I have been running through so many exhaust options on my car the last few weeks, I've finally got a plan until I have the money for a nice system. I plan to cut the cat off and replace it with a cutout. My dad is a long time mechanic. He is set and firm that if I do that, I will ruin my heads within 3500 miles. I want to believe him but so many of you use these things, I don't think they would do that kind of damage. Please any ideas, or comments would help me alot.

Car is a 1994 Z28 stock besides the K&N FIPK

 

I've had my cutout open for over 3500miles since I've owned the car. So no, it will not hurt your car.

 

no, it won't.

 

the location of the single cat on the 94s will be more than sufficient distance from the engine to prevent burning a valve.

running open manifolds may do it, but not a cutout at the cat.

there is some truth to what he is saying, but specific to your car...no

 

what about on longtube pacesetters would it hurt the exhaust valve with them open?

 

No. Like noted, running open manifolds would do it, and some report running open shorties. You will be fine. I've had mine open for about 10,000 miles with no problems...Except for an exhaust leak at the manifolds *not caused by the cutout, obviously.*

 

This is one of those old myths that refuse to die. A little thinking should make this obvious. It's 20* below zero and your car has been sitting out all night. You jump in and start it without a single worry, instantly exposing the valves to 1600* temps. Your valves don't warp. The intake air is hitting one side of the intake valve at -20* right after the other side was exposed to 1600* and they don't warp. So why would exposing the back side of the exhaust valve to 70* temps. after shut down warp the valve.
WWII fighter air craft that fly at 30 to 40,000 feet where the temperatures are very low (sub 0) have very short exhaust pipes with no mufflers of baffles and they don't damage the valves.
Burnt valve are usually caused by high combustion temps., due to a lean mixture, not low air temps.
Every race car in the world, including F1 engines that run 18, to 20,000rpm, use to run open headers with out fear of damaged valves.
If any one knows of a single scientific or technical paper that explanes how you can damage a valve by exposing it to normal air temps., please post a link so we can all be educated.

 

If you put your exhaust valves in a vice and beat on them with the cut-out, then they would damage them.

The cool air traveling back up and warping or such an exhaust valve is total BS.

 

I ran my pasesetter longtubes open until i got a ticket with no problems


Man i love that sound

 

Its not the cold air but the fresh air that can damage them, if its close enough for fresh air to come back up the pipe and theres any unburnt fuel... it will reignite the fuel and burn the valve.

 

This is a myth that wont die, I ran open long tubes for months.

http://www.auburn.edu/~doddsam/Beast.wmv

Just couldnt drive it on the street.

 

That doesn't make sense either- a lean burning engine will heat the exhaust valves (and make the headers glow) long before some exhaust backfiring will. The valves are subject to combustion temperatures and pressures on one side, makes sense that the other side could handle it. The only reason the valves could have problems from headers is from a lean fuel ratio that is a result of fuel management problems (tuning & O2 sensors).

 

green you sure about them glowing from running lean? everything i've heard says its not lean but running the timeing too retarded that causes them to glow.
and when they are subjected to cumbustion temperatures they are seated, being seated helps them cool, thats why running the valves too tight or otherwise unable to seat will cause them to burn.

 

Each cylender pushes some exhaust out about 8 times every second at 1000 RPM with one bank of cylenders pushing throug one collector how often does fresh air make its way back up to the exhaust valve?

 

Again this makes NO logical sense. The exhaust temps. at the valve during the exhaust stroke, at valve opening, are much higher then the temp. of any unburnt fuel that may reignite in the header. This also, usually, occures farther down the header not at the valve. Unburnt fuel normally comes from an over rich mixture during deceleration. You see this a lot at sports car races as the cars decel. into the corners. I can't think of anyone who has burnt valve because of an over rich mixture.
Back to my air plane example, private N/A piston air planes have manually ajustable mixture controls, so the pilot can lean the fuel at altitude, where the air is thin, to improve fuel economy. I don't know of a single example of burnt valves from running over rich, but it happens all the time from over lean mixtures. This is why many airplanes have EGT gages to warn the pilots if there exhaust temps. are getting to high.
One of the things your emmision air pump does is inject fresh air into the header right after the valve to help burn off any unburnt fuel. There is even a tube that gets the air as close to the valve as possible. So all modern engines should have burnt valves.