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[quote][i]Algselt postitas: Maku[/i] [u]Natuke lugemist väljalaskest[/u] Exhaust Turbo Performance. - The maximum exhaust energy should be transferred to the turbine. Energy expended overcoming flow restrictions means less energy to spin the turbine. Because of this every effort must be made to transfer the max exhaust energy to the turbo, over a wide band of engine operating conditions. Any efficiency decrease here will increase turbo lag. The Exhaust Manifold. - Maximise flow by ensuring internal surfaces are smooth, incl gaskets. - Machine away slag and extrude hone hard to reach areas. First make sure the internal surfaces are nice and smooth. This encourages flow and discourages carbon buildup. Casting slag should be removed as should any sharp edges or joins. The manifold should match the exhaust ports and the manifold gasget should be trimmed back as much as possible. The manifold to turbo joint should also be kept smooth. But be careful not to overly increase the internal size of the runners, because this will result in lower velocity exhaust gas hitting the turbine. Tube Manifolds. - Tuned length pipes can be used to maximise exhaust gas scavenging. - Steam piping is strong but heavy. - Stainless steel is strong and light, but turbos will need additional bracing. For the ultimate in exhaust manifolds we have to ditch the cast manifold and fabricate a multi branch manifold using tuned length pipes. For heavy turbos, a support system must be employed to carry the turbo. Manifold Dimensions. - Choose the minimum pipe size that will give the flow needed. Anything that adds weight, complexity should be avoided. The diameter of the piping will be dictated by the size of the engine and whether you want top end power or low and mid range power. Its always best to choose a diameter as small as possible to keep exhaust velocities high and therefore, keep spool-up times low and responsiveness high. Only when all out top end power is important should bigger diameter pipes be used. Exhaust Pipe Size. - Bigger diameter bores are not always better. Because of the big weights of big diameter exhausts and big diameter silencers, bore sizes should be kept as small as possible while still allowing maximum flow. A good guide, based on the experience of tuners is as follows: 1300-1600cc – 2.25 to 2.5in 2000-2300cc – 2.75 to 3.0in 2500-3000cc – 3.5 or 2x2.5in 3500-4000cc – 4.0 or 2x2.75in 5000-5700cc – 2x3.0in These figures are based on engines developing 120-150bhp per litre. Rally engines developing 200-250bhp per liter need pipes that are 0.5 to 1.0in bigger. [b]The tailpipe can be reduced by 1/4in without suffering penalty.[/b] But testing is the only way to go. On group A two litre turbo engines, a 3in pipe will give excellent power but a pipe 3.5in will cause a power drop and at 4in the power comes back. So testing is the only reliable method for choosing max power setups. With turbos, the biggest flow restriction is at the turbine wheel and housing. The use of a bigger housing, without suffering further turbo lag will give better gains than exhaust change. Then next most restrictive area is at the manifold between the turbo and the head, so improvements here will also give good gains. Tailpipe Design. -Can use a tailpipe or use CATs, baffles and silencers. After the header, we have to consider the rest of the exhaust system. On all out competition cars this can mean just a tail pipe. On road cars to usually means a cat and one or more silencers. Less tailpipe length will increase top end power and longer tail pipes will yield more low and mid range power. This is why some engines will have a tailpipe not much longer than the collector. However, most tailpipes go right to the back of the car. Tailpipe diameter is determined on the dyno and if a cat is used the diameter after the cat needs to be larger. A guide to blown and nitrous engines is: 80 to 120bhp – 1.875in 110 to 140bhp – 2in 130 to 150bhp – 2.125in 140 to 185bhp – 2.25in 180 to 220bhp – 2.5in 210 to 265bhp – 2.75in 250 to 320bhp – 3.0in 280 to 360bhp – 3.5in 400 to 500bhp – 4.0in 480 to 630bhp – 4.5in 580 to 750bhp – 5in As always the entire system must have a minimum of bending and adequate bore size. [b]When ground clearance is a problem then oval exhaust bores can be used with no penalty in flow. You can reduce the diameter by ¼ in at the end (beyond the real wheels) without incurring any flow restrictions.[/b] Silencer Design. - Straight through or reverse flow silencers are best. [b]A well designed silencer, placed to the rear of the car won’t drop power by anymore that 3-5%. The closer to the engine they are fitted, the more flow restricting occurs and the more power is lost.[/b] Straight through or reverse flow silencers are the best for power applications. Straight through provides the best sound deadening and are good for turbo cars. However, on NA cars two silencers or a silencer and a resonator must be used to stop popping occurring on overrun. The quietest silencers have an open resonating chamber in the middle. Reverse flow silencers are different and don’t contain any sound deadening materials. This makes them lighter, but poorly designed ones are loud and cause power loss. The main advantage is that they are good at suppressing popping when you lift off the throttle. CAT Problems. - Don’t use CATs if possible. - Otherwise use performance CATs with twice the flow of regular CATs. CATS that melt due to excessive temperatures caused by combustion in the exhaust will cause a problem by blocking the exhaust flow. However, even healthy CATs can cause problems. A poorly designed CAT can impede exhaust flow due to turbulence caused by the gas having to enter the honeycomb at 30deg angles or more and having to exit the honeycomb at the same angle. To overcome this a performance cat must have a gentle entry and exit taper of about 10deg. A performance cat will have double the flow rate of a regular cat. Pumping Losses. - This refers to the power consumed in pumping the exhaust gas out of the engine. Power is consumed because exhaust gases have to be pumped out of the engine. As soon as the crank rotates past BDC, the piston starts its way up the cylinder barrel on the exhaust stroke. During the exhaust stroke it must ram the exhaust gas out past the exhaust valve and through the exhaust system. This consumes power provided by another cylinder on its power stroke. This means that there is less power available at the flywheel. There are methods available to cut these pumping losses to a minimum. One way is to open the exhaust valve very early. This provides a net gain in the upper half of the powerband but causes poor fuel economy at cruise. A better and more considered route is to ensure that the entire exhaust flow route is free of obstacles and incorporates any elements that promote positive flow. Exhaust Pressure Waves. - The cylinder outlets should be mated to maximise wave resonance tuning. As mentioned above, wave resonance tuning is the primary means of increasing flow. This means connecting cylinders in a particular order using exhaust tubing of a specific length to take advantage of exhaust pressure waves to pull exhaust gas out of the cylinders and during valve overlap, suck fresh air/fuel into the cylinders. When we look at the firing order of the engine, we join cylinders so that exhaust gas from one cylinder won’t cancel the pressure wave from another cylinder. [b]EDIT1:[/b] Lihtne arvutus näitab, et kui kubatuur on 2,2l ja kuni tailpipe-ni (mis võiks olla ka 1/4 väiksem, ehk siis 2,1825") on 2,91" läbimõõduga väljalase, siis vastab see 308 hobujõule. [b]EDIT2:[/b] Mulgiga kahepeale sõnastasime ka asja iva, miks lõpust võib summutaja toru läbimõõt olla oluliselt väiksem kui eest otsast. Asi on nimelt selles, et kui õhk on kuum, siis molekulid on paisunud ja neid mahub X ruumalasse vähe. Kui aga õhk on jahe, siis mahub X ruumalasse rohkem molekule. Kui heitgaasid väljuvad mootorist turbiini labade peale ja sealt edasi downpipe-i, siis on heitgaasid loomulikult kuumad ja tahavad suurt ruumala. Mida summutaja süsteemi lõpu poole, seda jahtunumad heitgaasis molekulid on ja ei ole enam mõtet sama suure lõbimõõduda torul nagu seda oli downpipe. Sama süsteem on sisselaskega. Mida jahedam õhk silindritesse lõpuks jõuab, seda rohkem on X ruumalas molekule ja seda suurem on efektiivsus. [b]EDIT3:[/b] UrS4 downpipe toru lõbimõõt on ca 2,5" ja tema ressurss oleks arvutuste kohaselt ca 265 hobujõudu (264,55). Downpipe-st edasi lähevad 2 x 55mm torud ja ma ei oska öelda, kas kahe toru korral tehakse arvutusi 1+1 meetodil. [b]EDIT4:[/b] Rallikale ja sõidukale tulevad erinevad koefitsendid. Võtsin kahe koefitsendi keskmise ja siis sain, et 2,5" võrdub 303,27 hobujõuga (rallika koefitsendiga 345,4) ja 3" võrdub 363,9 hobujõuga. Asi on selles, et rallika ja sõiduka koefitsendid on suure erinevusega. Näiteks rallika koefitsendiga tuleks 3,75" 513 hobujõudu ja sõiduka koefitsendiga 396,8 hobujõudu. Eks siin mängib paljuski rolli, mida veel modifitseeritud on. Kui vaadata, milliste hobujõu numbrite juures on Dahlbäck summutajat vahetanud, siis tuleks igatahes ennem rallika koefitsenti uskuda (isegi sellest jääb Dahlbäcki puhul väheks). Kokkuvõtlikult siis nii palju, et rallika koefitsendi puhul tulevad järgmised numbrid: 1. 2,5" = 341,99 HP; 2. 2,75" = 375 HP; 3. 3,0" = 410 HP; 4. 3,75" = 513 HP. Nende arvutuste kohaselt peavad Hannese kunagise sinise S2 downpipe-i andmed täiesti paika. Autol oli oletatavasti 280kw ja downpipe 2,75". Arvutuste kohaselt 2,75" võrdub 276kw-ga. EDIT: Reverse flow: airflow in the silencer is in the opposite direction to the noise propagation. A tri-flow (reverse flow or "turbo") muffler takes the exhaust gas on an S-shaped path through the muffler. The exhaust gas travels to one end of the muffler, is turned through 180 degrees and heads back to the first end. There, it is again turned through 180 degrees before it passes to the outlet. Tri-flow mufflers normally have three internal chambers. [/quote]
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