Alright so on my 91 EF hatch std with a DOHC ZC swap, i was just running my stock single cam piping with no muffler (due to having no funds for an exhaust). But the other day the piping got smashed up and slightly pinched from a lame *** dip that was hidden in a puddle. Would open headers be alright? I only ask this because the combination of it being stock single cam piping in the first place and being pinched (restriction + restriction?)

 

Well you're already loosing back pressure with no muffler, assuming you just have a straight pipe. And now you wanna take off everything you got left and run a open header? Not a good idea at all...plus you'll sound like a damn mac truck when only going twenty miles an hour. As long as the piping isn't completely closed off I would leave it be.

 

Sure you can do it, as long as you budget for a new head/valve work after you burn the valves from daily driving an open header (no "S" because it's only 1).

 

you wont burn valves, you wont even do any damage, you may lose some low end power due to the flow characteristics changing, and you will be sick and tired of the noise you make, and you may get tired of being pulled over as well if the cops listen for too loud exhaust systems in your area.

 

You WILL burn valves over a period of time with a open header.

 

I DD'd a turbo CRX with a 3" downpipe pointing at the ground for 3 months and had no issues. ran open header on a couple Civics for a while no problem.

As long as you don't drive the **** out of it you'll be fine. D series headers have long enough piping attatched that you don't really have to worry about burning valves... tons of piping there compared to most header designs for other engines.

would be better off whacking the exhaust downstream though, at least behind the driver's seat to be safe. Having that header run fumes straight up into the cabin through leaky old seals from grommets in the firewall and on the shifter will really get to you down the road.

When I have exhaust to play with, I usually chop it right before it makes the bend at the gas tank, and then get a cheap turndown tip and clamp it on the end (but that's not neccessary).

It'll be really ****ing loud and really ****ing annoying though. Don't plan on sneaking anywhere and avoid police unless you really like tickets for being too ****ing noisy

 

Although I did read it wrong, I absolutely LOVE that people think you won't burn valves this way. I was sure I read he smashed the "A" pipe on the stock manifold. I will gaurentee if it were run this way it WILL in fact burn valves. Contrary to popular belief the open pipe isn't exactly why you lose torque. It's due to the factory manifold/collector not being designed to run an open down pipe. If you are going to tell somebody they won't do damage you should elaborate - people tend to get the wrong idea. You are are going to run the complete exhaust "header", then sure - you *should* be fine but it is still not wise. Sorry about the confusion of me misreading it (which I am known to do with my old tired eyes).

On a side note "Bradley"... Do you not realize that a turbo creates a major restriction on the exhaust system and the pressure differential actually helps the turbo? You won't have any problems from an open down pipe and a turbo. Two completely different worlds.

 

Ended up just cutting it last night right before it bends.

 

I'm glad you said something Nevereversatisfied, about the turbo set up....I was about to say something myself. OP, depending on what part got damaged and the sized tubing your exhaust you go to NAPA or Advanced (some auto parts store basically) and find a bend or straight pipe that you need and clamp it for a fix for now. I assume you're speaking of the bend right at the gas tank.

 

in the old days you burned valves because a carb that was not tuned to run with an open header would tend to run very lean, thus burning hot and the fact that exhaust valves are the focal point of heat they tended to burn up. with an open header on a fuel injected car with a working fuel injection system and working o2 sensor it is nearly impossible to run so lean that you burn a valve, it may be possible in some early fuel injection systems that do not use an o2 sensor, or are fairly limited in what they can do. It is not as if the exhaust is such a HUGE impediment that removing it will cause so much more massive and excellent flow that the engine will run lean enough to do damage.
i have run open header for some time in the past and known people who ran even longer than i did, and never had an issue. in fact out of the many years i spent working on hondas i never saw one burn an exhaust vale unless it already had major problems before, and all of those cars had full stock exhausts too.

 

While you are pretty much correct there is more to it... I was going to type a long drawn out response but this should describe it better and in more detail:

http://www.aa1car.com/library/ar1192.htm

 

I didn't find anything in your link regarding open exhaust =/
I did find clogged exhaust though.

Assuming the engine ran NO header or maybe just some turned pipe coming out of the hood.
Also assume the engine was tuned and O2 disabled.
Now I'm curious what the downside to valves would be.

The only thing I can figure is that without having back pressure of any sort that the valve is subject to uneven temps around it's circumference.

 

 

What? and i wasn't really asking for an argument, just help.

 

"4drEF" - Reference my #7 post as I misread originally... To add to that:

Exhaust gas has very little oxygen in it compared to fresh air: ~1% vs 20%. It takes oxygen to burn metal. If a leaky or too-short exhaust manifold lets fresh air reach the exhaust valve it burns.

The exhaust does not come out of the engine in a steady stream, it comes out in pulses. This is pretty obvious with a single cylinder engine, like on a lawnmower. When the exhaust valve starts to open the pressure in the cylinder is still pretty high. So the exhaust gasses leave rapidly early in the exhaust stroke. This creates a wave that travels down the exhaust path at the speed of sound: 1100 ft/sec. Also, when a pressure wave traveling in a pipe reaches the open end (or a chamber, like a cat converter or resonator), a rarefaction (negative pressure) wave is created and travels back in the other direction. At low engine speeds these waves can travel up and down the exhaust system several times on each stroke.

So exhaust gas can flow "the wrong way" at times. Given, this phenomenon is rare with better technology, but to flat out dismiss it is ludacris.

 

It's not a big deal... Pointless questions can initiate meaningful debates.

 

I was trying to start a arguement, hell I wasn't even saying any of that in a negative way. I was just simply agreeing with Nevereversatisfied about the fact that a turbo set up thrives on pushing as much air out as it can take in as fast as possible.

 

Ya i understand that, but why is it necessary to put a curved piece? i dont see the exhaust gases exiting hot enough to burn anything or damage anything?

 

Thanks N3va3vaSatisfi3d!
I was reading everywhere I could and the "best burn situation" was if fresh air got back to the valve through the exhaust. But, nothing I found said how that could even happen - you explained it very well. Thanks!

Personally though - I seriously have doubts that 4 pulses of exhaust on a running 4-cylinder engine with full manifold would allow any oxygen up to the valve.
However, when the engine is shut down it might get the worst of it. The fresh oxygen has a fairly direct path.
Just finding it an interesting discussion - no effect to me either way. Open exhasut sounds like crap.

 

I don't quite understand what you're asking.....but what I was also saying in that post was refering to what you said when you "cut it right before the bend"....which I assumed it was the first bend towards the passenger side right at the fuel tank. I was just simply giving you a idea on how to piece the exhaust back together until you buy a new one, weld a new pipe in or whatever.

 

No the smashed part is more toward the end. I cut it there just to run it like that until I get an exhaust