what makes more sense?
 

Im wondering what would make more horsepower: my mac midlength headers running down into the mac y-pipe then into my high flow cat and having the outlet on the cat disconnected so the exhaust vents out after the cat OR hooking an slp loudmouth (cuz thats the kind of cat back i want) up to the cat and utilizing the cat back. the slp claims a good hp bump but that is over stock of course so it stands to reason that no restriction at all (not using a cat back) would make more power. i actually am not using my cat back now since the connecting flange that bolts to the cat broke (i think its a magnaflow, i dont know cuz it came w/the car and its unlabeled). im not worried about noise since it isnt that loud right now anyway and im not concerned with the emissions test since i can just hook up the cat back again. so, what should make more power?
oh and to all the smart asses (everyone), i dont care if open long tubes would make more power!!!

You will make more power overall without the catback, although we are talking about maybe 2-3 hp difference total. But !catback is weight reduction, so that's a savings too.

- Justin

!cat-back will drop 60-75lbs normally.
i would go with the !cat and a normal cat back. it is less likely to attract attention from the po-po i fhe sees a muffler or at least tips sticking out the back than nothing.
the cat itself is also the big restriction in the exhaust stream. ditching that will easily add twice as much power as jsut dropping the cat back, especially after you get teh computer tuned for !cat.

Loudmouth only weighs ~20lbs, doesn't it? James?

- Justin

Don't know what would make more power between adding header or dropping the exhaust. I will tell you when I installed the macs on my 93 with the stock cat back there was a noticable improvement. When I went with the cat back there was only a slight improvement. So I think headers will give you more gains then a cat back will.

i was thinking of just keeping the headers, ypipe and cat and not hooking it up again but now im thinking of replacing the cat with a straight pipe and running it into a loudmouth after i go through inspection. does anyone know who makes a prefabbed straight pipe or will i have to have one made up?

If you have an aftermarket cat that is a true 3" inlet/outlet, then it's not costing you any real power at all(maybe 2-3 hp). The stock cat-back and muffler will cost 10-15 hp easily since it necks down to 2-1/2". But if you have an aftermarket cat-back then it's probably a real 3" cat-back and not costing much power at all. The Loudmouth sounds like crap on an LT1 car but it will make the most power since there is no restriction. The aftermarket cat-back exhausts don't weigh as much as the factory because they are thinner metal. Are you looking for the loudest, most obnoxious exhaust or are you looking for the best power combination? You don't want to run !cat with a Loudmouth.

hippie

SLP loudmouth vs edlebrock cat back..... I lost 20 lbs just by switching to loudmouth :)

i've read dozens of articles (taken with a grain of salt, natch) regarding a true 3" straight back, including catalytic converter and muffler. power was actually lost by leaving out components than by having the whole system connected correctly, OEM style. now, that's 3" all the way back (for the short bus people) from the header collector to the tailpipe, with no bottlenecks at all (all of the components were 3" in, 3" out, all pipe 3" OD). of course, if you are going to run true dual, then you'll need two cats and two mufflers.

LT1s are no different. this applies to all chevy small blocks. now, collector length is another story...

yeah, some people have said that i would be losing some low end torque as well if i just cut the system off after the catcon. i guess ill just keep the catcon, get a loudmouth and see what it sounds like. yes i like it loud! if its not loud enough maybe ill replace the cat with a straight pipe....

I remember when Randy had a straight pipe and loudmouth on his '93 'bird. Sounded great, but he couldn't stand the drone on the highway and the attention from the cops, so he swapped the loudmouth with a 3" spintech system. He still had stock exhaust manifolds and y-pipe.

- Justin

a stock cat robs waaayyyyyy more than 2-3hp. jsut look at the results from ditching a cat, people pick up a full mph or more of trap speed without any tunign or anything. i picked up 1.5mph through teh traps in my 91 with no other changes.
with tuning the difference becomes even greater.
go !cat and don't look back. you will see an immediate and very noticeable power increase and improved fuel economy.

Amen on the fuel economy

An aftermarket true 3" in/out cat will make almost the same power as no cat. The stock cat is not 3" in/out and even the Random Tech cat is not a true 3" in/out. The muffler costs way more power than a cat. I put a true 3" cat on my old Pace Car with the Borla y-pipe and it made a noticeable difference. I would have never passed emissions without the cat on that car.

i have macs 2.5in ypipe w/3in collector and their 3in high flow cat. i really dont mind highway drone since i have my radio up anyways!

Explain to me how this: http://www.magnaflow.com/images/mufflercutout.jpg

robs more power than this: http://www.car-sound.com/04converter/converter.jpg

There's a lot of science involved in exhaust systems so it can't be fully explained. But I've seen tests done on a 67 Firebird with a 455 and putting dual cats on only hurt the 1/4 mile time by .1 while the dual mufflers hurt by .27. A cat is not attempting to quite the noise so the exhaust flows straight through while the catalyst does its job. A muffler is basically an expansion chamber that allows the exhaust and noise to expand and that's what starts to hurt the flow as it's funneled back into the outlet pipe. I was at the Englisthown show one year and the guy next to me had dual cats on his 86 Camaro and no mufflers and it sounded great. He was running the Edelbrock EFI system on a built 383. He said he could feel the power loss with the mufflers on it so he removed them since the exhaust sound wasn't that loud with the dual cats alone. Removing the cat is only necessary if you plan to lean out the mixture so the engine is on the ragged edge of a meltdown. You'll make an extra 5 hp but you'll blow the motor in short time so why would you do it?

The cat vs muffler argument can vary greatly based on what type of muffler we are talking about. There are many different styles, and some will hurt flow way more than others.

- Justin

IMO, I would get the headers first. This is where much of power can be freed up. Stock exhaust manifolds are unevenly joined at the collectors causing for disruption of flow. With the headers in place, the flow of exhaust is evened out. If the headers are coated, that will cut down on engine bay heat thus causing better engine performance. Moreover, since the headers are mandrel bent, this does not cause for exhaust turbulence which can cause for an even bigger loss of horsepower. As for cat or !cat... if you switch to a "high flow" cat or stay stock, your not going to see that big of a difference. However if you do i-pipe and muffler work, it will help the overall aspiration of the engine. For the 5.7L LT1's, I would do a single 3'' I pipe (mandrel bent) into a _________ muffler (don't know much about them there fancy mufflers, you'll have to do the research yourself. Though, I never had a problem w/ my 80 series flowmaster).