Custom Exhaust question

[bcleaver]

So I'm having a custom exhaust built but want to solicit some advice from you guys.

My goal:
headers have to remain stock. Everything else can be open. I have to be below 95db at 50 ft. My goal is to save weight and not reduce performance (low end torque, etc).

Questions:
1. 3" or 2.5"? Save weight with 2.5" vs possible better 'breathing' from 3" Opinions?

2. I probably can't run straight pipes for the noise. Can I get by with a single resonator (glasspack) and be under 95 db?

3. If I stick with a single resonator is it worth some weight savings to put in an aftermarket one, or is the stock one light-ish? Anyone weigh the stock (front) resonator?

Thanks for chiming in.

[az3579]

I would think the dB level would also depend on what kind of exhaust you're putting on. If it's custom, I don't know if there's really any telling if that's going to be too loud. If you're worried about decibel level, I would go with a 2.5". I seriously doubt that if there's any performance benefit to be had with going 3" vs 2.5", it would be absolutely negligible. The way I see it is this: is it worth the risk to go with 3" and run the risk of it being too loud and being out of pocket $$ wise if it's too loud? If I was spending money on an exhaust and couldn't risk running over 95dB, I would go with the 2.5". It's not worth spending the money and then having to respend it to "fix" the noise issue, regardless of how much it would cost. If there was a huge performance benefit, then perhaps I'd take the risk, but there isn't, so in my eyes it's not worth it.

Also keep in mind that if you plan on tracking the car, depending on what track you're going to, they may have noise restrictions as well. Some of them may even lower their limit, like my home track did (Lime Rock Park). Nobody saw it coming, but the noise limit has been reduced and it could happen anywhere and sometimes for no reason as well. Something to consider if noise limitations are a concern.

[Nivo]

So I'm having a custom exhaust built but want to solicit some advice from you guys.

My goal:
headers have to remain stock. Everything else can be open. I have to be below 95db at 50 ft. My goal is to save weight and not reduce performance (low end torque, etc).

Questions:
1. 3" or 2.5"? Save weight with 2.5" vs possible better 'breathing' from 3" Opinions?

2. I probably can't run straight pipes for the noise. Can I get by with a single resonator (glasspack) and be under 95 db?

3. If I stick with a single resonator is it worth some weight savings to put in an aftermarket one, or is the stock one light-ish? Anyone weigh the stock (front) resonator?

Thanks for chiming in.

Low end torque loss can be seen on 3" cat backs, you can do the 2.5" with resonator and straight through muffler. if you slow down the exhaust by cooling off the exhaust gasses coming out you start losing low end. This is by using the 3" over the 2.5". Keep the exhaust hot for it to scavenge out faster. Exhaust systems are a balancing act. If it is not an all out race car 3" will most likely be too much for a street car that has 235 crank horsepower.

Stainless steel weighs more then Aluminized and both of those weigh more then aluminum, I have seen aluminum exhausts and they are lightweight but loud as the tubing resonates a lot.

are you staying twin tubing back? or are you going single with a "Y" pipe down to single?

Average weight of aluminum 3" tubing at one foot increments is about .740 lbs.
Average weight of aluminum 2.5" tubing at one foot increments is about .612 lbs.

Average weight of 304 Stainless steel/Aluminized 3" tubing at one foot increments is about 2.04 lbs.
Average weight of 304 Stainless steel/Aluminized 2.5" tubing at one foot increments is about 1.70 lbs.

The above is 16 gauge thick tubing.

[bcleaver]

Good stats and thoughts. thanks guys. The reason I'm leaning more towards 3" is that it's going to be crush bent, not mandrel which actually limits the diamater during the bends considerably (to proabably about stock or even smaller). Good call on the noise and it being hard to make it quieter. I may do a resonator and a very small exhaust at the end as well.

Other thoughts? Keep em coming.

[bcleaver]

are you staying twin tubing back? or are you going single with a "Y" pipe down to single?


Going single pipe just off the header

[az3579]

Good stats and thoughts. thanks guys. The reason I'm leaning more towards 3" is that it's going to be crush bent, not mandrel which actually limits the diamater during the bends considerably (to proabably about stock or even smaller). Good call on the noise and it being hard to make it quieter. I may do a resonator and a very small exhaust at the end as well.

Other thoughts? Keep em coming.

So they why even go through the trouble of 3"? If it's going to end up smaller, then I don't see why there is a choice... ??
Going for the badass look? :)

[bcleaver]

So they why even go through the trouble of 3"? If it's going to end up smaller, then I don't see why there is a choice... ??
Going for the badass look? :)

No one in my area does mandrel bending so if I want to keep a decent flow I have to start with a bigger pipe. Should have mentioned my crushed bending restriction in the beginning. I'm not sure what the final diamater will be after bending though, but guessing it would be close to stock?

[Nivo]

Any shop will use the bends you buy and weld them up.. you have choices:

http://www.mandrel-bends.com/catalog/?gclid=CKiW2-frhqkCFQbe4AodFR16pQ

http://www.mandrelbendingsolutions.com/servlet/the-Mandrel-Bends/Categories

I would go this route before press bent exhaust which will go from 3" to 2.75" and getting charged for 3".

[bcleaver]

Here's how the final product turned out--sound wise:


http://www.youtube.com/watch?v=090-WoEJ1fE

I didn't get a chance to weight it off the car but based on the specs I calculate it weighs about 28lbs. It's the stock exhaust for about 1ft past the headers. The merges into a single 3" pipe (crush bent) then into a 18" glasspack and then straight out all the way to the back.

A huge improvement weight wise over the stocker and sounds much better IMO

[danewilson77]

Bro.....that's a mini van in line to run!!!!!

Sounds good.