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Track sound restrictions

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  • Track sound restrictions

    Question to all, what silencer options are available , other than OEM, that will satisfy most track sound restrictions without sacrificing performance?

  • #2

    With San Diego having one of the most restrictive sound limits ([email protected]'), have lots of experience. Don't forget that the intake side adds much to the sound levels and will probably need to be addressed as well.

    Need to know engine and redline as a start. What limits are you achieve?



    • #3
      I am utilizing a 2.3 Duratec. I have limited at 7500. Wayne my goal is to be able to run on any California track without worrying about sound regulations.
      Last edited by Joe R; March 4, 2016, 06:50 AM.


      • #4
        I don't regularly run at tracks with sound restrictions, but have had trouble each time I've gone to Laguna Seca. I have had a quiet exhaust made, but the big problem was the noise from the intake. I always seem to be able to exercise self control going past the noise meter until the last afternoon, and then eventually fail the sound check.

        It was pretty easy and inexpensive to have a quiet exhaust made at a muffler shop to attach from the collector back, but I haven't found a solution to quiet the intake (other than a lighter right foot).

        Good luck!



        • #5
          Wayne (super7guy) sent me a few photos for post for him.

          I've always wondered how much simply covering the apeture in the bonnet might help. You would likely need to run without air filters, but it may help get there.


          • #6
            thanks Geoff,

            This is just the most complicated part of my solution. It is the part that is attached to a 1/4" backing plate attached to the ITB and air horns. Under the is a 3" tube holds a K&N cone filter and resides inside another airbox that allows air to be taken from inside the cockpit.

            The blanket approach loops over the outside air cleaners creating a scoop. The blanket is about 2" x 1.5' with one side attached to the hood and the other side attached to the fender. The Velcro allows the scoop to be removed and reattached before moving the bonnet. It worked for a hi rev BDA, just not very elegant.



            • #7
              Ron (escondidoron) has an elegant solution that also brings the air intake under the bonnet.

              A similar solution was on Wheeler Dealer for their cold air intake.

              More ideas which all require more fabrication.



              • #8
                After my divorce was final, I realized that I actually want to talk to my passenger. So, first I put on a really big muffler/gas pack, and I then realized that most of the noise was the intake and not the exhaust. Even though my head is only two feet from the end of the tail pipe, I can not hear the exhaust over the intake noise.

                So, I have designed and built a air filter for the outside of my bonnet that has a muffler built into it. I am not made measurements yet, but I now can comfortably run without ear plugs. The design uses longer trumpets, so I might need to adjust the Map. I do not feel any performance differences.
                Rod Swanson


                • #9
                  Can you post some photos?


                  • #10
                    Originally posted by super7guy View Post
                    Ron (escondidoron) has an elegant solution that also brings the air intake under the bonnet.

                    A similar solution was on Wheeler Dealer for their cold air intake.

                    More ideas which all require more fabrication.


                    Thanks very much for the compliment. Here is an explanation of my thinking and some pics of the aluminum air cleaner assy for my pre-Xflow S2 as it progressed:

                    The backing plate mounts to the top of the two carburetors by means of a pair of diagonally braced standoffs. Note the Dzus fastener mounting tab just below and to the left of the cylinder #1 velocity stack. It is the upper mounting tab for the fiberglass nose cone. The circular weld area on the air cleaner backing plate just to the left of the #1 cylinder velocity stack is for a -6 flare fitting. It provides a vacuum port for the crankcase vent hard line that runs to the opposite side of the engine. A short piece of vacuum hose connects the hard line to the AN fitting to provide vibration damping:

                    This view from the opposite side of the engine bay better illustrates the installation of the backing plate and crankcase vent line:

                    The airbox mounts to the standoffs via a pair of screws that mate with the standoffs. I installed Helicoils into the standoffs for long life as I figured that the airbox would be on and off a lot over time. The mounting screws and washers are SS for corrosion protection. My original plan was to install studs into the standoffs and use wing nuts to secure the airbox. However I gave up on finding appropriately sized wing nuts. The problem was clearance between the ends of the studs and the wings. Just not enough space to get them on and off w/o contacting the wings. The bung in the picture is welded into the top of the airbox. The counterbore in the bung provides an index to the standoff for alignment / mating of the finished parts when installed on the car:

                    This pic shows the raw standoff and bung assembled:

                    Here is a detail showing the plenum's interior X-section while setting up to weld the mounting bungs to the airbox. Note the sophisticated tooling used for squaring the standoff and setting the height of the airbox from the baseplate:

                    This is a side view of the three pieces that make up the airbox prior to welding them all together. The angular shape of the airbox was planned to make the outer edge be parallel to the taper of the wing and to maximize interior volume for good airflow to the velocity stacks. The minimum height inside of the air box is two diameters (80mm) above the end of the #1 intake trumpet when installed. Note the dimple in the left endcap. It was a late addition that was necessary to clear the nose cone Dzus fastener mount that is on the top rail of the chassis:

                    A separate airbox was fabricated to mount the air filter element. It seals to the bonnet via "rubber" push-on edge mount weather strip. The goal was to isolate the fresh air intake from the hot air in the engine bay. This is especially important here as the carbs are directly above the exhaust headers on this pre-flow engined car. This assembly mounts to the chassis using pre-existing holes from panel rivets. This view also highlights how the engine mounted plenum shape conforms to the taper of the wing:

                    This view shows the almost finished assembly with most of the weather stripping installed and scat tubing to connect the engine mounted airbag/plenum assy to the chassis mounted air filter assy. The scat tube allows both vibration isolation between the engine and fixed air cleaner as well as ease of mount/dismount of the airbox from the carbs for service:

                    In this view the nose cone is installed and the new bonnet is taking shape. It seemed like a good idea to make a new bonnet rather than chop up the original Lotus part. That allows returning to factory configuration should I ever want to show or sell the car (neither of which is very likely!). The large gap at the aft end of the plenum is designed to provide a clear air flow path for fresh air to reach the air filter:

                    Here is the separate cowling for the entire assembly temporarily mated to the bonnet. It closes up the hole in the side of the bonnet and provides a scoop/duct to channel fresh air to the air filter. I kept imagining a post-war Indy roadster kind of shape during fabrication. Again the trim of this piece attempts to match the tapering line of the front wing as well as the round headlight when viewed from the front or rear:

                    When I started this project I really only wanted to have a functioning air filter system. The climate here in SoCal is much less humid than in the UK (Really?) and I was worried that running with no air cleaner in front of the carbs would lead to premature piston ring failure. But at the end of the day, the overall reduction in intake valve noise turned out to be a big surprise and a huge improvement.
                    Last edited by escondidoron; March 7, 2016, 08:27 PM.

                    '62 Lotus Seven
                    '84 Turbo Esprit (x2)
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                    "A man must keep a little back shop where he can be himself without reserve. In solitude alone can he know true freedom." -Michel De Montaigne 1588


                    • #11

                      I think that we have provided intake noise solutions that are both aesthetically pleasing and functional.

                      Note is both cases, the concept is to get the "noise throat" into and under the bonnet and pick up air from the outside. In either case, our carb/ITB coverings are designed to be parallel to the flat side of the chassis. Both do require a fair amount of fabrication to accomplish.

                      My air box is fabricated from 1/8" alloy, using flat plate, 1"x4" channel and 3" tube. The back plate is 1/4". The thicker alloy provides dampening and in some ways was easier to work. In some ways, it was a fun project; one of those that "little by little" and finally done.

                      Feel free to contact me at "[email protected]".



                      • #12
                        Wow! Those are both very impressive! Thanks for sharing the pictures.


                        • #13
                          Thanks Wayne! And to all, your input on the intake side of the noise level discussions. I am incorporating a single throttle body intake set which is all in board under bonnet. That being said I am looking for some muffler solutions as well. Thoughts?