Hi all

I am thinking of getting rid of my stock exhaust pipe from headers, cat, back to the muffler

I have a L69 305 H.O. engine, cc Quadrajet (E4ME) with following modifications:

Quadrajet rebuild, DR & K Hangers & Rods

Edelbrock Performer Intake (2101? EGR Deleted..)

Cam 208/210@.050, cam lift .299"/.300", L/C 112° (Lobe Center Angle, not LSA)

Hedman Hedders Street Headers 68470
Primary Tube 1 5/8 to 3" Collector to 2.5" Y-Pipe to Stock Pipe and Stock Cat

AEM Wideband LSU 4.9 to controll, heated Narrowband for computer (check with ALDL & Laptop)

Flowmaster 80 Muffler



I know, currently the stock cat will be the restricting part, but when I replace it, I thought it would be a good time to swap the stock pipe asewell.

Some people stated that 3" will be a too big diameter and will lower the performance overall..

what do you think? have you made any experiences with 2.5" and 3" single pipe differences ? Do you whink 3" is too big for a 305 ?


Thanks

 

The complete 3in exhaust system IMO is one of the most sought after first mods there is for a 5.0 and 5.7 both.

If your going to be replacing the system then installing the 3in on a 5.0 is considered prepping the car for a larger engine.

 

I will stay with the L69 as I swapped from LG4 to L69, as its rather hard to get a cheap and good 350 or bigger engine here in europe.
So with this you would also do a 3" exhaust pipe? I heard the difference on a friends car. sounds awesome.. but I dont know how backpressure will act together with the engine.

 

you'll be fine.
now if you were doing true dual exhaust with 3" on a 305, that would be considered too big.

 

My 83 305 G20 Van had 2.25" pipes off the stock manifolds and a 3" exhaust after the factory Y pipe. It always ran great.

DR rods and a K hanger was stock. I swapped in a F hanger to richen up the transition to the secondaries.

LSA and LCA can be the same thing if your cam is straight up. 112* ICL and 112* ECL would give a 112* LSA.

The cam I put in my 83 305 was 204/214 @ .050, .422/.444" lift, 112*LSA and 107* ICL. With the stock flattop pistons, 14022601 heads and performer RPM intake it was fun to drive for a 305.

My 1997 Express van with the 255 hp L31 350 vortec came from the factory with dual 3" pipes that bumped up from 2.5 off the manifolds, massive 3" cats and dual exhaust pipes into the factory muffler. From there the restrictive trash can sized muffler choked it into a single 2.75" tailpipe. There was a substantial performance difference swapping to a dual 3" in, single 3.5" out magnafliw with a mandrel bent 3.5" diesel tailpipe.

 

My LB9 loves my SLP 3" 2OTL catback. I actually plan on upgrading from a single at to the factory N10 dual cat setup when I go ProCharger so I can run two 3" Catco high flows cats instead of just one like now.

Because of scavenging, most people consider a single 3" to even be better than a dual 2.5"

 

Dual 2.25" ~ Single 3" and Dual 2.5" ~ Single 3.5"

 

GM choked a lot of power out of the LG4 and TBI cars by using a 2.25" exhaust instead of a 3" one - something on the order of close to 30hp there alone.

I've done 2 LG4 cars with full 3" exhaust and both responded by dropping more than a second of their 1/4 mile times, which is a testament of how much GM choked out of them with a too-small pipe.

 

Every 3rd gen ive had has had the cat pulled and 3 in exhaust ran. Easy 25hp gain! These cars were severely choked by the factory.

 

I have the ebay OBX Stainless cat back( no cat obviously) 3 in system. Its pretty nice in my opinion. Idle after muffler break in is decent, not really loud, but you can hear it. and the pull though gears, and down shifting sounds amazing. Here's a clip. Pass it around! By the way, its a 3 inch set up, with the intermediate pipe 3 inches, tail pipes 2.5 and the tips are 3.5. Its pretty good looking as well. Heres a pic and a clip.


Also, this clip is with the 305, I now have a l31 350 Vortec, and the sound is even better