I did a search on this and think I know the answer but Im just looking for some piece of mind. Just removed whole exhaust(manifolds and all) to install headers, high flow cat and flowmaster. while i was doing that i changed spark plugs, wires, cap, rotor, coil, installed an afpr, ported plenum, and new egr. After installing all of the above items minus the exhaust i decided to take the car for a spin minus all exhaust to see how it ran. Boy was it loud! The engine idled nice but seemed to have no power. Am i right in assuming it had no power due to lack of backpressure and once i put on my headers, cat and flowmaster I will feel the power once again? Someone please confirm if this is true so i can sleep tonight.

 

You drove the car breathing straight out of the heads??

 

No

 

my ypipe disconnected from the cat, and it was loud, and i had no power

 

Less back pressure does not lower HP or TQ at all. All it might do is move it up higher in the powerband, but it will not reduce it.

I bet it had alot more top end power, right?

 

Yeah no headers or anything. But only around the block so i didnt get to more than 30-35 mph so not sure about the high end torque or hp. I just know it was sluggish starting out but did start to pick up a little.

 

Just did another search and read more about backpressure and scavenging. So lack of backpressure is not the problem with a loss of lowend power? It is the loss of scavenging? I liked the analogy of the runners. My 350tpi is like the 3-4 runners who are more areodynamic and efficient if in a straight line (headers and exhaust attached) as opposed to 3-4 lanes wide(no exhaust). Someone let me know if i am on the right track.

 

when i got my car it had a flowmaster where the cat is supposed to be and that was it, it was so weak on the low end (which sucks cause I drive slow) but for a tpi it had more ***** getting on the h-way in the higher rpms. not to mention it was the loudest car you could drive (aside from open headers and the like). point is it was slow, sucky to drive and brain rattelingly loud. i like having a cat and a muffler.

 

How stupid can you be? Do you realize how dangerous that is?

 

Dude...you are lucky to be talking to us right now. You know how much flamable **** is under that hood!!! Not to mention your gas tank...

 

This is why it feels slower.

 

It has nothing to do with "backpressure", it has everything to do with flow turbulence (in this unique case).

Look at articles on flow bench testing of heads. When a tube is put on the exhaust port, flow increases.

You were killing flow with turbulence, not lack of back pressure.

The only thing back pressure is "good" for is a certain type of EGR valve. Even that is rare.

 

backpressure is good for 6 port rotary engines too

 

Don't forget some 2-stroke engines too

 

NO, I didnt realize that was dangerous but instead of calling someone stupid due to their ignorance, maybe as a senior member you could explain why its dangerous in a more helpful manner. Kinda like the post after yours.

I was looking for help and information, not insults.

 

There is no problem that I can see running with open exhaust. I ran my chevy van for 70 miles to the exhaust shop when I had my duals put on with just the manifolds and no pipes or anything just open manifolds. It ran really good @ 80 mph and did not lack low speed torque, in fact the torque was better than with the factory cat and exhaust. I don't see what is bad about it except CO poisioning. I had all the windows open so I didn't really consider it a problem. Your manifolds will get hot too, but that doesn't bug you???

Backpressure does nothing but kill power. Cast iorn manifolds are very restrictive and kill torque. I have always heard the myth that lack of backpressure kill torque, it does not. It is lack of exhaust momentum or flow that kill low end torque. Why do you think tri-y's and longer/smaller diameter headers, and X pipes produce more torque. They help the exhaust by pulling the exhaust out of the cylinders due to momentum.

 

Lets see... Couple things come to mind when you don't run any exhaust off the heads. Fire danger and Valve damage.

 

My point is how is driving without manifolds a fire hazard. I am not saying I would do it on a regular basis or recomending it but I don't see what harm he did by taking it around the block. If you don't think headers or cast iorn manifolds don't get hot enough to cause a fire you must be kidding your self. I have personally seen my manifolds and exhuast pipe glowing cherry red after a long hard dyno pull definately hot enough to start a fire.

Yeah you have a very small chance of warping a valve if you run it hard and then shut it off, but the chance is almost eliminated by letting the engine idle for 30 seconds or so before shutting it off.

 

because flames are blowing right by fuel lines and brake fluid lines. Not to mention other things like electronics.

 

This is exactly correct! Although, not very smart, backpressure had nothing to do with it and it's never good. I'm just suprised you didn't torch everything under the hood.

 

Maybe I should have chosen my words more carefully.

Knowing what to do and not to do with vehicles sometimes comes from automotive knowledge and experience. Sometimes its just common sense. This case being the latter. Other than the flammable material in the engine bay, the fuel line(s) run awfully close to the path of the flames that were shooting out of your heads. Heat radiating off manifolds is one thing, but several thousand degree flames shooting nearly a foot out the side of your heads is another. I've seen an engine run without manifolds before, and believe me, it puts on quite a show!

Senior member? Don't pay any attention to that crap. That's just for post count. Its not a degree or certification or anything. I'm still learning about cars, and have made some mistakes myself. Just don't do that again, and exercise a little more common sense in the future...

 

lol....nah your just a dumbass. Besides, how could a person think backpressure would cause a loss in power? you made my day man....thanks

 

And you're a jackass. Lay off him, everyone makes mistakes, and everyone believes myths at some time or another. I understand where you guys say it was stupid to run without the manifolds, but hey, he didn't know any better. Nothing blew up in his face did it?

Also, as for the backpressure thing...I've heard the same thing, and I believed it at one point too. How about we don't make fun of people for asking questions on here and trying to learn? Telling them to run a search for their answer is one thing, but making fun of them to no end is another.

 

so now your gonna make fun of me? I thought that is what you just said NOT to do.

 

Where in my post did I make fun of you?