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#106
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Actually the flowmaster 80 muffler is about half the size of the stock SVX muffler, and it's thinner so it would be farther up against the body
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bLAh
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#107
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Back pressure in the exhaust never helps power. It always hurts, because it increases the mass of the products of combustion that remain within the cylinder when the exhaust valve closes. Tuned exhaust systems typically help within a narrow rpm range. When the exhaust valve opens there is an increase in pressure as the exhaust gases enter the header. That pulse will flow down the header and after it passes there is a period of minimum pressure before it bounces back again. The pressure wave travels back and forth along the length of the header pipe. If the next opening of the exhaust valve coincides with a minimum of the oscillating pressure at the entrance to the header, there will be a greater pressure differential between cylinder and header improving the exhaust gas exit from the cylinder.
The tuned exhausts on kart engines don't actually cause exhaust gases to re-enter the cylinder from the exhaust header. Instead the exhaust port is uncovered by the piston on the power stroke before the intake port. The exhaust gases rush out at a high velocity followed by some of the intake charge which is being pushed into the cylinder from the crankcase by the downward movement of the piston. Some of the intake charge actually goes out the exhaust port. The reflected exhaust pressure wave actually forces much of that escaping intake charge back in the cyclinder. Since the time between the opening and closing of the intake port is entirely a function of the engine rpm, and the time it takes the pressure wave to reflect back is primarily a function of the length of the exhaust chamber, the exhaust can be tuned to maximize power only over a very narrow rpm range. In a 4 stroke engine, most of the tuned pressure wave reflection effect will occur in the header. The idea here is to time the pressure wave returning to the entrance of the header when the exhaust valve is closed, rather than when it is open. High performance header design seeks to avoid combining pipes from cylinders such that the reflected pressure wave from one cyclinder bounces back to another cyclinder when that exhaust valve is open. Once again, the effect will be limited to a narrow rpm range, usually near the peak power point. By the time the exhaust gases mix with the pipes from the other cylinders and hit the pre-cats and, it's all over. The whole intent from the pre-cats back is to avoid back-pressure. I really don't think X-pipes that are downstream of cats do much to help engine power, except possibly to equalize the modulating flow in the two pipes to decrease pressure drop. I think they're mostly about customizing the exhaust system sound.
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____________________________________________ 95 LS-i Red, 31,xxx; bone stock for now; Daily Driver 94 LS-i Emerald Pearl, 106,xxx,; 246 whp; Tomyx snorkus and HKS Cold air intake; PWR aluminum radiator, silicone hoses; Inline thermostat; enhanced coolant routing; external power steering and oil coolers; Phenolic intake manifold spacers; 2004 WRX 5 speed transmission; ACT Clutch Kit, Heavy Duty Pressure Plate, Lightweight flywheel, performance disc; Group N motor mounts; ‘07 WRX 4-pot front calipers, cryo-treated slotted Tribeca rotors; Hawk HPS ferro-carbon pads; Frozenrotor rear slotted rotors; SS brake lines, Axxis Ultimate pads; Rota Torque 17x8 wheels; 245/40-17 Bridgestone RE01-R's; Koni inserts with Ground Control coilovers, Eibach springs; K-Mac camber/caster adjustable strut mounts; Urethane swaybar bushings; Bontrager rear sway bar; Urethane differential bushing; Custom Whiteline adjustable rear lateral links; Outlaw Engineering forged underdrive pulley; custom grind Web intake and exhaust cams (11 mm lift, 250° duration); solid lifters; CP custom aluminum forged 11 to 1 pistons, Brian Crower coated SS intake & exhaust valves; Brian Crower upgraded springs w/ titanium retainers; NGK sparkplugs; RallyBob (Bob Legere) ported and polished cylinder heads; Eagle H-beam rods; ACL Bearings; Cometic Head gaskets; ARP head studs & fasteners; Hydra Nemesis EMS; Wideband O2 sensor; 740cc Injectors; Walbro 255lph fuel pump; Upgraded WRX starter; Equal length SS headers (3 into 1); dual Magnaflow cat converters; 2 into 1 into 2 SS exhaust with Bullet muffler; OT Fiberglass hood; Oil pressure gauge; Programmable shift light, 2017 Subaru Forester XT, metallic dark gray, 29,xxx 2005 Porsche 911 Turbo S Cabrio, 24,xxx 2006 Subaru Outback LL Bean, 166,xxx sold 92 LSL Dark Teal, Smallcar Shift Kit - sold Last edited by shotgunslade; 10-07-2007 at 03:37 PM. |
#108
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It does however even out the powerband and make flat spots somewhat less noticable. NA Subie engines do tend to run better with some backpressure. I was talking with OT the other day about longer headers being a power source (yeah this is coming from the one who likes his 5.5 foot long unequal length 6 into 1). Look at motorcycles that are tuned for performance. There is very little in the way of back pressure and they make the header as long as humanly possible so they can still get the needed sound deadening device on it so that it doesn't stick out beyond the rear end. Most performance bikes do suffer from very uneven power maps that you can feel easily due to the weight to power ratio. My guess is this has something to do with the free flow exhaust.
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#109
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ohh wait.. the lack of driveshaft might not have helped either
forgot all about that... still, with stock heads it should still need at least a little right?
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-Mike ECUTune2v7 - 4.11 5 Speed - Sprung 6 Puck Clutch - D&S Rotors - SS Brake & Clutch Lines - HKS Panel Filter - HeaderBack Exhaust -80GB Hard Drive - GroupN Engine Mounts - - some other "tricks"
[SIGPIC][/SIGPIC] In progess: track down mystery noise <-identified, paint the new dash, get better pic Spring plans: Replace Trans - Integrate ECU with the carputer - Suspension - Go back to STI Filter - Paint? Maybe not - Next Oil change: Purolator L30165 Member #995 | My Locker | My New Locker Catch you next at: ? Auto-X ? |
#110
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I can't wait to hear the various custom exhausts at Cumberland this month, I'm **hopefully** getting mine done Monday.
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bLAh
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#111
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I think a lot of people are getting confused with the term back pressure. Here is my take on the subject. A good short primary equal length header will make more difference in power,than any other part of the exhaust. Why, because as the exhaust pulse is not flat. It leads with a higher pressure than ambient(positive pressure), and tails off with a pressure lower than ambient(vacuum). Now when a header is installed, it tunes the exhaust pulses so that the tail end of one cylinder pulse(vacume) actually pulls the high pressure pulse(positive pressure) from the next cylinder with it, like the - and + poles on a magnet. This is effective because the header keeps the pulses in sync, and keeps a pulse from one cylinder from backing into the next cylinder like a manifold does. Why do auto manufactures use a manifold then over a header? Because its cheep, and easy.
Now, about the rest of the exhaust. Back pressure will not make more power under any circumstance on a 4stroke motor. This does not mean that the bigger the pipe the better. Think about this. Cold air is alot heaver and denser than hot air, and therefore harder to move. The key to a good exhaust system is to keep the exhaust gas as hot as possible the whole way down the pipe with the least amount of turbulence from bends and diameter changes. How do we do this? By selecting a pipe diameter that is large enough to not cause restrictions, but small enough to keep the gases moving quickly, and with the least amount of turbulence from bends. As for resonators and mufflers. They dont do much for power, unless you are replacing a restrictive one with less restriction. There main function is simply to quiet the exhaust note. I see a lot of people focus on magnaflow mufflers here, but I think more people should take a look at Flowmaster and Walker mufflers. They are dyno proven many times over to be better flowing per db than most of there competitors, plus the noise canceling technique they use makes for a non raspy, deep sound.
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IT'S 5:00 SOMEWHERE!!! 92 Liquid Silver SVX LS-L Last edited by UPnorth362; 10-07-2007 at 11:13 PM. |
#112
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On a side note, two stroke engines require proper back pressure for both engine longevity, and peak performance. But that is a topic saved for another day
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IT'S 5:00 SOMEWHERE!!! 92 Liquid Silver SVX LS-L |
#113
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I'm not sure how many people are using Magnaflow mufflers, but I do know that a decent amount are using some sort of Flowmaster muffler.
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bLAh
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#114
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my $.02, i have magnaflow's on both my cars they flow better and sound better.
flowmasters are just annoying in my oppinion, but to each their own
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1991 xt6 eg33? 1993 gc track car |
#115
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Then why would the most powerfully tuned per liter engines (motorcycles) have disproportiontely long mostly unequal headers.
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#116
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Magnaflow vs. Aero resonator
Hi all,
Which resonator sounds better, the Aero like in the E3 on SVXCESS's car or the magnaflow #? Anyone heard both? I am going into the bullet Camaro muffler, like Shotgunslades. I only care about the sound. If appearance was a concern, the Aero wins, peroid. The two resonators appear to be different internally, based on the cut away on magnaflows site price is close... Is the Flow master resonator any better or different yet? Being near Nino's Performance in Bethany, and JP motors in Woodbridge, I get to hear a few Italian cars now and then
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Cheers! Gordon 1997 Ebony #308 113k "The Black Diva"SOLD 1992 Black over Liquid Silver 152k SOLD 1992 Ebony 251k 444 SOLD 1999 Silver SLK230 134k SOLD 1997 Green Outback 137k SOLD 2013 Honda Accord I4 SOLD 2015 Subaru Crosstrek 30k 2018 Tesla M3 30k |
#117
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Just got back from my exhaust guy and he quoted me $450 to weld everything up, and I have all of the parts except the tubing. That price is because my boss is good friends with the owner.
I called up Mufflex which is another shop by me and they quoted me $900-1200. Hopefully Monday I can take it to get everything welded together...can't waittt
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bLAh
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#118
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3rd O2 sensor
That third 02 sensor on the OBD2 cars is after the cat because it is there to check the operation of the cat, if you put it before the cat, it'll see the same reading as the pre-cat sensors, and will throw a catalyst failure code. There are "cheater" harnesses that piggyback one of the front sensors and fakes what the rear one should see if the catalyst is working, I see them on ebay all the time...
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1992 SVX LS-L #1222 Pearl White 1987 GL Turbo wagon, 5 lug conversion, D/R 5 speed (Rice killer) 1992 Dodge Ram 4x4 diesel (car hauler) 1968 Dodge Polara convertible (Camaro killer) 1990 Toyota Corolla FWD auto (330,000 mile grocery getter) 1986 VW Jetta |
#119
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Quote:
-Bill
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Retired NASA Rocket Scientist Most famous NASA "Child" - OSIRIS-REx delivered samples from asteroid BENNU to Earth in Sept. 2023 Center Network Member #989 '92 Fully caged, 5 speed, waiting for its fully built EG33 '92 "Test Mule", 4:44 Auto, JDM 4:44 Rear Diff with Mech LSD, Tuned headers, Full one-off suspension '92(?) Laguna, 6 spd and other stuff (still at OT's place) My Locker |
#120
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You win the prize!, Do you want your sheepdog wrapped?
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www.svxfiles.com The first SuperCharged SVX, the first 4.44 gears, the first equal length headers, the first phenolic spacers, the first Class Glass fiberglass hood, the first with 4, 4.44s in his driveway Fiberglass Hood thread My locker 4.44 Swap link |
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