pparaska Posted June 5, 2002 Share Posted June 5, 2002 Originally posted by Mike C (in Ross's thread):As you've found Pete, it's all about tailpipes. And with that thought, I have a little test I want to run. It seems that if I'm REAL lucky, I'd be making over 380 hp at the flywheel. Those two Hemi Super Turbos flow 415 cfm each, good for 378hp, based on the relationship:x HP * 2.2 = Y cfm So I'm thinking that's about right. But what if I create a bit of back pressure by putting something on the ends of the muffler, like a resonator tip that's a bit restrictive. Any thoughts? Quote Link to comment Share on other sites More sharing options...
Mike C Posted June 5, 2002 Share Posted June 5, 2002 I originally had intended that on the 2 1/2" Flowmasters on my Camaro. Never did it because I liked the sound when I was young. Now I just don't want to spend any more money on that exhaust! One great thing about adding something to the back of the mufflers is you can just clamp in on to test. You could even have your local tube bender make you some swedged 2 1/4" or 2" pipe for tips. (Kind of the anti-fart pipe) If you believe Walkers numbers, just one of those mufflers is sufficient... Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 5, 2002 Author Share Posted June 5, 2002 Originally posted by Mike C:One great thing about adding something to the back of the mufflers is you can just clamp in on to test. Yep, I'm all for that! My next options are to put something in the flanged connections just before the mufflers. You could even have your local tube bender make you some swedged 2 1/4" or 2" pipe for tips. (Kind of the anti-fart pipe) Good idea. My car is as "anti-rice" as I can make it. No non-weight saving carbon fiber, no big tip, no glitz, except for the wheels and underhood goodies. Just my way, I guess. The mufflers are painted with a high temp flat black paint, including those dinky 2.5" outlets! Rice is a long fad I don't want to be part of! If you believe Walkers numbers, just one of those mufflers is sufficient... 415cfm / 2.2 = 188.6 hpSo one muffler is only good for 188hp, without "losses", in the estimation of that equation. Two would be good for 377.2 hp. I'm willing to give up a few horsies to get some quiet and stealth. Anyone seen theses wire mesh cones you can put in a collector to "muffle" things? I'm thinking of trying something like that. The other thing is that I've heard two mufflers that identical can cause resonance - and I have some of that too. So mod one muffler or both differently and maybe get away from the resonance too. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 5, 2002 Share Posted June 5, 2002 This is interesting. Kinda similar to the Supertrapp concept. I think I saw Supertrapp replacement parts in a Summit catalog. Might be a good starting point. Or, maybe a motorcycle shop would have some baffles. Nice thought Pete. Worth a try. Quote Link to comment Share on other sites More sharing options...
johnc Posted June 5, 2002 Share Posted June 5, 2002 You might also want to weld a fitting in the exhaust pipe halfway between the header collector(s) and the mufflers. Connect a pressure guage to the fitting and measure the backpressure at various rpms during your testing. L6 engines like about 3psi of pressure in the exhaust system. I don't know what Chebbies want. Quote Link to comment Share on other sites More sharing options...
DAW Posted June 5, 2002 Share Posted June 5, 2002 Pete, I've been fooling around with an exhaust pressure staged system which has a fairly small dia. full length primary system with some backpressure inherently that is good for low-end torque and responsiveness, and is quiet. When throttle is increased the pressure builds up quickly, but instead of restricting performance, the pressure forces open a relief-valve which is at a "Y" with the smaller system. I'm thinking the valve would open typically at highway speeds during normal driving, earlier when driving harder, never at idle; and so could be relavively unmuffled since a portion of the flow is always fully muffled. I've chosen a brass sump-pump relief valve 1 1/4" dia. as the prototype relief valve and it has adjustable spring pressure. The valve has a stem, head and seat not unlike an external wastegate. This is an idea that seems worth a look but I haven't gotten to it in earnest...the I pick up a new issue of Auto Week and page through to the newest Ferrari road car and...doh! There's a shot of the twin exhaust outlets and one of them has a throttle plate! Same concept, different method. DAW Quote Link to comment Share on other sites More sharing options...
Oltmann Posted June 5, 2002 Share Posted June 5, 2002 Nissan is using a "variable capacity muffler" in some of their cars. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 5, 2002 Share Posted June 5, 2002 Hey guys, here's a link to a variable flow exhaust system simlar to what DAW mentioned. Variable Flow Exhaust Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 5, 2002 Author Share Posted June 5, 2002 Wow, that's pretty incredible (that last link). I'd need two, and they'd be best after the muffs (according to the article). I'm thinking there might be an easier way to skin this cat... What about a spring loaded baffle up inside the muffler output? Exhaust pressure would push it open. Wow, that sounds a bit silly - just thinking out loud. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted June 5, 2002 Share Posted June 5, 2002 Damnit Jumbo...they get to the best part "how well does it work", then say "....to be continued next week" What the hell is up with that! Anyways....sounds intriguing. Tim Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 5, 2002 Share Posted June 5, 2002 I poked around and found the second part of the article... I haven't read it yet. The site is pretty intresting. part 2 Quote Link to comment Share on other sites More sharing options...
Owen Posted June 5, 2002 Share Posted June 5, 2002 Pete, Whaddya saying, rice isn't good enough for ya??? just kidding Don't tell me that doesn't look sweet This variable thing is old news to me, there's a manual system in Japan which is actuated with a cable, the same butterfly concept is used. Since I originally wasn't planning to use the ebrakes, I was gonna use the ebrake handle to pull the linkage actuating the butterfly. A motorized system would be cool but I don't need to spend any more money. The manual system I could build with spare parts in my garage! Owen Quote Link to comment Share on other sites More sharing options...
DAW Posted June 6, 2002 Share Posted June 6, 2002 Simple is best, and a device that changes the path length of the gas flow while regulating back pressure would be more dynamic than just lowering the back pressure, i.e. like a variable runner intake manifold (except for the exhaust gases). Longer path with a scavenging effect for low-end torque and responsiveness, then transitioning to a shorter, direct path for high rpm. A simple split system (dual exhaust: one big/short, one little/long) would accomplish more than just effectively removes a restrictor. DAW Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 6, 2002 Share Posted June 6, 2002 Pete, yeah, the system on that site seems overly complicated. Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 6, 2002 Author Share Posted June 6, 2002 I'm not really knocking that system, but it seems a bit extreme for a way to do automatic "cutouts", kind of like what Owen is talking about. Those have been around in JC Whitney for along time (or used to be) and could be used to the same effect. DAW, I agree that your method sounds better. Throwing a jake brake on the exhaust like that just seems strange to me. I guess it gets the job done, but for all that complication, I'd rather seen the problem solve with something like your talking about. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted June 6, 2002 Share Posted June 6, 2002 Adding back pressure in the exhaust pipe? Duh! Let us go to the source. I was given this free 350 SBC at a garage sale and have been using MoreTec's identification #'s. It seems this discount rebuild crate motor with spun beaRINGS has early 70 cc cylinder heads on one side and later 75 cc heads on the other side. Now would you say this is making back pressure or adding back pressure vice a versa? Tee hee! Grumpy Vette warned about these rebuilt motors.My latest acquisition is a free GMC pickup with a #14016379 350 SBC and according to the exhaust pipes was producing high volumes of black carbon soot before retiring. I am hesitant to apply the identfication #'s on this application. Quote Link to comment Share on other sites More sharing options...
DAW Posted June 6, 2002 Share Posted June 6, 2002 So Tee Zee, if one bank is 10.0:1 c.r. and the other bank is 8.0:1 are you running a 9.0:1 engine? DAW Quote Link to comment Share on other sites More sharing options...
Owen Posted June 6, 2002 Share Posted June 6, 2002 BTW, the product I was talking about was meant to reduce sound, like when you're driving through a cemetary. I have no idea what it does to back pressure. There's also this Japanese muffler company that took the idea and applied it to their muffler. It has a sliding tube inside which varies the tone of the muffler. Kinda like building a speaker box and sliding the tube in and out until you get the sound you like? JCW still sells that exhaust thing, heavy cast iron SOB wasn't it? Owen Quote Link to comment Share on other sites More sharing options...
pparaska Posted June 6, 2002 Author Share Posted June 6, 2002 Owen, yeah, that part was a cast iron hunk. DAW/Oltmann: I found a site that says the valve that Nissan is using in that muffler uses Inconel to survive the heat. You might want to look at the deisel truck "jake brake" industry to see if parts for one of those might be good. Quote Link to comment Share on other sites More sharing options...
DAW Posted June 7, 2002 Share Posted June 7, 2002 Who wants to be working a flap valve manually while driving? Besides, that is not really the same re the dynamic function I'm referring to; it's just a dump or diverter valve. The concept of the sliding tubes is closer to what I'm describing because of the change in resonance. It could work well if it weren't for the carbon jamming things up. Another potential means of regulating a staged exhaust system would be to incorporate a flow regulator design that resembles very much a large SU carb with the throttle plate removed. This device goes up close to the engine at a "Y" pipe connector. One side of the Y is a small dia. full exhaust system (a very restrictive stock system will do fine) and the other side of the Y is a larger dia. pipe with the device in it, close to the Y. As exhaust flow increases off idle it flows only through the small system because there is not pressure enough to raise the "SU" piston due to it's weight and opposing damper spring tension. This is good because the high gas velocity associated with flow through the small cross-section pipe creates backpressure and has a scavenging effect both. The small dia. system will begin to build pressure when the gas volume increases and this occurs at mid-range. (Calibration of the primary (small dia.) system is done by pipe dia. according to how much low-end back pressure is optimal for that engine before it needs relief). Backpressure then becomes sufficient to lift the SU piston which allows flow directly in proportion to further increases in gas volume. Once the device is in operation, the primary system still has flow but essentially becomes a fixed "orfice" or bleed jet and is not really involved in the advanced secondary system operation per se. The secondary device then meters the flow of gas from the rpm which exceeds what the primary can deal with, on up. A little bit of high-end back pressure is maintained and tuned in or out by changes in piston weight, with transitional smoothness by damper spring choice. OK, so in operation, let's say you're coming full bore down a straightaway towards a hairpin turn which is at the base of a hill: Full flow @WOT/high rpm with what can get through the stuffy primary system and the bulk flowing out the SU side, pegging the piston full open. Hard on the brakes and vehicle speed is way down at apex of hairpin, lots of low-end torque is needed there and is available because the device has let the shunt lapse closed and good throttle response is enhanced by the backpressure/scavenging properties of the primary exhaust. Heading up the hill is a steady midrange pull and the shunt device can smoothly transistion as rpm rises or falls even though the throttle is full open (just as a SU carb does for induction). It's a nice concept because it is not just a pop-off valve but a smooth, fully automatic, exhaust flow tuner. Problem? Carbon would foul up the operation and the device could be expensive to make with the proper materials. Constructive comments welcome. DAW Quote Link to comment Share on other sites More sharing options...
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