Few questions..

Which has better performance gains?

And which is louder?

I have bbk long tube headers, bbk off road H, bbk cold air kit, and a 75mm throttle. and 40 series single chambers right now..

 

Performance wise i would have to say SLP. Its straight thru. Its pretty much a glasspack. The flowmaster is a chambered muffler, so it has baffles in it that block it from going to the other side. Think of it like a maze inside your muffler.

SLP is alot louder than Flowmaster..

 

+1, the SLPs are louder and would allow for a better flow of exhaust. Getting tired of the flows?

 

but lm1s also sound like chit with ur current setup. either go with lm2s or just keep what u have

 

lm1s are louder and would "flow" better.

if it actually sounds good, that would be up too you.

 

i have bbk long tubes and an off road h and had slp1's on it but it was way too loud for everyday driving. especially 15 miles to work each way. if it's a weekend car go for it. it sounds ridiculously nasty when you get on it. by the way i swapped out to 40 series flows and it just seems way too quiet now shoulda went with something more aggressive

 

You shouldn't be worried about minimal if any performance gains via your cat-back.

Pick what sound you like best.

 

You can't really compare the two. They are different like stated above. If you want to compare SLP LM1's to anything flowmaster, it should be the outlaw mufflers.
http://www.flowmastermufflers.com/outlaw.html

 

lol i agree that lm1's are louder and allow for a better exhaust flow.

also lm2's will be great like stated above.

 

i vote for the lm 2's