2.5 exhaust vs 3 inch for my setup?

[Jayme]

Yes, I searched.

I currently have 3 in mak cat deletes, 2.5 in lethal x pipe and 2.5 pipe to GT500 axleback. My plan is to convert to a 3 in x pipe, 3 in pipe to 3 in mufflers. I have a GT350 manifold and tb that spins to 7800rpm. Would the 3 in benefit me at this point? I also wonder at what point the GT500 axleback is a restriction?

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[DrDane]

Im debating a similar thing, with a little different setup. Im putting a paxton with the 3.33 pulley and plan on running higher boost perhaps 12-14lbs on e85, through a holley sniper manifold. Long tubes going into x pipe then necking down to straight pipes (SLP loudmouth), debating if I should just put an MBRP or some other 3" cat back in place to have some mufflers but minimize the back pressure with 3" system rather than one that necks down.

I'd think the setup you are describing what you have should be fine as you are below a GT500 power level, you may have very modest change up top 1-2hp? maybe, but not worth scrapping everything. I'm just concerned for me how much does it matter in the 700+ levels

 

[jasonstang]

3 inch is said to be the sweet spot for exhaust. Bigger you losing scavenge effect. Smaller, you have restriction.

 

[dubster99]

Unless you are going boosted, you won't see much difference if any at all.

 

[Jay-rod427]

2.5 is plenty for N/A.

 

[daltron]

The stock headers would still be a restriction. I wouldn't worry about it for NA, do the MAK cat deletes as the cats are a huge restriction and be done with it.

 

[4V Mayhem]

LOL, 2.5 inches is for manufacturers. 3 inches is for those of us who wanna play. Open that bad boy up and let it pass some gas...lol!!

 

[P51DNA]

Waste of money imo

 

[Terminator2]

Yes, I searched.

I currently have 3 in mak cat deletes, 2.5 in lethal x pipe and 2.5 pipe to GT500 axleback. My plan is to convert to a 3 in x pipe, 3 in pipe to 3 in mufflers. I have a GT350 manifold and tb that spins to 7800rpm. Would the 3 in benefit me at this point? I also wonder at what point the GT500 axleback is a restriction?

Wouldn't bother with full 3" unless you are planning on FI or an all out NA build (I'm talking 600 crank hp). I'd add 1 7/8" headers though and maybe go to a straight through mufflers.

 

[Jay-rod427]

LOL, 2.5 inches is for manufacturers. 3 inches is for those of us who wanna play. Open that bad boy up and let it pass some gas...lol!!

Those who wanna play with less torque, and gain zero horsepower:doh:

 

[Jayme]

Those who wanna play with less torque, and gain zero horsepower:doh:

So Corsa, Magnaflow and the other 3" catbacks out there lose torque?

 

[NightmareMoon]

Those who wanna play with less torque, and gain zero horsepower:doh:

This. Going too large has real downsides. Pick a diameter that is correctly sized to your power goals.

 

[Terminator2]

So Corsa, Magnaflow and the other 3" catbacks out there lose torque?

I doubt you will see any losses but rather lack of gains vs dual 2.5" until you reach a certain power level which I'd estimate around 600hp before dual 3" shows any gains vs 2.5".

 

[JaxS550]

3" Cat-Backs don't have a negative effect as the stock headers and cats are restrictive enough to keep the stock tune. The 3" CB is actually more for the type of sound you are after. Exhaust gases and sound waves will travel at different pressure/speeds in 3" vs 2.5" and those guys know this when designing a CB system.

With that being said, the new 5.0 engine is on the edge of HP levels where 3" losing torque really doesn't come into play as it moves quite a bit of air. It doesn't take FI to see benefits from a full 3" system and headers. (hence why people gain HP/TQ when adding headers). Although the tune being required when headers are added is what makes up for that additional flow of exhaust gases.
With the combination of pretty much every guy/gal running an H or X pipe, with most also running some type of muffler (even if straight thru) it controls the back pressure enough to not see that drop in TQ.

There was a full video on youtube regarding the advantages/disadvantages of running 3" vs 2.5" on modern engines with an actual dyno comparison between a few systems. Gave a full break down on how 99% of the time 3" systems show gains over 2.5"

Older engines making quite a bit less ponies and moving less air are where you may see a drop in TQ depending on the overall set up.

People need to remember that 435HP (yes I know at the crank) is a really impressive number when you look back at where we came from. The holy grail of amazing mustangs, the terminator, made 390/390 stock WITH a blower on it. Our NA 5.0s are making 45/10 more without the blower.
1995 GTs only made 215/285...

My point is the argument of losing HP/TQ going to 3" is in my opinion BS with these newer cars.

 

[4V Mayhem]

Those who wanna play with less torque, and gain zero horsepower:doh:

Whenever you wanna test that theory is fine with me...

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