eyefi Posted October 29, 2003 Share Posted October 29, 2003 if i have a 5cm diam exit on my turbo's exhaust side, giving an area of 19.6cmsq, and i have 2 of these pipes joining, do i want them to join into a 39.2cmsq (3" diam = 45.6cmsq) single pipe? thanks in advance, Link to comment Share on other sites More sharing options...
Thorin Posted October 29, 2003 Share Posted October 29, 2003 oooh oooh, is this like those maths questions we did at school? "John has £1.50, he buys 6 chocolate bars at 10p each, how much money does he have left over? How much does John weigh?" Link to comment Share on other sites More sharing options...
eyefi Posted October 30, 2003 Author Share Posted October 30, 2003 yes, its a bit like that. btw john has 90p left and weighs about 10 stone, thats if u mean john ridley from down the road. so how big does my pipe want to b? what chocolate bars r 10p these days? remember "texan" bars, lovely. Link to comment Share on other sites More sharing options...
Terminator Posted October 30, 2003 Share Posted October 30, 2003 If it takes one man a a week to dig a trench using a chair leg. How many trenches can two men dig in a cubic fornight using a hat stand. I think the question you should ask, is not whether it is the right size pipe to join into to but what should be the distance from the turbo outlets before the join. JM and a few glass of Scotlands finest HO. Link to comment Share on other sites More sharing options...
Steve W2 Posted October 30, 2003 Share Posted October 30, 2003 Originally posted by eyefi if i have a 5cm diam exit on my turbo's exhaust side, giving an area of 19.6cmsq, and i have 2 of these pipes joining, do i want them to join into a 39.2cmsq (3" diam = 45.6cmsq) single pipe? thanks in advance, The answer would be yes if you wanted to maintain the same gas velocity. If you used a 3" diameter pipe with a CSA (cross sectional area) of 45.6cmsq your gas velocity would be lower as would the pressure in that section of pipe. Don't know if that's okay or not but thats what would happen. Oh by the way the gas pressure would be reduced by the square of difference in area. :) Link to comment Share on other sites More sharing options...
Terminator Posted October 30, 2003 Share Posted October 30, 2003 I thought flow dynamics were very important in exhaust systems in high performance cars. So whilst there would be a pressure drop, simple to deduce from the maths, the point at which the drop occurs ie where the two pipes join, may be more significant than difference in pressure alone. Link to comment Share on other sites More sharing options...
Steve W2 Posted October 30, 2003 Share Posted October 30, 2003 Termie, you are correct. Again, I don't know the ins and outs of exhaust systems but can say that the pipe size and pressure changes need to be looked at when considering doing any mods. If the pressure change is to great whilst being split into two seperate streams you are like to get vortex shedding which will effect the even distribution of the gas. In a really bad case that alone can cause the pressure to increase due to swirling gases. Its all a bit OTT given the difference in pipe size which is minimal but as you said the flow dynamics of the exhaust system can be upset by such changes. It would be woth asking if anyone has done this before. Link to comment Share on other sites More sharing options...
eyefi Posted October 30, 2003 Author Share Posted October 30, 2003 nice. is that theory true for a pulsed flow of gas, along comes my fast pulse of exhaust gas, through the manifold, round the turbo (all alot smaller than 50mm diam turbo exit), so when it gets to the turbo exit and has a larger CSA to fill, does it slow down? and then further down i drop it into a 75mm CSA, does it slow down again? Link to comment Share on other sites More sharing options...
Steve W2 Posted October 30, 2003 Share Posted October 30, 2003 Originally posted by eyefi nice. is that theory true for a pulsed flow of gas, along comes my fast pulse of exhaust gas, through the manifold, round the turbo (all alot smaller than 50mm diam turbo exit), so when it gets to the turbo exit and has a larger CSA to fill, does it slow down? and then further down i drop it into a 75mm CSA, does it slow down again? Yes, it will slow down the larger the pipe you use. Remember the pressure will reduce as well. Pressure = flow/area therfore, if you have the same flow, bigger area, the pressure must be lower. It gets very difficult with pulsed flows and would depend on the frequency of the pulses and the resonant frequency of the pipe system. Can't see it being anywhere the frequency you need to get problems though. Link to comment Share on other sites More sharing options...
eyefi Posted October 30, 2003 Author Share Posted October 30, 2003 Originally posted by Steve W2 It gets very difficult with pulsed flows and would depend on the frequency of the pulses the pulses vary with revs Originally posted by Steve W2 the resonant frequency of the pipe system whats this? i suppose exhausts work at certain rev ranges better than others Link to comment Share on other sites More sharing options...
Adam W Posted October 30, 2003 Share Posted October 30, 2003 I don't think you get any pulses post-turbo, this is why "exhaust tuning" is far less critical on turbo cars. You just want the least restriction possible. Single-turbo supras in the states have shown big gains going from 3" to 3.5" to 4" setups in dyno testing. Link to comment Share on other sites More sharing options...
eyefi Posted October 30, 2003 Author Share Posted October 30, 2003 Originally posted by Adam W I don't think you get any pulses post-turbo this thought had occurred to me, but i can still feel pulses if i put my hand over the end of my exhaust. Link to comment Share on other sites More sharing options...
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