Muffler for C-7 with Race Spec Kent Crossflow Engine

[O Racer]

My new race engine is ready to go to the dyno and I have to provide an exhaust system for the dyno test that I will later fit to the car.

 

The header is the factory Caterham 4 - 1 stainless steel unit with a 2 inch outlet at the collector.

 

It will be used mostly for track days and I am trying to balance maximum power with the need to not exceed 92 db sound limit at tracks like Laguna. I will have the exhaust pipe exit in front of the wing with a tip facing outwards...away from sound pick up which is on the other side of the track.

 

I have been looking on line at Super Trapp, Burns, Magnaflow and Flowmaster. I would hate to spend $400 on a muffler only to be black flagged at my first event.

 

I am sure I am not the only one to have this dilemma, any suggestions for an exhaust that worked for you?

 

Thanks

 

John

[super7guy]

Hi,

 

I had to use two Magnaflow Ultraflow mufflers to quiet down a BDA. It takes volume to quiet down the exhaust noise.

 

Another consideration is the intake noise, which greatly contributes to the overall noise "seen" by the meter. I built an airbox that picks up its air from inside the cockpit through the heater opening in the cowl.

 

Here is San Diego, we are limited to 93db@50ft.

 

Wayne

[O Racer]

Wayne,

 

How long and what is the diameter of the two mufflers? Are they round or oval?

 

Thanks

 

John

[TheDingo8MyBaby]

I assume you're looking for something that's lightweight too?

 

I can't comment on Raceco silencers, but I think they're pretty highly regarded and extremely light weight.

 

You can also read about RNR's experience with his WCM here:

 

http://www.usa7s.net/vb/showthread.php?4728-Ultralite-exhaust-options/

 

Maybe he can update us on any further developments?

 

I have 2 2.5" ID (1 is 3" ODx10", the other is 4"x14) Coast Fabrication Mufflers on my pre-crossflow - I don't think it would pass 92db. When I finally get the chance to get to laguna, I plan to buy a supertrapp tip I can install if necessary.

 

http://i.imgur.com/D45DpMJ.jpg

 

I did see a photo of a caterham at laguna that used an oval shaped muffler that actually made a u-turn at the rear fender and turned around the other way. I can't seem to find it at the moment.

 

Wayne is right though - being a crossflow, your exposed webers on the right leave you at a disadvantage.

 

Be sure to let us know how much power you make. I'm certainly curious...

Edited November 14, 2015 by TheDingo8MyBaby

[super7guy]

John,

 

The Ultraflows are 6" in diameter and the body is 16".

 

The lengths were determined to follow the profile of the chassis side. I use a "trombone" on the side under the clams to get that much length.

 

You may be able to find a longer muffler that fits just along side the seating side of the chassis.

 

You do not want to use a supertrap. To get the BDA quiet enough, it was so choked that the back pressure caused the engine to stop running after about 30 seconds and this was using the larger supertrap.

 

The other area that has to be addressed is the intake noise. If you can see into the intakes, so can the sound meter. It was quite a bit of work to make my air intake using 1/8" alloy, but it takes that side to reduce the booming that occurs with thin materials.

 

Call me if you want to talk, We have worked hard to meet the restrictions at the stadium. Even the Emod champ, Jeff Kiesel had to make many modifications to meet the requirements. 93db@50ft means that you hardly hear the noise at the edge of the stadium.

 

Wayne 619-444-0840

[rnr]

You can also read about RNR's experience with his WCM here:

 

http://www.usa7s.net/vb/showthread.php?4728-Ultralite-exhaust-options/

 

Maybe he can update us on any further developments?

 

I ended up at 95db at Laguna despite turning the exhaust to blow under the car. Since a bigger exhaust was not an option I tried reducing intake noise by adding a Lotus Elise intake to the engine but still ended up at 95db.

 

I did see a photo of a caterham at laguna that used an oval shaped muffler that actually made a u-turn at the rear fender and turned around the other way. I can't seem to find it at the moment.

 

I believe that Caterham has two mufflers. He has his usual one at the stock location and for Laguna he adds a ubend to the stock exhaust and runs a second muffler in series and attached directly to his roll cage. Its a great solution and pretty much the only way I'll be able to run the Ultralite at a 90db day.

[escondidoron]

I put a new muffler on my 109E about 18 months ago. It's a large straight thru custom made glass pack unit.

 

After installation of the new muffler, with the much quieter exhaust note, I became aware just how loud the valve noise and induction roar from the open velocity stacks was. So with that in mind, as well as adding some real dirt and stone ingestion protection for the valves and piston rings, I fabricated the following air cleaner setup:

 

 

The new air cleaner required fabrication of a new bonnet as well (I didn't want to cut on the original unit):

[escondidoron]

One more post to illustrate the completed setup:

 

 

I can report subjectively that a significant noise level reduction has been achieved overall. And with no observable reduction in power. However I have not measured the sound level with a meter.

[super7guy]

As you see from Ron's pics and my text, that sound reduction requires work. The air intake needs to "hidden" from the meter and that requires the air intake to be from under the hood or from the cockpit for the long term. The air box should be constructed using denser materials to reduce the "booming" effect.

 

Another not as elegant approach that I have used, is a marine sound blanket that is attached to the hood using Velcro and double stick tape. Again the air intake noise is not directly seem by the sound meter and some of the noise is also absorbed.

 

Wayne

[O Racer]

Hi everyone and thanks for the input, somehow I missed the last few, I have been busy here.

 

The engine was dynoed last week at Cal Dyno in San Carlos. It is a Cross flow from the Supersprint that has been built to semi race specs. The dyno figures were 160HP at 7,200 RPM, the power curve was from 150 to 160 HP from about 5,400 to 7,200 with good power to 7,500. If I can ever figure out how to get photos on this site I will send some.

 

I have been focusing on exhaust noise but now realize my Webers are now my secondary concern

 

I raced Laguna in the early 70's when there wasn't a home within miles, this sound thing pisses me off, you cannot imagine how much.

 

Has anyone tried Burns mufflers, they make a two stage muffler, they seem to think it will work.

 

Sound is my next step, I still have a few things to do before the engine gets installed so my search continues