Right now I have a custom exhaust, its a 2.5 inch True duel, has an x-pipe and 4 resonators, no mufflers.

My issue is that some people have been telling me that 2.5 inch is too big, and that im losing some power. and that if I drop it to a 2.25 inch and replace two of the resonators with a single duel muffler that ill pick up some more power.

right now I have no issues about the sound, and it sounds sick with my nismo headers.
but what do you guys think I should do? Leave the current set-up or go with the new set-up.

Current set-up (2.5 inch Piping):


Possible New set-up (2.25 inch Piping):

thanks!

 

i dont think you lose any power having your exhaust too large.. i have a 3" topspeed exhaust (which probably doesnt make any power) but I doubt I lose thatt much power.. everyone runs 2.5" systems and gain power

 

oh Im also considering High-flow cats or test pipes, and I do not want the sound level to increase if I swtich to high-flows or test pipies. or not increase that much.

 

you most definately can lose power if the diameter of the piping is too large. it decreses backpressure (some of which is needed, especially in a n/a) and you will actually lose hp.
now 2.5" i dont consider big, and the hp loss would probably be minimal, however for example if a stock honda civic ran a 4" straight-pipe(like 850hp supras do) then it would probably result in a decrease in 10-12 hp.

 

does any one else have any input?

 

ur ok with what u have.. it actually seems like a pretty sweet setup..

 

I think the problem is that our drivers side tip sticks out further than the passenger side.


No but really, you may lose some low end power with a dual 2.5" on the NA 3.5L engine. Get a tune and you will make some of that power back up. The reason for this, well, clockwo12k hit it right on the head. An NA engine needs some back pressure to help scavenge the exhaust gasses from the other cylinders. Once you go FI this goes right out the window and you can go just about as big as you want (pressure differential around turbine).

 

2.5 inch piping is more than fine for NA.

Why not replace two resonators with mufflers?

.

 

Twin001, thanks for the input! I have osiris reflash, so I hope once I get the eTuning back ill pickup more horsies.

Skaterbasist, I was thinking of replace them with mufflers, but what would that do for the sound/power? I really doing have any clips under load, but it sounds sick as of right now.

 

Stick with the 2.5". You are definitely making more power up top and the x-pipe helps you from losing too much back pressure. Does it drone at all?

I would think if you switched to test pipes it would drone like crazy.

 

This has nothing to do with back pressure. Back pressure is never a good thing and it does not produce power, torque, etc. The key to the correct exhaust design is keeping up exhaust velocity. If you make the exhaust piping too large, you kill exhaust velocity because the large piping allows the exhaust gases to cool and become turbulent in the pipes. Keep the heat up and keep the velocity high and you'll make power. IMO, 2.5 dual piping is way more pipe then these NA motors need. The OEM exhaust is nearly 2.5" and that's pretty large for NA seeing that a 3" single exhaust flow enough air for a modded 350whp LS1 motor. I think you're on the right track with going with smaller piping. I'd even suggest considering 2" piping.

 

ok thanks for the input guys.

and yes it does drone some untill 3k.

 

i wouldnt do anything until you dyno'd stock vs new...check the numbers first to see if you're truely loosing power, it will be more informative and probably cost you less than building a whole other exhaust, just try to keep the dyno conditions as close as possible.

aside from having no true mufflers and only resonators, you're exhaust is very similar to other off the shelf designs when it comes to piping diameter. i'll agree with some of the comments above because yes 2.5 is more than enough to suppport 500+hp and yes velocity is important. i think what you have is fine.

adding test pipes or high flow cats will add/change volume so if you go that route you may want to replace 2 of the resonators with maybe a round magnaflow muffler to bring things back to an appeasing sound.

 

well said, but i would say to a certain degree back pressure and engine responsiveness go hand in hand.

 

the right amount of back pressure is a good thing. Zero back pressure(especially on a n/a motor, or most motors making <600hp A.K.A. not all out fully-built dragsters) causes an actual loss in HP.

Please get ASE certified or at least do a little research before responding plz.