Exhaust question.

[Brendan19]

Hey guys,

As we speak my nsx is getting a custom exhaust fabricated, I have had many discussions with the guy relating to sound, flow design etc. and we have decided to go for a 2.5inch pipes but using only 1 3.0" cat instead of the 2, has anyone tried this before, if so how did you find it?

Thanks.

 

[davidf]

Do you guys down under emissions test? It's a cool theory to have just one cat but it's not a guarantee to pass the sniffer. I'd like to see the exhaust once complete.

 

[RYU]

What's the proposed exhaust layout?

I've gone thru several renditions of layout designs so i'm guessing you're going to Y into this single 3" then what?

The bigger the pipe the better the flow but also will tend to sound raspy.

 

[Brendan19]

Yeah doin the Y, then straight into a 3" pipe + 100cel cat, then into the muffler which splits inside, I managed to get a couple of photos today.

 

[RYU]

This goes w/o saying but you're going to be replacing those OEM manifolds right?

Also, do you plan to keep your engine stock or are you installing Forced Induction? If NA your piping is on the "too big" side of things.

I didn't realize you're almost done with the fab work. Might be too late to go back but expect some rasp with that setup but the flowmaster should tone that down some. Otherwise, clean and simple. I like it.

 

[Brendan19]

Yes, will be replacing the oem manifold early next year, just dont have the extra money lying around atm to do it all in one go. Wont be going FI, sticking to n/a I am no exhaust expert but I just assumed that because both exits from the manifold are joining up 3" would be fine, but we'll see how it goes.

Tuning of the sound is happening today, so i guess ill find out how it sounds tomorrow, hopefully not to raspy.

 

[davidf]

Well the sound will change entirely when you install headers. For the better of course. Start saving $$ because you won't get the real affect of that nice exhaust until those manifolds are gone. Nice project.:wink:

 

[RYU]

2.5" is a bit big for NA. You not only want more flow but you want high velocity as well and when it's too big you lose the velocity and increase weight. You're best off keeping it at 2-2.25" for each bank. It will improve your sound quality also. I don't want to be a Debbie Downer since it looks like it's already done so you can tune down the rasp by adding resonators before the Cat if you can fit them. If it's not too late my recommendation is to step down to 2"-2.25" leading into the 3" cat. Though, the Cat + the baffled Flowmaster muffer might reduce a lot of that rasp to a point you're happy with it :smile:

I went with 2.5" into an X-pipe on a more complicated valvetronic design and when the valves are it's wide open at WOT it's loud, obnoxious, and a bit raspy but its also at full power due to there being no restriction whatsover. Almost a give-and-take so you may have to make some sacrifices given your goals. I'm also FI.

Good luck! I love DIY solutions!!

 

[davidf]

RYU, are those cats or resonators? I hope we get to hear that thing at some point.:wink:

2.5" is a bit big for NA. You not only want more flow but you want high velocity as well and when it's too big you lose the velocity and increase weight. You're best off keeping it at 2-2.25" for each bank. It will improve your sound quality also. I don't want to be a Debbie Downer since it looks like it's already done so you can tune down the rasp by adding resonators before the Cat if you can fit them. If it's not too late my recommendation is to step down to 2"-2.25" leading into the 3" cat. Though, the Cat + the baffled Flowmaster muffer might reduce a lot of that rasp to a point you're happy with it :smile:

I went with 2.5" into an X-pipe on a more complicated valvetronic design and when the valves are it's wide open at WOT it's loud, obnoxious, and a bit raspy but its also at full power due to there being no restriction whatsover. Almost a give-and-take so you may have to make some sacrifices given your goals. I'm also FI.

Good luck! I love DIY solutions!!

 

[dawk]

2.5" is a bit big for NA. You not only want more flow but you want high velocity as well and when it's too big you lose the velocity and increase weight. You're best off keeping it at 2-2.25" for each bank. It will improve your sound quality also. I don't want to be a Debbie Downer since it looks like it's already done so you can tune down the rasp by adding resonators before the Cat if you can fit them. If it's not too late my recommendation is to step down to 2"-2.25" leading into the 3" cat. Though, the Cat + the baffled Flowmaster muffer might reduce a lot of that rasp to a point you're happy with it :smile:

I went with 2.5" into an X-pipe on a more complicated valvetronic design and when the valves are it's wide open at WOT it's loud, obnoxious, and a bit raspy but its also at full power due to there being no restriction whatsover. Almost a give-and-take so you may have to make some sacrifices given your goals. I'm also FI.

Good luck! I love DIY solutions!!

Exhaust looks great! Nice fab work!

 

[RYU]

RYU, are those cats or resonators? I hope we get to hear that thing at some point.:wink:

The small oval round things? Those are CA smog legal cats. Sounds pretty great from inside the cabin but my brother said it's nasty when it's wide open. That's a good and bad thing depending on who's following me haha. There's a local cruise coming up in Oct i'll slap on the GoPro.

I uploaded a pretty rough vid here. This was when the vacuum valves where hooked up to intake vacuum. This means as they approach 3inches of vacuum they start to open automatically and when boost hits they're wide open. I did 3 back-to-back passes here just for kicks (wasn't intending to post it up!). 1st pass was low throttle input (valves closed). 2nd pass was WOT (valves open). 3rd pass moderate throttle (valves closed to partially open).
<iframe width="560" height="315" src="http://www.youtube.com/embed/jYKNzmgUi8w" frameborder="0" allowfullscreen></iframe>
The vid doesn't capture the full sound. At WOT it's raspier in person and a lot more obnoxious. While at low to moderate throttle it's a much deeper rumble almost hardly audible but you can feel it (listen at 1min 26secs). I love it but of course i'm biased

BTW.. I noticed my AFR leaning out by .2-.5 points. I also feel the difference in power all around. Need to get this puppy on the dyno soon.

Exhaust looks great! Nice fab work!

Thanks! I have Efren Built to thank for the fab work. I'm just the mad scientist.

 

[davidf]

Lower RPM's is very similiar to a Supra IMO. I mean that in a very good way.:wink:

 

[TURBO2GO]

Ryu I like it.

 

[RYU]

Lower RPM's is very similiar to a Supra IMO. I mean that in a very good way.:wink:

Ryu I like it.

Thanks guys :redface:

One of these days I hope to take better sound clips from a halfway decent camera.

Happy to pass on what i've learned if anyone is going thru such a project.

 

[Brendan19]

Ok so the exhaust is finished and i picked up the car a few days ago. here are some pics:

Unfortunately it is going to have to go back next month for some more sound tuning as the end result was quit drony, and lacked the note once vtec kicked in, between 3-5k rpm it sound great but either side it either gets a bit drony or loses the note.

 

[RYU]

How does he plan to remove the drone?