I heard this also. When we swapped the 400 into my 72 GS350, when I was in high school, the mechanic said that he'd drive it to the exhaust shop because you have to be careful with decellaration and cold air hitting the hot valves. I'm guessing the difference between some straight pipe and open manifolds is the length to the head. If you've got a staight pipe, there will be exiting exhaust always on it's way out. With open manifolds, you're only several inches away from the head, and there wouldn't be the consistent outflow of exhaust keeping cold gas from coming back in. ...or this could just be an old wives' tale o No:
An exhaust guy told me not to drive the car very far on open headers, for fear of burning a valve. This was just before I put headers on my car, and was looking for pricing info.o No:
the manifolds are not going to be too loud but it is not very good on the engine and it is going to get VERY hot under the hood this may melt and protective coating on wires etc i dont suggest that you drive it
I'm surprised that no one has mentioned that the exhaust from a stock cammed engine is much quieter than from one with increased exaust duration. I,ve driven four or five vehicles 10+ miles to the muffler shop without any problem.
