gnx7

iTrader: (28)

I have a fully forged dry sump 427 LS7 with WCCH ported heads/intake and upgraded cam 25x/25x with .650" lift on a 110+2LSA and hope to make 575rwhp n/a. I plan to spray a 100-150hp NX wet shot (shark nozzle).

I'm running 1 7/8" longtubes (JTR brand- specific for LSx/FD RX-7's) into 3" cats (hi flow) and then either dual 3" into an Xpipe and then dual 3" mandrel bent all the way back.... or.....

I have an HKS 4" titanium exhaust (muffler is Ti and piping is s/s): run a dual 3" with cats that merge into the single 4" exhaust.....

Which will make more power? Will there be more low end torque with the dual 3" due to the Xpipe? I know the 4" single will be a bit lighter....

Nasty N8

iTrader: (33)

use the single 4" will flow plenty just make sure the y-is built properly. we did dual 3 1/2" Y-pipe to a single 4" for our 800+rwhp blower car.

Nate

gnx7

iTrader: (28)

Can anyone else chime in?

I know that both can support the power levels I can achieve..... just wondering to see what the difference in power will be.... ie overall powerband

thingthatgoes

iTrader: (2)

I think this just might be the most basic inconclusive argument. I have a 3" to 4" back to duals. I think it's fine. I don't see how it could be restrictive at all.
I think this will be just like the "x pipe vs h pipe" discussion.

John B

iTrader: (10)

Personally I would run dual 3-1/2" pipes into an "X" and then 3" true duals. This will make the most power and the sound will be incredible!

ringram

Well 3" is 7.06sq inches area. 4" is 12.5sq inches. Finger around 112cfm per sq inch.
Dual 3 will flow 1581cfm and the 4" around 1400cfm. Not much in it.

They say allow 2.2cfm per engine BHP for optimal zero backpressure. The dual 3" should allow an extra 75bhp before losing some power to backpressue.

Personally Id go dual 3". You will lose a little due to the additional surface of the dual 3 to friction, but it should still edge ahead.

slick1851

True dauls with a x pipe....

I felt the gain with a bolton car over my Y pipe..

gnx7

iTrader: (28)

I think I'll be going with dual 3" as the sound is incredible from my previous setup (Magnalfows) on another LS1/FD. I'll save the 4" exhaust for a future turbo LSx build up.

Thanks for everyone's input.

Louie83

iTrader: (3)

Here is an interesting article you might find applicable: http://www.carcraft.com/techarticles...ion/index.html

We left the car at Magnaflow for about a week, and when we came back we found that after some preliminary testing, the guys had built a really trick system consisting of 2-½-inch tubing from the header collectors into the X-pipe, 3-inch out of the X flaring into 3½-inch tubing running for about 26 inches before necking back down into a pair of 3-inch mufflers with turn-downs. The theory behind this design is that it will keep the velocity of the exhaust gases moving quickly through the headers into the X-pipe to maximize the scavenging effect, while the larger-diameter tubing ahead of the mufflers prevents the gasses from stacking up as they pass through the mufflers to avoid excessive backpressure in the system.