Where best to fit an additional silencer

[banhama]

In other threads I've documented the new Gravity exhaust that I fitted.
It passed a 100dB static and 92dB drive-by on its first track day, but i know it's pretty near the limit, particularly under load on the drive-by.

Second track day the car went really well in the first session, but got noisier and was hitting 101dB on the drive-by, so wouldn't even pass race noise limits.
We immediately blamed the exhaust, and took it off the car, checked it all, re-fitted it and went back out.......it was even noisier, then the car wouldn't accelerate properly, and finally had a flashing emissions light, so gave up!
Back home I did a static test and it was way up, about 103dB, where it had been 98-99 previously

Turns out the actual issue was a slowly developing misfire caused by the left hand spark plug well filling up with oil.
Cleaned up the plug, put it back in and it's now all back to normal. (Although I still have to find and fix the leaky seal)

Anyway although the exhaust wasn't to blame it is a bit too close to the limit, so looking to cut in a small Jetex full flow silencer.
I have nothing on the exhaust except the lambda sensor and the 2 back boxes.
So where would be the best place to fit the silencer, close to the engine or further away?
It would be easiest to fit it directly to the downpipe, where the cat used to be, but would it be more or less effective fitted further back?

Any thoughts welcome
Ta, Andy

 

[MRBILLYUK]

On the original 182 exhaust the centre silencer was fitted a couple of inches after the cat/ olive joint so I'm guessing that would be the best place to fit one. The original centre silencer was quite a long one too as you can see in the pic.
If you're running without a cat that'll also increase the noise level.

 

[clio tyres]

(Although I still have to find and fix the leaky seal)

That will involve removing the valve cover to reseal and cambelt replacement.

It would be easiest to fit it directly to the downpipe, where the cat used to be, but would it be more or less effective fitted further back?

The original cat has a diameter of 4.5 inches and any mid silencer in the original location over 4 inches will touch the floor (heat shield)

 

[banhama]

Many thanks for the replies.

I'm just going to fit a short circular silencer, so probably just where the cat used to be would be ok. The one I was looking at was 125mm diameter so I might need to find one that's 100mm.
I only need a couple of dB safety margin for the noise tests as it's not road legal anyway.

Thanks for the info on the valve cover, I'm not ready for a cambelt change yet as I only do trackdays and races so I'll monitor it for now.
It did look like the oil was coming from the small breather hole from the cover straight into the intake manifold, where the weird shaped gasket is not sealing properly. There was some oil in the manifold itself, which can only come from there, as the crankcase breather goes from a catchtank to atmosphere.

Oddly the amount of breathing seems to depend on which throttle body I fit.
Standard 60mm or bored out 62mm. The larger TB seems to give better response and slightly quicker lap time, but noticeably increased engine breathing.
Reason I say that's odd is that the majority opinion on here seems to be that polishing and porting the manifold and fitting a larger TB does naff all!

Next time out I'll use the standard TB and try to improve the rocker cover to manifold seal, and see if that improves the oil on plug issue

Ta Andy

 

[clio tyres]

I'm just going to fit a short circular silencer, so probably just where the cat used to be would be ok.

Anything bigger than this https://www.ebay.co.uk/itm/111415264715?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649 will cause you problems.
Although if you have no cat you could run a longer version.

 

[M.C..]

@Andy P can supply you details he did his 172 recently

 

[Andy P]

This is a link to the one I bought.

Pardon our interruption...

 

[Andy P]

I bought the 4" Diameter one by 12" long so it is a total of 16" long if you choose the clamp on version.

 

[Andy P]

Installed, sorry it won’t let me add a photo for some reason 🤷‍♂️

 

[M.C..]

Photo attached for @Andy P

 

[JB21]

Could you not just fit a DB killer in the current silencer?

 

[M.C..]

What’s going on with this forum today

 

[JB21]

...

 

[banhama]

I bought the 4" Diameter one by 12" long so it is a total of 16" long if you choose the clamp on version.

Many thanks for the link, looks ideal. Unfortunately I can't see your installed photo.
I would fit it where the cat used to be, I have a straight pipe with the sensor boss welded in, I just need to get under the car to see if I have 16" straight pipe from the downpipe to the boss.
Otherwise I have seen a slightly shorter 14" clamp in one.

Ta Andy

 

[banhama]

Could you not just fit a DB killer in the current silencer?

I only have these two circular back boxes, so not sure I could fit anything in there, I was thinking of the clamp on disc dB killers that go on the tailpipe but I'd have to buy two, so looked a fairly expensive solution.

OOPs! I can't add a photo either!

You can see the Gravity Exhaust I have in this thread though https://cliosport.net/threads/gravity-cat-back-exhaust-clio-182.838191/

 

[Andy P]

@banhama In the link I posted they do a 10" & 8" so would be 14" or 12" respectively overall.

 

[M.C..]

@banhama can't edit my previous post

 

[banhama]

Just to round out this thread I fitted a Jetex (Simons) 14" long circular silencer.
I was quite impressed with the heavy duty clamps, better than the U-bolt as they are a lot wider, have an internal ring and 10mm bolt (17mm head) to graunch them up with!
Big test was the dB test. I 'borrowed' my wife's work dB meters, and scored an average of 96dB static at 5500rpm, which is good for all racing and almost every track day.
The final test will be tomorrow at Lydden Hill where I'm doing a couple of track sessions, that will confirm the drive-by dB is also ok.

Thanks for all the help, my apologies for the crappy photos, and remember......when using axle stands on tarmac in the summer always use a spreader plate, then if we have a mini heat wave the stands won't start sinking into the tarmac

 

[Chambers_RS]

Many thanks for the replies.

I'm just going to fit a short circular silencer, so probably just where the cat used to be would be ok. The one I was looking at was 125mm diameter so I might need to find one that's 100mm.
I only need a couple of dB safety margin for the noise tests as it's not road legal anyway.

Thanks for the info on the valve cover, I'm not ready for a cambelt change yet as I only do trackdays and races so I'll monitor it for now.
It did look like the oil was coming from the small breather hole from the cover straight into the intake manifold, where the weird shaped gasket is not sealing properly. There was some oil in the manifold itself, which can only come from there, as the crankcase breather goes from a catchtank to atmosphere.

Oddly the amount of breathing seems to depend on which throttle body I fit.
Standard 60mm or bored out 62mm. The larger TB seems to give better response and slightly quicker lap time, but noticeably increased engine breathing.
Reason I say that's odd is that the majority opinion on here seems to be that polishing and porting the manifold and fitting a larger TB does naff all!

Next time out I'll use the standard TB and try to improve the rocker cover to manifold seal, and see if that improves the oil on plug issue

Ta Andy

if it’s the left spark plug as your looking at the engine it’ll be the seal for the dephaser solenoid. It’s about £10 from dealer and 20minute job.

 

[banhama]

if it’s the left spark plug as your looking at the engine it’ll be the seal for the dephaser solenoid. It’s about £10 from dealer and 20minute job.

Many thanks for this.
After a couple of track sessions on Sunday some more oil appeared so I ordered a seal on Monday, good to know I might have done the right thing for once!

I do seem to have a much increased breather pressure after fitting a slightly larger TB, despite running the breather to a catch tank. I think the TB might be a red herring and there could be an issue with the breather plate. Do you know if you can remove the breather plate under the rear of the intake manifold independently, without interfering with the rocker cover and having bits flying out.

I intend to have the car mapped for the TB as soon as possible just to be on the safe side, but that involves trailering the car about 100 miles.

 

[Chambers_RS]

Many thanks for this.
After a couple of track sessions on Sunday some more oil appeared so I ordered a seal on Monday, good to know I might have done the right thing for once!

I do seem to have a much increased breather pressure after fitting a slightly larger TB, despite running the breather to a catch tank. I think the TB might be a red herring and there could be an issue with the breather plate. Do you know if you can remove the breather plate under the rear of the intake manifold independently, without interfering with the rocker cover and having bits flying out.

I intend to have the car mapped for the TB as soon as possible just to be on the safe side, but that involves trailering the car about 100 miles.

Personally I can’t see the TB making that much difference. I had one when I fist had the car and never mapped it.
You can remove the breather plate yeah 👍🏻

 

[banhama]

Personally I can’t see the TB making that much difference. I had one when I fist had the car and never mapped it.
You can remove the breather plate yeah 👍🏻

Thank you. The seal arrived yesterday, so I've got a couple of jobs to be getting on with!

 

[banhama]

Seal change fairly straightforward, the old one was rock-hard so this is looking good as a fix for the oil int0 the No4 plug hole.

I removed the breather plate mainly to check I hadn't pushed a plug of paper down the vent elbow when the engine was out.
The increased breather pressure, dipstick popping out etc, started after re-fitting the engine, enlarged TB and polished ports.
Fitting a catchtank hasn't made much difference.

Also I was very curious to see how the breather is constructed. To say it's very baffling would be a terrible pun, but also true!

It looks like all the exit venting is out of the rear chamber, either via the vent elbow or the tiny hole that goes directly into the intake manifold.

Question 1. Is that pinhole necessary, particularly if you have the main breather into a catchtank?

There are 4 vents into the breather plate.
2 large ones at the front that have to run through the maze of baffles to reach the exit chamber at the rear.
2 smaller ones at the rear that enter either side of the exit chamber, so have far less baffling.

Question 2. Which pair vents the crankcase and which pair vents the head.

My feeble logic would suggest the larger vents would be for the crankcase, but the positioning looks like they are from the head. It would also follow that they have more baffling as the head is directly below so would throw up more liquid oil.

Question 3. If under hard track work the dipstick pushes out it suggests the pressure cannot exit the breather chamber quickly enough (there are no nasty signs of head gasket failure etc.). Two simple solutions: Enlarge the pinhole into the manifold? Downside more oily vapour back into the engine. Or bore out the the main vent and run a larger hose to the catchtank?
Both of these seem pretty extreme for a car with around 176bhp, so what am i missing?

Some pics to illustrate what I'm blabbering on about:

BREATHER PLATE

BELOW THE PLATE

 

[banhama]

PS, by 'head' above my mean the part where the cams whizz round, not the combustion bit obviously.

I did have another thought.
Why is the last chamber so clean?
When you initially stamp on the throttle the manifold air pressure shoots up, and then drops back, presumably into vacuum, or at least that's what it looks like from the trace on my RSTuner.
So at that point is air blasting through the small hole into the breather plate?
This would correlate with the fact that I get absolutely no oily mist in the catchtank, just clean air.
Also at that point nothing could vent, or worse the positive pressure would push backwards, and maybe pop the dipstick out?

A test would be to block the small hole and see what happens.

Any thoughts welcome

 

[banhama]

if it’s the left spark plug as your looking at the engine it’ll be the seal for the dephaser solenoid. It’s about £10 from dealer and 20minute job.

Just to round off this thread, and say thanks for the forum's help once again.

The tiny silencer reduced the static noise test to a feeble 87dB, which means I will pass any noise test at any track, and probably even drive through a library without turning a head. The silencer had no adverse effect on performance.

Replacing the dephaser solenoid seal has virtually eliminated the oil deposited on top of the rocker cover during a hard trackday. What a simple fix!

I will of course need more help as during yesterday's outing two adjacent bolts sheared off the nearside front wheel.
Braking from 85mph and trying to turn right didn't go to plan, but that will be the subject of another thread.
As will the fact that the PMS alternator bracket, and the lug on the alternator, snapped off during the first session.
Metal fatigue day!

Thanks all for your help
Andy