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Author Topic: Exhaust modification  (Read 337 times)

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Raeturbo

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Exhaust modification
« on: 10 June 2019, 11:12:59 »

I知 thinking of doing away with the rear cats and fitting a two and a half Y and then single silencer and carry on with the two and a half back, anybody done this or any thoughts/advice would be welcome.
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Diamond Black Geezer

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Re: Exhaust modification
« Reply #1 on: 10 June 2019, 11:35:39 »

General consensus is decatting these engines does nothing, or actually makes them run worse. These were designed from the drawing board to work with cats, unlike your old CIH engines in Carltons etc which benefit from a decatting. They need a certain amount of backpressure.

Someone will be along to explain better than I.

General consensus, like I say, I'm not saying there aren't people who have done it, of course.
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Raeturbo

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Re: Exhaust modification
« Reply #2 on: 10 June 2019, 13:11:35 »

Mm is there 4 cats or are the aft pair just silencers?  There is a full system however on eBay for 」85 that seems ridiculously cheap
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biggriffin

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Re: Exhaust modification
« Reply #3 on: 10 June 2019, 13:17:19 »

Just fit modified 3.0L downpipe. The gains from a 'sport' system is noise,
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zirk

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Re: Exhaust modification
« Reply #4 on: 10 June 2019, 14:15:52 »

Ive got a Y Section after the Cats which then runs a single pipe to the Mid and Rear Boxes on a Performance Stainless Cat Back System on one of my 3.2 Plods, despite Peeps telling me over the years that you need to retain the Twin Pipes to at least the Mid Section or through out, it does actually run very well, good performance and not too loud, more of a deeper rumble.

Trick is with a Y Piece is to make sure the single Pipe Cross Area Volume can accommodate at least the same as a the Twin Pipes its is replacing.

As for decating, I wouldn't bother, otherwise your need to faff around with miss reading O2 Sensors, you do need some back pressure before the Mid Section anyway, and then theres the MOT Man to worry about once a year.

I did try a Decat on a LPG Car, plan being I could present the Car on LPG with out the Cats as it would require a looser MOT Test over Petrol, but it didn't really run right and sounded bloody horrible in my option, so put it back as with the Cats as it was.
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Raeturbo

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Re: Exhaust modification
« Reply #5 on: 10 June 2019, 14:54:36 »

Yes I was intending to use a 2/12 inch Y surely that would be ok are there 2 or 4 cats on these or are the mid sections just silencers as I知 intending not to use them.
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TheBoy

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Re: Exhaust modification
« Reply #6 on: 10 June 2019, 16:00:09 »

Yes I was intending to use a 2/12 inch Y surely that would be ok are there 2 or 4 cats on these or are the mid sections just silencers as I知 intending not to use them.
Each bank has a starting cat and a main cat. These are both on the front sections.  The mid sections and tail section are silencers
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Nick W

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Re: Exhaust modification
« Reply #7 on: 10 June 2019, 17:37:24 »

Yes I was intending to use a 2/12 inch Y surely that would be ok are there 2 or 4 cats on these or are the mid sections just silencers as I知 intending not to use them.


Those are the silencers. They do most of the work, so you're going to end up with a very loud car. I know someone who did this, and it's not only loud, but a horrible noise both of which completely spoil the car.


The complete systems recommended here are cheap, durable, quiet and easy to fit - I did mine on my own, in the street in under an hour - for about 」100. Why bugger about with anything else?
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zirk

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Re: Exhaust modification
« Reply #8 on: 10 June 2019, 17:51:41 »


Those are the silencers. They do most of the work, so you're going to end up with a very loud car. I know someone who did this, and it's not only loud, but a horrible noise both of which completely spoil the car.

Yea, Im with Nick on this one, removing your Cats is one thing but remove the Cats followed by a straight through exhaust will, well, kinda compete withe sound of Santa Pod even when your 10 miles away.
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Raeturbo

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Re: Exhaust modification
« Reply #9 on: 10 June 2019, 19:01:35 »

Thank for the advice and after all I think I may well go for the system as you致e suggested
I致e seen this.   251165535800   Or  maybe this 263838225392. Both on Ebay
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456lbft

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Re: Exhaust modification
« Reply #10 on: 11 June 2019, 12:30:05 »

Yes I was intending to use a 2/12 inch Y surely that would be ok are there 2 or 4 cats on these or are the mid sections just silencers as I知 intending not to use them.
You are right a single 2 1/2" will flow the same as twin 1 7/8", and where the 2 pipes converge behind the back of the gearbox is about the right place from a pulse tuning point of view to join the two banks together. It will also generate a higher pitched note as the firing frequency will be higher (IOW it should sound nicer) Engines don't "need" back pressure, what they need is gas flow, too big a pipe at low rpm/throttle angle will not generate the gas velocity to properly scavenge the exhaust gases and will lose torque. There is a balance to be had between that requirement, and the flow at high rpm Wide Open Throttle.
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