3" exhaust gains

[pboglio]

I finally got around to datalogging my car with my 3" Thermal catback vs. my old 2.36" greddy catback. I picked up a solid ~1.5-2 lb/min in airflow across the board just from the catback switch at the exact same boost settings and outside temps. I went from a peak of 33.5 lb/min on the Greddy to 35.0 lb/min on the 3" Thermal @ 19 psi dropping to 17 psi near redline, ~65*F temps in both cases.

I previously ran the Greddy 2.36" catback exhaust with 23 psi and race gas (same day as the 19 psi run) and got about 35.5 lb/min. So the 3" Thermal catback allowed me to drop my boost 3-4 psi, run 93 octane pump gas, and still flow about the same. I'd like to next drop in my 3" downpipe/test and log it to see the gains over my 2.5" downpipe/testpipe. I'm hoping this will promote a little boost creep.

 

[doug]

Solid info, dude. This is the kind of real data I like to see, and I've actually been a 2.5" exhaust supporter. But with good numbers like this, I can probably be convinced otherwise. Keep us updated after the downpipe install.

 

[pboglio]

Yeah, my opinion only, but I'd have to say there is really no advantage to a 2.5" exhaust, UNLESS you are boost creeping. I modified my thermal to be almost as quiet as my Greddy exhaust. I've already run a 2.5" exhaust (Buschur), 2.36" exhaust (Greddy), and now the 3" Thermal. The power difference is pretty noticeable between them. The 3" exhaust makes the engine hit like nitrous when you come on boost. Since I don't have boost creep, but rather boost drop off, I'd love to open up the exhaust some more by dropping in the 3" downpipe over my 2.5".

At the point I'm at right now, most of my gains in horsepower are coming from removing exhaust restrictions. I can't do anything about my restrictive turbine housing and wheel, but I can still make gains after that on the exhaust side.

 

[ivanr4g63]

You see thats awesome info, thanks for taking the time and posting this for everyone to compare.

And it makes perfect sense. The more restrictions you have you loose power, I have had a chance to drive a bone stock turbo car Vs the same car with open exhaust (no exhaust at all after the 02 housing) and the gains are amazing, obviously we had boost spike by doing this, but managed to control that and still the gains are simply jaw droping, eversince all I want is a 3" turboback exhaust. Though here's a very important matter, the bigger you go the louder it gets, and cops dont seem to like that, thats why we end up buying quieter exhausts... quieter meaning restrictive... restrictive meaning less efficeient, but unless you find a good way to quiet down your exhaust on the street I personally recomend going with bigger free flowing exhaust all the way.

 

[pboglio]

I think a savy guy can make a 3" exhaust fairly quiet, just takes some determination. When I first put on my modified 3" Thermal catback with 2.5"downpipe/testpipe I was like"Damn, this thing is too quiet, was looking forward to scaring people with my exhaust." The 3" pipes tend to drone even with generous muffler volume and midpipe resonators/mufflers added in, but that is the only drawback on my car. Only drones at exactly 3000 rpm though.

Got pulled over a few times for speeding and the cops never ever mentioned my exhaust, so I think thats a good "litmus" test that this baby is quiet. I can tell they wanna say something about it, since visually the tip is like 5" in diameter, but they really can't since the thing is whisper quiet during cruise and idle. WOT is fairly loud if the windows are down, but reasonably quiet with the windows up. I don't know, I never notice the exhaust noise of the 3" catback. I can still hear my damned lifter tick, injectors clicking away, cam snarl, airfilter/intake/turbo sucking noise and all the rest over my exhaust when I go WOT.

 

[beat90tsi]

I hear you on the volume. I am running the VRS TBE w/O2 elim. It was a little too much at WOT, so I had the local Meineke weld in an 18" long 3" resonator, which took out the WOT blaaat, and the circa 3000rpm resonance, but didn't affect the tone much otherwise. It has always been fairly quiet at idle, but the resonator really helped keep it less obnoxious when in boost.

I have found the right foot to be the best volume control for my 3" exhaust.

But that is all off-topic. Great post, I'm glad to see some hard data, that is awesome.
If you're trying to creep, run a full 3" and an Evo 3 16g.

 

[tighty]

Thats why you go with a 3" cutout...maximum flow, and silence when necessary...=).

 

[Mirage1]

pboglio, you don't have any of your mods listed in your profile. For the record, what turbo are you using in this test?

 

[CanadianTSi]

Have you tried making your wastegate arm shorter so it will hold the wastegate shut tigther so it won't blow open and cause you to loose boost?

 

[beat90tsi]

I put some washers behind the mounting points on my WG actuator to pre-load it, and it helped spool, but I doubt it would help hold it shut at high boost much. It's the same spring, you can take out some slack, but that probably won't keep it from blowing open.

 

[SethA]

Have you tried making your wastegate arm shorter so it will hold the wastegate shut tigther so it won't blow open and cause you to loose boost?

Wouldn't a shorter wastegate arm let it open easier? I would think a longer arm would give the actuator a larger lever arm to hold the flapper shut. Is it that the shorter arm wouldn't let the flapper open as far and therefore hold more boost at high RPMs?

Seth

 

[guitarXgeek]

Wouldn't a shorter wastegate arm let it open easier? I would think a longer arm would give the actuator a larger lever arm to hold the flapper shut. Is it that the shorter arm wouldn't let the flapper open as far and therefore hold more boost at high RPMs?

Seth

A shorter arm = more preload on the wastegate spring which means the wastegate flapper will be held shut with more force. This is the reasoning behind adjustable wastegate arms - they allow you to shorten/lengthen the arm to effectively raise/lower boost.

 

[UPGRADED2G]

Wouldn't a shorter wastegate arm let it open easier? I would think a longer arm would give the actuator a larger lever arm to hold the flapper shut. Is it that the shorter arm wouldn't let the flapper open as far and therefore hold more boost at high RPMs?

Seth

Negative. the shorter the arm, the tighter the flapper is held against the wastegate hole on the turbine housing.....keeping it shut (which should prevent it from blowing open before the acquired level of boost). I have tried lengthening and shortening the rod on my turbo. By lengthening it, my turbo did not build any boost at all. It is now as short as i can phisically get it and I still have slow spool (please rule out every other test....I've tried). My actuator is faulty (opens prematurely, bleeding out air before i hit full boost).

Thank god for my warranty. New actuator on the way.

 

[UPGRADED2G]

sorry guitarXgeek, didnt see your clarification.

 

[pboglio]

Mirage1:

I'm running a FPT28/28 (small T28), full exhaust port work, 1g tbody, 23"x10"x2.75"FMIC, HKS 264/264 cams, 2.5" dpipe/3" catback, 660cc inj, 150 lph fuel pump, DSMLINK, etc, etc. Turbo is max flow rated 37-38 lb/min @ 21 psi. I'm running 19 psi dropping to 17 psi with 35 lb/min compressor flow.

CanadianTSi:

I'm running the FP 17 psi adjustable wastegate actuator. I've already preloaded it quite a bit already, though I could crank it a bit more. With my electronic boost controller turned off, I get about 16-17 psi in the midrange, dropping off to say 15 psi near redline. One theory is that cranking the rod tighter just drives up my entire boost curve, so I'd hit say 20 psi in the midrange but drop to 17 psi near redline, which is what happens now when I turn the boost up via my boost controller.

My HKS EVC can handle boost spikes pretty darned good, but wastegate valve blow open seems to be confusing it. It must be throwing off its feedback control sensing somehow. I'm certain I'm not running out of compressor, because I'm flowing 3 lb/min below my turbos max limit. I physically can run 20 psi to redline, but I then get 23-24 psi in the midrange, which is too much boost on pump gas. I think there is a preload that would stop the valve from lifting and would give me a static/constant boost level across the entire rpm band, although I think that static boost value would be higher than 21 psi. I'll have to experiment, thanks for reminding me.

 

[CanadianTSi]

I assumed you were running a 16g style turbo, so the boost falling off makes more sense with a smaller turbo.