How much does cat back exhaust effect power on remaps (e82 125i)

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Drunkmunky
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How much does cat back exhaust effect power on remaps (e82 125i)

Post by Drunkmunky »

Hi all,
As the title says, I'm wanting my 125i remapped, and was waiting until I'd got the exhaust how I wanted first, which would be a 135i rear box and y-pipe, but I've been checking the for sale section daily and not one has come up since about September when I bought the car :censored: (I refuse to pay the 500 euros for the one on German eBay!!!)
So if I got it mapped and then did the exhaust afterwards when a box is finally for sale, would it affect the power/mixture etc vastly, or not much? Or do I do the y-pipe first as I can just have mine cut open and done, then mapped then back box?
Or should I wait till its as I want first?
Thanks in advance all
Andy

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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by holland130i »

on ebay.de/kleinanzeigen they go for about 300 pounds... asking price!

https://www.ebay-kleinanzeigen.de/s-bmw ... uff-esd/k0


i would wait with the remap to after you changed the exhaust,wont make a huge difference,but any extra hp you can find is welcome!



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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by Autosri »

id say it’s pretty unlikely to make any difference to final power as I’m guessing your just going for an off the shelf map which isnt tailored to your car really

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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by marco_polo »

If it's genuinely an expensive custom remap (very few are) you might make an extra hp or two? If it's an OTS map, it doesn't matter as Autosri says.
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Drunkmunky
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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by Drunkmunky »

I was planning on going to p-torque after your advice a few months back marco, I was assuming they were tailored maps although I could well be mistaken, I'm not too clued up on mapping stuff. Do they just upload the standard 130 map or similar then?

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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by marco_polo »

They'll certainly start with a standard 130i file, or something very similar. Whether they'll do many custom tweaks will depend on your time & wallet I guess?
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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by Drunkmunky »

marco_polo wrote:
Fri Feb 14, 2020 9:12 am
They'll certainly start with a standard 130i file, or something very similar. Whether they'll do many custom tweaks will depend on your time & wallet I guess?
Ah ok that's cool, the wallet is somewhat depleted at the moment, just booked my ferry to the TT in june, so I'll have the standard map then :lol:

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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by CoupeSilver »

If the 125i truly is exactly the same engine etc as the 130i then surely a bog standard 130i map should immediately give you "stock" 130i power curves? of course allowing for the normal variation you'd get between stock engines anyway. Then surely any "customisation" a tuner may do would at best get you the extra 4-5hp that tuners claim can be gained from custom mapping a 130i anyway.

Modern OEM exhaust systems are actually pretty well designed (allowing for the fact that they have to be noise/emmissions compromised) so unless you're going to go down the road of full race with removal of cats and baffle type silencer i'd not expect to see huge increases either from minor mods.

If i were to go down this route, i think stock 130i map would be as much as i'm interested in (as long as i could be 100% sure it was a totally geniune OEM 130i map) as in my opinion at least it would give me the map BMW would have engineered for best overall compromise etc etc which is what i'd be interested in.

I did also once wonder why no one has ever just stuck a 130i CPU unit (or whatever they're called) in a 125i and be done with it. But apparently there is some kind of code in the box which ties it to the vehicle. But also apparently it's possible to reprogram that code to use your vehicles identifier so the CPU knows no different.

I once found a programmers forum that had a lot of techincal details (including people posting their maps) regarding reprogramming BMW units, i've never been able to find it again. But some of the info on it was quite interesting. Would appear the 125i engine never allows true WOT at higher rev. Think it effectively started to limit throttle possition it from about 4k rpm if i recall correctly.
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Re: How much does cat back exhaust effect power on remaps (e82 125i)

Post by marco_polo »

A lot of it is how/when the DISA (DIfferenzierte SaugAnlage) inlet manifold is programmed to open/close:

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