How to reduce engine noise?

[Hammink Performance]

Hi Guys,

We are currently working to get a roadster street legal over here in the Netherlands.
One of the regulations we have to follow is the noise limit of 74Db, so basically we have to make a 350HP 302 v8 sound like a Prius.

We've built a hideous exhaust that go's from side pipe to under car and exists next to the gas tank on both sides, but we still have a lot of engine noise
coming from the air filter as soon as you hit the throttle.

My questions would be; has anyone ever built a closed air filter box for a small block Ford? (we run mass-flow efi on this car)
(have allready sealed of all the vents like side vents, and hood scoop, and have also installed a floor under the engine bay.)

[skullandbones]

Have you sound dampened the floor of the engine bay? That in itself could resonate unwanted noise like a reflector. That could explain the intake sound some. Do they measure the avg sound level over a test period or just at WOT? Also, what kind of mufflers did you install between the side pipes and the exhaust at the rear quarter panels? It sounds like you have an almost insurmountable task (no pun intended) at 74 dbl. I don't know if you have a cold air tube system. That quieted my EFI a little with about 375 hp/302. If you run the air tubes all the way forward to the grill that might help a little more.

I did see a boxed air gathering system for a small block but it was a long time ago. Also, it got its air from the hood scoop. Good luck, WEK.

[Avalanche325]

It sounds like this is for registration and then you can tear it out. Is that correct?

[Dan Babb]

This could be overkill for your setup, but I built a cold air box when I had a supercharger on my last car.

Put a blower hat on top of the mass-flo throttle body.
Run a hose over to the side of the car and to the front of the wheel well.
Put a cone filter in the box. Then pull air into the box via the oil cooler opening.

Here's the setup on my last motor:

http://i26.photobucket.com/albums/c105/DanBabb/General%20Cobra%20Stuff/ColdAirBox-Done4.jpg

http://i26.photobucket.com/albums/c105/DanBabb/General%20Cobra%20Stuff/ColdAirBox-Done3.jpg

http://i26.photobucket.com/albums/c105/DanBabb/General%20Cobra%20Stuff/ColdAirBox-Done1.jpg

http://i26.photobucket.com/albums/c105/DanBabb/General%20Cobra%20Stuff/ColdAir7-07a.jpg


You could hear the air sucking in with the filter in the engine bay, but when I move it to the setup pictured, no more air sucking sound.

You could build a turkey pan to seal the hood to the filter on your current car, but then you'd hear the noise through the scoop.

I have the mass-flo and I know what you mean. I have a sucking sounds just off throttle.

[CraigS]

I am thinking that you need an exhaust sytem but on the other end. think about mufflers that make the exhaust do two 180 degree bends inside the muffler. Think about any other type of baffles you have seen on the exhaust side and then figure a way to do something similiar on the intake side.I'd also look at the air intakes on some current model luxury cars to get some ideas on how they are plumbed. Look at all the hosing on Dan babb's car and do something similiar. Since you already have a bottom cover on the engine area, I'd put the end of the intake run down near that cover maybe behind the radiator. Good luck

[Hammink Performance]

Guys,

Thank you for all the imput!

@ Skullandbones; They measure from a roll in 3rd or 4th gear, and than between cones you WOT
The 74db limit is indeed ........ I have no words for it, but we are allready at 77db's, and since we rear exit exhaust you can clearly here the suction noise from the air filter when you punch it, so that is where I think the last db's should come from.

@ Avalanche325; Yes all is only for registration and than it go's, the car looks so hidious now that I am affraid to post pictures!

@ Dan Babb; Thank you for sharing, I will consider this an option because over kill is what is needed in this situation!

@ Craigs; We now run mufflers as you describe in the location of the normal side pipe, after which the exhaust go's under the car right before the rear wheels.
Below the IRS control arms we also have 2 smaller but simular style mufflers, and than exit next to the gas tank.

Thanks for helping out, more info is always welcome!

Will keep you guys posted on the process!

[tirod]

The open air filter element doesn't control the noise, entirely why factories don't use them much. The factory "beehive" air cleaners for the 302's and 351's could do the job. They enclose the filter media with cone shaped housing, and have a inlet trumpet to direct air into it. No fabricating necessary, hook right up to factory mass air.

Here's one: http://www.mpsautosalvage.com/sunshop/index.php?l=product_detail&p=3239

Local supply may be more problematic. The point is that most factory enclosed housings damp the noise, so it follows they are the first choice in an engineered, compatible solution.

[Dan Babb]

What exhaust headers are you running from the engine to the side pipe? If it's the FFR J-Pipes setup, then you use something like a 3 disc car chemistry insert. It will cut the noise quite a bit. Then take them out after you pass registration.

If you have a 4 into 4 setup, those are known to be louder than the J-pipes, but maybe temporarily use the mustang headers and j-pipes. I don't know the db difference, but I think there was a thread on the other forum with comparison readings.

[BS]

The quietest car in our entire Cobra Club is the one with twin turbos. All that exhaust noise gets sucked up by spinning the turbos and pushed down the carb hole. Just another way to go..... ;)

[Hammink Performance]

Thanks guys!

@ tirod,
We run a 302 small block that has a mass flow efi system on top, so I would not be able to use that air filter system, however might be possible with flexible hose and just the housing.

@ Dan Babb: We run shorty headers with cat converters, so these reduce sound even more. Standing on the sound of the road its really suction noise you get from the engine bay.
(oval cobra filter on top of the MassFlow efi) exhaust noise is almost completely gone.

@bs: Yes turbo's would be nice, probably whistle to loud for our stupid rules :-P

[jlahl3160]

Your assesment as to where the greatest noise is comming from may indeed be correct. My experience has been that I needed to have real data to determine the source of the greatest contributor. While working on the the item you believe to be the problem may help, it may in fact not be the location of the worst (noise) offendor. Perceived loudness by ear is tricky..

I believe you may benefit by haveing someone with some sound equipment analize the frequency vs dB level to ensure you are working one the correct proplem (source of the greatest noise).

You would be looking for someone who can map out a frequency responce curve..... then match the frequency with the source... attack that frequency source... measure again, & repeat until done.

John

[Hammink Performance]

Thank you John

[skullandbones]

How do motorcycles pass these restrictive rules? Do they have a different standard. They do allow motorcycles in Europe, right? How would the ruffians get around if they didn't (ha)? But seriously, those dealerships may have sound abatement strategies as well. Just a thought. WEK.

Note: The reason I thought of motorcycles, someone asked me what it sounded like when I started up the roadster and I told them it was like two Harleys starting up at once!!

[Hammink Performance]

Yeah that's true! The guy who made my exhausts specialises in both cars and bikes, so I think he did the best he could on the exhaust.
and really the 77 or something we have now is super quite, you just feel wind comming out the exhaust :-P

[ianhunter]

I thought we were in the EU! How come you have a limit that low? Ours is 99db, which basically required three balls of steel wool up each sidepipe. Strangely they all fell out on the way home! What do Ferrari, Lamborghini and Porsche do? What about Caterham? Do they indeed all have special modifications just for Holland?

[Dan Babb]

Buy something like this
http://www.superiorairflow.com/carb-hats/unpolished-aluminum-4150-series-gasketed-carb-hat.html

Buy some fleible hose...pegasus auto parts is a good source.

Then hit the junkyard and rip out some type of airbox out of a mustang v8. You could temporarily mount it to the x-brace or somewhere else. That should help quiet it down. It will look like crap, but yank it out when you are done.

[Hammink Performance]

@ Ian, you are in the good part of the EU with your own coin! They are pulling the country's that pay with the euro more an more to each other on every level.
Since TUV has the upper hand, everybody will be pushed in their direction, and they have come up with these rules. Just take a look at every mass production car there is, they all sound the same en somewhat look the same. How Ferrari, Lamborghini, and Porsche do this? I don't know but they have got a lot more resources to invest in techniques such as exhaust noise and note. The other day I was watching a documentary about Pagani Zonda, on their newest car, the huayra they use amplifiers instead of mufflers in some parts of the exhaust to make it sound good.

@ dan Babb, yes thank you, that is exactely what I need. I know I have an airbox from a Coyote motor laying arround so we should be fine than!

[mrmustang]

Hi Guys,

We are currently working to get a roadster street legal over here in the Netherlands.
One of the regulations we have to follow is the noise limit of 74Db, so basically we have to make a 350HP 302 v8 sound like a Prius.

We've built a hideous exhaust that go's from side pipe to under car and exists next to the gas tank on both sides, but we still have a lot of engine noise
coming from the air filter as soon as you hit the throttle.

My questions would be; has anyone ever built a closed air filter box for a small block Ford? (we run mass-flow efi on this car)
(have allready sealed of all the vents like side vents, and hood scoop, and have also installed a floor under the engine bay.)

Enclosing the filter box will not lower your exhaust db levels, as someone else has already suggested, you need a set of car chemistry exhaust inserts.

http://www.carchemistry.com/techinfo/

These will drastically lower your exhaust db levels to the point where you will pass your restrictive EU testing requirements. Only other way to further lower your exhaust db levels would be to add a secondary muffler or a larger, more restrictive set of mufflers to your existing system.

Bill S.

[Benji]

I think he was now suggesting that he had more induction/drivetrain noise now more than anything else (exhaust changes got them down to 77db), hence enclosing the airbox.

[Hammink Performance]

That is correct, never the less all info is helpful, we have plenty of cars to come (I hope) and therefor plenty of ways to try out.

I'll try to post a video soon, just got the car back and it sounds like a mouse.

[skullandbones]

It's too bad you have had to resort to the kind of strategies that will probably restrict the car's performance significantly and take away some of the things that people like about it the most(the exhaust note). Sounds like the rule in that jurisdiction has "run amuck" so to speak. I'd be surprised if the customer leaves it that way for long. It might be good to check the side pipe threads on the forum to come up with more effective "permanent" solutions" going forward. The change of the angle of the side pipe opening down about thirty degrees is one thing that may not reduce noise but changes the direction. Then the various side pipe mods can really make a difference. You may have a lot of experimentation in your future. Looking forward to all the feedback that comes out of this.

Note: I know this is the digital age and instrumentation has gotten a lot more accurate/precise but it would be interesting to know how the sound meter is calibrated (what standard is used) and what is the error limit of the instrument (+/- dbl).

Good luck on the final 3 dbl. WEK.