CALL911

Ever since I got my car running recently (LT1 in sig), with its larger AFR 227 heads, it has surpassed loud and mean, and is now at deafaning, obnoxious, and race car sounding (not what I want). I'm not sure I really enjoy driving it around anymore. Yeah its fast, but at the decibals it is expending, I can't even go for a nice cruise without feeling rattled. And this is coming from a military guy with bad hearing who is around loud equipment all the time!

I currently run Kooks 1 7/8" headers, into an off road Y-pipe, into a Borla cat-back with the second largest exhaust plate installed. I could throw in the smaller plate, but with my supercharged setup, I am already getting so much exhaust back pressure that I am blowing off exhaust clamps as it is every time I take it out for a good romping.

Would changing the Borla for a GMMG quiet things down and still not restrict the flow? Or any other cat-back for that matter? Or is the only way to really quiet things down be to change my setup as far as the engine and blower?

slick1hunting

I may be way off base but it might be worth researching if a dual setup with good muffler on each side would give better results. A 3" would definately help with back presssure issues. I fabbed up a 3" dual setup with xpipe running under the axle(didnt have room above with the d-60 extra size. Then have a flowmaster 44 tilted behind the axle then exits in stock location with a double 3" tip on each side. The exit looks stockish and noise is considerably good in the cab with windows up. The flowmaster 44 is not the quiet version lol. My guess a similar setup with quieter mufflers may work good for you.


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CALL911

Well the problem is that is quite a change from my current exhaust. It would require a bit of fabrication and expense to "theoretically" quiet it down.

I need some kind of proof via another thread/link where someone has done this before in a boosted loud car so I know going through the process that it will fix my issue.

blkchevyz

with the borla you are pretty much just running a restricted down cut out you could throw a resonator into the stream... but what i'd do is go get the 4 inch mufflex system and be done

slick1hunting

^^^^^ thats the other route I would look. My dual setup cost $350 for the pipe(box of 3"stainless bends from flowmaster) $60 stainless xpipe and the two mufflers and clamps and hangers were $175-200ish. I had to have two ends flared but muffler shop did it for free. Then bought a bottle of tri mix gas and stainles wire to weld it up. Bassanni makes an over the axle kit for 1200. There are three four boosted guys who post alot in the main lt1 tech page may be worth finding and pming them. Two of them have supercharged in their screen name, one is a 95 and the other a 97. I would bet they would have some good ideas. I could never find were to buy the 4" system back when I was choosing what direction I was going to go. Personally with the power you should or could be making anything less than the dual 3 or the 4" is going to be getting packpressure restrictions.


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CALL911

I have three inch. Four inch Mufflex will undoubtingly be louder (NOT what I am looking for).

I have the second largest plate in the Borla right now, so almost all the exhaust is straight out the back (not through the muffler). I'm gonna put a smaller plate in it and see how it does.

slick1hunting

I think most of your sound will be based upon the muffler design. I personally wouldnt want a restricted exhaust either for several reasons. Talk to a couple performance muffler shops and see what they would recomend. If you look at the sticky in this forum section you will see the 3" is a restriction at like 380 fwhp. In my opinion restriction in a boosted setup will add alot of heat as well as rob power. I actually question how much noise your sc and bigger heads would add to the noise level over my motor as we have the same headers. My car was one loud mother with open pipes. I even question if a severe restriction may add to interior noise. I really would look at the difference in muffler designs and get rid of some of the restrictions. I would bet you may have extra noise in exhaust leaks unless your welded at most of your connections. I do agree a bigger chamber will increase noise but it may also put more of it behind the car. My guess is a muffler shop could custom you something cheaper and quieter and pick you up some power if you go to 4" or dual 3" or some freaky combo of each.


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CALL911

Well if you are questioning how much extra noise is from the SC and new larger heads, the answer I have. Because I ran the car for years on the supercharger with the smaller heads and it was MUCH quieter. The larger heads move a lot more air. This is without a doubt the single reason it is louder.

Now, I'm not claiming Borla has the quietest muffler, but 90% of my exhaust isn't currently going through the muffler. That's why I'm going to try the smaller plate when I get the chance and see how it sounds and see if it pulls back the power first before I just start throwing money at it with various different mufflers.

blkchevyz

the 4 inch mufflex would be loud, but i bet it would be quieter than the borla, since all the exhaust is going through the muffler. i just dont really think your going to quiet it down much without killing power. if you want to try doing a cheap route first, put the full block off plate in the borla, then get a resonator or a bullet type muffler and put it in your intermediate pipe.

i've had just about every type of exhaust on mine, mac, flowmaster, just a cut out, dual cut outs in the y-pipe, then to 4 inch mufflex, after that went to true duals with bullet mufflers(way to loud) switched out the mufflers to flowmaster 1 chamber race ones....
the duals with the flowmasters sounded good, but was a little loud still. the mufflex i think was the best sounded i've had hence now i'm going back to a 4 inch setup with my turbo.

CALL911

Well, we will see how the plate works and go from there.

Injuneer

The 4" Mufflex is available with either a FlowMaster 30-series race muffler (single in/single out) = loud, or a much quieter Spintech single in/dual out muffler.

I had the Flowmaster and it was not deafening, except at about 2,500 RPM where it picked up a nasty resonance. I have ridden in a 99 SS with a Spintech, belonging to the owner of Mufflex, and it was throaty but not loud..... and they have run comparisons of 1/4-mile times with the FlowMaster and the Spintech, and have not found significant differences.

CALL911

I have the single in dual out Magnaflow muffler on my Formula. It's not bad, but I'm not pushing a fraction of the air I am in my Z through it.

For factual comparisons, I would really need to know how loud/quiet it would be in a similar supercharged big head setup that I have. Or a supercharged setup with someone who has what I have exhaust wise that changed it to something quieter.

slick1hunting

I will say it one more time lol the muffler selection will make the biggest impact. Most "cat back setups" are for power gains and a performance sound. To help picture it imagine a pipe within a pipe. It will quiet it some but is about not restricting flow. Now imagine a case with an inlet pipe and a maze that exhaust must travel through three pipes. Each pass quiets the exhaust. A straight through design will never even compare. An xpipe also will quiet things down. This is why I suggest going to a performance oreinted muffler shop because they will be familiar with sizes available in muffler that will perform best at meeting your needs as well as if any other "tricks" can be used. Very few of us on here have made quiet a priority for our cars we are usually looking for a good sound and better performance. I still think the bigger heads with greater noise may be a partial product of the restictive exhaust. The reason I say that is take a small straw and blow or suck through it then take one you can blow freely through. The free flowing one is quieter because of less turbulence and load on the "engine". Yes a bigger pipe does echo or amplify sound but I believe that 3" single pipe you are running has you so restricted that it makes it comparable. The way it looks to me is you are nearly twice the power level were the 3" single becomes a restriction. I believe if you get rid of as much restriction as possible and choose a muffler design that is intended to quiet the noise and add anything else that may soften the noise in your exhaust configuration you will get the closest to what you seek. After that some noise deadening material in key locations of car would also help. Would be great to have unlimited funds to try things and see what truly works the best . Good luck.


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CALL911

And again I shall say it was an enjoyable sound before I changed the heads (and that's all I changed). Now its WAY too loud. A true dual setup or x pipe I agree would potentially quiet it down and not restrict the flow, but AGAIN, right now very VERY little exhaust is actually going through my existing muffler.

A smaller plate would force more to go through the muffler. As it sits, I am at 695 RWHP. I really don't think the car will turn into a turd by putting a smaller plate in to see how much quieter it will be with more exhaust actually going through the single most quieting part of the whole car.

If I find its still too loud, or at that point it is too restrictive, I can further look at other options (the cheapest and easiest being a different muffler).

This will sound silly to some, but to change up the exhaust that drastically will without a doubt be fairly costly. My supercharger setup, with the expensive tensioner, ceramic coated Kooks long tubes, and everything else is actually worth quite a bit of money. Even though it would be much more labor and time intensive, I would probably break even to maybe even be ahead of the game if I sold the supercharger setup and went with a turbo (which would be more efficient, and quiet, all while making the same if not more power).

Nothing will be done, until I at least send the exhaust I have through my existing muffler on a much greater scale than I am currently.

slick1hunting

from my understanding a turbo setup will need the less restrictive exhaust even more than the sc and the heat of such a tiny exhaust will start giving you big problems. If you have a couple exhaust shops look at it and give you some quotes its still free at that point and will give you some good options. You may be surprised at how good of price some shops will give vs a catback. Even if you go muffler only at this point you could get inlet exit sized to accomodate future changes. Given you decide you will change the exhaust. I just cant help but think how restrictive your exhaust is and exhaust is a supporting mod for various reasons. I am familiar with what the restricted exhaust does in turbo setups and its not good. I also know that a jake brake is very loud and its from restricting exhaust and thats why I feel your restriction may be a part of the equation.


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