noise dilemma

[Noobrider]

ok so I have done a few mods to the 80 track car and one that is bugging me is the exhaust.

I have kept the manifold standard with the precat but fitted a glass pack silencer (Cherry Bomb) as a decat. I then have kept the standard resonator box and finished off with a Cherry Bomb tail pipe. sound gorgeous and feels like it has released a few horses.

However, a noise test at 1 metre at 45 degrees at 4000 revs shows 96db. If I rev it to 6500 it goes to 108db max reading. Track day approaches with a 105 db limit.

The half revs test is what is employed at Cadwell Park and our Pumesta read 88 db but at Blyton we were warned that we were right on the limit at 105db.

I'm thinking that Blytons test we will fail....how can I get the noise level down?

[Mark S]

its easy to confuse noise with power.

the manifold is the most restrictive part on the entire system.

It is so dire that it is believed that mgr altered to cam timing because of the issues the manifold/headers create, then had to mess about with vis to sort out the flat spots created by the many botched areas in the system design.
The engine should and could produce 300bhp - but thats another story.

My advice would be to fit a more standard back box rather than a straight through cherry bomb backbox.
A straight through pipe in place of the cherry bomb that replaced the cat would flow better for a start and with a typical backbox should be no less powerful than what you have at the mo.

It is very important to keep the pipe size the same all the way through, I don't know what bore the cherry bombs are, but you will be losing power if you have different size bores at various points along the way.

[Noobrider]

bore size 2 1/4 inch all the way, yes the manifold is the worst design ever but we are stuck with it. Decibels is the thing for track days

[Cally180]

That's something knockhill doesn't test for, they have a noise limit but they don't push on it.

[stamford]

As already said change the back box. I run a decat with a Janspeed system and it is noisy on the road but sits well within track limits.

[Mark S]

the old coupe/tomcat backbox can be made to fit quite easy (piper etc can be picked up for peanuts, tomcat piper is 2.25" bore) if you extend the tailpipe and are on a shoestring budget...

[Noobrider]

yeah I think another back box is required, I have a couple kicking around in the garage.

Shame as it really sings like a big bike up in the rev range. It's Blyton thats the problem, I know it would pass at every other circuit as they do a 1 metre test at around half revs, pass it then stick a sticker on your windscreen and never bother you again.

Blyton wave a tester behind your car in no scientific manor at all asking to rev your car until they are satisfied, plus they keep checking it hrough the day and have a drive by monitor on the start straight. I've seen a couple kicked for being too loud but I also think their tests are wrong and the meters uncalibrated.

I wouldn't have picked Blyton but we are taking some customers and its their first track day and Blyton is very good as a beginners track. We had planned to go to Cadwell or Oulton.


Was kinda hoping someone had a Decibel reducer trick insert I could make up or something

[stamford]

Many trackday enthusiasts with noisy cars have a bolt-on can for fussy tracks. Seen various cars with them fitted, looks daft but they get to play!

[Noobrider]

might have a go at making one of these just in case http://www.advantage-motorsport.co.uk/decibel-devil-exhaust-noise-reducer.html

[stamford]

They don't look big enough to make such a difference.