Since it's cold, let's discuss the whole, "you can't run an engine w/out exhaust mani

If a man speaks in the forest, and there is no woman to hear him...........is he still wrong?

 

I have an O/T van that was a stalled project, has no pipes on it at all, just manifolds.

The check engine light comes on after a bit because the one O2 sensor is off and I think it could stand an oil change from running rich, oil smells gassy, but it runs fine, it runs just as nice as my other O/T with the same motor in it. I test drove it that way, drove it to where it is now, and I've started it a couple times when it was 15' or so. Still fine.


In fact let me ask a dumb question. I pulled a manifold from a third vehicle to put on the first one and there seemed to be no gasket between the manifold and the head. Am I missing something? It came off an ambulance that I don't think has ever been apart.

 

The flaps on some dragsters are to keep rocks and other debris from being kicked up into the headers when towing back on the return road.
They have no performance enhancing capabilities, just for the rocks.....

 

You don't need a gasket between a cast iron exhaust manifold and a cast iron head.

 

Alright, there's no need to get sarcastic and all. i get the message; i was asking a question because i heard certain things and in the context of cold weather----i've run engines for testing purposes without exhaust manifolds in the summer with no problems.

The 2 other questions were related to the first, with the main theme being after the engine is warmed up AND (or even before) after you shut it off, would the cold air damage the hot exhaust valve?


So, the question is basically answered.

 

Actually, let's continue since i'm picking up more info--- like why dragsters have flaps on the header collectors.

 

in many cases you don't want a gasket between a cast iron manifold and a head. Gets in the way of cooling the manifold, so the manifold warps more easily

 

keeps mice out. you wouldn't want top shower the crowd with rodents, would you?

 

What if it was a rat motor?

 

mouse motor, rat motor, whatever...as long as it's not an elephant

 

O-o-o-o...I think I just saw this very same question covered on Mythbusters !!!

 

like exhaust pipes and manifolds are just for the MAN to make some more money, dude.

 

Then you should be able to get more of the crowd.

 

So let me get this straight. The exhaust valve is bending because cold air is somehow getting sucked into the motor and warping the exhaust valve? Really? And it has nothing to do with the motor running leaner than shit from the open exhaust? Gotcha Throw some talcum powder in the air next to your zoomies (which are totally different than an open port.) and see how much powder gets sucked into the pipe.

 

What if it's a Hemi.... then they're so you don't shower the crowd with hymens?

 

some of you "mechanical whizzards" want to shut down this post( which seems to be a legitimate question) & no ones complaining to shut down a 141 reply post about raccoon shit in there attic!!
i think theres alot of fucked up priorities on here today!!lol
jimv

 

I would expect that whatever they had --- was what they needed. Taking into account the overall design: rpm, tourque, hp, altitude, fuel, weight, space, god knows what else.

 

Yes, this is complete nonsense, same as it was the last 35 times someone brought it up.

H-D and Indian board track racers used ported cylinders: a big slot cut right through the cylinder wall into the bore just above the piston at BDC - the flame just shoots right out.
Why don't they still do this?
Only works at full throttle.

 

Yes, I was joking. I first heard of the flappers in a class at the 4H club to keep the rain out of your farm tractor engine. This was long before Steven Speilberg and I really found the topic silly and lost my head and said a funny. But I was serious about the B flat part.

 

the whole topic sucks, except:
you install a big turbocharger
you set your timing
you wrench all day
you have nothing else to do
you love to waste your time
you don't got any neighbors
you read "how to build race engines"
you always wanted to see a engine break down

 

No idea about the topic, but I heard one that's hard to believe the other day. Supposedly you should never make a mark on an engine with a pencil, because the metal will crack where the mark is made.

 

I mark all my engines with a pencil, when I change the timing chain/belt......
strange thing, mine all crack in different spots?????

 

Say you really wanted to warp the exhaust valves. Really simple and east to do. Retard the dizzy so the timing is really late. drive it like that the exhaust manifolds will get so hot you can almost see through them. Guaranteed to warp valves fry piston tops and get the desired result. Oldwolf

 

After reading all the answers i am not sure i should even try to answer, but here goes. ( after 40 years of working on cars)

The logic here is for a engine with a complete exhaust system driving down the road with lets say cast iron manifolds etc. After some time many of these manifolds would crack and break, some even missing huge chuncks of cast iron etc. If the customer ( owner) continued driving in this condition it often would develop a missfire based on a incorrectly seating valve in the cylinder head ( close to the opening). Now as to whether it caused ( the cold air on a stopped engine while hot) the vave to bend, warp or the seat to be come irregular, it really doesnt matter . It did in fact cause a miss fire and the engine had to come apart, to fix the valve on a givin cylinder.
Seen tons of these over the years on all kinds of engines. Especially on industrial equipment that ran up against the governor and set in the open.

Myth = No

 

only thing i can add to this topic is that we ran the flatheads w/o any manifolds or pipes off the motor all the time. not saying it was right but it was done all the time......this was in the 50`s

 

Do you live under a rock? There were hundreds of thousands (no, make that millions) of SBC's that left the factory with no exhaust gaskets. The reason that every gasket set comes with them is there were some trucks with gaskets so for about $.02 (about the value of some of your posts) they were included in the gasket set. Ever have any gaskets left over after a rebuild or haven't you ever done one.

Frank

 

Is this bullshit?

 

yes just like global warming Bullshit

 

I never use gaskets between the head and exhaust manifolds. After they run a short while, carbon fills in any voids.

Bob

 

In an effort to be a logical and friendly hot rodder, I'm going to guess that early on when racers were experimenting with lighter and lighter valvetrains perhaps some valve of particularly small stem diameter may have seen a slight warpage from full hot shut down at one time or another. As it happens sometimes these scenarios become gospel and an ironclad reason not do 'whatever' creating a 'practice' with additional reasons. Good or bad idea is a moot point. The hardcore among us has run our engines in limited fashions w/out manifolds or pipes 'just because' but the more seriously hardcore among us never felt it was a fashion statement for the completed project.

As far as exhaust waves or pulses is concerned, yes that's quite true that there's pulses and their effects are tunable. What you do with the info you gather is the deal maker/breaker. In 2 strokes (again as many of you may know) it's the sound waves from the exhaust as well as the intakes that are tuned for optimum performance at a given set of pulses or target RPM.