I've had some people tell me that in this cold weather and having the open manifold, my valves can be warped. This of course scares me. I have 2 questions

#1 - Is it true. The logic is sound I guess but hey it could just be a myth and I'd luck out (ok maybe not)

#2- What can I do about this? Am I forced to put on exhaust? Will having full length headers help remedy this at all?

I will be putting on exhaust, just don't have the means to now. But if it really is that bad, I might not run it til I have exhaust. And that would suck.

 

why are you driving the car with open manifolds?

 

Haven't been able to put on an exhaust yet... and its not been out daily or anything, just an occasional weekend night cruise (only had it done for bout 2-3 weeks )

 

Running with open exhaust ports can cause warped exhaust valves, but running with open manifolds is really no different than running with open headers. You shouldn't have any problems.

 

i have run all 3, open manifolds, open headers, and open exhaust ports. never warped a valve yet.

 

Well after reading what you guys had to say I thought nothing of running with open manifolds and now I have burned valves * crys*

 

I think there are a lot of factors here..header design and length, head design, head material valve material.....tons of variables. I believe what causes them to warp/burn is rapid heat cycling between exhaust pulses. Im not fully sure of the theory behind it but I believe its something to do with the extra exhaust retaining heat. Maybe its that the manifold itself is too open on its own and never gets hot enough to heat the air around it, causing the heat cycling. I dont know.....but what I do know is, why risk it? Only time I ran my motor open headers was doing the initial fire and timing/idle set, and making sure it was square. After that I shut it down checked it all over, and put the exhaust on.

 

Many times what causes the valve to burn is it not seating to the head properly. The valve is dependant upon transfering heat to the valve seat. If for some reason the valve isnt seating properly, it can cause it to burn.

 

So how much exhaust piping is enough to be safe from any problems?

 

The theory is that after the engine has gotten hot and then turned off, a couple of the exhaust valves will be off the seat. When cold air from outside gets up into the exhaust manifold, the unseated valve will cool unevenly and "warp" the valve head. When the engine is run again, the valve doesn't seat properly and burns.

"Enough" exhaust is enough to warm the air getting back into the manifold/header so that it doesn't unevenly cool the valve head. Long tube headers are typically enough.

I've never had it happen (but I haven't run open exhaust manifolds regularly, either).

The other theory is that when an engine tuned for muffled exhaust is run with open manifolds, the mixture leans out so much that the exhaust valves get too hot and warp/burn.

 

I had a 1205 watt light bulb near the door in my garage. It was on and very hot. I stut the light off and opened the garage door one january afternoon. The cold air hitting the hot bulb caused it to shatter. the same thing is *possible* with a red hot exhaust valve and cold air. It could crack. I would not run open manifolds. Open headers are generally ok because the tube has enough length that the air warms up quite a bit before it reaches the valve. However, manifolds are a bit on the short side.

You may have problems, you may not. The question then becomes...Do you feel lucky?

 

now she runs like crap and backfires. So now I have to get new heads or get these rebuilt now right

 

Five-seven is dead on with this. I did initial run-in of my most recent engine on a test stand with no exhaust. Had to screw the idle screws almost out of the carb to get a decent idle. I put long-tube headers on with it still on the stand and it ran so rich I had to turn in the idle screws 3 turns to get the idle back. I would have thought the diference between open headers and no headers would be negligable, but is not the case. I think that any carb that is setup for an exhaust will be more than lean enough to burn valves with open exhaust.
It's like the old wives tale that if you put a battery on a concrete floor instead of a wood block, it will "drain the juice" out of it.
Batteries have always been put on a block of wood to keep from making a permanent white rectangle on concrete, not to keep them from going dead.

 

actually, the myth comes from the first batteries being made with a rubber case. leaving them sit on concrete would cause some sort of reaction that would neutralize the acid in them, rendering them useless. since the cases have been switched to plastic, we no longer have to worry about it.

 

You'll probably need a few new exhaust valves. THere shouldnt be any permenint damage to the heads themselves.


I thought it was because during the winter months, when you'd likley be storing a battery, the concrete would cause it to freeze more readily. Now I know the real reason