but not becuase of the lack of back pressure. only way your going to do somthing like that is neligencee on the build of breakage.. o the word that i ment to put erlier is retainers (holds=reatainers)

 

i have seen it happen to peoples cars just running straight pipes on a car that isnt a race engine that has 65k to 85k on the motor they say they sisnt know that is could suck a valve when they needed a rebuild.

 

curious and wantin some awncers you arn't providing i have been doing some search sucking down a valve i have not found a damn thing about what i have found is rapid cooling of the exhaust valve

 

and warping it but everything i have found is on open headered cars, cutouts and verry little exhaust.. but no full length on daily driven cars

 

You wont find anything on it because IT DOESNT HAPPEN.

 

Only way a valve is going to bend is if it makes contact with the piston- it sounds like you are describing valve float due to too light or worn of valve springs for an application.

Also, wouldn't less back pressure actually help hold the exhaust valve in better? Think about it, lets say you have all kinds of mufflers, cat, resonator, etc on the car- and the exhaust has a hard time getting out- so lets say you have 10psig of pressure in your exhaust manifold (random number thrown out there), that 10 psig would be trying to push the exhaust valve off its seat. Now, cut everything off and straight pipe it- and say you lose all your backpressure- and the exhaust valve is at atomspheric pressure- or 0 psig. This should mean that the exhaust valve would actually have an easier time staying pulled into the head with less and less back pressure- even if you go so far as to say you end up with a vacuum on the exhaust side, that would actually help pulling the valve clsoed.

I strongly disagree here- they aren't rebuilding because their valves are bent. They are rebuilding due to metal fatigue- at those extreme power numbers, stuff wears far faster than normal, and stuff gets stretched and twisted to levels never seen in a street car. If that was the main reason, why wouldn't they run mufflers and just not rebuild the engines?