Urgent Bung Question - Track Day Tomorrow!

[Willcox]

I\'m going on my second track day on Friday at Castle Coombe.  Previously I was at Silverstone.  The difference as you may know between the two, is noise restriction, which is set at 100db at Castle Coombe.  

Running at 4,500rpm i got a reading of approx 104db, and i needed to get this level down.  I spoke with a friend who engineered and manufactured a tailpipe restrictor/muffler/bung out of a solid piece of aluminium.  The noise level has dropped significantly to around 98.5db to 99db.

I’m aware that I will loose a bit of top end performance and fuel efficiency, but I’m worried that the back pressure in the exhaust system may in some way damage the engine or turbo\'s?  Is it possible?  There is quite a difference in the diameter of the tailpipe exhaust now that the restrictor has been fitted, from 4.5 inches down to 2.75 inches.    

This is not a standard RX7 and has been significantly modified, running at about 380bhp.  I have listed the mods below so you have a better idea of what I have, and whether i\'d be stupid to run it on Friday with the bung in.  It was imported by Newera in 2006 and some of the modifications are currently unidentified.  

Apexi Super Suction Twin Induction Kit (with hard piping)
Apexi GT Spec Intercooler
Apexi GT Spec Radiator
Apexi GT Spec Air Seperator Tank
Uprated High Flow Front Downpipe
Catalyst Replacement Pipe
Cat-Back HKS Super Dragger Type II Muffler
Trust Profec B Boost Controller
Apexi Power FC ECU & Controller.
TEIN Coilover Suspension

I will attached some pics of the tailpipe bung (fitted) if that helps at all.

[Willcox]

Here are the pics.  If any further explanation is required please ask.  I would appreciate any help you can provide.  

http://someplaceelse.co.uk/images//bung1.jpg

http://someplaceelse.co.uk/images//bung2.jpg

[M@r]{]

I\'m not a technical guru so this is 2nd hand but I dont believe you should do a track day with a bung in.  I had the same dilemma not so long ago and I asked the question to WGT.  He advised against it.  I\'m running similar power / mods to you.

At the end of the day you are going to be giving the car some real stick so I definitely would do it

[AtomicRex]

I will second the above.  The Rotary needs to flow...the bigger the exhaust the better, and presumably it has been mapped to work with that exhaust.
 
You will stiffle the exhaust flow too much, and the car will run like a dog!
 
Get a silenced mid pipe, cheaper than a rebuild!

[M@r]{]

Or a quite exhaust! I was looking for a solution.  I love how loud my car is so didnt want to permanently quieten it, something I could take on and off. I looked underneath mine and the midpipe looks a bit awkward to get to (on jacks) so I reckon an exhaust with a bigger back box is a good bet, easier to take on and off.

[AtomicRex]

Stick a decent mid pipe in, doesnt mean it isnt going to have a good noise....sometimes a quieter pipe can be a more refined noise

[Nik da Greek]

I agree with Jon and Mark, bungs are a total lash up of a solution. They\'ve been common practice on bike exhausts for years, and I\'ve never had one yet that didn\'t make the bike run like a three-legged dog! The problems even more exagerrated on a turbo car where the last thing you want is to stick in a sudden unexpected lump of backpressure. I had to use one on my previous FD cos the HKS it had on was just stupidly loud, and it just made the car run like a bag of old sh!t, and that was on the road. It\'d have been horrible on track, there were flat spots all over the place. Get a proper silenced midpipe fitted instead!

[Willcox]

thanks very much for the opinions guys.

Now i\'m going to have to find a silenced midpipe and get it fitted in a few hours!  I\'ll try Dragon Performance as they are probably most local to me (i\'m in Devon).

By the way, i did test the vehicle last night with the bung fitted.  A noticeable drop in performance but all my temps remained normal, and the car still ran well.

[Willcox]

I managed to get the mid pipe fitted in time, and it worked a treat.  Not too sure how they go about measuring noise at Castle Coombe as i had 2 independent tests done beforehand using 2 separate noise meter levels - The results were 99.2 and 99.3db, yet at the track they rated it 93.0!!! I shouldnt complain however.

Thanks very much to John from Atomic Rex for all his help and advice, whom i met at the circuit.

[RedRummy]

phew... good result!

how can you test the audio level without buying a decibel meter?  Going to brands hatch soon.

[AtomicRex]

Well done for getting there Paul, shame I didn\'t get to go out with you in the end, but next time you are up we can get you a little more confidence!
 
I take it you and Dom made it home OK?
 
Such a good time out on track....I want to buy a Caterfield now!