Anyone running straight cat converters on their C4???

[3DFLYER]

I have a 1991 Roadster and wondered if anyone is running just cats, no mufflers???

Pros & Cons???

Tom

 

[TAC]

My TT has no mufflers...just a Rand Tech cat. The y-pipe w/precats was changed to one with no precats. The car was loud before the cat and precats were modified. I almost jumped out of my seat the first time I heard it start with the new cat. The bark was deeper in tone and a little louder. I don't even try to play the stereo when driving. The car is pretty loud...not that I would change it though.

 

[TAC]

Hey Tom! I just noticed it was you. It was good meeting you last night. Hope to see you on your trip back home.

 

[3DFLYER]

Hey Tim!!

You were right, this is a much better forum !!

Yeah, that's what I am afraid of! I don't want it to be that loud, so I hope the '91 I am picking up has a quieter set up.

I will contact you when I have this beast.

Tom

 

[poorboys831]

Hi 3d,My '93 has no mufflers.I think it sounds great and don't have a problem hearing the stereo.It is loud at wot but calms down at cruising speeds.As a matter of fact my next door neighbor,who happens to be a cop,tells me my c5 with Borlas used to make his front door rattle when I started it up but he hardly notices the c4 -I really think he doesn't use his ear protectors when he target practices so he probably has hearing loss anyway Dennis

 

[Redbob]

I have a 1991 Roadster and wondered if anyone is running just cats, no mufflers???

Pros & Cons???

Tom

The only problem you might have is that your '91 doesn't have a mass-airflow meter, and won't be able to compensate for the significantly increased airflow when you've taken off the mufflers.
It may well run very lean, leaner than is ideal for max power.
You'll be able to tell by looking at the plugs if you do a high-speed chop.
Or by the fact it feels like it's falling on its face when you stomp it!

 

[RubyDropTop]

What do you guys think of a chambered exhaust system? This system has no resonator nor any mufflers - only chambers in those areas.

Any thoughts/comments?

 

[Redbob]

It'll be LOUD!
Unbearably loud.
Window-rattling, neighbor-annoying, wife-riling loud!

Loud enough to announce your arrival to cops for blocks.

But if that's what you want...

 

[RubyDropTop]

Hmmm...part of me hopes that it's not overbearing as you state. The reason I ask is that I just had a chambered system installed on my car (the one in Mid-America) and the problem is that we have had such poor weather I cannot take the car out and listen to it on the road under throttle.

I have heard it idle (that sounds fantastic) and rev (that sounds great too) but I am concerned about interior resonance. A friend of mine has the same system on his '94 convertible, and after taking a ride in his, I wonder if I should pack Excedrin for a headache everytime I get behind the wheel?

Time will tell, I guess.

 

[dmrodco]

If your worried about resonance buy some dynamat . Its work fantastic as asound insulator. It is expensive but worth it. crutchfield has it and most high end audio retailers sell it as well.
See ya.

 

[RubyDropTop]

Would the proper installation of dynamat require removal of the carpet? How expensive is it to install in a car (average cost)?

 

[Redbob]

In all seriousness, you could alwys get a set of those noise-cancelling headphones. Bose and others make fairly effective sets, available by mail-order and a gadget places like Brookstone.

I've used them, they work well against the very low frequencies that will be present in your car.

A principal reason for the "boominess" in C4's (and C5 fastbacks) is that there are exhaust pipes that have acoustic resonances that coincide with acoustic standing waves in the cabin.
That is, one of the resonant frequencies of the pipe is the same as one of the resonant frequencies of the cabin, and the pipe resonance "drives" the cabin resonance.

One analogy is a kid swinging on a swing: if you're pushing at exactly the same rate he is swinging, he'll swing higher and higher. If you were to map out his swinging on a piece of graph paper vs time, you'd see a nice sine wave, looking like a sound wave, with peaks and valleys corresponding to height of the forward and backward swing. (see the picture)

A muffler in the exhaust system robs acoustic energy; in the swingset analogy, it's as if something were holding you back, preventing you from pushing the kid very hard, so that friction (damping losses in your exhaust) prevented him from swinging very high.

The resonators aren't very effective mufflers, although they're better than nothing! so you'll hear a bit of noise inside.

Your best bet if it's more than you care for is to use a cross-over pipe just ahead of the rear axle.

Regards,
Robert

 

[dmrodco]

Dynamat

Yes the dyna mat would stick directly to the floor of the car then the carpet underlayment then the carpet. I have hear of amazing results with this product. It will kill any resonance. Good luck:Twist

 

[Redbob]

If you want to try the Dynamat stuff, put it primarily in the rear luggage area and backwall of a coupe. Putting it under the seats and in the footwell area would be a waste.
The noise you'll be dealing with is coming from the tailpipes.

But then, I think a great deal of it will be structure-borne as well, and my previous experience with dynamat-like materials indicates you won't see much if any improvement.

But I've been wrong before...

Regards,
- R

 

[oldace84]

Who the the heck would run without mufflers??????
tony

 

[RubyDropTop]

Many people do; they put "muffler eliminator" pipes in their place. Check out the aftermarket catalogs (Mid-America Direct, Eckler's, etc.) and they should be in there.

Who the the heck would run without mufflers??????
tony

 

[Redbob]

Who? indeed...

 

[RocketSled]

Who the the heck would run without mufflers??????
tony

Me (although to be honest, there isn't really ANY exhaust system on the car just now. Just headers, offroad pipe and resonator tips while testing the car.)

Unfortunately, the starter didn't like the headers, and the tranny didn't like the motor, so now the car's just sittin' while I earn a little cash.

 

[3DFLYER]

Mufflers?

I am going to pick my Vette up on the 19th and drive it back up to the NW. My brother in law has compared it to another fella's Vette with a stock muffler system and there was only a minor difference in the DB levels between the two Vette's.

I realize if you get on the throttle your gonna hear it, but my main concern was being able to hear your passenger while cruising. This does NOT seem to be a problem.

I am told that the stock mufflers are pretty weak anyway.

Thanks for your thoughts, I still want to hear from others without mufflers.

Tom

 

[Da Hawaiian Punch]

HE,HE,HE! I'm not only running with no muffler's, but gutted cats also, all 3 cat's. It's sound's gooood!!