z28]

^^^But not really a danger to the engine, unless it is so rich with the excess fuel that the oil gets contaminated/too thin with fuel contamination that it ruins the bearings.

Other than that, you are right since the engine will run too rich due to a false lean condition being reported by the O2 sensors, but that is a safer way to run an engine than being too lean.

It can most definitely run that rich. Think about it, those o2 sensors never see air that is even close to that good of quality. It will run rich enough to wash the cylinders and get in the oil, and if not caught soon enough, toast the bearings.

I have been running my 400 chevy powered truck with long tubes and 14 inch downtubes for 7 years without any problem, most of it in the winter. Not sure I understand how cold air is going up the headers with the engine running. I just let it idle for a minute after driving. No problems yet.
No cats or o2 sensors of course.

Because you don't have upstream 02s that adjust the a/f ratio, this is a non issue. Even if you did have active o2s, the 14" extensions are enough to keep all unburnt air out of the header.

[Mr. Luos]

At 25% the engine will throw a code....

I see no problem with doing this....aside from the O2's going bad faster than normal.

[Too Fast]

I have been running my 400 chevy powered truck with long tubes and 14 inch downtubes for 7 years without any problem, most of it in the winter. Not sure I understand how cold air is going up the headers with the engine running. I just let it idle for a minute after driving. No problems yet.
No cats or o2 sensors of course.

The relatively cold air won't travel that far on a running engine, but it *may* get up there after you shut it off. That's when a few people have bent valves, or so they said. But your situation with LTs and a downpipe, I hardly think it's possible.

As for cars with O2s, any small crack anywhere near the sensor (let alone a couple pipes missing) will have them report as (false) lean to the PCM, which will command a richer mixture. I've dealt with small cracks in an exhuast that's done that, you must remember that the exhaust flow isn't a constant thing, there are pressure waves under most circumstances, and a little negative wave will suck in outside air giving a wrong sample to the sensor.

[dennis ss]

I lost some low end torque but thehigh end was worth it. I will just pull the y only on track days so I can avoid any problems. I have stock manifolds so I didn't expect the gains I received. Thanks for the info guys.

[Z28_Driver]

The relatively cold air won't travel that far on a running engine, but it *may* get up there after you shut it off. That's when a few people have bent valves, or so they said. But your situation with LTs and a downpipe, I hardly think it's possible.

As for cars with O2s, any small crack anywhere near the sensor (let alone a couple pipes missing) will have them report as (false) lean to the PCM, which will command a richer mixture. I've dealt with small cracks in an exhuast that's done that, you must remember that the exhaust flow isn't a constant thing, there are pressure waves under most circumstances, and a little negative wave will suck in outside air giving a wrong sample to the sensor.

Thanks for the explanation. I see the pulsation in the smoke when its cold, just never thought about it. It makes sense.

[Too Fast]

Thanks for the explanation. I see the pulsation in the smoke when its cold, just never thought about it. It makes sense.

Your welcome, that's what I try to do here.

Disspell rumors, and occasionally get corrected!