3.5" Downpipes and 3.5" Single Exhaust (SHO)

N

NITSOOB

New member
Hey, so finally heres my set up. 3.5" Downpipes, which neck down to 3" then 2.5" at the Y Pipe. Y Pipe is then 2.5" to 3.5". It does have a 2.5" choke at the merge, itll be cutout soon and replaced with a 3.5" oval to round transition

AR25 Resonators and 3.5" Borla XR1. All stainless, Tig, done by DMC Exhaust Fab Werks in Azusa CA

https://preprod.instagram.com/p/BVvuXYSAy1R/?taken-by=dmcexhaustwerks
https://preprod.instagram.com/p/BVvlCcsAtYA/?taken-by=dmcexhaustwerks (full throttle clip)
https://www.youtube.com/watch?v=7uuVxCF_fRY (inside cabin cruise clip)

Sound Impressions: With the OEM catted DPs, it was very very deep. Tons of deep drone at around 2-2.5k. With the 3.5" DPs its louder overall, but less deep and more throatier. Turbo whistle is loud as hell. Modified a cheapy Ebay 3.5" Silencer, to include a 2" to 3" cone; does its job and helps lower the sound overall

Butt Dyno: Definitely feels like it builds boost faster. Comparing to the stock DPs, this is about 3x more area, so the greater pressure differential the better after the discharge. Seems like BOVs open earlier and are louder too. Taking it to the track end of July..

Still on stock tune, stock everything else, except VTA.

(edit: added comment on silencer)
 
Nice custom setup there NITSOOB.  :thumb:
I'm sure a TUNE will wake her up and make it sound even better. Z




 
Looks good, great job on custom fab but just a heads up, you're only as good as the smallest pipe so you really have 2.5" downpipes, you can't flow more than the most restrictive portion of the downpipe/exhaust.
 
EcoPowerParts said:
Just a heads up, you're only as good as the smallest pipe so you really have 2.5" downpipes, you can't flow more than the most restrictive portion of the downpipe/exhaust.
Click to expand...

Sorta... but a counter point would be header merge collecrors. Some guys run as small as a 2.25" choke, while running 2" primaries. Yet these flow more than a collector with no choke, due to scavenging.

But in this application, yes, I want flow for a 2.5" pipe. In turbo applications, the exhaust out the discharge is turbulent and never lamimar until a few feet. You want the largest pressure differential possible(less pressure=faster spool), then neck it down to aid flow.

Granted, Im way over sized for my power, but its not hurting or adding much. The flanges are actually universal 3.5" 3 bolt, so it saved me some money vs custom.
 
I just don't want everyone to read into this scenario thinking it's a 3.5" downpipe and start asking for them. :) 2.5" is enough flow for 800HP, more than enough for our needs. :D
 
2.5" is more than suffiicient.. my set up at 3.5" single actually flows a hair less than dual 2.5". But less surface area so less friction.. theres a trade off.
 
I just about choked on my coffee when I saw the thread title.  This is almost the exact same thing I've been wanting to have done.  There's a fantastic fabrication shop in town that I've had look into the measurements, and after seeing your thread I'm sold!

I can really only speak for myself, and I don't think I'm alone in saying this, but the exhaust note our motor makes with dual 2.5" pipes.... leaves a lot to be desired.  Too much rasp, and not enough tone for my taste.  Not to mention the additional cost and weight of all that extra piping.  What's ironic is that the Z32 300zx community has a similar issue.  The VG30DETT which is also a twin turbo DOHC V6 like ours, ends up sounding...not great when piped with true duals.  Then some body got to thinking.  Why not run it GTR style?  They sound dramatically different.  The stock R35 GTR's run two downpipes into a Y-pipe then back into dual mufflers/resonators/outlets (because of the lack real estate under the car).  All the aftermarket companies that make a replacement exhaust keep this same style.  Now there are plenty of guys that go that route.  This car is one of the more well known examples of this:  https://www.youtube.com/watch?v=6Wti1yBhHyk

I don't claim to understand all the fine mechanics of how the sound waves, exhaust pulses, and resonances work to make the car sound so different, but it works.  Of course the downside being, there's no off-the-shelf option so it would have to be fabricated.  But thanks to your post, I've got all the motivation to go and have my downpipes and exhaust fabricated.  Great post man, and nice work! 

Now I'm just going to have to track down the lower bumper trim from a base Taurus that only has one exhaust outlet.  Hmmm
 
Mustang mufflers have made a nice upgrade for Gen 1/2 SHOs, might be worth considering if you can source from J/Ys.  GT, Cobra, etc that level of trim.
 
that's pretty cool however not a fan of the single tail pipe angled out like that. I would like to do the same single mid pipe for sound and maybe some performance too but would maintain my dual exit appearance.

what's really funny is to learn all that exhaust at one point is passing through the hole about the size of a quarter on each side lol

 
single exhaust SHO video clip

https://www.youtube.com/watch?v=-U2oYtP51fg

Robert Christopher Posey1 year ago

2 vibrant 2.5 inch to 3.5 inch merge collectors,  one vibrant 3.5 inch ultra quiet resonator 1 3.5 inch dynomax bullet

Robert Christopher Posey1 year ago

https://www.youtube.com/watch?v=_MZa2QY48XY

"It has some drone,  it was a little too much for the wife,  so I have modified it to tone it down.  I added 2 magnaflow magna pack mufflers right before the tips."

 
It sorta lingers after a few small revs at idle..Im used to it when warming up in the mornings, but never see it during the day. It does appear to be condensation, but a bit too much. Might be eating up coolant :(

Im only at 60k miles.

I did remove the y-pipe merge choke today, with a 3.5" oval section. Maybe the compression in the exhaust masked it? ugh..feeling paranoid.
 
It is rare that it is a coolant problem, in the SHO at that mileage anyway.  The cats treat the exhaust stream, and unavoidably, mask what is going on in the engine.  Most commonly it is a puff of blue rather than white smoke,, but the issue, some say, is a question of sufficient backpressure to maintain turbo seal integrity.  IDK.  Do you have access to a shop that can check the backpressures for you?  May want to check the piping at the turbos periodically as preventive maintenance. 
 
Apparently it happens to many vehicles after a downpipe install after a quick google search. But found this interesting..

There are various band aids like raising the idle which gives just enough relief in the system to allow oil to drain but eventually it will start to smoke again. I tried all kinds of "fixes" on my car and found the best hands down fix is a UPR Dual Valve Catch can and gutting the PCV valve. You need to gut the PCV and let the UPR DV setup take over the all the PCV duties for it to work properly. On my car not only did this 100% solve all the burning oil, smell, and carbon buildup all over the back of the car but I also have not had any more problems with heat melting the reflector and causing it to peel off the car and I noticed the paint is not yellowing around the exhaust either. Leads me to believe the recall for the excessive under body temps is because of the constant oil burning. Anyway I am curious to get my hands on the revised oil separator from ford and give it shot just to see what they changed and see if there is less oil in the catch can. At this point I drain about 1/4 cup of oil every 1000 miles. Hope this helps!
Click to expand...
https://www.svtperformance.com/forums/threads/aftermarket-downpipes-causing-smoke.1100422/

I recall reading someone advocating for this, but didnt have success with it. Or maybe didnt have the right catch can set up
 
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