I have a 99 SS with the stock 3" dual SLP exhaust and im looking to take it off and replace it with a Flowmaster 80's series. Ive heard a lot about the performance catalytic converters and im not convinced if there the way to go or actually how much better they are than the stock ones. Yet i dont know if i should just have a pipe put in place of them because im not sure what that will do to the car. Im looking to gain a big difference in sound and hoping that without putting headers on this will do it for me. If anyone knows anything about the cats or if thats the best muffer for sound let me know which way i should go without spening a ton of money. thanks

 

one of the best mufflers is the dual/dual, from in the sense that it is a good muffler. the difference in a cutout to D/D would be maybe 5 hp, not noticable. Like I said, the D/D is an excellent muffler, and is pretty quiet, which i like b/c of the convertible. Flowmaster is also nicknamed flow-crapper or flowcrapster because they dont sound hte best, they dont do much muffling, and it increases exhaust popping. The best sound and flow in most everyone's opinion is an SLP loudmouth or dualed 3" pipes that dump after 2 dynomax bullets.

Now deleting your cats will make any exhaust louder, and headers will increase the loudness as well.

With me having the slp D/D I sometimes wish mine was a little louder, but then again, when i have the top down, and am cruising around, I really enjoy a quiet car thats just as fast as the loud ones.. makes it a bit more of a sleeper to the ricers that know nothing about f bodies too.

 

Yeah, that's exactly right. I dynoed mine with the cut out open and picked up that number.

BTW, modern cats are pretty efficient. If it is illegal to not have cats in your state, it probably isn't worth the risk to pick up only a couple of hp.

 

Highflow cats are better than stock, with exception of the bullet styles.
Stock passenger's side cat (the least restictive out of the 2):
299.5 CFM @20.4" H20 and 350.9 CFM @ 28" H2O

Compared to a carsound/magnaflow that you can get off ebauy for under $60/ea:
372.7 CFM@ 20.4 and 436.7 CFM@ 28"

Notice the carsound flows more at low pressure than the better flowing stock cat can at high pressure. Bullet cats flow less, so leave them for the riceboys.

http://installuniversity.com/install...sity/index.htm
Look under library, then converters.

Going from stock cats to !cats you'll pick up from 8-10 hp. The difference between !cats and high flow cats is ~2 hp. Of couse this totally depends on the set up, but since you mention you don't have headers I'm guessing you're not very modded so it should be near 2 HP.

Now for Blowmasters. You're going to lose some hp and tq by going from the great flowing dual/dual muffler to a relatively restictive FM. Plus if you do go !cats it'll become quite raspy.

You want more sound w/out spending a ton of $$$ or picking up too much rasp? Slap a bullet or twister muffler in the I and a cutout after it. This is basically a dynomouth set up with the option of further silencing. This way you'll actually GAIN some power and you can cork it back up when you get tired of it. Bullett is ~$30, cut out ~$50 and welding shouldn't be anymore than $50. Now if you want to go electric cutout, you'll pay more.

 

By the way Magnaflow is comming out with a new line of catalytic converters that flow around 600CFM each. These will get the job done.