Other than noise what harm would be done if the engine were run for a short period at low revs with all of the exhaust/mufflers off from the manifold back?

 

I don't know for a fact, but I have been told buy a few mechanics that: running open headers/exhaust manifolds is OK for short low rpm runs. However, one risk is "drawing cool air back into the short exhaust manifolds and potentially warping your valves."

I will defer the the "Might Mechanic Gods" of the list to confirm or deny.

 

I have heard about the exhaust valve issue as well..

 

Well... I'm gonna call BS on bending the exhaust valve. The temps involved in the combustion chamber are several orders of magnitude above ambient. Any reversion thru the pipe has been superheated before it ever sees the valve seat. How do you explain generations of drag racers running open headers? The 2 ft header pipes coming out of dragsters is a good example. They tear down between rounds to look at bearings but I've never seen anyone replacing exhaust valves.

 

To Mikes point, I've seen plenty of people at the drags w/ all kinds of car/engine combos that unbolt their exhaust for a night of racing.

 

If you look closely, after a dragster/funnycar has been started and shutdown, a custom cover fitted over the the ends of the exhausts. This is to prevent the cool air from reaching the valves and warping them. It is not an airtight cover, but it substantially limits the reintroduction of outside air. It is typically just held in place by gravity.

 

Power boats often run at high throttle all day long with open exhausts and don't have any problems.

 

Perhaps the 7000 degree exhaust valve temperatures (and exotic materials?) of a dragster are more likely to develop problems than those subject to the more modest circumstances encountered in our passenger vehicles.

 

The warped exhaust value caution was always around running without exhaust manifolds, not open headers or open exhaust manifold.

Run it all day without the mufflers or even the down pipes.

Just don't kill anyone when you knock off from the fumes.

 

My first concern would be the heat generated from the exhaust and the areas near the exhaust outlet..if your moving along it may be better, but i wouldnt sit idling for long! <img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

 

I drag rcae four valve motors all the time with VERY short exaust on nitros. These valves are ver small 1.3litre engines.....you wont have any problems running it with just the exaust manifolds on. Maybe with the neighbors and the cops.