2.5 to 3" downpipe upgrade - definitely an improvement

[turboglenn]

Well, for years i've been running a 2.5" mild steel Down pipe but as many of you probably have seen i've been working on a 3" unit from scraps and today i finally installed it as something to do to keep my mind off the fact that my father passed away yesterday. (been going nuts unless i keep busy)

Well after getting it in and going for a test ride there's a few things i definitely noticed.

1.) the spool up is much better, maybe not the initial first few PSI but once the turbo gets to where it starts to climb freely the needle flies up to the preset wastegate pressure.. It also was making 1.5 - 2psi more than what i previousely had the wastegate setup to run (well spiked it untill the EBC got control anyway)

2.) the power improvement was fairly dramatic, but at the 500hp range that's something i sort of expected, just not to this degree. Previusely the 67mm turbo was laggy to the point where third gear didn't really break the tires free and road them like my hard hitting 57 trim did (mainly because of the later torque peak) BUt een today which is fairly warm the tires screemed in agony and the needle raced towards 8500 RPM liek there was nothing holding it back

3.) recovery between gears is better as well

All in all 3 improvements i am happy to have and were well worth the 17 bucks i spent on new exhaust gaskets )and the time and argon iu put into making the pipe to begin with)

Another thing i noticed that isn't as good right now becuase i can't afford new injectors is the fact that at all higher boost levels the AFR's were almost a half point leanner than normal showing once again airflow has improved.. With the new 3" DP the car feels a LOT stronger at 27 psi than it did previousely pushing 29-30psi

Although i'm sure i'm probably one of the few that actually has this much of a setup/build and was still running a 2.5" down pipe, If there are any of you out there and you're pushingn anywhere near the 500HP mark on your vehicle i can say without a doubt that you should upgrade to a real 3"er as the results will be well; worth your time/money spent, I'ma frugal person (mostly out of neccessity) and i can say that this is somthing i wish i had done a long time ago!!

 

[gofer]

First and foremost, I'm sorry to hear about your father passing.

Thanks for the post, I've always wondered about my 2.5" to the flex dp was holding spool and flow up a bit. I might put this a bit farther up on the "to do" list now that I've read your post.

 

[turboglenn]

Gofer, Looking at your numbers (almost identical to my past numbers) I'd say you'd probably benefit from it for sure. I'm not sure so much about spool being that you're running the "16g on crack" , but to be hoenst i wish my old 57 trim was still in goos shape so i could go back and get a good "before and after" comparison. The main thing that made me want tp upgrade was that i went to the PTE6776rs turbo and there ahve been a few dissapointing things about it liek spool times. boost recovery, and the lack of an early "punch" from the torque coming on later on this setup. I would think that the bigger the turbo the bigger the effect this is going to have butthat's only my thoughts and i could be wrong.. just when i looked at the turbine wheel on my new turbo it was almost bigger than the 2.5" DP I had been runing and i felt it had to be a restriction, thanksfully i was right.. i wold have been rather upset to do all this labor, welding, test fitting and not to mention the cuts and bruises and hair fuill of oil-dry, had there been no gains anywhere

but being that you're flowing enough air to make almost 500 ponies i'd say you might pick up a little bit of power, and MAYBE (just my thoughts) be able to hold a little more boost till redline

_______________________________________________________________________

I should also add that aside from the DP its' self, the "test pipe' is 3", and i also removed the thremal cat-back, removed it's small section where it reduces to 2.5" and enlarged that to 3" as well making for a "true" 3'' turbo back exhaust.

 

[gofer]

I am running a cracked 16g but I don't hit full boost (29psi) until 4200 and I get surge at part/WOT throttle, I believe its because I have so much on the intake side and not enough on the exhaust. I'm also down to 24psi by 7.5k, so it drops boost significantly up into the higher portion of the RPM band.

Intake

- Speed Density
- 2.5" IC pipe on a VRSF core
- 1g N/T TB
- BJ SMIM
- FP2 cam​

Exhaust

- FP2 cam
- ported 2g exhaust manifold
- ported 7cm hotside
- PR ext. gated/dumped o2 housing
- 2.5" inlet and flex to 3" dp
- 3" test pipe
- 3" HKS hi power exhaust (with resonators removed to make a true 3")​

I just recently bought a FP race exhaust manifold and have been debating on dropping the downpipe and getting a 3" inlet/flex section welded in while I was at it. I think you convinced me, hopefully this improves spool 100 - 200 rpm (increasing tq) as well as letting the turbo spool up more efficiently so it holds boost further into the RPM band.

I'm at the limits of the turbo in terms of airflow but that doesn't mean I can't get it to hold boost better and spool faster while I've still got the stock 7 bolt bottom end under the hood.

 

[Boostinsideways]

Nicely done. I am sorry to hear about your father. My grandfather is currently having lots of health problems. He has been in and out of the hospital for weeks due to congestive heart failure.

Seems like that 3" exhaust is a pretty nice upgrade. I am not a very good welder and the best I could manage with mine is a 2.75" Inch flange that narrows slightly at the flex section, then opens up fully to a 3" just after the flex all the way to the cat back. No cat , just extended pipe.

I will be upgrading it soon, I used alumnized mild steel, and its starting to get surface rust. Figured I would thermal coat and sell it to get funds to have a true 3" fabed with some nice pie cuts.

 

[turboglenn]

Thanks for the thoughs on my father, it's a real bummer, and the rest of my family is making it even harder wanting to drag out the visit and mourning time by a whole freaking week when the services are only one day.. I'm like fawking god how long do i have to sit and have misery in my god damn face?

Anyway, just did some more test pulls and realized a few things.. power is up everywhere that i'm in boost as low as 10-12psi (it's torque steering and breaking tires loose in 2nd easily at mere 1/2 thorttle and less at low pressures) I'm also making more boost in first than i ever could before.. previousely 1st gear would see 8psi by redline, now i'm seeing about 15, spiking 31-32 in 2nd and holding a solid 28 the rest of the tim and a solid 28 in 3rd.. the AFR's have went from a solid 12.8:1 to 13.5-13.6:1 (deinfitely moving a lot more air than i thought from the first test spin)

power is phenomenal, this is what this turbo should feel like IMO (or to the best of my knowledge) BAd thing is the 13.5 AFR is still at 100% IDC so i need bigger iunjectors (like i hav emoney for that - NOT)

The car is a lot more streetable now, although it still takes a little more pedal input than the 57 did it's amazing how much i picked up just from making it a true 3" system (my wastegate is still dumped to the atmosphere)

one thing's for sure, wether i keep this thing or get the hx/hy-35 i really want, i feel some larger injectors are desperately needed at this point

 

[pboglio]

Interesting results, glad you showed an improvement. I also went from a 2.5" downpipe/3" catback to a straight 3" open dump downpipe. Car was at the time running about 402-406 w.h.p. or so. Other than being loud and obnoxius, not an ounce more power. I went back to a 2.5" downpipe cause it felt better off boost. Maybe dumping back into a full 3" catback exhaust would have shown gains.

 

[turboglenn]

pboglio, i wonder if it 's the turbo you're running? I didn't see it in your profile. Also like i mentioned the 3" doesn't seem to have benfits untill you're in the ~500hp range. From my readings i've found that on smaller turbos and lower HP builds (not that 340'ish is low) but in the same respect you can benefit from more back pressure. MY car is setup with NOTHING down low, everythig relies on boost, and my injector pulse, AFR's and size of injectors are showing in excess of 500hp so that's probably why it was such a notable differenc ein my car.. not saying it's best for eveyrone, jsut those in this range and possibly higher, or those shooting for these numbers. I agree that you'll get better off boost responce with a smaller exhaust / DP

 

[pboglio]

Hmm, I'd imagine if your running 500 w.h.p. then that is probably why it makes such a difference. I'm running an EVO3 16g. Good to know you improved with just that simple change.

 

[forcefed86]

Another way around a loud droaning 3" pipe (and what I wish I would have done) is mounting a small 32mm WG on the 2.5 DP. The small cheapo $60 ebay unit works great. Large pressure drops in the system can be had with a very small opeing.

Just an idea for some 2.5 guys. Small, boost activated, and reliable...

Also FWIW I tried open DP on my e316g and gained nothing VS full 2.5" exh sys with 3" dynaflow muffler. At 35+psi.

 

[goodbuds]

thx for the research Glenn.. i will be looking for a 3in dp, when i go hx40.

 

[PieEyedPiper]

Another way around a loud droaning 3" pipe (and what I wish I would have done) is mounting a small 32mm WG on the 2.5 DP. The small cheapo $60 ebay unit works great. Large pressure drops in the system can be had with a very small opeing.

Just an idea for some 2.5 guys. Small, boost activated, and reliable...

Also FWIW I tried open DP on my e316g and gained nothing VS full 2.5" exh sys with 3" dynaflow muffler. At 35+psi.

I think it's been long proven that open o2 provides the least performance. Your results are in line with this.

But it just seems so counter-intuitive..

 

[turboglenn]

well, being tha the day following the install i had to pack up and head for the east coast to attend my father's funeral i haven't had much wheel time wi th new exhaust. BUt today while running some errands (pharmacy and other places) i had some more time to play with the car and compare past resutlas to the current state.

Once again the improvements are fairly dramatic in my ownobservations anyway, as sated by forcefedan open dump w/g is help full but i have been running an open dumped 38mm tial for many many years and the improments were still quite large (still duping external also) I had planned to re-route it but due to time and otehr variables i deciedn to keep it open dump. The good part is the more boost i run the less noise it makes.

One thing rahter dissapointing about the new turbo setup in general is you don't get to hear than initial wind up ot the turbo durning take off, I"m not sure if it's because the BB unit is already spinning much faster than a J.B. counterpart of what but man what i wouldn't give for that good old holset whistle

OVerall, I'd say anyone in the 430+ range (with external dumped gate or not) would probably find a benefit to a larger DP (compared to a 2.5" one anyway) Although i am not to sure how large the gains would be on something smaller like a EIII16G, I'd say it's at least worth a shot if it's i the budget or somethign you can fab up yourself

 

[forcefed86]

Hmmm.... don't think I made myself clear on the external gate thing.

I'm not talking about dumping your actual WG to the atmosphere. I'm talking about installing a wastegate on your exhaust pipe post turbo to act as an exhaust cutout. Instead of using a standard electrical butterfly type cutout.

Shame about the silent turbo syndrome... That noise makes me smile evey time I drive! I'll even start out in second sometimes to load it up for some extra ear pleasing action!

You must be logged in to view this image or video.

 

[turboglenn]

Now that's an idea i hadn't thought about, and you're right, i didn't understand what you wre saying at all.. Kinda expensive form of a cutout for no bigger than it is, but reliable as hell i'm sure. If i go AWD the pull will be worht the silence, but if i din't i'm gonna tos an hx-35 on htere and let that bi*** whistle

 

[hurricanecris24]

So with my setup using the hx52 you think it would be wise to just get a side exhaust rather than get a fully custom 3in. downpipe with 3in.catback? i think cause it being a bigger turbo ill see more gains with the side exhaust

 

[turboglenn]

Yea, I think (from what i've read anyway) that with those kind of power levels you'd be better off with the side exit like many now do. Maybe a 3.5" dump (would look pimp as hell) or go 3.5 DP to a 3" cat-back and run a cut-out igf you choose

 

[forcefed86]

Now that's an idea i hadn't thought about, and you're right, i didn't understand what you wre saying at all.. Kinda expensive form of a cutout for no bigger than it is, but reliable as hell i'm sure. If i go AWD the pull will be worht the silence, but if i din't i'm gonna tos an hx-35 on htere and let that bi*** whistle

If you used one of the cheapo ebay units they are around $60 shipped. Thats about half the price of most cutouts. Even a small opening like 38mm would make a huge diff in back pressure. I believe I've seen 60mm units for around $80. They would be exposed to less heat post turbo as well. The small units are less bulky than most of the cutouts I've used. Makes for easier install.