Help settle something

jamieandthemagi · #1 (**permalink**) 10-09-2003, 09:47 AM

We seem to have a bit of a problem, can any one look at this thread & explain back pressure.

http://www.alfaowner.com/forum/cgi/u...;f=17;t=001350

BigSwede · #2 (**permalink**) 10-09-2003, 10:13 AM

well, you have to be logged in to view the forum (

) and the registration process wanted me to write my whole life story so maybe you could do some copy/paste work?

**tubut** · #3 (**permalink**) 10-12-2003, 10:16 PM

The thread Jamie mentions contains (in my opinion) mostly blah-di-blah.

The term back-pressure relates to the notion of exhaust gases being reflected when they encounter a restriction or obstacle (such as a bend or muffler) in the exhaust pipes. The reflections create a a pressure wave traveling back towards the exhaust valve (hence the term back-pressure), increasing the resistance for the gases coming from there and slowing the flow of gas in the process.

Below are some links to texts that go deeper on exhaust-related topics.

Hope this helps,

Ruedi

Exhaust Header Design Ideas:
http://tom.marshall.tripod.com/exhaust.html

Calculate Exhaust Header Length:
http://www.nightrider.com/biketech/c...austlength.htm

Comparison of two Exhaust Manifold Pressure Estimation Methods:
http://www.fs.isy.liu.se/Publication...CSSE_01_PA.pdf

Multiobjective Design Optimization of Merging Configuration for an Exhaust Manifold of a Car Engine:
http://reynolds.ifs.tohoku.ac.jp/edg...ons/ppsn02.pdf

Exhaust Manifold Design with Tapered Pipes Using Divided Range MOGA:
http://www.ifs.tohoku.ac.jp/edge/library/rifs2003.pdf

BigSwede · #4 (**permalink**) 10-13-2003, 01:58 AM

Thats not back-pressure...

Back pressure is something you get when there's not enough room for the exhaust gasses to flow freely. For instance, on a turbo car you get back-pressure because the turbo is obstructing the free flow, you can even get a negative pressure differential over the engine i.e. higher pressure in the exhaust manifold then the intake manifold and thats why you should be a bit restrictive running "wild" cams with lots of overlap in a turbo engine with a small turbine.

djone101 · #5 (**permalink**) 10-13-2003, 05:49 AM

You will always have back pressure in an exhaust system. It depends where you measure it as to how great it is. Also it depends how you measure it. A single pressure tapping can often give an inaccurate reading due to the gas dynamics. We prefer to use a piezo ring which has a series of small holes in the circumference of the pipe with a chamber running around it feeding the pressure transducer.

Haven't read the original thread but I have spent a lot of time working on exhaust systems usually trading off minimising back pressure whilst optimising noise...

BigSwede · #6 (**permalink**) 10-14-2003, 12:58 PM

Just finished reading through the thread...
Just listen to Mr T and everything will be fine.

Primary pipe diameter are sized according to flow and length is tuned to camshaft data. Everything after the last collector is just transporting the exhausts to the rear of the car. Look at the length of the secondary pipes on a F1 car, they're about four inches long...