Track day: gundo = too many dBs, what to do?

[tob_today]

I've got a standard C2 3.4 with:

- Dansk Sport exhaust (regular, not loud) - from previous owner
- 1.5 inch gundo bypass
- larger EP410 oval tips

I've booked to go on Porsche Club trackday at Goodwood which has 105dB static test limit.

I've bought a semi-decent £25 db tester from Amazon, to give more accurate results than iPhone app. Warmed up (with no AC) at 5k RPM it gives ~104-106 dB (0.5m away, angled) which is really surprising as the exhaust doesn't sound that loud compared to many other 996's I've heard. Just nice upgrade to stock. Although my engine does like to kick-on from 4.5k onwards, so noise escalates quickly.

I heard about Decibel Slayer https://www.demon-tweeks.com/uk/decibel-slayer-bolt-on-exhaust-noise-decibel-reducer-insert-birdbs1/

It says it supports ovals up to 4", but my tips are 5". So doesn't seem an option.

It's cost decent money to book the trackday, and don't want to get sent home immediately after arriving. The car was away when I booked, and I assumed it would be fine. If this is too loud, then no way will my 993 pass.

This might be when my "cheap" gundo mod instead of buying switchable system might come back to bite me.

Any suggestions / ideas to get me through the trackday please?

 

[martin t]

https://www.merlinmotorsport.co.uk/p/merlin-mild-steel-racing-muffler-m-ex-muff-4?vat=on

Unfortunately noise limits take no prisoners!

Goodwood are very stricy as are castle coombe.

Castle coombe were the worst and most unforgiving so i did not go there again having been forced to either go home or buy one of the above for the car i had at the time.

Even at bedford autodrome i had never had a problem.

Be prepared to be kicked out.

However of you could fabricate a 5 into 4" pipe then you could fit the additional silencers. A very expensive solution which believe it or not might not work.

 

[Senoj]

Goodwood normally run a sessions day. This is to combat their noise issue by having smaller groups of cars out simultaneously.

So, if you are loud then they could potentially Group you with quieter cars. I think you'll do ok, db meter reading is wildly variable depending on position etc. Clutch down, air con off. They know Porsche's are noisy with all the mechanicals in the rear. I'd advise to understate your max revs a little when testing static and Rev towards were they tell you but not right at it. If you get a flag on the drive by then you can always short shift if really need to.

105 static is relatively high so they have set it up as 'noisy" day.

:thumb:

 

[Hugh_]

I had issues getting through the noise test at Brands Hatch with mine, which has Cargraphic ETR (the middle of their 3 options) boxes with gundo hack. I scraped through the 105dB noise by test being conservative with the revs they asked me to hold, but didn't hold back on track and didn't have any issues.

 

[crash7]

Decibel devils / slayers do not work, save your money, I have been through this.

Unfortunately if your looking at doing regular trackdays you will need to change your back boxes this was the only fix for me after having several days ended early via the black flag.

With 997 X51 manifolds, standard 3.6 cats and Top Gear Mild Sports I can pass at all of the UK circuits, just, including Bedford which is about the most problematic.

Standard 996 systems can pass without issue, however any mods seem to tip the balance.

If they do not do carry out drive by tests, you can cheat a little on static, but if they conduct drive by's you may struggle, if the drive by is via fixed meters, you can lift and coast or short shift, if its via a mobile meter you may get the black flag of doom!

Generally if you pass the static you will get a noise board before getting flagged.

 

[4076simon]

I take my 996C4S around Goodwood. It has a Topgear exhaust and always passes the dB test. I live 6 miles away, you are likely much further, however if you find yourself going for a drive call them and pop in for an early test dB. Tests results can vary by circuit.
Also for any tiptronics, its impossible to rev to requested limit as the limiter kicks in.. Helpful in these circumstances.

 

[MaxA]

105db is pretty loud; I'd go and ask for a static test at the circuit in question as in my view the results can be quite variable, as - even with the same club, using the same equipment, by the same operator - on different days. :dont know:

 

[tob_today]

Thanks for the feedback. I also called PCGB. Apparently it's relatively rare for members to fail noise restrictions on club track days but it does happen, more at some tracks than others.

They said my set up "should" be ok, however there's a lot of variability in testing & environmental conditions (especially for drive by tests), so it's still a risk. So they offered me a refund as I really don't want to go all the way there only to be sent home. Especially as I convinced my wife to go with me (not really her thing), and she will never go again!

So now I need to decide what to do about my exhaust so I can book again with confidence. Shame as I like my current set-up.

 

[tob_today]

I've posted new thread asking for replacement exhaust suggestions: http://911uk.com/viewtopic.php?t=147304

Please post there if you have any. Thanks!