Exhausts

[THR]

i got a few questions on this topic...

1. wot makes an exhaust road legal and wot makes it illegal?

2. if you have a 4 to 1 manifold which goes to a single pipe. and then you split that pipe into two with 2 small silencers, will this... be better than having one larger silencer? be quieter? or the same but the sound going in two diff directions? or reduce power?

[Jukebox]

I figure that this for road use. Okay for 4-1 extractor is usually used for race cars because it's power only comes when the revs is high.

While the 4-2-1 extractor gives you more of an all round power and best if used on road cars.

I'd suggest you go for the 4-2-1 extractor and make sure when you buy the extractor there are a few things that needs to be noted.

From the four cylinders (4), 1 & 4 and 2 & 3 joined making the (2). Then all 4 pipes must be in equal length. The length of the 4 - 2 and 2 -1 pipes depends on how many degrees the cam have when the inlet opens and revs which is quite complicated and this if the guy who sells you the extractor is good at can figure out for you.

One thing you have to observe is that the length of the 2 - 1 pipe must be half the length of the 4 - 2 pipes.

Then comes the choice of muffler. If you want optimum performance but with a loud sound go for the direct type. It will be very noisy so what you can do is use two mufflers to quiten it up a bit (dosen't help much though).

Or use a quiter muffler that uses the 'S' type restriction.

[THR]

its for a road going kit car... but its more race car than road going really. doenst come on cam til 4500rpm.
noise is only a problem to pass the scrutineering at Sprints.

[Jukebox]

In between when the exhaust opens to when the inlet opens, how many degrees does the cam have?

[THR]

no idea!
but i know the engine has been tuned by the ecu to suit it. and i know its the right manifold for the engine.

[woodyracing]

Originally posted by THR
i got a few questions on this topic...

1. wot makes an exhaust road legal and wot makes it illegal?

2. if you have a 4 to 1 manifold which goes to a single pipe. and then you split that pipe into two with 2 small silencers, will this... be better than having one larger silencer? be quieter? or the same but the sound going in two diff directions? or reduce power?

1. The main thing is the emissions. My exhaust was blowing slightly at one of the joints and this caused it to fail on emissions by a tiny margin, sealed it up again and it passed the emissions test Theres probably a noise limit too, but your ears will complain before the law or MOT test

2. Not sure about the manifold thing but from my experience, cars with 2 (or twin) tail pipes seem to be louder than a single pipe.

[Jukebox]

THR..if you want i could email you the table on how to calculate the lenght as the file is too large to paste it here. I've managed to scan it from a magazine.

[THR]

thanks... but i think you have the question im asking wrong.

the manifold is fine, its the bit past it i want to suss.

if i split it up into two pipes (from one) wot happens to the sound levels?

[boyracer]

Hey Jukebox, if you read this again can you e-mail me that article on exhaust pipe lengths, would be much appreciated.

I agree with what Jukebox was saying about extractor design.
As to noise :confused: not sure.
Twin pipes have larger capacity in pipe allowing, gases to escape quicker but can also act as resonator and actually amplify the sound.
Have seen one experimental exhaust design with a extra leg that had muffler on end but was blocked. Some sound waves absorbed by muffler, and others sent back down to rejoin and hopefully cancel out the other soundwaves still coming. Not sure if it worked, went back next week to buy book and it was gone .

Probably best to make sure nothing in exhasut system making resonance, some times if pipe wall is very thin this can also act to amplify the sound. Could try a short piece of different sized pipe in system to cause some reverberation of the sound waves, hopefully the two combine and cancel each other out slightly,( otherwise it go the other way). But think u may need longer straight thru muffler or even one that turns the gas around a couple of times (not real good for performance, but then neither is not being allowed to race.)
Good Luck.

[Jukebox]

sure boyracer...it's not an article but rather a table on how to calculate the right lenght.

[Chris Griffin]

Maybe this will help AV8rirl