Originally Posted by 72Chevy_Shane
Would it hurt to run the motor straight pipes...Ive always heard it would hurt the valves and this that and the other
Probably not hurt the motor, probably won't help either, just make noise.
If your running factory manifolds, these are restrictive enough that running open pipes just bounces against manifold capabilities which going beyond duals with decent mufflers is just no further help.
If you're running tuned headers and a cam or have an emissions tuned fueling system you can go from nothing happening to serious trouble depending on cam timing, compression ratio and whether the fuel delivery system can recognize and adjust for the mass flow efficiency changes. When headers are involved open pipes can really and suddenly make them work as intended which will pull really hard on the intake and fueling system. The more aggressive the cam the more it will respond to exhaust system improvements. If the fuel delivery system (carb or FI) can't adjust to this change the mixture will fall lean resulting in an increase of in-cylinder temperatures which can themselves damage the valves and they can foster preignition or detonation which will damage to destroy pistons and spark plugs as well as valves.
In most cases you will find it necessary to tune for the reduced back pressure which minimally involves richening the mixture and changing the ignition timing.
People seldom realize how much fuel is used to manage in-cylinder (combustion chamber) temperatures. Liquid fuel takes a lot of heat to vaporize so used to excess at wide open throttle positions it is used to cool the mixture below the detonation limit. This is in addition to all the other mixture ratio issues you can get into. The manufacturers use exhaust backpressure to keep a little residual exhaust in the cylinder which has the same effect on temperatures as over-fueling but provides better fuel mileage. So when increasing the engine's mass flow efficiency, you can expect that you'll have to pay for it with decreased gas mileage across the operating range.