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Discussion Starter #1
so I am in a pickle. I am a college student therefore I have little money throw at a problem. I was hoping that someone who has had this same problem could help me out. I have a 94 vette no cats (done before I got the car) and aero turbine mufflers. I am going on a long trip in the next 2 weeks and want to kill the resonance I am getting in my vette around and under 2000 rpm. I have heard three ways to attack this and I want some advice from someone who has done it (and yes I already searched)

1. put stock back on-4 to 500 bucks and no good exhaust sound anymore

2. exhaust weights and an x pipe-$175 and every exhaust shop has said the xpipe probably wont fix it

3. chip from pcm for less-$175 and have been told by exhaust shop and bryan at pcmforless that this might fix it as well as 30 hp plus increase in gas milage...considering I am making 19-20 on the highway


please help I need help from someone who has ACTUALLY done this thanks!
 

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El Teafive
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so I am in a pickle. I am a college student therefore I have little money throw at a problem. I was hoping that someone who has had this same problem could help me out. I have a 94 vette no cats (done before I got the car) and aero turbine mufflers. I am going on a long trip in the next 2 weeks and want to kill the resonance I am getting in my vette around and under 2000 rpm. I have heard three ways to attack this and I want some advice from someone who has done it (and yes I already searched)

1. put stock back on-4 to 500 bucks and no good exhaust sound anymore

2. exhaust weights and an x pipe-$175 and every exhaust shop has said the xpipe probably wont fix it

3. chip from pcm for less-$175 and have been told by exhaust shop and bryan at pcmforless that this might fix it as well as 30 hp plus increase in gas milage...considering I am making 19-20 on the highway


please help I need help from someone who has ACTUALLY done this thanks!
best, most guaranteed option will be #1..
 

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best, most guaranteed option will be #1..
I agree, number 1 is the best option.
Number 3 will not work at all. A chip will not decrease the drone, at all.

Another quick fix is: Go to Home Depot or Lowes. Go to the plumbing section, buy a few rolls of insulation that plumbers put around water heaters. This is the insulation that has foil on one side and a rubber type stuff on the other side. It has adhesive on the rubber side.

Place a few layers under the rear carpet. This works like the more expensive sound deadeners. It will take the sting out of the drone, but nothing will eliminate it completely.

I put some of this under my carpet when I installed my new carpet.
 

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El Teafive
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Another quick fix is: Go to Home Depot or Lowes. Go to the plumbing section, buy a few rolls of insulation that plumbers put around water heaters. This is the insulation that has foil on one side and a rubber type stuff on the other side. It has adhesive on the rubber side.

Place a few layers under the rear carpet. This works like the more expensive sound deadeners. It will take the sting out of the drone, but nothing will eliminate it completely.

I put some of this under my carpet when I installed my new carpet.
Been There tried that, It will not work for DRONE, but works for road noise and such..
 

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i got straight pipe on my my car and flowmasters on (40series) anyway the sound was defining couldnt have a decent conversation or really listen to the radio so i ask the man do what ever you need to do to get rid of that sound so when i got the car back he put turbo mufflers on there i know they dont look that good but they dont look that bad either and i got to tell the sound is perfect not to loud not to soft either i'm relly pleased with it.
 

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Discussion Starter #6
the chip was recommended to adjust the timing which might be causing the vibration which is causing the resonance. I will try the home depot fix as I had already considered dynamat and home depot sounds a lot cheaper, If I put it in the front will this decrease more road noise? that would be great. Also I dont want to do option one b/c then Ive spent upwards of a grand to go in a complete circle, the chip will at least have some gains with it... any more opinions? thanks!
 

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DC Crew
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How about just tossing the stock LT-1 mufflers on there and leaving the cats gutted? You can get those cheap. 357Flyer has a pair for sale for $50.:thumbsup:
 

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I have the x pipe. I like the sound and have taken the Vette to the coast in one long trip (325 miles). Very pleasant for driving. Still a bit loud for conversation. I just crank the stereo and nod at my passenger (if I have one).
 

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this seems to be a common complaint with performance exhaust on these engines. i have a borla system and it resonates also, dynamat under the carpet did not help. eventually i got used to it, or else i've gone deaf. going back to stock mufflers should be no more than 300 bucks.

neil
 

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Dampening material will not give you the relief you need. Been there done that.

First, top polluting the air and gets some cats on the Vette. Shame on the guy who took them off. They do wonders in dampening out the sound. Universal cats can be found for < $200 a pair + installation cost. The car will smell better too.

Second, buy a Magnaflow 5x8, dual-dual, tru-x, p/n 14468 - and have it mounted right behind the tranny. This muffler has a X-pipe built in inside it.

Keep the turbine muffs as resonators.

Good luck!
 

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Discussion Starter #11
well the big prob. with going back to stock is that I already spent upward of 300 getting these on and love the sound on the outside (just what I wanted) so I really dont want to pay another 300 to put stock back on and go in a big ol friggin circle you know? I think Im gonna try the cats and home depot stuff... I might try the exhuast weights too it sounds like a decent idea.
 

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that DRONE is the result of the engine harmonics and the exhaust length having a similar frequency at that rpm, changing the frequency will change where in the rpm range the drone potentially occures
adding a few inches or subtracting a few inches can make a noticable differance, something as simply as adding a 6" chrome exhaust pipe tip to the existing tail pipe can make a differance, but to maximize the results youll need to design the system harmonics up into an rpm range above or below the average opperating rpm range

in many cases the (DRONE) is a SYMPATHETIC HARMONIC RESONANCE FREQUENCY that feeds from the engine exhaust pulses at a specific rpm frequency,and is amplified by the muffler design. on most corvettes it falls in the 1600rpm-2200rpm band, above and below its noticably lower,as the exhaust won,t vibrate at a matching level, if you modify the pulse frequency by adding an (X) as close to the headers as it can fit and an (H)pipe, just before the muffler enterance with the tail pipe extending past the rear bumper theres a noticable reduction in that (DRONE) WHAT ID DO FIRST AS IT HELPS CHANGE THE FLOW AND REDUCE RESTRICTION because youve altered the frequency reaching the muffler, high enough that its not entered untill much higher rpms are reached than normal street driving uses. you can also break up the pulse strength by adding these inside the collectors but INSTALLING the (X) which you have alreadyand (H) pipe must still be used for the full effect which you don,t appear to have

now keep in mind minor changes in exhaust length or cross flow or breaking the pulse strength, can make noticable improvements, and about any changes move the freq level in relation to the RPM adding 2" to the exhaust tip can even effect the harmonics, but realize that the effective length is from the back of the exhaust valves to the center of the (X) not all the way to the tail pipe. 1800rpms equates to an exhaust freq wave length of about 4.7" so a 2" change in effective length should be noticable,example placing the (H) a mulitple of 4.7" would have little effect, placing it at a mulitple of 4.7" plus 2" would have a noticable effect

http://www.spiralturbobaffles.com/

http://www.secureperformanceorder.c...tore/vortex.cfm


Exhaust Drone
Submitted by: Richard Kwarciany

Drone in the exhaust is due to the engine driving the exhaust system at its resonant frequency. You can't get rid of it, any length of pipe has a natural frequency, but you can change the frequency (RPM) it happens at. Stock exhaust systems are tuned to put the resonant frequencies outside the normal RPM range the engine is run in. Sometimes they add resonators for this purpose. To raise the resonant frequency of a system, shorten its length. To do this, you can try tail pipes that exit by the wheel (like GN's have), or you can try a muffler with a shorter internal flow path. If you have a true dual system, you can change the natural frequency of the system dramatically by adding a balance tube. If you can't shorten the system, then you can add slightly less than one wavelength of pipe. This will also raise the resonant frequency of the system. The wavelength in a single converter system (not true dual) is a little less than three feet at 3000 RPM. Shortening the system by a foot or so will move a resonance at 2000 RPM to about 3000 RPM.


To move a resonance, calculate the wavelength at the RPM that gives the resonance you want to move. Then calculate the wavelength at the RPM you would rather it be at. The difference is the length of pipe you need to add or delete. Add to lower the RPM, delete to raise it. If you want to raise it but you can't cut any pipe out, then add one wavelength of pipe minus the amount you calculated. This will have the same affect. If you add or subtract a multiple of a wavelength exactly, you will not change the resonant RPM.




Wavelength = 1100 X 60 X 1/RPM X 1/4 X 1/2

or

Wavelength = 8250 / RPM

Wavelength = standing wavelength
1100 = speed of sound in air in feet per second
60 = convert RPM to Revs per second
RPM = RPM
1/4 = four cylender firings per revolution (make this 1/2 for "true dual")
1/2 = standing wavelength is half the wavelength of a "normal" wave
NO ITS NOT A CURE BUT IT HELPS MELLOW the TONE SLIGHTLY..........you may also want to consider a layer of sound/heat reflecting material




heres an old post that may help, YES you NEED TO READ ALL THE SUB LINKS and USE THE CALCULATORS...and the collector size predicted is always too large in dia. try for a collector size of about twice to two and one half the sq inch area of the primairy,tubes ...if the primairys are 1.65" with a 2.14 sq inch cross sectional area, thats NOT a 3" collector with its 7 sq inch area its a 2.25" to 2.5" collector a 2.5" collector with its 4"-5" sq inch area

http://victorylibrary.com/mopar/header-tech-c.htm

http://www.majer-tech.com.pl/Exaust_Theory.htm

http://www.btinternet.com/~mezporting/exhaust_length.html

http://www.racerpartswholesale.com/flomstr1e.htm

http://store.summitracing.com/product.asp?d=8&s=127&p=608&searchtype=ecat&l=FLO


http://www.headersbyed.com/chevsbv8.htm

http://www.stainlessworks.net/Header%20Flanges.htm

http://www.stahlheaders.com/Frame%20Flanges.htm

http://www.headersbyed.com/hdrkits.htm

http://www.cachassisworks.com/header.htm

http://www.mazdatrix.com/fabricators.htm

Ive tried to stay out of this but I might as well jump in and get involvedIve done this many times its not that hard. heres what I do, get some of that plastic smurf tubeing in the 2" dia size and some ceiling hanger wire and some of that hard set constuction insulation foam. now weld 1" stubs of the exhaust tube to the header flange exhaust ports and bolt it to the cylinder heads. clamp the collectors to a 6 foot section of 2x6" wood and jack it up solid under the car (collectors not touching the car anywhere)to position them where you want them under the car, now cut (8) sections of smurf tubeing too about 36"-42" long(theres a formula to figure the exact length)slide 4-6 pieces of ceiling suspension wire in each tube with the ends looped over inside the tube. now startin with the upper inside collector position and the rear exhaust port, bend and fit the smurf tubeing to fit, the next forward exhaust port goes to the lower inside collector port the next exhaust to the upper outside collector port and the furthest forward to the lower outside collector port , once they are all bent to fit shoot the tubes full of hardening construction foam, let it harden and then pull each individual tube off one at a time and duplicate it in steel tubeing,(or have your local muffler shop duplicate it) this method REALLY makes the fit and try time minimal. and assures equal length tube headers.SMURF TUBE is flexable plastic electrical conduit thats normally BLUE or ORANGE and COMMONLY called smurf tubeing by contractors its a plastic version of that metal GREENFIELD tubeing that electrical contractors use but its cheaper and easier to work with, it resembles a canister type vacuum cleaner pickup hose but stiffer, its available at big hardware stores,and electrical supply houses dirt cheap in 10' lengths about $6 each or les you will need (3)BTW the 4-6 wires act like rebar in concrete, the loops keep the wires from moveing in the foam while their incased in the construction foam, the hard plastic foam is what keeps it stiff and no it will not be exact you will still need to tweak it to get it to fit but it will speed up the process of making the tube pattern shapes. just keep in mind that you can buy headers fairly cheaply (under $300 in many cases) for most cars its when you go and get an odd ball combo this comes in handy, like putting a 502bbc in a 57 vette or a 392 hemi in a 63 falcon, or you need headers for a LS1 in you 67 camaroHERES INFO YOU CAN USE




http://www.headersbyed.com/hdrkits.htm<P><A http://www.ssheaders.com/header.htm" http://www.ssheaders.com/header.htm
heres a quick way to figure your true primairy tube length (use 1250f degs(950k) and 5000rpm for race cars, 1200 degs(922K) and 3000rpm for street cars ) if you want other temps look here
http://www.convertalot.com/downloads.html
heres a quick cross check http://www.btinternet.com/~mezporting/exhaust_length.html

http://www.slowgt.com/Calc2.htm#Header

http://www.prestage.com/carmath/calc_headerlength.asp
or if your really lazy http://victorylibrary.com/mopar/header-tech-c.htm

and the answers in meters (about39"=1 meter)
but if you just use 36"-40" it will just move your tuned rpm level up or down slightly, not enough to make much differance except on a very peaky engine combo in a very light car.and this assumes your tube dia. is the same size as your exhaust port size.(never smaller, slightly larger dia. is ok)
btw mild steel is much easier to work with than stainless http://www.racerpartswholesale.com/flomstr1e.htm
http://www.holley.com/HiOctn/ProdLine/Products/ES/ESH/WeldUp.html
the pipes should be slightly oversized rather than so small that they partially block the exhaust port.
a pipe dia. that is small enought to partly block the exhaust port can hurt the cylinder scavageing by causeing turbulance and restrictions at the port exit, while a primary tube size slightly larger than the port leaves a ledge that partly retards returning pressure waves from reduceing the scavageing effect,...USE THE CALCULATOR PROGRAMS THATS WHAT THEY ARE THERE FORand keep in mind the displacement and rpm levels effect the dia. and length of both the primaries and collectors, these MUST VARY IN DIA. and LENGTH TO MATCH THE ENGINES EXHAUST PULSE TIMEING so that a NEGATIVE PRESSURE WAVE WILL BE CORRECTLY TIMED to SCAVAGE THE CYLINDERS EFFICIENTLY at the desired rpm range
if you want other temps look here http://www.convertalot.com/downloads.html heres a quick cross check http://www.btinternet.com/~mezporting/exhaust_length.html http://www.slowgt.com/Calc2.htm#Header (
(btw its not((Degrees ATDC)they mean subtract the BBDC from 180 degs. then use the answer and the rpm level should be picked for the expected torque peak http://www.prestage.com/carmath/calc_headerlength.asp [
or if your really lazy http://victorylibrary.com/mopar/header-tech-c.htm
and the answers in meters (about 39"=1 meter
example , my 383 vette has a cam with exhaust cam timing that opens at 83degs bbdc, thats 97 degs atdc,
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=119661&B1=Display+Card
Bore: (Inches) 4.03"<BR>Exhaust Valve Opening Point: (Degrees ATDC) 97 degs
Peak Power RPM: 5500rpm Calculated information appears below
Header Pipe Diameter: (Inches) 1.84"<
Header Pipe Length: (Inches) 37.65
Collector Diameter: (Inches) 3.5 (according to the calcs but use a 2.5" dumping into a 3" exhaust,where the collector extends a few inches inside the 3" exhaust, the step helps block reversion pulses and help scavaging
Collector Length: (Inches) 18.82
 

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Lengthy, but interesting. On one of mine, I actually cut the tips off (couldn't add more length for it would stick way past the bumper, like a pair or tailor hitches. This change made a world of difference in terms of resonance and made the car very livable, but it does look better with the tips.

The catalyst being restrictive does help dampen the pressure pulses (or widens its pulse over time) and pipe length does play a critical role in tuning the resonance to a specific frequency band, as stated above.
 

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I just had a set of true duals (no cats-yet) installed on my car, and it is quieter at cruising speed now then when it had the stock exhaust system on it. The resonance is gone completely. The reason is that the shop installed the mufflers (Flowmaster 50’s) so that the tips come just past the edge of the bumper.
If you can, see it your mufflers can be adjusted so that they do the same, and it will really quiet it down in sixth gear.

Good Luck :thumbsup:
 

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Discussion Starter #15
The extenders I have seen look really bad so I will try new tips after I just throw some high flow cats on, and do the insulation thing.
 

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Discussion Starter #16
just called aero and they ran me a deal of buy one get one free on their resonators... Supposedly this is GUARANTEED to fix it and only at 90 bucks. Also they said if it doesnt fix it i can send them back. Finally they said that this will not affect the flow whatsoever but will smooth out the sound a bit. I dont really see a point in spending all that money for an x pipe when Ive been told that it already has an H pipe in place. We will see this week hopefully and I will post if I have found the cure to resonance!
 

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Discussion Starter #17
wow, thats all I can say, this just about completely killed the resonance in my vette, I can actually hold a conversation now its great! Im going to home depot today to pick up that other stuff to kill some of the road noise but the resonators worked really well and car still sounds pretty mean Im impressed. Oh and I put them AFTER the stock resonator because it was just easier.
 

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could you post more info,
like part numbers, ?
phone numbers?
contact links for suppliers,?
pictures of the parts?
info on the installation?
Im sure a few guys will be interested in both what you did and the results.:thumbsup:
 

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Discussion Starter #19
ok, the resonators are from aero turbine, the part number is AR25 and the site is www.aeroexhaust.com. All I did was use extenders and a welder, cut off the straight section after the stock resonator and weld in the resonators, done. My job looked pretty hacked up at first and I had to take it to a muffler shop, 50 bucks and it was fixed they redid some welds my buddy did and tucked the resonators up as much as possible. They do sit about an inch lower than the stock resonator but not any lower than the y pipe did on my trans am so i really dont think I will have any issues. Anyways last night I went to lowes and bought the insullation 25 ft roll and put all of it under my carpet, took about thirty minutes. Now the car is even more bearable, and at 18 bucks it was really worth it.
 
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