Standard Exhaust or Trackday Silencers?
Discussion
Hello all,
I'm off to Brands on 22nd May, and I need to reduce the noise output on my 2001 4.5.
Does anyone have any opinion/experience of these so called 'trackday silencers' (the bolt-on cylinders that fit directly over the tailpipes)? Do they actually work? Do they reduce the power output by blocking the flow of gasses?
If there's any doubt, I'd be inclined to see if I can fit a standard system for the day, just to make sure that i'll be allowed on the track.
Any info would be great.
Thanks in advance,
Charles
I'm off to Brands on 22nd May, and I need to reduce the noise output on my 2001 4.5.
Does anyone have any opinion/experience of these so called 'trackday silencers' (the bolt-on cylinders that fit directly over the tailpipes)? Do they actually work? Do they reduce the power output by blocking the flow of gasses?
If there's any doubt, I'd be inclined to see if I can fit a standard system for the day, just to make sure that i'll be allowed on the track.
Any info would be great.
Thanks in advance,
Charles
They shouldnt affect your track performance, unless you're going to be shifting over a tonne continuously.... you will notice a slight change in torque though... not in a bad way, the backpressure will help a bit more in the mid-range, but you will lose some grunt in the bottom end and a slight reduction in acceleration after a tonne or so....
Also depends how well the silencers are designed, good ones can bring benefits in some ways on the track for NA engines....
Also depends how well the silencers are designed, good ones can bring benefits in some ways on the track for NA engines....
Huh? A silencer will only improve things if the exhaust was bad to start with. And you will not necessarily gain torque in the midrange - it may move around or be less everywhere - impossible to say without measuring.
Anyway, your primary concern should be "will it make my car quiet enough". From this point of view, putting the standard exhaust in is by far the safest option, at least without experimentation and a noise meter (which you can hire from places like Bookatrack). Some bolt-ons work really well on the Rover V8 for example, but make much less difference on the AJP8, e.g. the Merlin Motorsport ones.
danny
Anyway, your primary concern should be "will it make my car quiet enough". From this point of view, putting the standard exhaust in is by far the safest option, at least without experimentation and a noise meter (which you can hire from places like Bookatrack). Some bolt-ons work really well on the Rover V8 for example, but make much less difference on the AJP8, e.g. the Merlin Motorsport ones.
danny
The change of torque in the midrange and decrease in the low end, obviously constitutes some form of torque shift - squeeze, but an increase in the middle end is noticeable... this doesnt mean you've suddenly got more power - it just means you can play around with how quickly you want your power - and thats always a benefit for the track... if you're a hardcore nut racer - all these things mean the world and the difference.... for the rest of us, horses for courses...
a back to back rolling road test will give you a clue to what happens when you change the flow rate and pressure by adjusting tubing sizes and shapes... but from what I've seen so far... for normal trackday silencers - this torque change seems to be the trend with most NA cars....
>> Edited by PHØENIX on Thursday 14th April 16:36
a back to back rolling road test will give you a clue to what happens when you change the flow rate and pressure by adjusting tubing sizes and shapes... but from what I've seen so far... for normal trackday silencers - this torque change seems to be the trend with most NA cars....
>> Edited by PHØENIX on Thursday 14th April 16:36
dannylt said:
Ok so let's see some graphs shall we? What "normal trackday silencers" have you tested, and on what NA cars?
It's very possible to lose torque EVERYWHERE not just move torque around, so all that waffle is rather redundant.
You are right in one way but only in certain situations - just troll the internet forums... you will find many similar views... again it all depends on the current exhaust system setup....
Also i've seen a number of charts in a rolling roads database that have done such tests and more, not necessarily bolt on silencers, but adjustable exhaust bits, at the back and post collector.
I dont have a NA car at this stage, so cant do any test, but with free access to a rolling road i am more than willing to play if you bring a car along...
I dont think my aspirated engines on either current cars will appreciate any silencers.... with just over 500hp flowing out of the current one and a 1000+ out of the eventual phoenix...
There is a great technical article on exhaust flow and pressure... i'll see if I can dig it up...
I have been in deep discussions with pro's in this area who design racing collectors and exhaust systems for cars of all calibre (yanks)... and also have developed my own too (which is to be used on the phoenix), using solidworks with flow/pressure addon and using baseline technical data taking into account the cam timing and induction rate as well as intake temperature, fuelling and overall combustion efficiency... if my ideas work - I might just brag about it in the near future...
But silencers dont have the same effect on all cars, it really is down to the existing setup and there are many factors in the equation eg. rpm, flowrate, backpressure, venturi principles, engine firing order and relative collector design... also if the vehicle is fitted with CATS - then you are more restricted in what you can do with a catback let along a trackday silencer, unless of course the system was poor to start with.
With the cerbera engine as it stands, the current design of headers and the feeding into the exhausts is not optimal to say the least, if things are inefficient at the main source where velocity is at its greatest, theres very little you can do if anything on the rear, but silencers can help increase backpressure to a certain degree, and depending on overall velocity and pressure loss through the system, there is a chance you can shift torque around, doing down at some points in the rev range and shifting up or down the rev range... never did I say the torque goes higher than peak - thats not realistically possible unless the fuelling/breathing compensates for backpressure.. which some more advanced engines out there do... also the fuel overrun with extreme cam profiling does work wanders with a certain level of backpressure... and many tuners out there have played in this field to gain quite a few extra horses... again, I have no idea if any of these 'clever' tricks will work on the AJP... I believe Joolz has already stated in the past that just changing the headers has no performance gains whatsoever on stock setup... of course if the right internal changes are made with cams/fuelling/breathing - then headers can be optimised... and so can the rest of the exhaust system... its an expensive game... I just hope I get it right first time, titanium tubing is not cheap.
I know all of the above might not be what you expected, but a bit of background to my post wont hurt.
Oh gosh - forgotten about the 8-pots. Yes, they're still at Fernhurst in a box, haven't been used since being on my car. Mail me via PH if you're interested.
As for trawling the internet - there is plenty of opinion out there. Back pressure is a misnomer, and if the exhaust system is anywhere near optimal bolting a crube silencer on the end will only be negative. You will NOT guarantee to increase midrange torque by any means.
Anyway, I hardly think it was relevant to this thread - whose main point was NOISE. The standard 4.5 backbox is the simplest best silencer without losing power.
As for trawling the internet - there is plenty of opinion out there. Back pressure is a misnomer, and if the exhaust system is anywhere near optimal bolting a crube silencer on the end will only be negative. You will NOT guarantee to increase midrange torque by any means.
Anyway, I hardly think it was relevant to this thread - whose main point was NOISE. The standard 4.5 backbox is the simplest best silencer without losing power.
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