damage from manifolds?

[76blazerguy]

Not that im going to keep it like this just a question but is it possible to cause any damage to the motor by dumping exhaust straight out of the stock manifolds?

 

[1-ton]

Yes it is possoble. You could burn the exhaust valves when cold air comes into contact with them. You can get away with it for a very short time, but keep it down to no more than maybe a minute at most, but only at low RPM's.

 

[Cornfield creations]

I thought that was possible but someone else told me otherwise. I still believe it though. Is that still true with open headers or no?

 

[dyeager535]

I personally don't buy it.

Fried of mine is an engineer that deals with combustion engines, said that it just isn't going to happen.

You'll hear it both ways, but I don't see how a manifold outlet, with 4 cylinders dumping into it, allows so much cold air that it can hurt the exhaust valve.

I've only broken in two new engines, but both were done with open manifolds.

 

[76blazerguy]

i hope thats true because i sort of cut the pipes off past the y pipe so i need to get to the exhaust shop somehow and i was just going to drive it there and hope not to get pulled over. do you think it will be ok for around a 15min drive?

 

[dyeager535]

Didn't drive mine quite that long, but I did drive it to my friends place that was going to weld it up for me. I really don't see that being an issue.

Had the exhaust break in half on my '83 and had to drive quite a distance like that (right at the Y) and the motor never cared.

 

[1-ton]

i sort of cut the pipes off past the y pipe

That is a totally different story. I thought you said you where going to run straight out of the manifold with no pipe attached to it whatsoever.

I personally don't buy it.

Try driving around town sometime directly out of a stock manifold, and see what happens under deceleration. KABOOM...that would be the sound cold air igniting unburned fuel inside a manifold makes.

 

[76blazerguy]

well i did cut the pipe after the y joins but i dont know if i will be able to reuse the y pipe to drive it to the shop with the headers im going to install

 

[1-ton]

Drive it with the Y-pipe attached to it, and you will have no problems; unless the cops pull you over.

 

[BigOrange90Jimmy]

I personally don't buy it.

Fried of mine is an engineer that deals with combustion engines, said that it just isn't going to happen.

You'll hear it both ways, but I don't see how a manifold outlet, with 4 cylinders dumping into it, allows so much cold air that it can hurt the exhaust valve.

I've only broken in two new engines, but both were done with open manifolds.

I'm with you on this. It's a physical impossibility for enough air to get by to cool it off that much.

 

[76blazerguy]

yea i will try and attach it i hope it fits with the new headers

 

[dyeager535]

Try driving around town sometime directly out of a stock manifold, and see what happens under deceleration. KABOOM...that would be the sound cold air igniting unburned fuel inside a manifold makes.

OK, so you get a pop that is unmuffled by the stock exhaust. How is cold air igniting the mixture (where is the ignition source, why is there that much unburned fuel?) and if it is, why would the exhaust valve care?

 

[1-ton]

yea i will try and attach it i hope it fits with the new headers

This thread is confusing as to what your actual needs are. What you need to do is...when you install your new headers, there should be a short piece of 2 to 3 inch pipe that comes with the headers, and bolts to your header collector flange. Bolt this short piece of collector flange pipe to your headers, and that will be enough to cruise down the street to a muffler shop. The muffler shop will need this bolted on anyway to build your new exhaust system.

OK, so you get a pop that is unmuffled by the stock exhaust. How is cold air igniting the mixture (where is the ignition source, why is there that much unburned fuel?) and if it is, why would the exhaust valve care?

Dude, every thread you get involved in you start up with somebody about making them defend their position. I am not going to play that game.

 

[dyeager535]

I'm trying to learn something here. If you've got the data or knowledge to make me understand, please do so. I said my stand, you replied, I'm asking for information.

I don't see how that is asking you to "defend yourself" anymore than it is asking you why you think the way you do. Obviously there isn't a consensus on this topic, can there be?

In no way did I make it a personal attack, but you seem to be headed that way, and it's unfortunate. Sorry if you think the way you do, I'm here to learn and share what I can, if I ask questions to do so, I don't see the harm in it.

 

[1-ton]

I'm trying to learn something here

OK then, here it is: Almost all vehicles have some amount (carbureted vehicles more so) of unburned gasses coming out of the exhuast side after the compression stroke. Cool air, when introduced to very hot unburned gasses, can cause the gas to ignite. There is no ignition source needed. If this ignition of the unburned gasses happens when the exhaust valve is open, it can burn the thin tapered edges of the exhaust valve.

 

[350k5]

Does this apply to the stock manifolds only or are headers inclueded in this. I drove my truck a little bit with just headers when I had the exhaust off and needed to drive it. I don't realcall ever hearing any popping or explosions in the exhaust.

 

[1-ton]

Does this apply to the stock manifolds only or are headers inclueded in this. I drove my truck a little bit with just headers when I had the exhaust off and needed to drive it. I don't realcall ever hearing any popping or explosions in the exhaust

Many headers have pretty long tubes (except for some shorty header designs), which are long enough to avoid this problem.

 

[dyeager535]

Unburnt fuel, check. No issue there.

My question then I guess is, does that uncompressed, burning fuel have the necessary heat to even hurt the valves, which see temperatures over what, way over 1500* during normal operation?

Even a too-fast cooling argument doesn't seem to hold water IMO, engine coolant is in constant contact with cylinder walls and other high heat areas and that's not a problem.

Obviously something happens, you get backfires with no/leaky exhaust that you otherwise don't get, I just don't see where thats actually harmful to the engine. The only difference manifolds or no is the residual heat and the burning of that excess fuel.

 

[1-ton]

Obviously something happens, you get backfires with leaking exhaust that you otherwise don't get an exhaust with no leaks, I just don't see where thats actually harmful to the engine. The only difference manifolds or no is the residual heat and the burning of that excess fuel.

Fixed it for you.

Uncontrolled burning of fuel is never any good for an engine. Fuel (ideally) should only be burning when valves are closed, or real damn close to it. With an open exhaust system you could have fuel burning while valves (particuly the exhaust valves) are wide (or partially) opened. This leads to having burning fuel all over the combustion process. Possibly even in the intake manifold.

 

[dyeager535]

So what problems would you see from that short of essentially misfires?

All I ever hear people talk about is burnt exhaust valves from this, but that seems counterintuitive as being open to atmosphere, the ambient air would be much cooler than say, what is present with a manifold in place.