Help - 90db limit @ WFO

[Mudge]

I have twice pipes and a stock exaust manifold on my 73 240Z, the car is definately going to be louder @ WOT (aka WFO) than 90db, but I have the chance to run Laguna next month if I can do something about it.

Does anyone have a muffler idea, or should I just run another muffler in the center? If I get black flagged for sound 3x I will get booted from the track, and that would be a waste of big moola. No I do not want a disk type muffler, too many horror stories. Most other adjustable mufflers cost way too much.

Since the twice pipes route RIGHT under my damn rear end, I wouldn't mind ripping the setup off the car anyway and making up my own exaust, so I may do that, if I can do it reasonably inexpensively since I'm jogging multiple project here, on a budget of course.

I do have a 280ZXT car, but I dont imagine I could steal that setup as with the downpipe/turbo setup it wont be the same dimensions as a 240Z NA car I imagine. Otherwise, I bet the muffler is relatively quiet, it looks either stock or low-performance, bah.

Ideas for getting down to 90db or a tad less for safety? I dont expect to see more than maybe 6k RPM tops, I dont want to nuke the engine, especially since I dont know its timingchain /oilpump life.

[Mudge]

A lawnmower is apperantly 90db

http://www.howstuffworks.com/question124.htm

[Bambikiller240]

Keith Thomas (Chet Wittel's ITS Crew Chief) reccomends,

"I'd stick to a Dynomax Super Turbo. Much less obnoxious sounding than a Flowmaster. I think the P/N is 17723 for the 2.5 diameter in/out. Only loses 1hp at the wheels over a straight pipe in my tests."

I don't know whether they also use a pre-muffler.

[2ManyZs]

I'd go with a 2 1/2 inch pipe with a muffler, preferrably a turbo muffler such a Carl mentioned. The twice pipes were always by far the loudest cars on the tracks as many racers were using them when I was racing in the early 90's.

Just to give you an idea, my 280 had one of MSA's 2 1/2 inch pipes with no muffler, and I was usually in the 102-105 range depending on the weather. I did have a slightly turned down tip on mine though, not an 90 degree elbow, but a 45 angle cut tip with it pointed straight down.

FWIW, before I sold the car, I replaced the rusted out tip with a Dynomax 2 1/2 inch straight thru race muffler (bullet style) and it was nearly as quiet as the car was with the Turbo muffler that came with the system. I think the muffler was about 40 bucks from Summit Racing.

Don't forget, you can always use a angled tip or even a 90 degree bend at the tip to aim it at the track.... or away from sound control to quiet it down if it is too loud when you get to the track, just go get a cheap one at the auto parts store and take it with you wherever you go just in case......

[Mudge]

Ok, this is good news. I was very worried that 90db would be nearly impossible without choking the crap out of it. My open exaust 94 Camaro, 2.75" pipe and about 470HP pegged the meter at 125db, and I swore my old 69 Firebird was always louder, but maybe it was cabin resonation.

[MistressMotorsp]

When my car had the ITS motor in it, it was able to meet 90 db through a Nissan Motorsport header, a 3" exhaust, with a Borla race muffler and a 90 turnout to the left after the muffler. It was pretty darn loud on the left side of the car, but almost silent on the right. Now that I have a 13:1 compression motor in, I'm not sure if it will still pass, but I would think it would be close. The best thing to do is get the exhaust exiting either to the left or on the left side of the car.

When I had my Corvette, I normally ran dual exhaust with no mufflers. At Laguna I would add a pair of Supertrapps, but I had to run so few discs (11), that the car lost about 50 hp (out of 430) and 500 rpm off the top end.

Mike

[2ManyZs]

Take a note of where the sound control is located... and point the exhaust away from it with a 45 or 90 degree tip if worse comes to worse.....

Another thing you could always try is using one of the bullet style race mufflers in place of the resonator in the tunnel and another at the back.

[Mudge]

Yep, I was advised to setup the muffler to accept a varied position for my turndown. They will measure at 2 points apperantly, and at least one is on the right, I will probaly turn it just flat down, but we'll see, maybe down/left.

Since I just have the exaust manifold, and will probably not run a 3" I should hopefully be fine, plus dont expect more than maybe 6200 RPM and am not making much HP either.