autoxer6

I now have the suspension on my 04 Z06 set up well for SCCA autocross stock class.

I wondering what the national level guys are doing for exhaust? How much weight savings and power gains can be had with a cat back?

TedDBere

The national guys do everything from stock to straight pipes. The stock system is pretty good and very light.

With straight pipes you can shave off about 7 lbs and gain anywhere from 4 to 14 hp. But you won't be able to run your car at all venues. YRMV

Bimota Guy

SCCA Solo Regs Section 3.5 requires mufflers for all Solo events.

To answer the original question, don't waste your money unless you are looking for a zoomier sound. The titanium Z06 exhaust is quite good.

A good T1 car w/o cats and mufflers and running 100 octane fuel with a tweaked ECU is making about 20 more rwhp than a stock Z06.

TedDBere

That's just wrong.

3.5 Mufflers

Adequate mufflers are required for solo events. The criterion of "adequacy" is not what the exhaust system consists of, but the sound level. Any car deemed by the Event Chairman or his designated representative to be excessively loud shall not compete without acceptable modifications installed on the car.

13.10 ENGINE AND DRIVE TRAIN

E. Any part of the exhaust system beyond (downstream from) the
header/manifold or catalytic converter, if so equipped, may be
substituted provided the system meets the requirements of 3.5.
Stainless steel heat exchangers are permitted only if the physical
dimensions and configuration remain unchanged.
Modifications of any type, including additions to or removal of,
the catalytic converters, thermal reactors, or any other pollution
control devices in the exhaust system are not allowed and the
system must be operable. Replacement catalytic converters must
be OE.
Exhaust hangers which are bolted or welded on the car are
considered part of the body and may not be changed or removed.



Many venues have no sound restrictions, including Nationals, so straight pipes are allowed at those venues. How do I know? Because I run them!

If the Event Chairman thinks your OE mufflers are too loud they can toss you out too. That's what 3.5 says, the Event Chair decides acceptable sound levels.

autoxer6

It's interesting that a T1 car only picks up 20 HP. I thought those mods and the 100 octane would be worth more than that...?

Ted,
Now I know why your exhaust sound is picked up so well on the video you posted. Straight pipes have to be pretty loud!

Bimota Guy

Right, Ted, Event Chairs decide what is acceptable sound level. Wrong, Ted, Event Chairs do not have the authority to allow a car w/o mufflers. Please explain what part of "...adequate mufflers are required..." is confusing to you? Whether some event chairs turn their heads to your setup and this rule is another story.

Bimota Guy

You and a lot of others. The stock setup is very good. I suggest spending the money on an Evo school or tires or...

christoc

Bimota, perhaps in California you read the rules like that, but nearly everywhere else in the country mufflers aren't required, unless local rules designate DB limits

USAsOnlyWay

I remember seeing a winning AS Corvette's "exhaust" for sale. If I remember correctly, it had a turn down about an inch or two after the main cat (C4, remember) and that was it, just dumped right under the center of the car. Said he cut a good amount of weight with that setup.

TedDBere

You can read the rule anyway you want, but cat-back is free in SCCA Solo. As long as the Event Chairman or his disignates determine it's not too loud for the event.

You have to read the whole rule, you can't just stop at the first sentence. "The criterion of "adequacy" is not what the exhaust system consists of, but the sound level."

The car is loud at WOT at 5000rpms, but because I must retain the stock exhaust exhaust manifolds and the cats it's less noisy than you might think. Three local Event Chairs have ruled that I can run at their "sound restricted" sites because the car meets their sound limit restrictions. But I can't run it at Devens or Philly region events.

The first video in my Sig is with stock mufflers, the last two are straight pipes. FWIW

Bimota Guy

Ted, If a lot of places are not enforcing the rule, okay, I am not disputing that. But to say the rules do not require mufflers is absurd. It says that required at solo events are "adequate mufflers" not an "adequate exhaust system." No?

Again, I think a modded exhaust on a C5 Z06 is a waste of money unless you are losing out to national caliber drviers by the smallest of margins.

-Steve

TedDBere

Read the second sentence in the rule: The criterion of "adequacy" is not what the exhaust system consists of, but the sound level.

Fine, I have a muffler. It's usually called a catalytic converter but I call it a muffler. If the Event Chairman says it meets his sound restrictions then I'm OK to run my exhaust system with my muffler.

Erik Strelnicks won his SCCA SS National Championship in a Z06 with straight pipes that turned down to the ground...FWIW.

You run your muffler, I'll run mine. OK by me.

Dave OH32

I'm not sure how many other ways it can be said... Or how many times the entire rule needs to be posted for you to "get it"...But as Scott and Chris have already stated, repeatedly, Mufflers are not required in SCCA Solo, unless they are needed to meet a specific dB sound requirement. Period.

Bimota Guy

Dave, Now you have stated something that is not in the rule at all. There is no comment about specific dB readings, just what is clearly a judgement call by the Chair or designee as to the car being too loud. And if the first sentence is superceded by the second, then all that is required is "acceptable modifications", which may not necessarily be mufflers. So...

Let me try this approach. The rule is actually VERY poorly written. The first sentence says "...adequate mufflers are required..." It is unambiguous standing alone. Right? However, the second sentence clearly states "adequacy" applies to the "exhasut system." Where the heck does it say the car must have an "adequate exhaust system"? Not in 3.5. It reads "...adequate mufflers..." So maybe this is just classic poor SCCA rule writing. Seens it many times.

In any event, I still say modding your C5 Z06 exhaust is a waste of money unless you are looking for that last tenth or so.

freefall

For what you're saying to have merit, they would need to add a definition of "muffler" - Websters agrees with TedDBere: "a device to deaden noise; especially : one forming part of the exhaust system of an automotive vehicle"

Bimota Guy

Right, muffler being such an uncommon term the rules would require a definition. I suppose you want to argue over what the definition of "is" is.

TedDBere

It's easy to see why one might be led to think that a standard "muffler" would be required by reading the first sentence in 3.5 but, the term "adequate muffler" is attempted to be defined by the second sentence where it says "adequacy" is determined not by the components but rather by the sound level. Which, after all, is the purpose of a muffler.

I can tell you from experience there are some CSP Miatas that have higher db levels with mufflers than my car without, and they can't run at some venues that I can! It's not having the muffler that's important, it's the noise the car makes that's the issue. Particularly when dealing with neighbors around a site.

The acceptable sound levels in SCCA Solo are determined by the Event Chairman. In all the National Tours, ProSolo events and Championships the sound levels are posted in the supplemental rules as either "no sound restrictions" or an acceptable db limit, usually either 92db or 95db. Local regions will post their requirements for their venues in their local rules and regulations on their websites.

Some local regions post "mufflers required" or "muffled event", but as I've previously stated I've been allowed to run at some of these sites after the event chair has evaluated my car. By posting these requirements it gives the event chair the ability to toss excessively loud cars, ie FM.

There is a push to set national db limits in an attempt to perserve sites and level the playing field. FWIW. But at the present time, the way the rule reads, I can claim my straight pipes are mufflers (poorly baffled) since the word "muffler" is not defined. This is why the exhaust system from the cat back is free in SCCA autox as long as the system meets the sound requirements of the Event Chairman.

And you are correct, the advantage gained by using straight pipes is so small that it's a waste of money for most people. And you also lose the ability to drive the car on the streets due to the loud exhaust...it's a cop magnet! In my case, since I compete nationally, I will do just about anything, legally, to gain 6 inches on my competitors. Unfortunately it won't help me when I lose by 3 feet! Unless you are within 100ths of the top guys you'll never need anything more than the stock Ti exhaust system.

Have fun and good luck out there!

TedDBere

Just to complete this old post, the SCCA just amended the rules to the following per the November 2008 Fastrack:

The first sentence of 13.10.E will now read:

“E. Any part of the exhaust system beyond (downstream from) the header/manifold or catalytic converter, if so equipped, may be substituted or removed provided the system meets the requirements of 3.5 and 3.3.3.B.15.


BTW, section 3.3.3.B.15 says the exhaust must exit either to the side of the car or behind the driver.

Have a happy off season.

acrace

Chris:

See what you started