trying to get below 103dB for Spa track day

Hi there,

I´m desperate trying to get my GT40 below 103dB to participate in the Spa Open Pitlane track day. Take a look at the attached pictures. It was measured at 106dB with the Kooks alone and they sent me to my trailer.

For this year, I´m adding some mufflers outside, but I´m not sure if that gets it below 103dB. I fitted a couple of extra silencers with V-Bands. They hang outside of the car. What would be your idea to sustain the extra mufflers ? How'd you build such a muffler bra ?




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Chris, just a suggestion, but I’d angle both of those extra silencers in the same direction away from wherever the sensors are placed to measure the dB level, or maybe just replace the extra silencers with simple deflectors angled away from the sensors if you only need to come down 3 dB.

Paul T.

Have you looked at Supertrap disc muffler system or if anyone on here has used them. One of the options I was going to look into when I get to that point. Where I run have to meet a 98 db level.
These are pics taken at Spa 6hrs and are a very common sight during free practice wher DBs are limited.


Thats what made me decide to go a differend route.
I run a Hooker Aerochamber muffler and was advised by Hooker to add length before entering the muffler.
Ian, my design was for 103 - 105 , and these are still being used by several original GT40 race cars for testing etc, particularly at Goodwood. The other criteria was to get this performance with very little ( no ) performance loss, these are straight through but with some ingenious internals that gets both benefits. Geoff Taylor and I did a lot of development laps to prove them ! Frank See pics 1088 running these silencers )


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Simple answer is the Frank Catt design fitted to my car 23+ years ago and still in use on many race GT40s. Accepted at Goodwood, Spa and hill climbs over a ten year period. Fine for road use too, doesn’t wake the neighbours or frighten the horses.


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Randy Folsom

Similar to Greet-Jan is an earlier iteration of the Ruffian GT40. The main difference is that on that car is that he used suit case boxes to hide the mufflers. Now the Ruffian has twin turbo’s. They probably do a pretty good job of muffling the exhaust.

Randy Folsom

What are folks using for valves to switch between straight pipes and muffled. Anyone using valves that can be switched while driving. Cheers, Randy