This is the argument presented by my engine builder who builds Hot Rods for a living. I told him I would be using Hooker Long Tubes headers w/3" collector and Mufflex 4"Catback. He insists that no matter what size I use after 3" I'm not going to make any more power. It would be useless to increse catback size to anything larger than the collector. This guy works on heavily modded vehicles on a daily basis and tunes custom DFI. I kind of take his word as gospel so is he right or wrong? Why or why not?

 

3" bottleneck well before the cat...so why bother opening it up past that? dont get me wrong though, i wouldnt consider 3" much of a bottleneck.

 

I kinda agree. Although there are some dudes with engines the size of yours with 4" exhaust that are having good results. If u are looking for TQ I'd go with 3", for HP I'd go with 4".

------------------
89 RS

STILL Looking For:
An 87 IROC-Z28 350 TPI


[This message has been edited by IROCZTWENTYGR8 (edited August 13, 2001).]

 

The collectors are each 3" right, and then they would bottleneck down to one 3" intermediate pipe. The fact of the matter is however much air you get into the engine you need to get most if not all of it out. Now since you are using a 383" you have a lot more air flow than a 3" exhaust can handle expecially if you are making good power. If you dont mind shoehorning the 4" in there i would go with it, and since you can get a 4" y-pipe off the headers you can have a hugh exhaust which will function well for the larger engine

------------------
82 Z28 have LG4-305"
Rebuilt heads-3 angle valve job,ported and gasket matched. edelbrock performer, chevy 1.6:1 roller rockers,MSD6AL, rebuilt carb,15x4" K&N
3"flowmaster american thunder, Mac high flow cat,headman headers,
700-R4--B&M shift kit, B&M tranny cooler.
Sub-frame connectors, boxed lower control arms and torque arm. 1.5" front sway bar, new BFgoodrich radial T/A's--215/65 front 255/60 rear
RADIO-- premier Deh-p300
2-10"kicker SPLs,ZR240,premier 434x(4 way), custom built fiberglass box for subs. pioneer 6X9 & 4X6, grant GT steering wheel

 

3" collector to a 4"catback? with a Y pipe?
that makes 6" of exhaust right? i may not word it right, but if you have two 3" collectors going into a 4" exhaust, isnt that better than a 3" catback? why not run dual 3" all the way back? that is my next project in the long line of projects.
also, wouldnt system flow better through a 4" in 4" out muffler. THEY MAKE 4" IN/OUT DONT THEY???

http://people.ne.mediaone.net/gdm/

------------------
87 z28 bowtie aluminum 420small block dry sump crower lt. wt. knife edged crank oliver lt wt rods brodix track 1's super ram intake slp 1 3/4 headers accel dfi art carr 700 r4 3.42 gears ssm sub frame/ladder bars.....other parts on the way ,soon to be finished!! couple more weeks!!!