camz28arro

iTrader: (12)

I had a custom Y-pipe made up for my car with a flowmaster Y yesterday and the rasp from my Mac headers and Mac Y (with cats) is gone but I noticed when Larry from Kooks cut my old y-pipe out that the pipe going from the merge to my muffler is only 2 3/4 in. outter diameter plus the pipe from the Y was shrunk at the end to fit in the 2 3/4 pipe to have something to weld to.

My dyno graph stopped climbing fast at around 5000rpm 350rwhp/360rwtq and I was wondering if you guys think this is where the HP is hiding. Thanks.

hitmanws6

iTrader: (20)

yes it is. the stock pipe diameter maxes out at 310. 3 inch piping maxes out at 370. i would go with TDs or up the pipe diameter

camz28arro

iTrader: (12)

Thanks hitman, so I'll have a 3 inch put in from the y-collector to the muffler. That should be enough even after my 243 heads (11.0-1 comp) and ported TB right? Maybe 410rwhp. Thanks.

Siciliano15

iTrader: (7)

i did the same thing u did except i have the ory. it made a big difference for my top end that i could easily feel. also sounds a little better too.

RevGTO

iTrader: (12)

It amazes me that so many systems with dual 3'' pipes in the Y neck down to a single 2.75". What's the benefit of all that big flow if you choke it off a couple of feet back?

camz28arro

iTrader: (12)

Yea, My neighbor who bought the car new said he put an exhaust on and I saw the crappy welds from wherever he went and it looked like a 3 inch pipe so I never thought he would have only did a axle back exhaust. I can't believe that!

I had full bolt on's and a 224 cam going through the stock exhuast pipe. At least my next 20hp is only going to cost me $100.

Siciliano15

iTrader: (7)

they are made to be plug and play with the stock or most aftermarket catbacks so thats why they exit in the stock 2.75" size. but yea swapping the y-pipe makes a huge difference.

RevGTO

iTrader: (12)

I know that, but then why the 3" tubing on the Y? 2.5" would be more than enough if you're going to go down to a single 2.75" anyway.