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gledy2
Original Poster
56 posts
53 months
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Hi, away from my car just now and was thinking, does anyone know the exhaust diameter after turbos on a 3r, sure they will all be the same though? And Also do aftermarket exhausts, roush, hayward and scott etc have larger diameter pipes? Thanks, allan
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Gadgeroonie
4,998 posts
105 months
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i am guessing 2.5 " will be ok for each bank
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gledy2
Original Poster
56 posts
53 months
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Thanks gadge, was thinking of getting a custom exhaust made at some point, not many options up in scotland, so i was just trying to source some hi flow cats and wondered what size to look for.
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Gadgeroonie
4,998 posts
105 months
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the easiest thing to do is keep the downpipes and chop them off where they go into the y piece
then craft up 2 silencers one for each bank
you might be able to make them so they slide over the old pipes and welding will be a minimum
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gledy2
Original Poster
56 posts
53 months
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Yeah i had priced up a couple of exhausts and they werent cheap, i have a friend of a friend who teaches welding, did some work on the other halfs car and i was impressed with his work, I just thought i might get something done with him as it would be cheaper and a lot easier for me. I thought i might upgrade the cats to higher flow ones, not sure what they are like as standard, or whether it would be worthwhile. Has a look on fleabay and some cheap stuff for sale, but i know nothing and cheap doesn't always mean worthwhile! 2.25" cheapies http://www.ebay.co.uk/itm/RAMAIR-2-25-HIGH-FLOW-CA...2.5" magnaflow http://www.ebay.co.uk/itm/2-50-63mm-Centre-200-Cel...3" ones http://www.ebay.co.uk/itm/UNIVERSAL-HIGH-FLOW-EXHA...Just want rid of the y piece, and needing to re-wrap my system now anyway so thought i might get it done now anywyay. From what i read you need a remap after removing the y though, and yellowshed is a long way from me, from what i read that is the best guy to do it.
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R0162
2,435 posts
33 months
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R0162
2,435 posts
33 months
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if i were to build a new exhaust it woulsd look more like this.. 
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gledy2
Original Poster
56 posts
53 months
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Thanks for that, sounding good ro162. Might stick with the 2.5" magnaflow ones since turbohoses in the states gives them the thumbs up
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andygtt
6,379 posts
133 months
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stock is 2.5" downpipes... enough to flow 1000bhp lol
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R0162
2,435 posts
33 months
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Turbo back exhaust sytems. I found this very informative and mythbusting write up by a turbocharger development engineer for garrett, acording to this guy... " 300 hp and you're definitely suboptimal with 2.5". "At 250 hp, 2.5" is fine." So there is difference between "being good for 1000bhp" and being optimal, anything approaching 500bhp and 2.5" is no longer optimal...especially not on a non divored wastegate...where you need a bigger bore for the first 12-18" after the turbine. http://www.tercelreference.com/tercel_info/turbo_e...Basically downstream of the turbine where the wategate mixes with the main turbo discharge, they really should be separated and reintroduced 12-18" further down the line, because we do not do this it is better to have bigger bore for this 12-18" after the turbine, it is not good to taper the exhaust size down so therefore it makes sense to have bigger thoughout the entire system. Basically anything above 500bhp and you need 3" to keep the exhaust gases flowing optimally.... and that is with external wastegates.. which ours are not.
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joust
14,468 posts
128 months
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Interesting this debate, so I've done a bit of the back of fag packet calcs
Density of air ρ in kg·m−3 1.2041 at 30C
Dynamic pressure pascals 150000 = 1.5bar
Velocity
q = 1/2 p v^2
1/v^2 = 1/2p/q
1/v = SQRT((1/2p)/q) 0.002003414
v = 1/SQRT((1/2p)/q) 499.1480159 m/s
cm/s 49914.80159
mm/s 4991480.159
3 l engine
6000 rpm = 3000 cycles
Total litres to shift per min 9000
per second 150
Volume = PI * R^2 * L 290.4402408
If L = 500m (499m/s in 1 second), diameter
(V=300) / ((L=500) * PI) = R^2 0.095492966
R = SQRT 0.309019362
1 inch 0.0254
Pipe radius = 12.1661166 - diameter = 24"
So, if that is all correct (Adrian - please check the maths!!!), then you need a 24" exhaust for it to be truly "free flowing". As volume decreases with a square law, 3" seems the very minimum for a 3l forced induction car at 1.5bar as it's a lot smaller than what is needed for "free flow".........
J
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TuxMan
7,151 posts
107 months
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On the down side Joust I have no idea what the hell you are talking about !!!! On the upside I have 3" down pipes on my new H&S exhaust  Tux
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R0162
2,435 posts
33 months
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TuxMan said: On the down side Joust I have no idea what the hell you are talking about !!!! On the upside I have 3" down pipes on my new H&S exhaust Tux I also have no idea, but I am never going to get into a physics or maths debate with Justin that's for sure.
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joust
14,468 posts
128 months
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Thinking about it it's worse as the forced induction mean you need to shift more air, so it gets even bigger (although not much bigger as it's a square law).
Throw in that you need to create some pressure to get the turbos spinning and clearly the free flow isn't that telling.
What is clear is bigger is better. Interestingly they are 4" on the GM 3l turbo engine.
J
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Hollowpockets
4,772 posts
85 months
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Is the roush system 3"?
cheers
Graham
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sjc
6,715 posts
139 months
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TuxMan said: On the down side Joust I have no idea what the hell you are talking about !!!! On the upside I have 3" down pipes on my new H&S exhaust Tux  Does that mean you have anothe non standard one you want to get rid of...?
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Blu3R
1,399 posts
68 months
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Hollowpockets said: Is the roush system 3"?
cheers
Graham Nope, 2.5"
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gledy2
Original Poster
56 posts
53 months
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Thanks for the thoughts guys, joust, lost me on that one too i'm afraid! Just looking to remove the obvious restriction on the y pipe, but looking like 3" is a better option if i decide to get power hungry in the future. Will away and see if i can get some pics of the other systems to see what sort of design looks best to go for, hopefully reduce the amount of bends somehow too as that should help flow easier.
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joust
14,468 posts
128 months
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It seems from the article that it's a balance pre turbo between getting response and enough pressure to spin the turbo, but post turbo you just want to get the gases out as quickly as you can so bigger is better. I'm just not sure what a dustbin size tube coming out the rear of the car is going to look like 
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Blu3R
1,399 posts
68 months
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joust said: I'm just not sure what a dustbin size tube coming out the rear of the car is going to look like Aren't there many Corsas or Saxos round your parts?
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