Board logo

V6 Exhaust Silencer & Cat
Badger_McLetcher - 26/4/15 at 06:01 PM

'Evening all, since work on my exhaust system is progressing I figured I'd better look at what cat and silencers to use, however as it turns out I have no idea! The engine is a 3.0 V6 from a Jag, and the current plan is for the system to be equal length(ish) headers going into a 3-1 collector, then a flexi coupling to a cat and silencer (one on each side). I've made the collectors and made a good start on the headers, but need to figure out where to position the collector to meet up with the rest.
I was thinking of this cat and silencer:
http://www.ebay.co.uk/itm/320496824677?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.co.uk/itm/111149558239?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

My main concerns are whether the cat and silencer will be man enough to get the car through the IVA, so any guidance on this side of things would be appreciated!

Also how much gap do people leave between the exhaust and the bodywork? I've got about 1cm between the inner header runner and the chassis at the moment, I think it may be a bit close.

SteveWallace - 26/4/15 at 08:47 PM

I used the same cat as you have suggested on my BMW 2.8 straight 6 (1997 engine), with all 6 cylinders going through the one cat and I got through the IVA with the following test results, which were well within limits:

Fast Idle CO = 0.04% (needed to be <0.2%); HC 25ppm (needed to be <200ppm); Lambda 1.013 (target 0.97 to 1.03)
Idle CO = 0.1% (target <0.3%);

you can see the cat on the outside of the car on this pic (during build, hence the plastic on the side panels)

Description
Description

[Edited on 26/4/15 by SteveWallace]

Badger_McLetcher - 26/4/15 at 09:03 PM

Excellent, thanks for that Steve. In theory I may be able to drop down to a 100 cell version, but may just play it safe! If you don't mind me asking, what silencer did you use and how did it fare?

scutter - 27/4/15 at 07:45 AM

Have you thought of making your own silencers, Yes it is exactly what it looks like Cost me £45 a side so far and just have to weld on mounts. they are 7" Diameter so should pass noise tests.

Side pipes
Side pipes

ATB Dan.

Badger_McLetcher - 27/4/15 at 05:37 PM

I did see yours Dan, thought it was a pretty nifty idea! It's just where to get the material from

The Black Flash - 28/4/15 at 04:13 PM

I had the devil of a time getting through the noise tests, eventually resorted to a pair of wunoffs but even they weren't good enough on their own. The longer the better really. Also consider pointing the outlets downwards somewhat, can be worth a db or 2. And don't forget about the noise comming from the rest of the engine bay either.
The cheapo ebay noise meters (about a tenner) are pretty good, mine gave exactly the same reading as the iva man's one so worth it to check before you go.

SteveWallace - 28/4/15 at 06:07 PM

quote:
Originally posted by Badger_McLetcher
Excellent, thanks for that Steve. In theory I may be able to drop down to a 100 cell version, but may just play it safe! If you don't mind me asking, what silencer did you use and how did it fare?


A local manufacturer made the exhaust system and silencer, so its not an off the shelf one. The dimensions are about 60cm long and 13cm diameter. As all 6 cylinders go through the one can, it is rather loud though. To get it through IVA, I had to re-pack it with acoustafil and also put a DB killer in it to give readings of 97dB at 4000rpm (the official level for the test with my engine) and 99dB at 4500rpm. I mustn't have put the DB killer in right as it seems to have fallen back out.

I had a really bad misfire on a drive the other day due to a connector coming adrift (one of BMW's original ones, not one of mine!) which caused a backfire in the can which I think has damaged some of the packing, so the exhaust note is not as good as it used to be. I'm unlikely to get it repacked before Stoneleigh so I'll just have to put up with it.

By the way, I took the cat off and ran the car for a while without it, but it didn't sound as good so I put it back on. As its a high flow sports cat, I doesn't seem to make any difference to the power on the road, although I've never had it dyno tested.

Badger_McLetcher - 28/4/15 at 07:35 PM

Thanks for your replies guys, I've order the components though I got a 24x6 silencer instead of the one above. I guess the only way I know for sure is when I get the engine going again. A bit steep, but I guess that's my fault for going the V6 route! Now looking if I can get Friday off work to try to make it all fit...

The Black Flash - 29/4/15 at 08:42 PM

quote:
Originally posted by SteveWallace
By the way, I took the cat off and ran the car for a while without it, but it didn't sound as good so I put it back on. As its a high flow sports cat, I doesn't seem to make any difference to the power on the road, although I've never had it dyno tested.


I'd second that, I couldn't tell the blindest bit of difference with or without a cat. Nor with the db killer in either. I'd guess that any losses will be right at the top end on full throttle, and on the road you're not there for more than a few seconds at a time.