Exhaust noise solutions

[Gary]

heloo

i'm currently designing a new exhaust for my cressida, and have now ran into the problem of noise limiting

the goal here is to be as quiet as possible, but allowing for the most flow. i understand that to a point, silencing and flow are inversely proportional, but in the case of a twin turbo engine i thought perhaps it wouldnt be so bad. i was hoping to stick with straight through, or semi straight through designs to limit resistance as much as I can. baffled designs dont appeal, specially since theyd be fitted to a turbo engine - though if i have to resort to them to keep it as quiet as i want, i will. the noise level i'm hoping for it to become close to silent (not quite silent). though really as long as i can kill low RPM drone, and excessive noise at idle i'll be happy as a clam

the system will be 2.25" from each turbo, mandrel bent and independent for about 650mm, then merging into a shallow 3" collector, straight into a 3" magiccat (ie highflow), then mandrel bent 3" through to the back, with a dump tip (shallow angle of incidence) ending about where the stock muffler ends and tip begins. the whole system will be mild steel (including mufflers if i can help it, those alu plated mild mufflers)

i certainly intend on putting mufflers in somewhere along the line, one large one in the stock position roughly half way, and another small barrel silencer fitted in the rear mufflers position (small enough to fit inside the stock muffler, if i can find one). ive got room for another small muffler, and another large muffler in addition to the two already planned

what im asking really is what sort of exhausts have fellow 1J owners had fitted to theirs, and what sort of results noise wise? (any 1J powered car; soarers, chasers, converted celicas, whatever) has anyone been able to shut their system up pretty good with a few straight through mufflers or have they needed baffled/other mufflers jammed in there?

edit i'll show all results once ive made and fitted it, so videos etc - in case anyone else is interested in a silentish high flow system

[jak]

you dont need to be worried about that system putting out noise if it has more than 1 muffler.

if it only has 1 muffler, you will be best off with a silencer in the rear. but having a dumpy tip that might be a bit difficult.

if you have a cat in there and 2 mufflers u will be fine. just dont remove the deading on the rear floor if you can help it or the headlinign as it will drone like a bastard at about 3000rpm.

Cheers
Jak

[PlacentaJuan]

linden from roadrunner did my exhaust on the 2jzgte mx83.

from the custom dump piped i have a 3.5 inch exhaust with the biggest metal cat (5 inches i think with 3.5inch inlet and outlet) running through two straight-through truck mufflers.

it is very quiet and absolutely no drone (unless i drive around with paralell turbos) and even then it is still quieter than any car with an aftermarket exhaust.

it still puts out 250rwkw and has run a best of 12.8 secodn quater mile so far.

[1jz68u]

my cressida had 2.5 inch dumps, 3 inch mandrel bent system, had cat, 1 hotdog and a muffler it was fine never any drama, i had a muffler on the rear not a cannon though. have heard a few with cannons and they are a bit louder so decision is yours there but doubt you will have a problem.

[Gary]

awesome, seems i might have overestimated the noise produced through a 3" system

the car its going on though is a straight sleeper, stock height, stock wheels, roof racks, bumper stickers, no added interior guages or things, invisible cooler, beat up bodywork... the lot

so getting the exhaust to sound stock is the ideal... reckon i could get it quite that quiet with straight through glasspack mufflers?

[jak]

yeh just throw a heap of straight thru mufflers in line and that will shut it up.

on ours we have 2 2.5" dumps right down till the 3.5" cat where it merges into a 3.5" system all the way to the back where it goes through 1 cannon and its one of the loudest cressies out. so dont do that lol.

Jak

[PlacentaJuan]

stock look is awesome.

shame about the wheels not fitting a brake upgrade though, i love the series 1 wheels

[Dieseltrain]

IM running Dumps into a 3 inch Catco Metal cat, splits into twin 2.5 inch rear straight through Cannons. Its not quiet, but i like it... SO i suggest for limiting noise, dont copy that

[Gary]

stock look is awesome.

shame about the wheels not fitting a brake upgrade though, i love the series 1 wheels

ive got some UCF11 stockies thatll hopefully do the trick, if not some z30 wheelios

[fixeruperer]

on my ae86 i have 3" from turbo 3" in out hi flow cat 1 3" muffler and then out the back after diff it splits to 2 3" pipes, and in those pipe i made up some muffler inserts.



i bought some 1 3/4" perferated exhaust pipe from the exhaust place and welded a core plug at one end, welded a mounting/sealing flange at the front with the pipe welded in the middle and rapped it up in steal wool.

i past the sound test at 89.9db hahahah 90db is the limit, tho they can do a drive by sound test if the stationary tests dont pass.

tho my pipes were only made to pass the sound test, ive taken them out becuase there to restrictive.

[cambelt]

I have 3 in stainless mandrel from the steering rack back with 2 custom made baffled stainless mufflers and a metalcat . It passed at something like 86db . No drone at all just a nice slight audiable note.
Dave

[Gary]

yeh just throw a heap of straight thru mufflers in line and that will shut it up
Jak

will do i think

i'll start with 3, the wreck i got my engine from came with a catback - small silencer and what looks like an offset straight through muffler. was alright, wasnt loud but certainly wasnt quiet either

thanks all for contributions so far

[abently]

High flow isn't inversely proportional to transmission losses anymore.

Ideally, you want to record the exhaust noise of a non-muffled Engine. Ideally the exhaust outlet (of a non muffled system) would also be at the rear, not underneath where specific frequencies will amplify and null etc and influence the data's true accuracy.

I can send you the software you need but you will need a laptop to be able to capture the data during 4th gear pulls along with stationary noise at various revs.

After that, you know what you are working with and know exactly what frequencies you need to null.

But if that's all too hard, the best advice I can give is that muffler diameter is proportional to sound losses. Also fibreglass density is proportional to sound losses, especially after 500Hz. 2 mufflers isolated of 500mm total length increase sound losses compared to a single muffler of length 500mm. These generalisations are valid for straight through systems.

Things get interesting when you add an internal baffle/s splitting the fibreglass volume into two parts as this produces an increase in transmission losses (40+db extra ) for a particular frequency range without effecting the other frequency performances compared to a non baffled muffler. Things get even more interesting with the addition of perforated baffles and empty spaces (min 30db loss from 0-800Hz). This is all for straight through mufflers still so you can see that there is a real possibility of engineering an exhaust system which meet ALL your requirements i.e. sound and performance. But to do this you have to datalog (lol) the raw exhaust noise as unfortunately their is not one muffler design that can do it all.

[Gary]

nice one

id thought resonance tuning and cancellation of various frequencies was largely limited to baffled and empty-spec mufflers, where glasspack was sort of a hacks option. just jam em in and it'll shut it up reasonably well

didnt know you could get that tricky with frequency killing in packed straight throughish mufflers recording the exhaust noise to analyse it is a little beyond me i think, only because id need to then make an appropriate muffler the easy way appeals interesting stuff though, might get into it some day for shits. cheers

[TERRA Operative]

I'm interested in that software. I've been thinking of using something like Adobe Audition myself to sample my exhaust and work out sizing of resonators to cancel the prominent frequencies.