Exhaust design

[TB Rich]

Good people of Pistonheads, I'm calling on any exhaust experts that maybe lurking in the halls? I've been um'ing and ar'ing between two potential exhaust systems which use different silencer designs and am not sure which would be the best, in theory at least.

Option 1, appears to use resonater style straight through silencers, one in the middle section and then 2 at the rear in each tailpipe section.
These as I understand it are typically the best style of silencer for flow? It's an Akrapovic so typically well regarded.



Option 2, no central silencer and instead a much larger and what I presume is a baffled muffler at the rear servicing both tailpipes.
These baffled mufflers are as I understand - not so good for flow?



Trying to work out which is potentially the better performing system, 3 straight through vs 1 baffled seems to be the difference. Bore size should be the same at 2.5".


So to put a bit of context around this, the car is a 2.0 NA Clio. Currently pretty well tuned with cams and forged bottom end etc. And plans are afoot to put a standalone in and run ITB's.
My current exhaust however was previously so loud I had a central silencer added to it, and the sports cat was replaced with a decat too. These 2 changes together caused it to lose 10bhp on Surrey Rolling Road's rollers, power runs seperated by a few weeks. I've since been under the car and it appears the bore shrinks before it goes into the silencer - possibly the culprit and a sign of a bad job perhaps? I'll get a calliper on it to confirm exactly how much it shrinks by.
The car has since been mapped with the 'poorer' exhaust fitted and is now making a decent enough figure but of course I'm considering putting a nice new system in over my cut'n'shut exhaust, to see about finding some of those 10 missing French horses.

Help and advice much appreciated.

[TheEnd]

The first looks like there's a big T junction for the exhaust gasses which ain't that great.

What you've got in a bit of styling and marketing, The first one with a T looks a terrible idea, the second one looks like it could have been a smart idea until you realise they doubled back on one side to still keep twin exits which it doesn't need.

[TB Rich]

Ah that's not a T section, it's just plated over the top for support.

You can see it a bit clearer here:


Not sure what you mean by the not needing to double back on one side? The Clio 200 has twin pipes and would look a bit silly with only one. Fine for a competition car but not for something needing to look seemingly standard on the outside.

I don't know the exact design of the large rear silencer, nor would I expect I can find out. But I guess it goes into the silencer and stops in the middle, then equally distributes from a centre chamber out each side which I'm told are equal length 2.25" exits.

Cheers

[k20erham]

Hi when you have messed about trying to find out what works ..... then go to see Joe at BTB ex, he knows and it works, I used to struggle with noise with my K20 Honda in my Caterham, I fitted a raceco silencer that made it quieter then went for remapping and had got a bit more power but less torque than before, got told to go see Joe to make a silencer that fitted and worked, pulled up outside his works out he came took a look at the primaries and said!! they don't work!! to which I pointed out on my Dyno plot the numbers which were impressive to which he gave me his numbers that were even more impressive £££££££££ when I got up off the floor I said what for an exh? he said if it does not do what I say then you don't need to pay the bill!!! 3 weeks later on the same dyno as before making 264 BHP and 168 Lb ft at the hubs and no more black flags at Brands and Bedford. It's wonderful work, chat to fellow PHers on here with vast knowledge they will tell you it costs megga money to get it spot on, inlet tract length to suit the cams injectors placed to suit the revs, cams, comp ratio, exh primary length and diameter to suit, mapping what fuel, race car, WOT all the time gearing etc etc etc, change one aspect it messes up everything else.

[TB Rich]

k20erham said:

Hi when you have messed about trying to find out what works ..... then go to see Joe at BTB ex, he knows and it works, I used to struggle with noise with my K20 Honda in my Caterham, I fitted a raceco silencer that made it quieter then went for remapping and had got a bit more power but less torque than before, got told to go see Joe to make a silencer that fitted and worked, pulled up outside his works out he came took a look at the primaries and said!! they don't work!! to which I pointed out on my Dyno plot the numbers which were impressive to which he gave me his numbers that were even more impressive £££££££££ when I got up off the floor I said what for an exh? he said if it does not do what I say then you don't need to pay the bill!!! 3 weeks later on the same dyno as before making 264 BHP and 168 Lb ft at the hubs and no more black flags at Brands and Bedford. It's wonderful work, chat to fellow PHers on here with vast knowledge they will tell you it costs megga money to get it spot on, inlet tract length to suit the cams injectors placed to suit the revs, cams, comp ratio, exh primary length and diameter to suit, mapping what fuel, race car, WOT all the time gearing etc etc etc, change one aspect it messes up everything else.

Yep I know BTB, and I'm not sure why I didn't think about using someone like BTB or Simpson!
I'll give them a buzz, and thats very interesting to hear about the results vs payment scenario.

Yeah everythings of course related but I'm sure my current system can easily be improved due it having been cut about twice and I think the silencer that was last installed is causing a restriction.
I'm running the long primary manifold from the works R3 cars so that shouldn't need replacing.

This was the effect of the last cuts to the exhaust, 195 down to 185 peek


I then fixed the induction setup (which was also dynoed at a 10bhp loss!), and thus taking me back to 195bhp and then mapped properly, acheiving 215bhp.
So the aim is to simply replace the exhaust with a quality item and try and see if the 10bhp that went missing from the exhaust can be found. The cams I have should be doing 220bhp, if not 225bhp - so numbers tieing up on the dot with those 10 horses who never came back from the pasture!


I know things don't always materialise as planned, but the theory to above is sound at least.

Edited by TB Rich on Friday 22 May 15:00

[CarsOrBikes]

Out of those two definitely use the Akrapovic, the absorption silencers will flow well and quite likely produce a quieter system as there is a resonator up front, where the other has no resonator, and likely as not the pipe into the silencer terminates in such a way that sound is amplified off the endplate. Leave your long primary manifold on, and keep the cat unless you can specifically fine tune the map without it. Only my2p though.

[TB Rich]

CarsOrBikes said:

Out of those two definitely use the Akrapovic, the absorption silencers will flow well and quite likely produce a quieter system as there is a resonator up front, where the other has no resonator, and likely as not the pipe into the silencer terminates in such a way that sound is amplified off the endplate. Leave your long primary manifold on, and keep the cat unless you can specifically fine tune the map without it. Only my2p though.

Thanks, if I go off the shelf then it looks Akrapovic is the way to go.

I phoned BTB, and whilst difficult to give an accurate estimate without seeing the car, I was told £1200-£1500+vat and they would want the car for a week. I wonder if something was lost in translation because that seems ludicrous for a manifold back system, makes me think they simply don't want the work.

I've also sent Simpson an email with pictures so will see what they say.

cheers