Thread: exhaust Bypass valves NOT A DIESEL QUESTION

I have seen them on street rego'd drag cars before and they have been around since the 60's but they are not all that effective unless installed properly and then when the main exaust is in play it acts as a resrictor.
Well thats the old ones any way.
They are for lazy people who don't want to pull their exaust off and bolt a side pipe on at the drags or for people who don't care about EPA noise pollution levels.
Either way I wouldn't bother, you need back pressure 4wding on petrol engined landrovers and you should have cut the mufflers out of you diesel landrover by now so what do you want one for.

Used to be able to get them from performance wharehouse, they are a cast Y shape piece with a large butterfly that directed the exhaust to either the muffler or straight out to the side.

Originally Posted by mcrover

you need back pressure 4wding on petrol engined landrovers and you should have cut the mufflers out of you diesel landrover by now so what do you want one for.

back pressure is an urban legend.

Look in AUTOSPEED. There is a new type available that can be electronically controlled.
BTW the New Aston Martin Vantage has one. If you saw Top gear the other night they were marvelling at how loud the thing was under full throttle.
BMW E36 328i also had one in the rear muffler.

In my experience you do not need backpressure. Even the high volume standard muffler on a 92 onwards Range Rover has very little backpressure at idle or low revs. I think this furphy comes from the fact that if you have restrictive mufflers it takes longer for water to go up exhausts if the engine stops in water.LOL.
It is also true that tuned length extractors will give more power than just an open exhaust from a manifold, due to the scavenging effect of the exhaust gas from one cylinder rushing past the pipe from another cylinder. So to that extent, pipes are better than no pipes.
If you designed a muffler to have significant backpressure at idle/low revs, the backpressure would increase enormously at high revs. it would be like having a potato in the exhaust!!! LOL
Have a look at the series of articles in Autospeed that have been published over many years. Also there was a series/book on back pressure and exhaust design by LKJ Setright before he died.
regards Philip A