I'd like to mod my exhaust, but it must be legal - ZR-1 Net Registry Forums

MuRCieLaGo · 11-11-2015

Hi,

I'm pretty much an expert regarding the road laws where I live, especially regarding exhaust systems.

1. We do not have emission tests, never.
2. Our primary concern is the noise, it is measured by the police officer's ear only (sonometer has no value in court).
3. Police officer usually goes under the car to take some pictures of the modified exhaust system, if he suspects it is too loud. I don't think he'll be able to do that with my ZR-1 (too low and he is not allowed to use a jack).
4. I live in a 50,000 people city, nearest ZR-1 except mine is 200 miles away. So the police officers have no idea how loud a ZR-1 should sound.

Rule #1: I don't want to be harassed by police officers.
Rule #2: I want to mod my exhaust performance-wise.
Rule #3: A bit louder than OEM should be OK, they don't know the OEM sound of a ZR-1.

Project:

I want to install headers and I want to empty the catalytic converters.

Do you think it will much more noisy doing that?

I would like to simply install a full exhaust system, but I can't because it is much louder for sure (and it would have that aftermarket look). If you know an exhaust system that is as loud as the OEM (or less), everything would be fine buying it. But I don't think it exists.

Sorry about all the threads I've been posting lately, I just have too much free time now and I'd like to work as much as I can on the car.

We Gone · 11-11-2015

If you install headers you will do away with the cats as the stock cats are part of the stock exhaust manifold, headers you would have to add them aftermarket. The late model stock set-up flows better.
Everyone has their preference as to exhaust choice, Personally I like the sound of the old flowmaster best and have them on my 93, I have Corsa on my 91 for better flow. Both will pass sound laws but the Corsa is loud at WOT.

http://www.zr1specialist.com/HAT%20W...%20Systems.pdf

Gunny · 11-11-2015

a few thoughts ...

Since you don't have to deal with the emissions aspect then headers sans cats would be a good start. The SW long tubes (they might refer to them as off road) have adapters for a direct fit to the OEM exhaust. The late OEM exhaust (94 & 95, possibly earlier) will become a little louder with headers/no cats but should be within the sound limits that you're looking for.

For performance the big restriction of the OEM exhaust is the mufflers ... if you wanted the best of both worlds, consider adding electric cutouts just prior to the mufflers. The cutouts can be opened just enough to get a little more sound, closed fully for almost stock OEM sound, or opened completely to completely irritate the sound police ... i.e. I'm sure you would be cited for noise pollution at that point. You can read more about the cutouts and see some pics by searching for WarpTen's thread.

I recently had cutouts installed and Marc did some porting, removed the secondaries, burned a new chip, and did back to back dyno runs with the cutouts open and closed. The difference was 15 HP at the wheels from closed to open and yes, I'm very pleased. As far as I'm concerned cutouts should have been a factory option.

There are several 3rd party solutions for the cat-back exhaust (or in your case attached to the headers). There are plenty of threads on this topic and no one correct answer. Beauty is in the ears of the beholder. Just remember that the greater the performance, the louder the sound so you will have to find the balance that works for you and your local regulations.

If you're not in a hurry I would recommend that you attend a gathering where several ZR-1's can be heard so that you can listen for yourself. The next big gathering that I'm aware of will be in Bowling Green in May, 2016. Hope to see you there.

MuRCieLaGo · 11-11-2015

We_Gone thanks for the article, very interesting stuff there.

I don't care if it is loud at WOT or partially opened throttle. Needs to be quiet only at idle.

Not super interested by the electric cutouts Gunny, as I like to have a car as simple as possible. Good to know that the mufflers are the big restriction of the exhaust system. I'd love to go to Bowling Green but I live in Canada which makes it quite complicated...

On my RX-7 I bought a resonated midpipe and I welded a plate under it so it looks like OEM.

I'll try to find some sound clips of different ZR-1 exhaust systems...

Thanks guys!

MuRCieLaGo · 11-11-2015

I just found some sound clips on YouTube.

OBX
https://www.youtube.com/watch?v=9Btec_YDAfs

vs.

5ABIVT's SW headers/Corsa Exhaust
https://www.youtube.com/watch?v=yfLcyPJZpS0

5ABIVT's is WAY too loud, however the OBX seems to have a very quiet sound, which would be perfect. Can't find any deep review on the OBX headers/exhaust system on here though...

Important question: does it say "OBX" on top of the tip?

Thanks!

RussMcB · 11-11-2015

I don't think that headers or lack of cats will add much noise. The biggest factor will be the mufflers you choose (and/or the resonator, too, if used).

When does an officer listen to the car to determine if it is too loud? Is it after they've heard you on the street and they thought it was too loud? If yes then I think you should also be concerned about WOT sound.

Personally, I really like the cut-out option. It's the best of both worlds. I'm not surprised Gunny is happy with his. But I do agree it adds complexity.

MuRCieLaGo · 11-11-2015

RussMcB yes it's after they heard me on the street, but "official" ear measurement is done at idle.

But now wait...

I just found out that my ZR-1 doesn't have the stock exhaust. I think it is Borla.

It has a very stock look (very dirty, not shining at all) and most of the police officers have seen the car now. So I guess I can simply buy some headers. Do you have headers to suggest or cheap OBX headers are OK?

We Gone · 11-11-2015

Yes they look to be Borla

Cat back flowmaster Stock manifolds and cats.

https://www.youtube.com/watch?v=7gsYgGZN1fY

Same car headers cats and Corsa.

https://www.youtube.com/watch?v=delqgeptb2A

efnfast · 11-11-2015

The OBX has a little tag on the side of the tips that say OBX. I have OBX headers and exhaust. I love the sound, but it is pretty loud.

MuRCieLaGo · 11-11-2015

Thanks We_Gone,

efnfast, I'm surprised you say OBX is loud.

However, now I'm only looking for headers, since I just discovered I got a Borla catback.

11-11-2015	#4
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: I'd like to mod my exhaust, but it must be legal We_Gone thanks for the article, very interesting stuff there. I don't care if it is loud at WOT or partially opened throttle. Needs to be quiet only at idle. Not super interested by the electric cutouts Gunny, as I like to have a car as simple as possible. Good to know that the mufflers are the big restriction of the exhaust system. I'd love to go to Bowling Green but I live in Canada which makes it quite complicated... On my RX-7 I bought a resonated midpipe and I welded a plate under it so it looks like OEM. I'll try to find some sound clips of different ZR-1 exhaust systems... Thanks guys!

11-11-2015	#5
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: I'd like to mod my exhaust, but it must be legal I just found some sound clips on YouTube. OBX https://www.youtube.com/watch?v=9Btec_YDAfs vs. 5ABIVT's SW headers/Corsa Exhaust https://www.youtube.com/watch?v=yfLcyPJZpS0 5ABIVT's is WAY too loud, however the OBX seems to have a very quiet sound, which would be perfect. Can't find any deep review on the OBX headers/exhaust system on here though... Important question: does it say "OBX" on top of the tip? Thanks!

11-11-2015	#6
RussMcB Join Date: Jan 2015 Location: Marietta, GA USA Posts: 1,160	Re: I'd like to mod my exhaust, but it must be legal I don't think that headers or lack of cats will add much noise. The biggest factor will be the mufflers you choose (and/or the resonator, too, if used). When does an officer listen to the car to determine if it is too loud? Is it after they've heard you on the street and they thought it was too loud? If yes then I think you should also be concerned about WOT sound. Personally, I really like the cut-out option. It's the best of both worlds. I'm not surprised Gunny is happy with his. But I do agree it adds complexity. __________________ Russ McBride, [COLOR="Red"]Car Sold 8/2020[/COLOR] #1635, Marietta, GA USA, 1991 ZR-1, #766 (bought 1/1/2015) MS3-Pro, OBX, SW X-Pipe, Borla, Hurst, SLP, Goodyear F1 GS-D3, Kenwood. HOTB 2016Q3 [IMG]http://zr1.net/forum/picture.php?albumid=316&pictureid=2873[/IMG] [IMG]http://zr1.net/forum/picture.php?albumid=336&pictureid=2985[/IMG]

11-11-2015	#7
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	Re: I'd like to mod my exhaust, but it must be legal RussMcB yes it's after they heard me on the street, but "official" ear measurement is done at idle. But now wait... I just found out that my ZR-1 doesn't have the stock exhaust. I think it is Borla. It has a very stock look (very dirty, not shining at all) and most of the police officers have seen the car now. So I guess I can simply buy some headers. Do you have headers to suggest or cheap OBX headers are OK?

11-11-2015	#8
We Gone Join Date: Apr 2004 Location: ATL. GA. Posts: 2,170	Re: I'd like to mod my exhaust, but it must be legal Yes they look to be Borla Cat back flowmaster Stock manifolds and cats. https://www.youtube.com/watch?v=7gsYgGZN1fY Same car headers cats and Corsa. https://www.youtube.com/watch?v=delqgeptb2A __________________ Steve 1990 Steel Blue/Black #2355 1990 Red/Red #1473 1991 Quasar /Black #118 Sold 1991 Turquoise/Black #766 Parted Out 1993 Yellow/White #179 Sold 1990 Black/Gray #1361 Headers/4:10s Sold

11-11-2015	#1
MuRCieLaGo Join Date: Aug 2014 Location: Trois-Rivieres (QC) Posts: 473	I'd like to mod my exhaust, but it must be legal Hi, I'm pretty much an expert regarding the road laws where I live, especially regarding exhaust systems. 1. We do not have emission tests, never. 2. Our primary concern is the noise, it is measured by the police officer's ear only (sonometer has no value in court). 3. Police officer usually goes under the car to take some pictures of the modified exhaust system, if he suspects it is too loud. I don't think he'll be able to do that with my ZR-1 (too low and he is not allowed to use a jack). 4. I live in a 50,000 people city, nearest ZR-1 except mine is 200 miles away. So the police officers have no idea how loud a ZR-1 should sound. Rule #1: I don't want to be harassed by police officers. Rule #2: I want to mod my exhaust performance-wise. Rule #3: A bit louder than OEM should be OK, they don't know the OEM sound of a ZR-1. Project: I want to install headers and I want to empty the catalytic converters. Do you think it will much more noisy doing that? I would like to simply install a full exhaust system, but I can't because it is much louder for sure (and it would have that aftermarket look). If you know an exhaust system that is as loud as the OEM (or less), everything would be fine buying it. But I don't think it exists. Sorry about all the threads I've been posting lately, I just have too much free time now and I'd like to work as much as I can on the car.

11-11-2015	#3
Gunny Join Date: May 2005 Location: Georgia Mountains Posts: 927	Re: I'd like to mod my exhaust, but it must be legal a few thoughts ... Since you don't have to deal with the emissions aspect then headers sans cats would be a good start. The SW long tubes (they might refer to them as off road) have adapters for a direct fit to the OEM exhaust. The late OEM exhaust (94 & 95, possibly earlier) will become a little louder with headers/no cats but should be within the sound limits that you're looking for. For performance the big restriction of the OEM exhaust is the mufflers ... if you wanted the best of both worlds, consider adding electric cutouts just prior to the mufflers. The cutouts can be opened just enough to get a little more sound, closed fully for almost stock OEM sound, or opened completely to completely irritate the sound police ... i.e. I'm sure you would be cited for noise pollution at that point. You can read more about the cutouts and see some pics by searching for WarpTen's thread. I recently had cutouts installed and Marc did some porting, removed the secondaries, burned a new chip, and did back to back dyno runs with the cutouts open and closed. The difference was 15 HP at the wheels from closed to open and yes, I'm very pleased. As far as I'm concerned cutouts should have been a factory option. There are several 3rd party solutions for the cat-back exhaust (or in your case attached to the headers). There are plenty of threads on this topic and no one correct answer. Beauty is in the ears of the beholder. Just remember that the greater the performance, the louder the sound so you will have to find the balance that works for you and your local regulations. If you're not in a hurry I would recommend that you attend a gathering where several ZR-1's can be heard so that you can listen for yourself. The next big gathering that I'm aware of will be in Bowling Green in May, 2016. Hope to see you there. __________________ George Jones Founding Member #14 www.zrwon.com

11-11-2015	#9
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,486	Re: I'd like to mod my exhaust, but it must be legal The OBX has a little tag on the side of the tips that say OBX. I have OBX headers and exhaust. I love the sound, but it is pretty loud.