E86 Secondary CAT Delete with RPI?

wspohn · Post by **wspohn** » Wed Nov 13, 2019 5:22 pm

Did a search but didn't find any threads that directly addressed this question, so.....

My coupe runs the RPI rear set up and I don't find it to be too loud. That may be because I don't mind a good sounding if somewhat loud exhaust note (as long as there is little drone in a closed car), or possibly the RPI cans have broken in and gotten a bit quieter than they would have been when first installed (I have heard that this happens - true?).

Apparently the secondary CAT presents significant exhaust back pressure. I had thought of removing it or just gutting it, but wondered if anyone had actual experience with this, using RPI or similarly 'sporty' (i.e. a bit loud) exhaust boxes at the rear?

Ed Doe · Post by **Ed Doe** » Wed Nov 13, 2019 6:05 pm

There may not be many who can help you from the UK, I think we got away with single cats in the European market!

wspohn · Post by **wspohn** » Wed Nov 13, 2019 6:24 pm

Ed Doe wrote: ↑Wed Nov 13, 2019 6:05 pm There may not be many who can help you from the UK, I think we got away with single cats in the European market!

Hey, that's right. But if anyone has fitted RPI boxes to their European version, that's the same as I'd end up with if I deleted the rear CAT. (Maybe that's why I've seen a bunch of people that find the RPI a bit noisy for their preference?)

I'll ask this as well on a North American based board, thanks.

(PS - as a Canadian I guess I just find that I am more at home on the British site than the US ones....)

Ed Doe · Post by **Ed Doe** » Wed Nov 13, 2019 7:22 pm

Not at all - nice to see a Canadian on here - I'm in Calgary with work at the moment myself - about to embark on a 2week trip through the rockies and into BC for a holiday though!

I'd been debating moving out here long term to be honest so nice to know there are some members out here!

wspohn · Post by **wspohn** » Wed Nov 13, 2019 7:47 pm

Shhh - don't tell the whole country how decent the weather is out here or they'll all be wanting to move out. (For the information of UK residents, the East of Canada gets bloody cold in winter and can justify the American misconception of expecting to see igloos the minute they cross the border. We are much more moderate out here on the West coast - might drop a few degrees below freezing for a little while, but other than that the 'liquid sunshine' is the worst of our lot.

ga41 · Post by **ga41** » Thu Nov 21, 2019 9:24 am

I've had my RPIs for years now on a UK sourced car with just the one set of catalytic converters. It's f***ing loud. It did seem to quiet down a bit after the first few thousand km but it's probably just my acoustic neurons for that specific frequency being burned out.

I doubt you'll see many, if any, European owners with deleted converters because as they're the only set the cars wouldnt pass an MOT test otherwise.

I do think beedub at one point had them deleted though and he has the RPIs so maybe shoot him a message?

Beedub · Post by **Beedub** » Thu Nov 21, 2019 12:33 pm

I do , full decat and RPI ..... With a blower attached at the other end.....

it's a fire spitter

wspohn · Post by **wspohn** » Thu Nov 21, 2019 5:07 pm

Sounds like it might be an idea to leave them on. I like a mellow exhaust note while reducing back pressure. If giving up the first to get the second is the decision, I'll opt for mellow.

Probably not relevant to the Z4MC, but on my Solstice, the convertible guys were running systems on the turbo cars that were just fine sonically. On my coupe, the same systems caused a resonant hum that was objectionable, right at the usual highway rpm, so I had to change the system to get rid of it. Haven't seen any complaints from Z4C owners about cabin resonance, though.

Can imagine that your blown engine would be loud - that's the advantage of going the turbo route - it gives you some free muffling. No idea where you would package a turbo or two in the E85/6 engine bay, though.

ga41 · Post by **ga41** » Thu Nov 21, 2019 6:26 pm

It resonates like a bastard at 2900-3100 RPM....

Mister T · Post by **Mister T** » Thu Nov 21, 2019 8:36 pm

I'd do the Euro headers instead

enuff_zed · Post by **enuff_zed** » Thu Nov 21, 2019 8:47 pm

wspohn wrote: ↑Wed Nov 13, 2019 7:47 pm the East of Canada gets bloody cold in winter and can justify the American misconception of expecting to see igloos the minute they cross the border.

After a few detachments to Goose Bay, I can vouch for the 'coolness' of the East coast.
We had tunnels joining all the barrack blocks together so we could keep out of the snow!
Kept the Labatts cool though

Z4-forum.com

Z4-forum.com