Doug G

A good point was brought up.... what size exhaust you run ?

2.5" Flowmaster American Thunder system here.

I guess I'm restricted ?

speedtigger

iTrader: (16)

Weld in some cut outs. Then you will know for sure what there is to gain.

newschool72

iTrader: (12)

Doug, that is your restriction, Id bet money. The Flowmasters are the most restrictive LOUD mufflers on the planet! In a 2 1/2 " system, you will need a very free flowing muffler to get all you can from your combo. I swapped from Pypes street Flow mufflers to the same companies Race Flows. My combo use to nose over at 6200rpms, now I cant get the gears changed fast enough to stay off the 7000rpm limiter! The only things I have done to address that is the mufflers and added a few more holes in my fuel bucket in the gas tank. Im not sure if both made the difference, or which, but the car is a different animal now! I think the Race Flows are about 70 bucks a pop from Summit. Id go straight to them ,if I was you. They are a straight through muffler, but are very quiet at cruise and idle. They blast wide open when you slam the loud pedal !

ZONES89RS

iTrader: (25)

3" X pipe with 6" bullet race mufflers.(don't know how much muffling is going on)

cruisin'73

iTrader: (8)

Specs.
-Carb'd 5.3, TOTALLY stock (for now)
-Ebay 4th gen SS headers, 1 3/4" Primary, 3" collector
-Dual 3" pipes, all mandrel
-No X or H function
-Thrush welded mufflers
-Turndown dumps at the axle

Verdict: The sound is spot on IMO. Mellow with a slight lump at idle, a good burble at cruise that just gets louder. At wot it has a nice rip that is just enough to rattle your ears but no awful "rapping". Dumping under the car does lead to reverberation and drone that is unfavorable but livable.

The whole sysem is oversized, and I belive it does negatively affect torque production. But the system is what I could piece together from mail order parts for a good price. AND I have plenty of room for future HP growth on the current 5.3 or a healthy 450HP'ish 6.0.

My $.02 contribution.

snook

iTrader: (1)

Aerochambers here, mild cruising, fairly loud at wot



Ive got a stainless set ill sell for 125 bucks plus shipping, usually one stainless muffler is 150 or so. They are 3 inch, offset inlet/offset outlet I believe, ill have to check

Doug G

OK.... As for the Flowmasters and my old combo (406ci SBC) Same system, untouched.
I had a muffler and tailpipe come off at the track one time. It was easier to remove the other one instead of trying to put the one back on.
Less than .1 mph and less than .1 ET difference...was running just the H-pipe.
I know a lot of people call them "Slowmasters"... But I haven't seen it.....now this would be a good excuse to go 3" though ....more OT I guess LOL

newschool72

iTrader: (12)

The Flowmasters are proven to be restrictive in independent testing, but your story is interesting. Something else is interesting too. The LSX is running almost identical to the 406 ! Could it be that the exhaust system you have will only allow enough exhaust flow to go 11.3x with your drive train combo? If the engine hits a wall, the max flow the exhaust will allow, does it make sense that it could hold both engines back at a given RWHP level? The 406 might have been getting all it needed, so the exhaust falling off didn't make a difference. The LS might need more flow to go to the next level.
I am a master at coming up with plausible excuses to make the wife let me do things to the ol hot rod. Doug, you are more than welcome to use the one above to explain the NEED for a new exhaust system. Hehe

snook

iTrader: (1)

I thought it was flowbastards

Doug G

May have to use that one LOL

I know the LSx liked the better timing...lower shift points...and has more breathing ability than the ol'406 did too.

Looking at 3" kits now..... Knew I should of got the 3" back when I bought this kit.

6D9

iTrader: (1)

I did some back to back testing 2.5" vs 3" on my old 408 sbc. Old set up was 2.5" mandrel x pipe/40 series flows/2.5" mandrel tails. Larger set up was 3" mandrel x pipe/Hooker aerochambers/3" mandrel tail pipes. Both set ups ran the same. Both went 11.8 at 115. Just my experience. This was a mild 408 sbc/small flat tappet cam/dual plane/3.50 gear.

toxic99

I say throw some 3 inch torque tubes on it wide open and see how it runs. If you like the straight through design mufflers, aka loud as hell, and you're worried about weight, take a look at the vibrant aluminum 3" bullet style mufflers. That's what I'm getting for my 67. 2 lbs ea hehe.

3pedals

iTrader: (3)

I'm getting old enough that loud is not my style for cruising, but I want all my motor has to give at the track ....
If I was in your shoes Doug, I'd keep your 2.5" full exhaust, but I would put in some 3" cutouts past the collector, and make sure there was at least 12 or so inches of the 3" before the cutout to act as collector extensions.
Just uncork it at the track , but quiet for the street.

fast89stang

iTrader: (2)

mines not built for the neighbors. 1 7/8 headers in to 3 inch collectors, bullets bolted straight to the muffler. Anti roll has no room for tails, although I have thought about installing some quiet exhaust, just to be fun.

Doug G

the old 406" SBC

the LSx 366"....sounds tamer....but has a bigger bite

331camaro

iTrader: (1)

id say thats perfect. i doubt you would gain much with cutouts. deff wont feel it by the seat of your pants. electronic cut outs would be cool for cruise nights n stuff for when you want it to be obnoxious for a few seconds