SubieDriver Posted December 17, 2006 Share Posted December 17, 2006 Anyone ever consider that losing back pressure through leaky flange (hogzaust!) would actually decrease horsepower, albiet minimal? Is this not an issue with an exhaust-side turbo? Id rather keep my 4hp for stock sounding exhaust. BRING ON THE CRITICISM! Here, I found this article that discusses backpressure. Lot's of fascinating info: http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm Destroying a myth. Some say that "an engine needs backpressure to work correctly." Is this true? No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning. The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below. The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure. The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well. Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating. Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque. Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached. - Adapted from Thomas V. Link to comment Share on other sites More sharing options...
Guest Gitster Posted December 17, 2006 Share Posted December 17, 2006 So its safe to say that everyone use Hozaust is burning valves ? Heheheh. Link to comment Share on other sites More sharing options...
SubieDriver Posted December 17, 2006 Share Posted December 17, 2006 So its safe to say that everyone use Hozaust is burning valves ? Heheheh. Nah, with all the ECU computations and compensation for everything measured by all the sensors, it would be tough to really harm these engines. Link to comment Share on other sites More sharing options...
SubieDriver Posted December 17, 2006 Share Posted December 17, 2006 Nah, with all the ECU computations and compensation for everything measured by all the sensors, it would be tough to really harm these engines. #800 !!!!!! Link to comment Share on other sites More sharing options...
Guest Gitster Posted December 17, 2006 Share Posted December 17, 2006 I know im jk. Ill try to think of 199 more dumb things to say today. Link to comment Share on other sites More sharing options...
hogmeat Posted December 17, 2006 Author Share Posted December 17, 2006 WOW! Thanks guys. You've appeased me so much, I'll try to forget the previous blasphemous words. By the way, the hog got his 2nd warning today for pwning noobs. As long as I have your support, I will continue to pwn noobs who think that coil packs add 25% HP. hehehheheheh I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
mccorry Posted December 17, 2006 Share Posted December 17, 2006 hogmeat... it isn't cute to treat others with disrespect. Link to comment Share on other sites More sharing options...
bskey Posted December 18, 2006 Share Posted December 18, 2006 Hogging was my frst mod, and one of my favorites. Definately cost effective! It sounds even meaner now that I have gutted my mid and up pipes. Bump for a kick ass mod!! 196 left! life in spin cycle..... Link to comment Share on other sites More sharing options...
hogmeat Posted December 18, 2006 Author Share Posted December 18, 2006 I'm sorry. I'll play nice. I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
SubieDriver Posted December 18, 2006 Share Posted December 18, 2006 .... By the way, the hog got his 2nd warning today for pwning noobs. As long as I have your support, I will continue to pwn noobs who think that coil packs add 25% HP. hehehheheheh Did you mean pwning n00bs on this forum, or out on the street? On this forum = not so nice. On the street = they deserved it! Link to comment Share on other sites More sharing options...
SeeeeeYa Posted January 1, 2007 Share Posted January 1, 2007 Here it is 2007! and I have missed Hogger's input ( by and large ) for some time now. Because I installed a new AEM CAI recently I had decided to revert from Hawgzaust Stage1 back to stock so that I could evaluate the new intake's sounds. Before I could formulate my own opinions, other than the car was TOO QUIET now, my wife repeatedly, and pointedly, made her opinion clear; "it was PERFECT the way it was (with the Hawgzaust), why did you have to mess with it!" She doesn't like the new intake's sounds, especially the BOV's dramatic Psssshhhhhtttt. I do . Knowing her she will get used to it in time. The added performance the AEM enabled is worth the difference. Tomorrow, using my wire version (now slightly modified with teflon tape wrapping to provide a better seal on the upper flange area) I will reinstall my Hawgzaust. The wife can't wait. Is this the perfect exhaust solution? No. But the problem is, after years now, I haven't found an aftermarket exhaust I am certain a) justifies its cost, or b) has that 'perfect' sound, not to mention looks. Too many people have jumped on exhaust setups that have caused them regret. Frankly, the stock exhaust allows my car to quietly rip off 0-60 times and 0-100's that will shock big name performance cars, including STI's. What is missing, however, is a little soul to go with that performance. So far the Hogger's Hawgzaust provides 90% of that missing element, and can be removed, changed, or modified in minutes............for virtually pennies. Thanks, and Happy New Year, hogmeat. Link to comment Share on other sites More sharing options...
hogmeat Posted January 1, 2007 Author Share Posted January 1, 2007 Hey man. Nice thoughtful post. My woman likes the zaust too. Why? Cause I didn't spend any money on it. I will say this, I have to agree with your position on aftermarket exhausts - can't justify to expense along with being unable to sample the sound before purcahse/install. Not to mention inability to change back/modify afterwards if you feel it's too droney. Listened to many clips from other peoples aftermarket ones, and honestly just not impressed. Sounds too raspy or racery. 90% - it may not be 100%, but close enough for me I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
bosco Posted January 1, 2007 Share Posted January 1, 2007 ^ chilli recipe? bosco Stay Stock Stay Happy Link to comment Share on other sites More sharing options...
hogmeat Posted January 2, 2007 Author Share Posted January 2, 2007 ^ chilli recipe? bosco OK, i had to wait for snow before i could make chili. This is the first time in 25 years that it hasn't snowed in Iowa in Oct-Nov-Dec. Light dusting of snow, more on the way. That means chili season!! I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
gianspi Posted January 2, 2007 Share Posted January 2, 2007 I saw your video and noticed the washers inbetween the pipes. I didn't think that was all that was done to create that nice of a sound. I would highly suggest you spill the beans in text on the first post, outlining exactly what was done. It would save newbs like me many hours of reading through this long thread Thanks for the tip, I am definitely headed over the Home Depot tomorrow morning! enough zip ties and duct tape will fix anything. Link to comment Share on other sites More sharing options...
SubiGT Posted January 2, 2007 Share Posted January 2, 2007 I saw your video and noticed the washers inbetween the pipes. I didn't think that was all that was done to create that nice of a sound. I would highly suggest you spill the beans in text on the first post, outlining exactly what was done. It would save newbs like me many hours of reading through this long thread Thanks for the tip, I am definitely headed over the Home Depot tomorrow morning! Reading thru the whole saga is part of the joy:) Stage 2 custom boiler gasket cutout Hogwawst FTW Many Shuvs and Zuuls knew what it was to be roasted in the depths of the Slor that day, I can tell you! Link to comment Share on other sites More sharing options...
hogmeat Posted January 3, 2007 Author Share Posted January 3, 2007 Pics of your custom gaskets!! Or, at least an explanation... I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
SubiGT Posted January 3, 2007 Share Posted January 3, 2007 Pics of your custom gaskets!! Or, at least an explanation... I took the stock gasket and traced it onto some 1/16" Garlock gasket material. After cutting the duplicate, I then trimmed the bottom of the gasket out. End result is a kinda bell shaped opening. Put two together per side, and all soot blows toward the rear of the car. An added bonus is that the sound pulses also do not hit the body now, and what droning there was is gone. I can pull them out and snap pics if you like. Many Shuvs and Zuuls knew what it was to be roasted in the depths of the Slor that day, I can tell you! Link to comment Share on other sites More sharing options...
hogmeat Posted January 3, 2007 Author Share Posted January 3, 2007 I think I get the idea. Very similar to another type of mod - where the guy took some 8ga copper wire, and bent it in a curve to follow the shape of the gasket, and coiled it around the bolts. I tried it, worked quite well. Still went back to Stage 4 though... I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
SubiGT Posted January 3, 2007 Share Posted January 3, 2007 Variations on a theme, but still basic Hog to the core:) Many Shuvs and Zuuls knew what it was to be roasted in the depths of the Slor that day, I can tell you! Link to comment Share on other sites More sharing options...
SeeeeeYa Posted January 3, 2007 Share Posted January 3, 2007 I think I get the idea. Very similar to another type of mod - where the guy took some 8ga copper wire, and bent it in a curve to follow the shape of the gasket, and coiled it around the bolts. I tried it, worked quite well. Still went back to Stage 4 though... http://legacygt.com/forums/showthread.php?t=35764&page=27 Post #397 (I actually use 12/2 wire, but use whatever to achieve your particular effect) This one works best for me, only this time I wrapped the section between the ends with teflon tape figuring it would be a heatproof seal. It works. This, as others have since found, keeps the sound pulse (and soot) from hitting the floor with the resulting exhaust 'port' aimed back along the muffler. To further shape the sound (old speaker stuff) I have shaped the resultant openings with my Dremel and a carbide bit, aiming for a bit of exponential horn effect. Well, it ain't no horn but the sum effect is to remove most of the exhaust leak effect (to me, of course). The different frequencies emerging from those hawgzaust ports and the mufflers seem to combine into a single, fuller spectrum, soundfront I like. With my windows down on the autocross course, and the engine singing at the top of first and second gear, it actually sounds like a race car. It may not change my times, but it is a lot more thrilling to me than stock. On the street, hammered, it will definitely turn heads, and is a fact to consider when chosing to do so. Link to comment Share on other sites More sharing options...
hogmeat Posted January 3, 2007 Author Share Posted January 3, 2007 I've always like to travel and engine brake through a crowded parking lot in 1st!! LOL! You know, where you are 5000 RPM in 1st, holding it steady - just ROARING through the lot, nice and slow... and you let off the gas, and it really turns the heads. People are like WTF?!? All that noise from that little car?? OK OK, I'm stupid. I'm pleasantly surprised... It was most certainly worth the couple bucks and 10 mins of my time. CLICK HERE FOR THE HOGZAUST Link to comment Share on other sites More sharing options...
SubiGT Posted January 3, 2007 Share Posted January 3, 2007 OK OK, I'm stupid. Best quote of the new year, so far...... Many Shuvs and Zuuls knew what it was to be roasted in the depths of the Slor that day, I can tell you! Link to comment Share on other sites More sharing options...
BMac1203 Posted January 4, 2007 Share Posted January 4, 2007 I'm not gonna lie. I just did this about 2 days ago, and makes my LGT sound like an STi. WOW...that's all I have to say. Need a CarPC bezel? PM me! Link to comment Share on other sites More sharing options...
one69chev Posted January 4, 2007 Share Posted January 4, 2007 ^did you expect anything less??!! this is the hogg we're talkin' about:icon_bigg Link to comment Share on other sites More sharing options...
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