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Took car in for its warrant of fitness test (compulsory here for all vehicles to check for road worthiness). Mechanic said the car is now a little too loud and I need to tone it down a bit. I have not touched the exhaust, this came about through a cam and head change (more compression). My question is will an H pipe make much difference? I don't see resonators fitted to early Vettes ('70) but exhaust shop think this is the best option.
The existing mufflers are oval chambered models of unknown make.
An "H" pipe won't make the exhaust any 'quieter'. It might smooth out the sound (less pulsing), but just as loud. I think your choices would be to add resonaters or to just replace the mufflers with a quieter brand/type.
The only mention of exhaust "sound" during that video was that "The X-pipe sounded 'cooler' ". I interpreted that as it was either louder, raunchier or both. I didn't hear anything that said it sounded "better". And there was NO measurement of sound level during any of those tests.
I think your mechanic just wants some 'coin' out of you....
Last edited by 7T1vette; Jun 30, 2017 at 01:13 AM.
I will try and make a recording of what it sounds like at the moment. Still waiting on some more air bleeds to sort the carb out. I had forgotten you could download a db meter so I must do this also!
straight duals it will sound pretty old school, brappy ras[y etc
The H will tone down the high pitch stuff a hair
The X will smooth the tone out a lot (think 80s 5.0 stang)it will sound "smoother"
none will make it "quiet". I only put one on to tone down the high frequency noises...pulling trans is easiest with none of em and x2 on no power gain with any.
Get a good resonator or the best stock style turbo/biggest case you can fit under the car.
on an old car personally like the sound of dual straights the best
op if you can lower the idle thats the cheapest way for your inspection lol.
Edit: best way to quiet a system is with a big case turbo muffler and the X. Still sounds great on WOT.
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
How much are you needing to quiet down your system? There's several options depending on the magnitude.
An H pipe, correctly installed close to the headers/manifolds, will quiet the system down a bit. Vizard claims a solid 1 or 2 dB reduction, while one of our posters here saw a 3 dB reduction. I put an H pipe between the header reducers, and noticed a slight reduction in noise level (and a significant reduction in bodywork drone). I did this prior to purchasing a dB meter, so I can't quantify the actual improvement on my car.
If you need to make a large change in the noise magnitude, then a muffler change may be necessary (I prefer Dynomax turbo mufflers. They're pretty quiet, and flow very well.).
I will try and make a recording of what it sounds like at the moment. Still waiting on some more air bleeds to sort the carb out. I had forgotten you could download a db meter so I must do this also!
Haggis: Just FYI, I used an iPod app called SPLnFFT after some limited review of these meters. Went from 80 db on their meter to 77 db at idle standing where the video was taken. My car has kind of a fast idle so your meter reading will likely be different, but I would be interested just the same if it is possible to make a comparison.
Basically I copied 69427's setup albeit with different connections. The clamped type come apart very easily and I figured if I ever wanted to regress I could put a thin metal diaphragm at the interfaces.
straight duals it will sound pretty old school, brappy ras[y etc
The H will tone down the high pitch stuff a hair
The X will smooth the tone out a lot (think 80s 5.0 stang)it will sound "smoother"
none will make it "quiet". I only put one on to tone down the high frequency noises...pulling trans is easiest with none of em and x2 on no power gain with any.
Get a good resonator or the best stock style turbo/biggest case you can fit under the car.
on an old car personally like the sound of dual straights the best
op if you can lower the idle thats the cheapest way for your inspection lol.
Can't lower the idle, mechanic road tests car as part of the inspection.
Resonator it will have to be I think as rest of exhaust is in good condition, add H pipe if need more "calming" Top of the line dual mufflers (full stainless steel) run to about $700 - $800 here and still have to fit them.
1) If all you're trying to do is pass a test the easiest way is to stuff some steel wool into the tail pipes. Drill a small hole so you can stick a piece of wire through it to keep the steel wool from blowing out. Once you've passed the test just remove the wire and rev the engine to remove the wool. I've passed inspection that way once upon a time when I had glass packs.
2) Replace mufflers. The larger the body, and especially the longer, the quieter.
3) Add header inserts. These are very cheap and go into the header collectors. To see what they look like, go to summitracing.com and search for "header insert".
Haggis: Just FYI, I used an iPod app called SPLnFFT after some limited review of these meters. Went from 80 db on their meter to 77 db at idle standing where the video was taken. My car has kind of a fast idle so your meter reading will likely be different, but I would be interested just the same if it is possible to make a comparison.
Basically I copied 69427's setup albeit with different connections. The clamped type come apart very easily and I figured if I ever wanted to regress I could put a thin metal diaphragm at the interfaces.
Idle db is 105 average and interestingly is exactly the same at 2000 rpm.
92 db is the max allowed here lol.
I question the measurement - that level of noise maybe for a big block with sidepipes. If true however a completely new exhaust system is warranted. The db scale is logarithmic, so the difference between 92 db (required at Laguna Seca forinstance) and 105 db is roughly a factor of 10X for a noise power measurement. Can this car really be as loud as a chain saw? Haggis, you might want to confirm your problem before spending gobs of money. My car which is fairly loud comes in under 80 idling and 88 under hard acceleration.
Idle db is 105 average and interestingly is exactly the same at 2000 rpm.
92 db is the max allowed here lol.
From how far away is it being measured. Decibel meters are often misused. Most ordinances will have a distance and angle to test from. I have seen officers stick the meter right at the end of the pipe, which will fail you with just about any non stock muffler.
End of car was sticking out of the garage when I took the reading and I was standing about 2 metres behind it. When I stopped off at the exhaust shop to ask them to take a reading, he said no need as car was well above the limit. I would estimate it was a bit higher than the limit before the engine changes but was not as sharp and no lumpy idle which seems to attract more attention. I would post a sound recording but haven't figured out how yet.
If I get it back down where it was it will be fine, they don't tend to pick on classic cars and old drivers here the same as they do on the young drivers in their modified whatevers.
Last edited by Haggisbash; Jul 1, 2017 at 03:07 PM.
When I stopped off at the exhaust shop to ask them to take a reading, he said no need as car was well above the limit.
If it is your exhaust shop that does the "warrant of fitness test ", seems to me they have a conflict of interest. Do you have a AAA membership or equivalent that might help tell you how close you are are to the limit, according to an approved measurement method? Sounds like you'd like to squeak by with a minimum of investment.
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H pipe or resonators, which to choose?
". I interpreted that as it was either louder, raunchier or both. I didn't hear anything that said it sounded "better". And there was NO measurement of sound level during any of those tests.
