Oh no a 3" vs 2.5" exhaust question on vr4.org

[jnava]

My flange at the 02 is 2.5 but it opens up to 3" just after the flange. Afterwards, the 3" catco and the rest as well. Isn't very loud in comparison to other cars but I feel that it is as nonrestrictive as it could be with a catalytic conv.

 

[trunks]

I've got an 18" long round vibrant resonator and then one of those little oval ones (not sure on brand) that's like 10" actually in front of the cat. I had read a thread on the evo forums about putting one at the front helping quiet it down.

Don't get me wrong, it's pretty quiet for a 3" exhaust. I once had a 3 inch world sport II on a talon and that was really good sound wise better than my current exhaust noise. I don't think it was staight through though. From what I've read a resonator is a simplified muffler and putting the two biggest mufflers that you can fit under there would be the ticket. I'm thinking with 2.5" piping it would really shut it up.

 

[thedsmguy]

I've been considering a 3" downpipe that splits near the rearend to two 2.5" pipes, one going towards DS that is open pipe and has a electronic cutout in it and the other going to a stock muffler. Assuming the 2.5 is on a boost related switch ie opens at 3psi or something, you would be able to drive around a lot without much noise.

 

[KiNgMaRtY]

I had a RRE Stealthback exhaust on my 2g GSX I had and it was just a snitch louder than stock. Full 3" Turboback exhaust. It had 2 huge resonators and ended with a magnaflow muffler.

A local is using full 2.5 TBE in his 1g Talon. He is running 11.1 in the 1/4 with a HX-35 and about 30-35psi on E-85.

 

That 1g Talon wouldn't happen to be red with an auto would it? If so, that thing scoots bigtime. The owner is a cool dude to boot.

 

[KiNgMaRtY]

Yep, that's Dustin. Recently did the MTX to auto swap.

 

[thecman02]

If you need to quiet your *shi....* down. Put a small restrictive exhaust on, and install a cutout that can open electronically or mechanically depending on how much jack you want to spend. Leave it closed, but if you want a race car you can dump. There was also some muffler on tuners I remember reading about that worked off of flow and opened under WOT conditions.

 

[EMX5636]

Quoting trunks:
I once had a 3 inch world sport II on a talon and that was really good sound wise better than my current exhaust noise. I don't think it was staight through though. From what I've read a resonator is a simplified muffler and putting the two biggest mufflers that you can fit under there would be the ticket. I'm thinking with 2.5" piping it would really shut it up.



Might be an isolated case, but a good buddy of mine recently replaced a 3" straight through Magnaflow on his Evo with an Apexi World Sport 3" inlet muffler. He wanted to quiet it down as well, and it should have because the muffler case itself is HUGE! But for some reason, it's definitely louder now. In the car is a bit better, but from behind, it's got the raspy (even Honda-ish) note of a race exhaust. He's far from happy with it.

 

[Vr4junkie]

Quoting thecman02:
If you need to quiet your *shi....* down. Put a small restrictive exhaust on, and install a cutout that can open electronically or mechanically depending on how much jack you want to spend. Leave it closed, but if you want a race car you can dump. There was also some muffler on tuners I remember reading about that worked off of flow and opened under WOT conditions.



This is the same route im going keeping my stock exhaust and plan on installing 2.5 or 3in electric exhaust cut outs best of both worlds the only thing with the cut outs when you do open them there loud ass hell.Cops would never suspect anything from a 4dr stocked exhausted car /ubbthreads/images/graemlins/devil.gif

 

[curtis]

Think about it this way. The turbo flows what cfm/lbs per minute. I've been sick and can't remember the conversion. I sat and looked it all up and did the math once and I think 65lbs a minute at wide open 100% is something like 880 cfm I think. Now do some conversions and see what a 2.5/3 inch pipe flows. Probably the best thing to do is find some throttle body flow numbers 60mm/65mm/70mm/75mm. Make sure all data is a 28.8 and not 28.8 vs 20.8 or whatever the person on the bench decided to flow it at.

 

[trunks]

Okay just came across this:

click

Thoughts?

 

[gramkrakr89]

My Galant has a homemade (by P.O.) 3" turbo-back exhaust with a gigantic magnaflow muffler poised at the very end of the system. keeps the tone at a low rumble/groan until boost hits... after that it sounds retarded...

They pay engineers decent money to design good-sounding (annoying noise free) exhausts for today's automotive needs... I think it's safe to say that finding a really nice-sounding exhaust that performs well is a crap-shoot.

EDIT: keeping in mind that "nice-sounding" is in the ear of the beholder

 

It means that my IC piping is way too big.

 

[gramkrakr89]

Quoting trunks:
Okay just came across this:

click

Thoughts?



I think this is about intake tubing...

 

[trunks]

Yeah, sorry. FP states the 68hta flows 47 lbs/min which is 618 cfm. Most of the info from googling is telling me 2.5" flows around 560 cfm. So the numbers back up 3" piping aparentely. Now more searching for 3" dp to 2.5" cat back..

 

[VR_IV_MR]

if you had a custom turbo back made, would it be possible to do 2.75" piping? or are there like standard pipe sizes that they use?

 

[trunks]

I think it's possible to go 2.75" but expensive. There's a 2.5" for sale locally and that's why I'm considering it.

It seems like a lot of the Subi and VW guys go with larger downpipes to a smaller catback. Just the dsm/evo community seems to frown upon the 3" dp to 2.5" catback combo for some reason. I was thinking of redoing my downpipe at 3", pulling out the cat and putting my 18" resonator on it. Then putting two mufflers on the 2.5 section - as large as will fit by the driveshaft and at the rear. Getting rid of the cat and going 2.5" the rest of the way might end up equalling out anyway /ubbthreads/images/graemlins/dunno.gif

 

[Ian M]

Actually,the VW guys were not the first to run a larger diameter DP into a smaller diameter exhaust. It was mid-late '90s,but I'm pretty sure it was Josh Jones (owner of JNZ for the newbies) who ran a 3" DP into a stock catback on a 14b Galant and was running 13.0s or 12.90s with it.

Seemed crazy at the time,but not the first time something that shouldn't work based on conventional wisdom and bench racing math worked ok in reality. /ubbthreads/images/graemlins/wink.gif

 

[vr4play]

I run the opposite. I have a 2.5" downpipe to a 3" exhaust. I get really good torque numbers which is what I wanted for auto-x. The last time I dyno'd on a 16g I did 305hp and 350 ftlbs tq on 93. I am still using that setup on my dd but I don't know what kind of numbers it makes with the old high milage motor put back in. I'm running a moroso spiral flow resonator with a ATR pitbull muffler. It was loud as hell and sounded like a rice rocket before the resonator. I think most of the packing in the muffler is burnt up from all the racing but it is not bad with the spiral flow. I sometimes wish it was quieter but I couldn't imagine how quiet yours could be with a cat and resonators and a muffler. I used a dynomax super turbo muffler before and it was almost stock sounding. Maybe you could just throw one of those on your current setup and have it really quiet.

 

[trunks]

I've been reading more and seen some test results and it sounds like dynomax has the quietest mufflers. I've got a magnaflow at the end right now and maybe just swapping would help. It seems like they are all pretty short or offset though. My magnaflow is 14" and most dynomax mufflers (at least on jegs) not that long. Maybe that doesn't matter when they are engineered correctly.

I bought the 2.5" exhaust on the cheap but am kind of disappointed because of all the bends a small resonator and muffler would be all that I can fit. I think if I modify it a bit I can fit a super long glass pack on there and then find a dynoflow muffler of some sort to finish it off. I've also read that if the pipe after the muffler is up to a foot long that helps a lot as well.

The other thing is I'm going to wait until after winter to put my jdm bumpers on and I suppose that would affect the length of my pipe at the rear as well.

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