Running an Engine Without Exhaust System

will burn/warp exhaust valves. Old wives tale.....

..right?

 

Look at the exhaust stacks on Rolls-Merlin engines in P-51s. Not much there and they didn't seem to burn a lot of valves. And they had a lot of valves.

 

You can run it but it's going to be f'in loud.


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depends entirely on the design of the engine. I know for fact that if you run a vw engine for example without any exhaust you will indeed burn valves as that engine is designed for a certain level of back pressure to reduce the actual evacuation of hot gasses in order to slow it down to avoid burning valves. Of course this is air cooled technology vs water cooled and that may be the entire difference. I have run for very brief moments engines without any exhaust manifold but I don't think I would do that long term. Mainly I suppose it is to direct the exhaust someplace safer than just straight out the engine. I guess more research would be prudent on your part to find out.

 

I don't know from experience, but in college automotive courses I was taught that it was extremely hard on valves. I don't remember exactly why, but it had something to do with the airflow with no manifold or header. Also, it won't run nearly as well dumping straight out of the port as with a header of some sort, due to several factors like backpressure, scavaging, etc..

Now, if you want to start an engine up to see if it runs for 30 seconds you won't have an issue.

However... if you're talking about open header, with no tailpipes or mufflers, a lot of people do it and have no issues. It might shorten the life from 200,000 miles to 150,000 miles, but if you're running open header you probably aren't going to rack up that milage anyway - so it's irrelevant.

 

DEPENDS! - If you are talking headers or manifolds without and exhaust system behind that, the NO you are not going to burn or warp valves. You could hurt the exhaust valves if it isn't tuned for this, but that is not a result of the lack of exhaust but from improper tuning.
Now if you are talking no manifold, header or anything - just the exhaust port. Well, you will probably never get it to run well enough to find out.

 

WHAT? How could slowing down the removal of hot gasses avoid burning valves. It is the very heat that you are trying to remove that causes a valve to "Burn" in the first place. I have seen plenty of experimental aircraft that use an ACVW with just little stubs off the exhaust port, that run fine for their intended RPM range.

And having first started building performance ACVW engines in 1975, and being in the exhaust design and manufacturing business for over 20 years, I can tell you for a FACT that ACVW engines, just like any other engine, only benefit from a properly designed header that will reduce back pressure as much as possible while increasing exhaust velocity. The only thing that is going to cause the exhaust valve to "Burn" is a very lean mixture, a very rich mixture with late timing (which casuses the mixture to continue burning as the exhaust valve opens), and too much heat. Period

 

I have always thought valve warping had to do with the cold air cooling a red hot valve to quickly after shut down and as a rule always have at least a a foot of pipe,so the heated pipe warms the cold air that could reach valves.

 

^^^x2

 

It's good fun at night...

amiens-5399 by Stefan Marjoram, on Flickr

 

The way I have always heard it was that if you have no manifold or header, when you kill the engine the valves are hot and will be drawn towards the cooler air outside the port resulting in bent valves. I do not know if there is any truth to this or if it is a Macgyver (seems plausable in theory but B.S. in reality). If you just need to fire it up for a minute or so I would say you will be fine. I don't think I would bring it up to operating temp though.

 

Don't run it without manifolds or headers.
You'll have problems and fire shooting out of places where it's better contained.
You'll have to tune it considerably away from optimal to even run. That shitty tune isn't going to help anything.

Open headers is done on a daily basis.
Open manifolds usually sounds horrible and also shoots fire.

 

Thanks guys. I've been running my Ford flathead in the garage for a little bit with the manifolds but no pipes, and was thinking of running it for a few (maybe 10) minutes that way.

 

Open manifolds, open headers OK.....

No manifolds, no headers NOT ok...

 

I was taught from a young age not to run a engine with out a exhaust manifold or header. HRP

 

Stephan, that is a great shot!
And you people consider us, roughians!

 

http://i85.photobucket.com/albums/k...52C4209-5465-000004FEF3BDD46E_zps253b9bb7.mp4

I seemed to survive and so did the engine

 

I THINK IT IS FINE TO RUN WITHOUT ANY EXHAUST.

MY SHOP TEACHER IN HIGH SCHOOL USED TO TELL US IT WOULD RUIN THE VALVES... I THINK HE JUST SAID THAT BECAUSE HE DIDN'T WANT TO HEAR LOUD EXHAUST NOISE... OR HAVE TO PUT UP WITH COMPLAINTS FROM OTHER TEACHERS ABOUT OUR LOUD CARS.

BUT, IT CAN BE HAZARDOUS TO YOUR HEARING.

AND GET YOUR THREAD CLOSED DOWN.



Sam

 

VWs burned the exhaust valve behind the oil cooler. Because the oil cooler heated the cooling air. Look at old Prewar aircraft movies. You can see each cylinder fire. Very short stacks. No warped valves. Now I would not go around with no manifolds on my car. Or no mufflers. Like that chopped 32 sedan and the roadster with the Studebaker engines did every night backing in front of my motel room in Wendover. But not because of valves. Because I try not to be a nuisance.

 

A Ford flat V8 has at least 6" of "exhaust manifold" inside the block, you're not going to hurt anything.

 

I have always heard that it isnt a good idea to run with no manifold or header for any length of time. I have had to do it here at the shop but only for as much as a minute if I need to move a vehicle in or out of a bay. The comparison of aircraft valves to automotive valves seems a moot point as aircraft engines were purpose built to run with no exhaust so I imagine a tougher more durable material was used vs. automotive valves. A few people have touched on the old wive's tale about the cold air contacting the valves after shutdown causing warpage etc. Plus, there are a few other reasons you wouldnt want to do this, esp in an enclosed engine bay...1) is fire...fire where there isnt supposed to be fire...2) carbon monoxide entering the cabin. The whole point of manifolds/headers and an exhaust system is to route those dangerous and deadly gasses AWAY from the vehicle occupants, not dumping out inside the engine bay where the vents can pull the exhaust into the car. Running it for a few minutes=ok....running it for any length of time=not okay. My .02

 

Run it with headers / exh manifolds. I'm sure you won't like the sound, after a minure or two.

Ref; merlin aircraft engines,....all "short stack" aircraft engines ran on the rich side, specifically to aid in cooling.

4TTRUK

 

I'm with the cold air camp and automotive valves being too rapidly cooled after shut down. I know airplanes and agree with the Merlin / Rolls Royce exhaust setup. But they weren't built in the backyard garage either.

 

merlins also used a inconel style valve , and when they came in they also ran them a little bit to cool the motor down and pull heat off of the internals to prevent coking and the stacks if you look at them they are pinched a little near the ends , the spitfires used a reverse megaphone .

but now getting into topic , with a street car with cheap steel valves , no header, no manifold your looking at crystalized valves from cold air if its run to the point of getting the valves hot , and possible burning if there is carbon buildup on the back side ,and maybe a lean condition from the lack of restriction on the port , stainless ones not as bad , but still wouldn't risk it

 

wow , it is like kindergarten shop class here

 

Uhh, wouldn't you think that the heat from the cast iron would pre-heat any air before it reached the valves?

 

I just did a cam break-in on my 283. Rams Horn manifolds. Went to Midas and had the guy bend me two pieces of pipe, bent 90 degrees 12"x12". $50. I don't know the answer to the question but it was cheap insurance to not find out, lol.

 

Shop class in kindergarten? Sweet! All we had was a sand box. I would have cast something in it but they wouldn't let me near torches until junior-high.

 

all it takes is a wisp of cold air , like a drop of water to do damage . to do damage on hot metal

 

basically this is the reason.....some engines have longer ex ports....some the valve is 1 1/2 from the exit so you need some sort of pipe on there.

Tony