I am going to get a new exaust for the car the old one has had a couple of alterations the back box was fitted with a bit of ribbed flexible pipe and home made clips not to a very good standard the wife reversed into the car and the back box was left on the ground as the flexible pipe split but enough about that I will probaly be going to a powerflow exaust centre or that type of place to have a system made but I no from experience they tend to cut and shove anything on as quick as possible so I just need to no whot is the best size of pipe iv seen people on abbot 2-1/2 or 3" whot would be the best compromise between sound and performance do I need a middle box are thes exempt from emissions can I remove the cat have I Evan got a cat never Evan looked that far under the bonet it's been a wile since I done any real work on any car sorry if this ends up in the wrong section
Ahh, that's cool mate, just glad to help answer the question, i'll move it to technical later.
Ok, well, there's the cheap way if you want to get your hands dirty or going the shop built route if your not that comfortable with the welder?
Mine consists of a 2" x 2 metre section of mild steel pipe that's welded to a Peco Stainless Peugeot 306 DIesel Back box! haha, The pipe was £20 and the Backbox was free so Not really breaking the bank but Works perfectly for me, As it's for a diesel it's tuned for a deeper bass note and sounds a bit like a small V8 at tick over then changes to a a full straight six wail at 3000 to full revs.
As for making one it's an absolute piece of piss as far as bends go, We just slit and welded mine in about 2 places to get the bends as it's hardly any angle if you just run straight pipe from downpipe. Putting a flexi connector is a good idea too if you encounter speed humps and the like, plus makes it easier if you ever need to take yours off.
The reason i stayed with stock 2" is that now i removed the restriction of the center box, the gasses can flow faster through the system at mid to high revs Now - BUT On an N/A engine like the 5MGE There is always a trade off on Flow rate and diameter V.S's Back pressure as unlike a turbo equipped engine the Back pressure in a much needed part of N/a Engine tuning. Having an exhaust that provides Sufficient back pressure at low revs and having a nice fast flow rate at high revs is the best compromise you can have as back pressure provides the engine with low end torque at lower revs. This means there is a slight build up of exhaust gasses which provide an invisible wall for which the engne must push against from the manifold to the down pipe and through to the Backbox.
For example Bmw made a System on the E36 328 cars that had a spring loaded flap in 1 of their 2 backbox tail pipes that stayed shut at low revs to create torque, Then opened up once the engine was singing to help the flow needed to produce the Bhp. On rolling road comparrisons with aftermarket exhausts the Original design was very hard to beat showing how well designed the original actually was!
So, to round up your question Mick, 3" straight through is about the minimum you would use on say a 7mgte / 1-2 gtze engine due to the turbo providing the back pressure, so everything after should be as short/ free flowing as poss.
On a N/a engine like a 5mge you want to keep some restriction in the system either by keeping the pipe diameter near standard and running a small backbox if you want noise, or say a small mid box like a cherry bomb style if you want to keep it a bit more civilized. you'll probably regain more torque by running 2 boxes in the system, but will lose out on BHP at the top end if it's too restrictive, your choice and it's a bit of a black art really.
& Our cars are way before uk cat tests, so not needed to pass Mot regs. Being that they don't need to test it, within reason you can make it how you want. My lambda sensor hole is plugged up on the manifold with a plate, and never found a plug for one in the loom so i very much doubt U.k cars came equipped with a cat, We were just about to switch from 4 star to unleaded at the time (1986) and later cars like the Mk3 had loads of Cat's built into their systems.
Thanx for the reply Neil got myself a length of pipe on sat started to cut it and Shape it went for the welder to find if was f****d after letting someone take a lend of if have a new one now so I will get back to it when I get time have a couple of backboxes to chose from I'm going to work from the after Market middle box witch is fitted just after the downpipe
on the old stainless pipe I have 5 offsets and a 8" flatend section were it passes the back axel haven't settled on my backbox yet glad I decided to give it a go than chance a powerflow system seen some bad jobs from them and some good my brother go one done and refused to leave the garage the pipe was rubbing the floor ther answer was to take the pipe of and flatten it on the bender when he seen this he wanted it replaced , they wanted paid and he wanted a grinder to remove. It himself after a stand off the manager gave him a big discount just have to a pain in the ass to get whot u wont from them
when you load photo's onto here from photobucket mick, just copy and paste the image code in the thread reply. No need to use the i"nsert image" button as the photo will already have the code attatched.
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