V8 noise levels?

[Rob]

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[bac1023]

I

[neal]

First off, going from 111dB to 100dB is a hell of a reduction. Decibels are a logarthmic scale to match the ears sensitivity but in absolute terms you're seeing (well, hearing :-) a reduction of more than half in the absolute sound pressure level.

Secondly, was this definitely a Lotus sports exhaust? I thought they were little more than a standard exhaust but with all the internals (baffles, wadding, etc.) ripped out and replaced with a simple U-bend at each side - little more than what you have with straight though pipes.

My straight through pipes read around 106-7dB but I can't remember the distance I measured this from the tailpipe which obviously has a bearing!!!

Neal

[Rob]

Yep, i was surprised by the numbers too - which is why i posted.. i'll check it again at the weekend. I'm thinking now maybe it "popped" when i measured it with the straight pipes on... maybe that explains the high reading?

The exhaust is lotus sports exhaust, modded slightly to have bigger tail pipe - ie 3" instead of 2.5". Will bring the db meter with me to oxford this weekend if anyone else wants to measure their cars.

R

[senna21]

The exhaust is lotus sports exhaust, modded slightly to have bigger tail pipe - ie 3" instead of 2.5".   

<{POST_SNAPBACK}>

How was this done? Did you use a Resonator tip(s) or just use a Megaphone style extension. If you used a Megaphone tip that may be your culprit. Ferrari had used this style exhaust on the 288GTO (factory labeled it as an F1 option) and from what I've heard makes the car sound unbelievably good and loud.

A lot of the old Porsche 911s in the 70s used to run with Megaphone exhaust as well.

http://www.burnsstainless.com/Megaphones/megaphones.html

[Rob]

Ok, so i did my trackday on friday. Their equipment put my v8 with the lotus sports exhaust at 95.8 compared to my reading of 100, which means my own db meter must be over-reading somewhat

I think it was also helped by a stiff breeze - they were measuring 0.5m from the tip but were upwind of the car.