Running an engine in "cold" weather with no manifolds.
 

Let's discuss, and get into it whole-hog once and for all, the whole running and engine with no manifolds in cold weather thing.

b) with manifolds but no further exhaust pipes.

what about it? probably would disturb the neighbours

As a teenager (which was a looong time ago), I was told that running an engine with only the exhaust manifold could result in warped valves, because after you shut it off the valves would cool too quickly. I never really knew if that was true or not. I just remember being told about it. However, I never had a problem with warped valves on any engine.:confused:

Old wives tale

Here is what will warp the valves... Detonation....make the valves real hot.
(usually too much timing @ WOT)

lack of idle timing on a cammed up motor... makes the valves real hot.

lean AFR @WOT (usually from a stock fuel system that cannot keep up) makes the valves real hot.

Add these three together and you are guaranteed warped-tuliped valves.

What happens when you run a engine with open ex manifolds or no manifolds at all is raw cold air (oxygen gets to the valves
(THAT ARE ALREADY WAY TOO HOT) and warps them. Sometimes the valves even crack.

One or more of these hot valves overheated valves conditions has to be present. (the valves actually glow red hot)

When the engine is running correctly, without one of these conditions present causing the valves to overheat, open manifolds, no manifolds, open headers etc etc
WILL NEVER warp valves.

All three of these tuning errors are common with inexperienced tuners.

Ayuh,.... My question is,... Why would you Want too..??

Had a friend back in the 80's who let his 64 chevelle sit outside with no manifolds on it.Valves rusted to the seats and engine wouldn't turn over.He sold me the car and I soaked it with Kroil and it freed up!

Old wives are pretty smart sometimes. It is absolutely true, allowing "cold' (ambient) air to get to hot exhaust valves (the "open" ones) WILL warp them. I have seen a Harley valve bend so bad it broke when he tried to fire the engine again. It makes perfect sense. The air approaches the hot valve from one direction, cooling one side much more rapidly than the other.

When we "run engines in", and use only the manifolds, each of us are ready to stuff a shop towel into the manifold immediately upon shut-down. I would never consider firing an engine without at least manifolds.

FWIW

Jim

Well, to put to rest once and for all the whole, you'll warp a valve thing.....

Like here, we have first hand anecdotal evidence of such an occurrence. Perhaps a first hand "mythbusters" type experiment is really necessary?

Of course it is.

I watch oval track races at the Taft track (Orlando Raceway) back in the '60s that had many low-buck race cars that used absolutely NO exhaust manifolds at all- nothing, zip, zilch, nada.

These guys were not front runners, mind you- they were in it for the fun of it. But these same guys- running the same engines- were there week in week out, for the entire season, and there's no reason to think these same engines weren't run for several seasons, and know what? Nary a warped valve to be seen.

Completely untrue. Keep in mind the components in contat with combustion are are feeling 1200 degree exhaust gases. Just because our subjective interpretation of 70 degrees is "warm" and 30 degrees is "cold" doesn't mean the stainless steel in your valves is going to notice. 40 degrees compared to 1200 is a drop in the bucket, and probably won't make almost any difference in how long it takes the valves to reach ambient temp.

K

At minimum use manifolds. No way the cold air is gonna come backwards up the manifolds at hit the valves. I wouldn't run with no manifolds, although nothing would probably happen i wouldn't want to risk that the "myth" actually be true.