So I just got a new exhaust manifold , and I need to know if I should get new bolts to bolt the exhaust header onto the engine , also can I keep my new manifold on without a heat shield ? Lastly , what are the torque specs for the manifold ?

 

Google my friend.

They use studs, not bolts generally. Reuse what is on there. You don't need a heat shield. Very few aftermarket exhaust manifolds have heat shields. Torque specs for header to cylinder head is 22 ft-lbs.

 

If the manifold is cast iron it will need a heat shield to prevent cracking. If it is a tubular steel manifold it should be fine without one.

I don't have the spec off the top of my head for torque, but it is around 20ish some foot-pounds plus or minus. If you replace the nuts make sure they are corrosion resistant.

 

Really? Why do they crack? I have my cast manifold without a head shield right now. Never heard of them cracking. Also, my turbo manifold is cast iron with no heat shield, should I be like super worried about that? I'm being serious. I've never heard anyone ever say anything about heat shield preventing cracks. I thought it was to prevent heat soaking of the radiator/AC.

 

Cast iron is a very rigid material, pushing cold air directly over it while at the same time throwing hot exhaust out will cause the material to stress, and eventually crack. This is particularly bad if the manifold has stress on it from installation. (IE doesn't quite fit)

Any parts that get super hot should have a shield around them to stabilize the difference in air temperature flowing around them.

 

While technically that is correct about the temperature change possibly causing cast iron to crack, it is not at all a common occurance from not running a heat shield. Over a period of time, heating up to operating temperature and cooling to outside temperature, will eventually wear on the material and crack the object.

Very much like anything that gets very hot and cools over and over, it will take its toll on the structural integrity of the material.

The primary function of a heat shield is to prevent heat from getting to other objects. When they put a heat shield around the wires going near your exhaust it has nothing to do with keeping anything into the wires, it is to keep the heat away from them. The early civics, before the days of crossflow cylinder heads, had heat shields between the carburetors and the rest of the engine so that the high temperatures from the exhaust manifolds didnt get up the the fuel in the carburetor bowl.

 

In my opinion the primary function of a manifold heat shield is to protect the manifold. Vehicles produced with a tubular steel manifold do not require a heat shield, as the metal is ductile enough to comply with the temperature extremes. (cant speak for the welds though). Thin cast iron will break very easily, so cast iron manifolds must be much thicker. While saying this does prove your point of shielding heat to some degree, I believe it is of secondary importance. Either your first and I am second, or I'm first and your second, we both have good points.

In my defense most engineers would not route wiring near the exhaust if they could help it.

 

If they could help it. But that O2 sensor! Anyways, I thought you were going to bring up something completely crazy. I understand the cooling cycle thing. Would heat crap help a cast manifold?

 

Fair enough...lol.