Exhaust harmonics

[y-not]

I am being drummed out of my 302 powered 280Z at 1500 & 2300 RPM under load. Tried softer exhaust mounts- no help. The system consists of block hugger headers into 2 2.25" pipes to a 4' long 3" pipe then splits into 2 2.25" pipes and mufflers.

[2126]

I am being drummed out of my 302 powered 280Z at 1500 & 2300 RPM under load. Tried softer exhaust mounts- no help. The system consists of block hugger headers into 2 2.25" pipes to a 4' long 3" pipe then splits into 2 2.25" pipes and mufflers.

 

The description you provide on your exhaust set-up is interesting at best! Are you saying that the two headers feed into a single 4' long 3" diameter pipe and then slits into two separate 2 1/4" diameter tail pipes? If so, you my consider installing a race type bullet muffler in the 3" diameter pipe to attinuate and change the resonate frequency of the exhaust. Typically on Mustangs, to resolve this issue, the pipes come straight off the headers and out the tail pipe, but a crossover pipe (H pipe) is positioned between the two tail pipes shortly after the exit from the headers.

[grumpyvette]

in many cases the (DRONE) is a SYMPATHETIC HARMONIC RESENANCE 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

[y-not]

Knowledge is power. My exhaust shop was amazed at what was available through the internet! This is the third custom exhaust system that he has built for me and he is willing to work on it until it is perfect with no additional cost to me! Thanks for all of the input, if anyone has more ideas, please post them.

Thanks Again,

Bill

PS this car is really F... fast!

[Guest 305240]

I'm not trying to hyjack your thread Y-not, but I have a question for Grumpyvette.

 

I'm constantly amazed at the vast amount of knowledge you have. I hang on every word and try and learn. The question I have for you is also about exhaust. I'm running a 5.0 with factory shortie headers. I'm also going to be building sidepipes. They will look like the old Cobra pipes. I'm going to run each header into a 3" pipe, welded to a 3" ID straight thru glass pak which will be welded to a 3" turndown. I believe I'll have to put a flexable pipe right after the headers so I won't be breaking or cracking my exhaust. With the turn downs facing at a 45 degree away from the car, should I also put in a cross over? I know this sucker is going to be loud. Thats why I want it turned toward the ground, but not straight at the ground so it doesn't kick up dust. I'll have enough room under the car as I'm building it 60 and 70s muscle car style. Oh, I'm also running flairs all around. Thanks. I'll definatly go with your recommendations.

[y-not]

I had a Factory Five Cobra for 5 years. They used the factory headers into the exhaust system that you described without any flex pipe. They hang the back of the exhaust on the stock Mustang rubber mounts. There are 4000+ Factory Five's running the system that you want to build without any cracking problems.

Bill

[Guest 305240]

Thanks. I was figuring on hanging them off the rocker someplace. I never thought of the f five mounts.

[Graeme]

anyone tried the mufflers on their zed????

 

http://www.aero-turbine.com/how/index.html

[grumpyvette]

305240

 

if your going to run SIDE PIPE exhaust like the COBRAS and SOME CORVETTES used , (I had them on my 496 BBC corvette)adding a ballance pipe (H)between the sides just after the header collectors tends to mellow the exhaust tone, and you usually won,t have many other options due to space/packaging limitations with side exhaust, if you look at most glass pack insert mufflers youll see that they consist of a metal tube with hundreds of louvers cut directionally wrapped in a fiberglass blanket inside an outer metal cover with all the louvers facing the ecpected exhaust flow direction. this tends to restrict flow slightly and does not help hp, an old trick is to insert them (the inserts )backwards, so the louvers face towards the exit, this usually shows slight hp gains and surprizingly does not make a big differance in noise levels.

you may want to look over the spiral baffels,like Graeme pointed out, btw heres a differant source/design

 

http://www.spiralturbobaffles.com/

 

heres a picture of a similar set to what my corvette had

I had a custom welded 2.5" pipe stubs welded /connector clamped between the collectors,

 

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

 

 

[Heavy Z]

anyone tried the mufflers on their zed????

 

http://www.aero-turbine.com/how/index.html

 

 

I've got Moroso's version of the same muffler and am happy with the results.

[hat1324]

I've got Moroso's version of the same muffler and am happy with the results.

is it quite? or is there a nasty tone?

[Heavy Z]

is it quite? or is there a nasty tone?

 

 

I use 2 of them in 2 1/2" off the headers back to a y-pipe, to a 3" hooker aerochamber. Great sound IMO, not too loud (or too quiet either) and the tone doesn't get annoying anywhere as flowmasters can.

[74_5.0L_Z]

Grumpyvette,

 

I currently have dynomax block hugger headers, dual 2.5" exhaust, 2 two chamber Flowmaster mufflers, and H pipe on my 5.0L powered 260Z. I like the sound and I get a lot of compliments, but I want something a little better than the Block huggers, a little lighter than the flowmasters, and something more unique.

 

My engine is mounted using a front plate / mid-plate set-up, and I have the late model rear sump pan. The engine configuration opens up a ton of space below the motor ahead of the rear sump.

 

The engine currently displaces 302 c.i, but I plan to build a 331 stroker. The heads are Edelbrock Performer RPM, the intake is an Edelbrock Performer RPM with 30# injectors. The cam is a Crower 15511 hydraulic roller with 1.72 roller rockers. I plan to build the new motor with 10.5:1 compression, and want a usable 7000 rpm (I may change the cam to a solid roller). The car is used mostly for autocross and some track days.

 

Here is what I want to do: I want to build some custom 180 degree headers such that the center two tubes from each bank cross under the oil pan and go into the opposite side collector. I plan to have the collectors mounted at an angle behind the front tires such that they exit the from the fender midway between the wheel opening and the door. From the collector exit they will run parallel to the rocker panel(higher than the plane of the floor) and dump outward and down in front of the rear tire.

 

 

 

My questions are these: First, what size primary tube would you use (packaging will probably limit my minimum length to 36")? Second, what size collector (length and diameter)? Third, what would be the lightest/smallest muffler that will pass SCCA sound allowance (90dB at 50' I think).

 

Thanks,Dan McGrath

[grumpyvette]

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

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

heres a quick cross check

 

 

or if your really lazy

 

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

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 heres a quick cross check (

(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 [

or if your really lazy

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,

Bore: (Inches) 4.03"

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

[74_5.0L_Z]

Thanks,

 

I knew you were the one to ask.

[grumpyvette]

btw read these (yeah its another old post but theres some good info)

 

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

 

 

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

 

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

 

http://www.popularhotrodding.com/tech/0310phr_burns/

 

http://www.burnsstainless.com/TechArticles/Theory/theory.html

 

the short answer is ANY BACK PRESSURE IS BAD!

what your trying to do with a correctly designed exhaust is to have the majority of the exhaust system act like extended collectors on the headers, in effect useing the inertia of the hot exhaust pulses from each cylinder to cause a cyclic low pressure wave to be timed to assist the next firing cylinders to scavage the cylinders

 

heres the info you need,

http://www.enjoythedrive.org/content/?ID=26046

 

http://www.enjoythedrive.org/content/?id=10185

 

 

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

 

 

to adjust for your altitude

http://rshelq.home.sprynet.com/density_altitude.htm

 

and if you want to get it perfect you should usr your DYNAMIC COMPRESSION RATIO VOLUME in the formula at the rpms for peak hp that your engine makes

 

http://cochise.uia.net/pkelley2/DynamicCR.html

most of the time that comes out close to the same as the static cylinder volume at the peak torque f.y.i.

 

LET ME ASK THIS QUESTION?

WHATS THE FIRST THING YOU DO AT THE TRACK TO YOUR EXHAUST SYSTEM?

you open the headers to have less back pressure correct!!

BACK PRESSURE IS BAD, BAD,BAD, the idea has gotten around that you need back pressure to build torque, FALSE!!!!!! that IDEA was prevalent because if you stick too large of an exhaust pipe on a low rpm engine it loses the ability to scavage the cylinders with the exhaust gas pulse in the exhaust with stock exhaust manifolds, some how the old wifes tale got around that you needed back pressure...FALSE.. what you need was EFFECTIVE CYLINDER SCAVAGEING which the smaller tail pipe dia. was provideing by acting like the collector on a set of headers! if you have headers , especially full length headers with a merge type collector OF THE CORRECT LENGTH,you can,t make the exhaust too large,THINK ABOUT IT! the first thing you do at the track is un-cork your headers....why? because YEARS OF TESTING PROVES, less BACK PRESSURE MAKES MORE HP WITH HEADERS!!!! now some one is saying yeah but thats at the track and your running the engine at 5000rpm-6500rpm , well true and a good point because we typically only run 1000rpm-3000rpm on the street what it shows clearly is the collector on a low rpm engine needs to be about 10ft long for max effect so you need an exhaust that works with a collector thats about 20" long at 6000rpm and one 10 feet long at idle, THATS WHERE THE IDEA OF TOO LARGE A EXHAUST comes from but as long as you follow these rules youll be fine, READ THIS,

 

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

 

 

btw Im writeing this like this to get you guys to think about it then we will look into the answers of how to get both ends of the rpm range covered and yes Im leaveing out some info on purpose

 

 

 

 

 

is exhaust back pressure killing performance ?

its a fast easy test that needs to be done and more than a few cars running older cats are having a restricted exhaust thats hurting your performance badly, and because the problem tends to build up slowly many people don,t notice the gradual power loss

first thing youll need to realize is that the TEST POINT needs to be after the header collector and in front of the CAT AND MUFFLERS. next thing you need to know is that to get a valid answer youll need to have a long connector hose so someone in the pass seat can CLOSELY WATCH the gauge as you accelerate under load (FLOOR THE CAR THRU THE FIRST 1-2 GEARS and watch the pressure surge. readings above 1psi mean somethings partly restricted, readings above 3psi are hurting your performance BADLY

the test kit is about $50.00

http://www.jdsdiagnostic.com/eptspage.htm

 

ITS NOT RARE TO LOOSE 20% or more of your hp to a restricted cat

your unlikely to lose much if any hp especially if you install an (H) pipe just before the reduction in tail pipe dia. and use a gradual reducer to change from 3' to 2.5" mostly because the exhaust gases have cooled a great deal by the time they reach that point in your exhaust system and with that heat loss a reduction in voluum and potential back pressure

 

 

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1313&prmenbr=361

 

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1306&prmenbr=361

[rudypoochris]

Si9nce you seem like a genius grumpy can you help me with a 302 exhaust setup, i would like to use 2 of those aero turbine mufflers (http://www.aero-turbine.com/buy/index.html) and i was thinking of using them right at the bottom of the headers then making them join into a 3.5" pipe. is this a good idea? would i cross over before the two mufflers or no need? willt he sound be ruined from the super long distance aft of the muffler? back pressure issue? thanks!

[grumpyvette]

theres two major factors working on that,layout idea,

 

first the FURTHER from the collectors you place the mufflers the cooler and more dense the exhaust flow becomes and the lower the effective restriction to that flow on any given exhaust size. you want the exhaust to scavage the cylinders and mufflers tend to (by design) break up pulse harmonics that can be used to enhance cylider scavaging, cylider scavaging that the headers are there to promote. you want as little restriction at the collectors as you can get.

 

next the restriction effectively drops off significantly as the pipe inside dia. increases after an (X) pipe on a dual system or a (Y)on a single exhaust that will have a cross section area at least close to the cross sectional area of both collectors,

 

IF your designing a single exhaust,ideally youll want the twin header collectors to enter a (Y) to blend the pulses and not use an (H) and the single exhaust behind the (Y) should have a cross section area at least close to the cross sectional area of both collectors,then one of these

 

slipped inside a 3.5" exhaust pipe should pose little if any effective restriction to a 302-331 displacement engine, especially if its as far back as possiable from the (Y) to allow the exhaust too cool and reduce its voluum, the (Y) will help maintain the peak cylinder scavaging only if its before the mufflers

 

http://www.spiralturbobaffles.com/

 

this design may OR MAY not run quietly but it will effectively scavage the cylinders

you may or may not even need a SINGLE muffler past the spiralturbobaffle but having the room to install a system designed like that could be a potential problem

 

some guys have found that welding in a restriction cone listed below in each of the header collector tail pipes exiting the headers before the exhaust pipes leading to each muffler helps with the sound

 

http://www.spiralturbobaffles.com/

 

http://www.secureperformanceorder.com/dynatechdragstore/vortex.cfm

 

http://search.ebay.com/search/search.dll?query=header+flanges&newu=1&krd=1?keyword=header+flanges

 

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

 

http://www.ssheaders.com/Collectors.htm

 

http://www.burnsstainless.com/MergeCollectors/mergecollectors.html

 

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

 

http://www.holley.com/HiOctn/ProdLine/Products/ES/ESHHA/SplitFlow.html

 

http://www.holley.com/HiOctn/ProdLine/Products/ES/ESHHA/Cutaway.html

 

http://www.holley.com/HiOctn/ProdLine/Products/ES/ESHHA/HPipe.html

 

http://store.summitracing.com/section.asp?d=8&s=577

 

And...

 

 

http://www.grapeaperacing.com/GrapeApeRacing/tech/exhausttubesizes.cfm

[Z-Dreamer]

www.headerdesign.com is another useful resource for the design of headers and exhaust systems.

 

Mark

[rudypoochris]

see my problem was that the aero mufflers i linked only allow for a 2.5" inlet or a 3" if i go with the suv model, sow does it make sense to use headers to a 3.5" (Y) with one of those cones in it, and then at the very end limit the pipe down to a 3" to use the aero suv muffler?