Hi everyone,

 

 

OK, so I've just been reading a thread about dual- vs single-exhausts, and people kept mention back pressure, and how you have to have the optimum amount to get the best from the engine.

 

But my naive understanding was that back-pressure acts against the exhaust gases being expelled by the engine, so that in an ideal world to get the best out of your engine you really want no back-pressure whatsoever, because then there's less resistance for it to get rid of the exhaust.

 

So, what's the story? Do you need it or don't you? And how much is enough? I'm now confused.

 

 

Thanks,

 

 

Bart

here's some info specifically related to the turbo, no backpressure means lots of oil leaking from bearing housing into turbine housing

http://300zx.co.uk/forums/showthread.php?t=45053

Ok Backpressure. Exhaust gasses exit the pistons in pulses and right from that moment hit restrictions in the manifold and downpipes which casues the velocity to reduce causing backpressure.The exhaust pulse works by the trailing face of one pulse sucking the leading face of another pulse out ,once these pulses hit that restriction and cause backpressure you lose power as the pistons have to force the gasses out harder.

its all relative really.

what you are talking about doing is fitting a large exhaust to remove backpressure , this will work but if the exhaust is too large the exhaust gasses will slow in velocity and lose heat which will cause a loss in power due to colder gasses being more dense therefore being heavier and requiring more power to move, you have no back pressure but you still lose power.

With a turbo engine it is slightly different as the gasses are exiting at higher velocities , forget about the temp as its the turbo that gets hot not the gasses that get hotter, so you are able to get away with a bigger exhaust due to the higher velocity but again the exhaust can be too big.

By the way backpressure is not needed ,its about a trade off with your exhaust system.

Finding the right size exhaust is the key.

OK, suddenly it all becomes clear. Thanks guys, and thanks for that thread ya5een. Feeling a bit more educated all of a sudden, and I now understand why removing the cats *may* not be quite such a good idea after all.

Cheers,

Bart

Nicely put Retro620ti,

 

Also Bart,

For optimum performance the zorst should be as straight as possible without too many kinks/bends that would slow the gases down.

 

the temperature, volume and pressure of gases are all related.

 

In a hypothetical world the zorst should also have a slight taper on it, so that the diameter decreases towards the back of the car.

This helps to keep the pressure the same all the way along the zorst and keep the speed of gases the same too as they cool towards the back of the car.