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#16
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Cool, thanks Tom. I had the wrong photo, but the number I grabbed (59") just happened to be right. Coincidence ? I don't think so.... |
#17
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I believe the Subaru engineers built a well thought out exhaust system, and for most owners its fine. But there are some gearheads out there who are all about more! More power, more speed, more braking, more road handeling, more! More later.
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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 |
#18
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(NOTE: things get long and detailed here; bail out if you're not in the mood...) Actually, as I type this, I'm picturing a second effect that could contribute to resonance at the same frequency. A positive pressure wave from an exhaust port hits the expanded volume of the main cat. From this interface, a negative pressure wave reflects back up the same pipe. This is the desired effect. But at 3k RPM, I'm guessing the exhausting cylinder is coming close to TDC, but not there yet, and the intake valve hasn't opened yet. (i.e., the system is tuned for higher RPM) So that cylinder is gonna look like a rather small. closed volume. And the other two exhaust valves on that side are closed. So, for the most part, this bank will act like a closed pipe, and the negative pulse will reflect (as a negative pulse) and travel back to the main cat. This time, the negative pulse will reflect off of the large volume in the main cat and travel back as a positive pressure wave. What's interesting is that this reflection will coincide exactly with the arrival of the strong exhaust pulse from the other side of the engine. So, from the point of view of the main cat, every time a strong positive pulse arrives from the LHS of the engine, some (small) portion of it will pass though to the RHS. At the same moment, a negative pulse will arrive from the RHS and reflect back (positive pressure) to the RHS. Both of these will contribute to a positive pressure wave travelling back to the RHS just in time for a new exhaust valve opening. This is assuming we're at the magic RPM around 3k. Anyway, both effects are weak, but it's interesting that they combine exactly in phase. This is true if the collector pipes are equal in length; making them unequal would break up the critical RPM into 3 different RPMs for the left-only, right-only, and side-to-side mode. Also interesting is that altering the volume of the main cat shifts the importance from one mode to another. If the volume is negligible (i.e., Y-pipe) the side-to-side mode dominates and the one-side-only mode will be tiny. (There's always some reflection off a discontinuity, though.) If the volume is huge, the side-to-side mode is non-existent, but the one-side-only will be stronger. Anyway, if anybody has read this far , I'd be interested in hearing some comments. |
#19
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Just a plug for www.verociousmotorsports.com very high quality resonators reasonable price.
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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 Last edited by svxfiles; 10-12-2006 at 11:30 AM. |
#20
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Like I really need to be typing more ....
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I guess the one thing that's not clear to me is how "strong and sharp" the exhaust pulse is from a modern engine (like, say a Subaru ?) compared to the ancient beasts that Robertson, er, I mean Morrison, worked with. Maybe that's a factor that isn't considered in his work. But a sharp pulse reflecting off the closed end of an interference pipe will still produce a fairly sharp spike in the middle of the extended waveform travelling down to the resonator. It should be a copy of the original, more or less, reduced by half. Cheers, Jeff Last edited by jsteele22; 10-12-2006 at 11:33 AM. |
#21
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Thanks Trevor, your a wealth of information. I get it now. While both valves are slightly open the backpressure helps keep the new fuel&air that's coming in the cylinder from escaping out the exhaust vavle. Get that part, now I'll have to think about what your saying about the affects of overlap at higher RPM's. Is it that the exhaust flow at higher RPM's helps suck the fuel&air into the cylinder from the intake, or did I get that wrong also. Wish I could re-pay you for your time explaining, but New Zealand is kinda far away. I'll buy more Kiwi to boost New Zealands exports
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#22
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i think the other problem is that the factory main cat is not meant to have the pressure change that you get with the pre-cats removed, i believe the added back pressure from the pre-cats are also part of keeping the sound down, so in effect, with the less restrictive exhaust flow going into a cat that is made for a different application there is bound to be some sort of sound problem, not to mention the missing baffling and sound deadening provided by the two pre-cats. i was talking with my professor about this today infact, and his thoughts were to run the pipes off the headers a little larger size and run them like duals and then join them into a single cat or into a single pipe.if this makes sense at all
I II I I II I I V I \ I / I I
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98 Impreza Wago-O-Doom & Datsun Roadsters |
#23
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Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#24
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Here's the next problem then.
Based on Tom's post, true dual system is the best...that's all well and good, but for packaging reasons, I can't do that. What's the best option for a single sytem, with no cats and the standard headers (I have to use them). The other thing in the back of my mind is the 4 cylinder Subaru engines have different pipe lengths from the extractors...is this again a packaging exercise or are there reasons that they've done this? |
#25
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Development of resonate tuning in cars has been slow. I have been using it for two strokes engines for some time. It was started back in the late 40s by Walter Kaden at CZ. After the end of the war, CZ became MZ, and the resonate tuning was developed to a very high state. The start of the wave is vital to the action of the wave. The faster the wave can be established, the stronger the effect. In strokers, we use a port with a very straight opening edge, to provide a sudden start. The auto engines are getting the message, as the the quest for more power from the same capacity, is needed. The EG33 has very fast opening cam profiles, that can establish a strong wave action. This action intensity increases with engine speed. The faster the opening, the stronger the wave. In the EG33 the resonate action becomes strong enough at about 4000 rpms. Below this rpms the wave action is weak. So the engine depends on the low. speed inertia action of the exhaust gas to pull a low pressure in the cylinder as the piston is rising. We don't have to worry about creating a low pressure at TDC (overlap) below 4000, as the Inlet Inertia system provides a positive pressure as the inlet valve opens. The point is that you do need the longer header pipes to allow this action to operate. If you were to use the interference pipe to shorten the headers tuned length, you will lose the low rpm torque. Harvey.,
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#26
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Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#27
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Then again, you could wait until a certain set of SS headers and custom "mufflers" are fabricated and dyno tested Right, Harvey?
-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 |
#28
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Thanks Harvey, great answer. If I finally start to piece this all together, I'll have to start picking your brains about IRIS.....
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#29
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So what are the options for a 2-into-1 chamber ? Clearly a Y-pipe is not the ticket. I've seen mention of the Magnaflow 2-in, 1-out cat, the Stebro Euro-resonator (I think that fits the description), and that's about it. It seems that for such a generic application there would be a ton of options. Is there a brand or website that I haven't seen yet ? Q) Would a 2-input muffler be appropriate (i.e., more than just expanded volume, but also baffles) ? Usually it seems that a muffler would come after a resonator. Q) If a 2-input cat is used, then you want a larger resonator very soon after it, right ? The cat by itself isn't gonna have much volume. Q) When someone says "resonator" I've kind of learned to substitute the word "glasspack". I've only come across one or two products actually called "resonator". Is this just a marketing issue, or is there something about a "real" resonator that's better than a glasspack ? |
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