Does anyone have a smog legal header? I can't see the point of tricking out the exhaust and keeping the manifold.

Also, concerning the discussion of louder exhaust, you can use a Supertrapp exhaust tip to tone it down during the week and remove it for the weekends. <a href="http://www.supertrapp.com/Automotive/automotive_page.htm" target="_blank">http://www.supertrapp.com/Automotive/automotive_page.htm</a>

we did this on a GT-1 vette because Laguna Seca was pretty stringent on noise levels where other tracks weren't. seems a bunch of yuppies built houses near the track and then started complaining about the noise. <img src="graemlins/nono.gif" border="0" alt="[nono]" />

 

Street legal headers, depends on the how the laws in the state that you live are written. I would think that in most states any header on a 928 would be legal, as the 928 cars don’t have their exhaust manifolds plumbed for fresh air like many others cars.

As far as the Supertrapp exhaust tip, I have experimented with only two of them in the last 15 or so years. On neither projects were we concerned with noise and were only using them as a final tuning aid. Yes they will lower the tone a little bit, but at the point were some maybe happy with the db level you will have added too much back pressure and your performance will than suffer. If it is db’s you are looking to reduce try adding a pair of small glass packs in the rear muffler area or right after the cats before going into your intermediate muffler of choice.

In other words:

1. Header – Crossover – Catalyzer – intermediate muffler – short glass pack – tail pipe.

2. Header – Crossover - Catalyzer – short glass pack – intermediate muffler – Rear Muffler Bypass.

Third choice

Header – Crossover - Catalyzer – short glass pack – intermediate muffler - Supertrapp exhaust tip.

Cheers

Max

 

In California I heard you can have headers, just as long as you have some sort of smog device implemented on the car. An aftermarket catalytic converter would work great with headers.

I currently am working buying Bursch headers and bolting up a 2.5" diameter piping Dynomax HighFlow cat to the car. That should give some more power and fix the gas mileage on her.

Perhaps the 928 would really take advantage of the piping and power! <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

 

Yea, I forgot to mention, I'm on the left coast, in Cali. Worst smog laws yet. There's talk of using catalitic underpants to reduce methane emissions.

We've got roadside smog checks happening here, maybe some of you do too. They're like drunk driving checks, they block off a street and pull people over at random (actually they profile, anyone who looks as if their car is modified gets pulled over to the portable dyno). I have heard that if they are missing smog equipment their car is impounded. Land of the FREE!!!!!!!!!!!!!

So I guess I better keep my car legal if I want to legally keep my car.

 

Max,

I have a GT with no cats and I'm thinking about RMB or something high flow for the rear(currently stock) to compensate for the db level. Do you know of a similar setup with no cats and something like a supertrapp at the rear or have any suggestions? At least with the supertrapp I can pick up a couple hp at the track.
Thanks

Jim Stoops
90GT / 85S

 

Chris, I have heard of a few 928’s running around Cali with headers. On the 928 (86-up)the smog pump, pumps air straight to the Catalyzers via tubing not associated with the stock exhaust manifolds so installing headers with a set of nice high flow cats hooked up to the this same tubing should not cause you problems in the hood Call either 928 International or DEVEK to verify if need be.

Jim, I through in the super trap option because Chris sounded like he may have made up his mind about using one and if used on say a single 3in. with Dyno time might help to eek out few more HP's (My fault for not clarifying conditions of installation).

I would not recommend a super trap on a 928:

1. With a dual pipe set-up for the obvious reason that it would require one to cut out the rear bumper for a dual exit.

2. If one didn't have a small wad of duckies to drop and the proper time to spend at the Dyno to set everything up right.

Maybe I shouldn’t have just thrown out my opinions in my previous post without emphasizing how hard and expensive it is to R&D a well-balanced exhaust system. The Don Marc from DEVEK, the evil scientist Ott and Mr. Tom the Power Brokers have all come up with a few nice designs (IMO) with proven results for a full range of applications that in the end would come out cheaper to buy than doing the R&D yourself.

With that said Jim, not having Catalyzers will add a few more db’s after you install a RMB. If you feel strongly about not replacing them with high flow cats you could add in a couple of long glass packs in their place to bring the db’s back down.


I have read a lot of posts here and on other BB’s over the last year and have noticed that most who want to improve their HP numbers by way of exhaust mods are only willing to do so if it doesn’t increase the db levels inside the car to monster truck levels.

I like most wouldn’t mind a few more exterior db’s but really enjoy listening to my stereo and chatting with the occasional risk taking passenger so adding more interior db’s would have to be minimal if any at all.

Things that increase interior db’s:

1. Thin wall headers.
2. Lightweight, thin wall exhaust pipe.
3. Large diameter exhaust pipe.
4. Single wall mufflers (most HP mufflers fall into this category).
5. Removal of heat shields on the exhaust manifolds and between the catalyzers, mufflers and stock pipe and the body of a car.

What can one do to reduce the db’s?

1. Wrap the headers (stock exhaust manifold can be done also!) with a high temperature fiberglass header wrap. This will deaden the sound and reduce under hood temps.
2. Stay away from thin wall and large diameter pipe unless your super **** about a few extra ounces per foot or could care less how loud your car is.
3. Most performance muffler companies use single wall construction, which resonates under the car. OEM mufflers are double walled to help them last longer and to reduce resonance. All is not lost however; the same high temperature wrap you used to wrap the headers in can be used on each muffler and catalyzers. The only thing you may want to do after wrapping them with header wrap is to cover that with a lightweight aluminum cover to protect the fiberglass and help retain sound inside the mufflers.
4. Don’t remove any factory-installed shields unless you plan to fabricate better replacements.

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Max