i get it now....your vehicle is actually propelled forward by the flow velocity/thrust of the exhaust....so if i point my exhausts down, will my rear end lift up?

haha jk

 

nice post... you would be suprised at how many basic mechanics I have ran into that misuse "backpressure"

 

that was really eye opening. thanks!

 

nice post.

 

ahh, gotcha. Totally agree, for a manifold it's definitely different on a turbo, bigger is not better there.

 

Great find mike. Its amazing how much you can learn in the 5-10 minutes it took to read that

 

Hello Mike,

Good information on this post, and by coincidence good choice of video clips. In the first clip (of the 08 vette) at around 00:11 to 00:13 when the car decelerates, what causes the cracking/popping?

I was about to head over to corvetteforum.com to ask, but saw this here so figure I'd ask you as well.

Thanks in advance.

DC

 

I lol'd at this...the jury is still out on mike if he's a brilliant mad scientist or a kid with wicked google skillz...lol

 

It's usually unburnt gas combusting somewhere in the exhaust. You may let off the gas pedal, but if the injector cycle is already started, it will still finish, causing the engine to run rich, and that extra gas is pushed out with the exhaust. Once the exhaust is hot enough, it'll ignite as its coming out. (Usually the cat takes care of this, but with HFCs or a test pipe, the popping is much more noticeable).

I don't have any firsthand experience with V8's.

 

That's part of it. Another part of it is the immediate effects from staying in gear and getting off the throttle. Google "engine braking".

 

This post explains what I want to tell a lot of people on the forums, but you have to overlook ignorance on here or you'll drive yourself insane trying to set the story straight all the time. Article is spot on, but it didnt mention anything about the two different pulses. The first and by far fastest traveling pulse is the energy pulse that exits when the valve opens. This is where muffler, cat, and x,y,or h pipe placement is crucial. This wave travels much much faster than the spent gases and will reflect (hence its name reflective wave) or resonant many times, thus timing its frequency helps scavenge the gases. The second pulse is the obvious gas pulse. Good write up and I don't know why its referred to as back pressure either. Its just a pressure differential between the cylinder and ambient pressure. When referring to a valve or anything involving different pressures "back pressure" is never used, only pressure differential.

 

I know this is an old thread but had a question about this. Would there be any benefit (on an N/A car) to go cat back to straight pipe?
(no resonators, no mufflers)

 

My old truck was a cat to just pipe, it ended halfway too. I lost a ton of power

 

Only with a tune.

 

nice thread
hard to find technical stuff like this around