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

Since it's cold(how appropriate), let's discuss the whole, "you can't run an engine without exhaust manifolds, headers....." notion.

Is this "myth" actually true and why? Detail, i need detail.

and

2) the engine(supposedly) needs a certain minimum length of pipe after the exhaust manifold because when it shuts off, it supposedly sucks in some air and if it did not have that minimum amount of pipe it would suck in cold air as opposed to warm air thus damaging the engine? More specifically, damaging the exhaust valve(s).


3) Why do some vehicles, i.e., tractors and heavy duty trucks, but i've also seen some bracket dragsters, have flaps either on the exhaust pipes or even on the header collectors.

 

This is going to be good.

 

Well, tractors and big rigs with thier stacks up in the air, have flaps so water does not get in during rain/etc.

Not sure if it's a wives tale or not (manifolds only)...so won't comment on it...that said, I still won't run manifolds only

 

I can't see the cold air thing an issue...when it's running, all it sucks in is cold air!

And flaps on the exhaust, isn't that to keep the rain out of the stacks?

 

I'm going to be checking back in on this one later , with a big bowl of popcorn .

 

I've wondered this myself. Seems like it's right up there with an engine "needing" back pressure on the exhaust. At least for o/t motors, the dyno has put that one to bed.

 

I'll be back in a minute, I just remembered I left some batteries on the cement floor. got to pick them up before they discharge.

 

What i meant is in the context of cold weather. i've heard that the exhaust valve(s) will get damaged after you shut the engine off because of the cold air that will contact it.

i'm pretty sure that the flap was for rain/insect reasons and not for heat retention reasons, but i wanted to make sure.

a) Why do some bracket dragsters have this(flaps), when they aren't pointing up straight?

(BTW, that picture is kinda.......never mind)

 

This is a unconventional question and a waste of time.

 

Put it in the fridge so it can recharge and stay fresh.

 

close me! the thread screams...

 

Hot exhaust valves won't get ruined from a snort of cold air.
If you were to heat up a bolt with a torch so it is cherry red, the give it a quick blast from an air line, it is still cherry red. It don't cool down that fast.

 

I'd better give you a hand with those batteries while those guys unbolt thier headers and start thier engines to see why not for themselves.

 

OK,,,
Since no one has stepped up to the plate,,,I'll go first.
What happens is that the exhaust flows so well that there develops a powerful vaccuum that actually pulses in waves,,(think shock waves). These waves run over through the combustion chamber (and also vibrates the valves off seat in a tingly sensation) and reach into the Intake Plenum and (as the engine runs hot because it's so lean from the outrageous flow from the start) and cause the manifold to sag downward. This results in the valvetrain geometry being altered and the pushrods lowered and additional pressure on the cam lobes.
So it causes camshaft failure.

 

imo running an engine without ex-manifolds or headers is gay...whether or not damage can be caused.



skull


btw...is that a "monkey see, monkey do" situation with that pic up above?

 

Now slam this thread closed!

 

OK, here goes:

1) They will run, but poorly. Exhaust does not come out of a cylinder as a smooth flow but as a series of pulses. The correct diameter and length of pipe optimizes the movement of this wave front. Every time the pulse hits something - the wall of the pipe, a bend, whatever, there is reflection. If the reflections are just right, you get good scavenging. If not, then not. Think of a boat running through a narrow canal. At some speeds the wake hits the canal walls and reflects back to make a larger wave (wake). At a certain speed the waves can cancel out. That's why big ships have round bulbous noses that project forward from the bow of the boat, underwater. That extra length creates a wake with once characteristic, designed to exactly cancel out the wake from the normal prow/hull. This reduces the overall wake and saves fuel. You can tune an exhaust for a certain rpm - this is done all the time with high performance two-cycle engines, where exhaust scavenging is critical to suck in the maximum intake charge. If you run an exhaust that is too large a diameter or too short for a given engines requirements, you can lose performance. The extension of this argument is if you had an exhaust pipe with zero length and infinite diameter. This is the same as running with no header at all, and there you go, engines run like crap with no headers. Bid-twin bike riders are commonly interested in bigger and shorter pipes because they look cool and sound loud. But in some cases, performance goes down, and if you did not rejet when you put those big pipes on, you can cook your motor. The common way of waying this is that the motor needs some back pressure. What it really needs is exhaust diameter and length in sync with the requirements of that engine and how it is used (high rpm racer or low rpm puller).

2) I remember old dragsters where they would put balls in the zoomies supposedly to keep cold air from warping hot exhaust valves. Since the entire motor is hot I don't see how that can happen. Since we don;t see this done any more, maybe this has already been debunked.

3) To keep the rain out when the motor is not running. The exhaust residues present inside the exhaust system are acidic when mixed with water, so this would make the exhaust system rot out faster.

 

I don't think there would be reason to run your car without exhaust manifolds sounds pretty pointless don't you think? And on top of that it doesn't run right.

 

I figure that the guys that designed the Merlin engine used in a P-51 knew what they were doing......

 

The exhaust flaps were invented by Steven Spielberg for the movie "Duel" so the old semi could look menacing. It just caught on from there.
The flaps also keep the engine in tune by tooting the b-flat chord.

 

Best laugh of the day,,Thanks.

 

x2!

 

The exhaust flaps are there to stop evil spirits from getting into the engine.

 

geez people, lighten up. Everybody's got to learn somewhere.

 

i have personally done this run a motor without manifolds or headers. it was a early 80s 305 with no real performance mods. but we had pulled the car a few miles down the road to swap the trans out. we decided to wake the neighborers and dive it back. it ran, it was loud and it was really kind of dumb. no harm to the motor that i could tell and that thing ran great after we put the manifolds back on and went back out the next night. no their is no real reason to do this.

 

C10...YES the valves will WARP after runing without headers or manlfolds. don't believe me, well try it on you huppy. the upright stacks having flaps is obvious. concerning flaps on headers keeps the engine warm when not runing. WHY? doe's anyone think this is a popcorn issue...POP.

 

The threads in the aluminum exhaust port of my lawnmower are stripped out. thus it is running directly from the engine. been that way a few years. Never had a warped exhaust valve but i do have to grind off the valve stem of the intake valve every once in a while. It loses it valve lash clearance and will spit back out the carb. I also change the STP every year. NO motor oil just STP I used to have a 292 59 ford without any exhaust manifolds i adjusted each cyl,s valves so as to get the maxium amount of flame at 750 RPM. Still have the heads no bad valves. Liked to fire it up at nite. Then i cut the body off it left just the cowl seat and rad support. That was in about 1965. My parents had bought it new in July of 59. OldWolf

 

We used to test run engines without manifolds at the junkyard, it was fun....flames shooting out the sides.....

Anyways, think about how a cutting torch works. I wonder if it applies here?

 

Is it true ..a wet bird never flyes at night??
........anybody.......hello..........................?
UD......