[binkydognose]

Good on you Ann!
How'd you jack your MINI?
I've got one floor jack and two stands. Looks like I can access it fine by jacking one side but I'm wondering if raising only the back would be better for gavity alignment purposes... and if so... what jacking point to use to raise the back so that I can place stands under the rear jack point dealies.

[Ann Jones]

I had an austin Healy a long time ago... It had a very sweet sound.

It seems like that aluminum plate under the battery box could resonate, (is vibrate a better word?), and add unwanted extra noise.

Ann Jones

[Ann Jones]

We drove the front of the car up on ramps, then jacked the back up and put 5" or so of blocks under the rear tires. That got it up high enough. Be sure to put the rear piece on first, then the middle, then the front piece.

Ann Jones

[Romhog]

Quote:

Originally posted by Albert
Yes, but maybe I can stifle some of that curiosity by saying that I've already been notified by Magnaflow that there will be very little difference in dyno HP numbers.

Oh well, I'm only doing it for additional volume anyway.

On another note, I did dyno the MCS w/the Magnaflow last Saturday and it recorded between 158-160 peak HP at the wheels! This was done with approx. 1800 miles on the ticker. Unfortunately, I don't have a baseline reading b/c I was too impatient to put on the exhaust, and we were still hovering at around the break-in period.

Anyway, I'll post more specifics and photos on a separate thread.

Oh man, this is really nice. nice I say. please post here when you start that thread!

[CooPz]

Quote:

Originally posted by The Helmet
moan moan moan moan moan moan moan mona

I'm sorry but if you buy a performance exhaust and moan about the noise is makes then there is no hope for you.

It's like buying a wheel and saying that it is too round!

Please fit it and have fun

Regards

Andy

P.S. no harm intended and I should be in bed by now.

I think you've just become my own personal Hero

[Romhog]

I'm ready, who has the updates on the magnaflow install, someone was going to run dyno tests or something???? I think it was back on page 2, but my eyes hurt

[Keith]

I ordered a Magnaflow over a week ago and then got worried when the post started appearing about how loud it was. I tried canceling so I could wait until there was more feedback but it had shipped.

I got it installed today – took just over two hours. The whole job can be done with just the back of the car on ramps. The part that was a real pain was getting the OEM hangers separated from the rubber mounts. It look lots of WD40, screwdrivers stretching rubber and pulling in all directions. There has to be a trick to this but that one part took 45 minutes. There was another post about a muffler shop having to trim one of the hangers to stop a rattle. The problem is the hangers on the resonator. They are longer than original and can touch the heat shields on the sides of the tunnel. Reaching under the car and pulling the heat shield to one side stops the rattle so I expect to be able to fix it with a little bending – I don’t really want to take it apart again.

Oh - one other thing. One of the pipes was a really tight fit at the join and needed loosening up. Well worth checking this before starting as doing it from under the car when half of it is bolted together is tough.

The sound is great – the car now has a real attitude!

I haven’t driven enough to comment on performance but there is that bass reverb that has been talked about. The car is loud under acceleration – but that’s to be expected. I want to reduce the deep constant background noise when cruising at a constant speed or at idle so I will be putting soundproofing on. With the car in idle I went round various panels to see where I could feel vibration and it was much worse under the back seats so that is where I’ll start.

HELP – how do you remove the back seats? The front edge unclips but I couldn’t see how to release the back edge.

[Keith]

Quote:

Originally posted by Ann Jones
I had an austin Healy a long time ago... It had a very sweet sound.

It seems like that aluminum plate under the battery box could resonate, (is vibrate a better word?), and add unwanted extra noise.

Ann Jones

Interesting idea - should be easy to test by trying the car without the plate. I was wondering what the plate was for.

[Keith]

I wouldn't take it off permanently. But before finding rubber washers, it may be worth driving around for a bit without it to see if it contributes anything to the noise.

[Keith]

Anyone compared Dynamat Extreme with B-Quiet Extreme? They are both available from www.b-quiet.com and the site shows that Dynamat has slightly better sound absorbtion. Dynamats's loss factors are .26, .42 and .26 at 10, 20 and 30 degrees C. B-quiet is .19, .29 and .20. However Dynamat is really expensive - B-quiet is $85 for 50sq. ft. and the best price I have found for Dynamat is $200 for 36sq. ft. I could put on two layers of B-quiet for much less but will it get the job done?

[Romhog]

Like others have said elsewhere, because of the bass your going to get, I don't think that even dynamat on 2 layers thick will help in what sounds are just coming back though the windows, etc. Some have tried and still got rid of the magnaflow because of the 3k rpm levels.

[minimc]

Got the mic in the car today - did a back seat set up & ran the feed through pro tools.

When we ran through the revs we found a big spike (like a tent) at 119hz. The other frequencies are relatively benign, although there is a little peak at just above 62hz also.

The lowest frequencies are at idle - really low! But they aren't obtrusive whatsoever - low db levels. BUT... as one increases revs through the range noise grows in decibels in a fairly controlled & uniform manner until around 2800rpm at which point the spike starts. The resonant spike continues on right up until 3900rpm where it promptly dies off. After 3900rpm the higher frequency mechanical noises of the motor & supercharger grow louder (500hz-2000hz). These frequencies are less obtrusive & can be easily damped with dynamat or similar.

I have a few concepts of what might work to damp the relatively low frequency resonance. I'm going to start at the boot, and try to stop/reduce the resonant frequency(s)before the rest of the car can be excited enough to resonate sympathetically.

Sorry for the techie bits... just suffice to say I'm on the... (fill in blank with appropriate cuss words)


Will report back after damping project underway.

MC

[Romhog]

now we are getting scientific!!! Pro Tools! I think this weekend I will finaly get to hear this baby first hand. So I think I will make my mind up then and there, if this is going to be something I'll buy. Sound material or none. Oh and yes OBEHAVE, I still plan to put in the dynamat, just for musical reasons, bot still don't hold much hope for the magnaflow. I have to accept its levels, as is. Then I know i'll be happy or now. For those of you that are still thinking about it like I am, like it for how it sounds when you get it. Anything you do after the fact is small coins in the pond to kill all that noise.

[ram_one]

Quote:

Originally posted by minimc
Sorry for the techie bits... just suffice to say I'm on the... (fill in blank with appropriate cuss words)



MC

Looks like Mr. Wallace has sent the Wolf to take care of the job.

Seriously, this is would be a great thing.

[stryder]

For us equally techie types, can you screencap/export a Frequency vs. time graph and if its simple with the approximate RPMs?

Very cool you're looking into it in any event.

[minimc]

I'm looking into it... ...Not sure how to do a screen print on a MAC. And it was a BIG file! Recording engineer friend (my guru) says he'll try to get something for me. Did see/play with a graph of it today though. He went all out - recorded it @ 192khz, then down-sampled it to 44.1khz & burned a CD. If my father (who was actuating the gas pedal with glee) wasn't doing a voice-over for each RPM range I'd of posted the sound-byte here.

calling it an evening.
lates,
MC

[supersport]

Quote:

Originally posted by minimc
Got the mic in the car today - did a back seat set up & ran the feed through pro tools.

When we ran through the revs we found a big spike (like a tent) at 119hz. The other frequencies are relatively benign, although there is a little peak at just above 62hz also.

The lowest frequencies are at idle - really low! But they aren't obtrusive whatsoever - low db levels. BUT... as one increases revs through the range noise grows in decibels in a fairly controlled & uniform manner until around 2800rpm at which point the spike starts. The resonant spike continues on right up until 3900rpm where it promptly dies off. After 3900rpm the higher frequency mechanical noises of the motor & supercharger grow louder (500hz-2000hz). These frequencies are less obtrusive & can be easily damped with dynamat or similar.

I have a few concepts of what might work to damp the relatively low frequency resonance. I'm going to start at the boot, and try to stop/reduce the resonant frequency(s)before the rest of the car can be excited enough to resonate sympathetically.

Sorry for the techie bits... just suffice to say I'm on the... (fill in blank with appropriate cuss words)


Will report back after damping project underway.

MC

Interesting. I suspect that the big spike at 119Hz (between B and A#) could be the resonance of the car's cabin -- the air volume -- and 62Hz is almost exactly an octave below 119Hz (i.e. it's the same note). The exhaust likely produces a very broad range of pitches, and when some hit the cars interior resonating frequency, they are amplified by the car itself, and it drones like a beer bottle being blown...
MAYBE.
One way to tell would be to decrease the air volume of the interior with a couple of big, empty sealed cardboard boxes (or whatever)..... If this reduces the drone, then there is very little that can be done to damp it significantly. (as it is the air in the car making the drone -- capishe?). It is possible that the Magnaflow is tuned to an unfortunate pitch -- one that doesn't match the car.

If changing the interior volume of the car does nothing, then you are on the right track already.

It sure would be nice to kill it at it's source, though, as it is very, very difficult to damp low frequency noise. Some cars have a tuned tubular resonance eliminator in the exhaust to cancel out a specific offending frequency and reduce drone (they are like a branch tube off the main line). I don't know what this does to power though... Recording studios use similar tubes for the same reason..... This is not damping...it's cancellation. Wouldn't THAT be nice! The drone is at a very specific frequency, so I think it should be easy to do this -- if you could just figure out how....

Just ideas.... But (almost) certainly the problem isn't just due to the volume of the exhaust, but to how it is tuned relative to the car (or a part of the car).
...And absolutely certainly, the air volume of the car will resonate at a very specific frequency if given the input.

Clear as mud?

Check my www below....(except it ain't done...but there are pics...)

[Keith]

Great info!
A 4 cylinder 4 stroke engine fires twice per revolution so at 3570rpm there are 119 pulses per second going down the pipe. I bet its not a coincidence that this is in the middle of the range where the noise is the loudest.

Something in the car clearly resonates at this frequency. These are my ideas so far...

My guess is its not the air as the wavelength of sound at 119Hz is over 8ft (if I got that right) and there are no parallel surfaces that far apart to cause the resonance.

I have noticed a strong vibration from below the back seat cushion - there could be a panel there that is resonating. It could also be the whole pipe assembly as the middle support does not stop sideways movement. Something suitably heat-proof could be jammed beside the pipe in the middle to dampen it to see if that affects the vibration. (I don't have anything to use to try that test.) Alternatively, someone with a lift could get under the car while it is being run at 3000rpm to see if there is anything visibly vibrating.

[jlm]

you will get standing waves in a closed volume when any of the primary dimensions of the volume (L,W,H) are 1/2 wavelength of the applied sound. The standing waves are a resonant mode which will increase the volume of those wavelengths. Should any room dimensions be equal, the effect is increased. This doesn't require that any panels resonate.

typical room accoustics with an 8 foot ceiling cause resonance at about 80 hz., a 5 foot wide interior in the mini would have a primary mode at around 120 hz.

[supersport]

Quote:

Originally posted by jlm
you will get standing waves in a closed volume when any of the primary dimensions of the volume (L,W,H) are 1/2 wavelength of the applied sound. The standing waves are a resonant mode which will increase the volume of those wavelengths. Should any room dimensions be equal, the effect is increased. This doesn't require that any panels resonate.

typical room accoustics with an 8 foot ceiling cause resonance at about 80 hz., a 5 foot wide interior in the mini would have a primary mode at around 120 hz.

Exactly!....Harmonics (partial waves or multiples of waves) fit together to produce the Fundamental (full wave) ...So air resonance within the Mini is a possibility...or a contributing factor. I know the instruments I make have 'body resonance' at wavelengths much longer than the instrument...

BUT it could just be the howling exhaust tubes.
It sounds like the Magnaflow system is just a good amplifier of the offending frequencies -- maybe a long straight run of tubing is not stiff enough, or a can is too resonant -- something isn't stiff enough to resist resonating -- or a tube is an unfortunate length. I have heard many loud exhust systems that do not drone at cruising rpm -- it all has to do with tuning, not volume.
It's easy to make a lightweight free-flow exhaust, but it's tricky (and expensive) to make a tuned one -- unless you get lucky. Adding insulation to the car is a drag.

I'd love to hear about the other brands' drone.