Parry_10 Posted May 19, 2013 Share Posted May 19, 2013 How far away from the turbo should I go from 3" to 4"? does it matter? Cheers Quote Link to comment Share on other sites More sharing options...
johnny g Posted May 19, 2013 Share Posted May 19, 2013 As soon as possible, IMO Quote Link to comment Share on other sites More sharing options...
Parry_10 Posted May 19, 2013 Author Share Posted May 19, 2013 (edited) Cheers Johnny. Also any reason why you think that? Just trying to get a better understanding. I could just go 3" dp+mp then go to 4" for the rest which would be easier and cheaper and would be good for the power I want but as im making it from scratch I think I might as well go 4 inch all the way and be done with it... Anybodys opinions, experiences on this i.e bhp/torque gains, noise etc would help me out:) (Im looking to make as close to 700 bhp as possible). Ive already got a 4" back box and enough 4" pipe to make a catback exhaust. Ive ordered some more 4inch pipe but that can be sent back and changed for 3 inch. Edited May 19, 2013 by Parry_10 (see edit history) Quote Link to comment Share on other sites More sharing options...
johnny g Posted May 19, 2013 Share Posted May 19, 2013 Just going my the logic of minimising any restriction and gas expansions mate. I remember Jamie putting a 3" exhaust on his 4" midpipe and it felt like the car was held back. I made 640@hubs with 3" all the way. If you push more boost, you might make 700, but you'd make more at the same boost with 4" Quote Link to comment Share on other sites More sharing options...
Parry_10 Posted May 19, 2013 Author Share Posted May 19, 2013 Just going my the logic of minimising any restriction and gas expansions mate. I remember Jamie putting a 3" exhaust on his 4" midpipe and it felt like the car was held back. I made 640@hubs with 3" all the way. If you push more boost, you might make 700, but you'd make more at the same boost with 4" Ok mate thanks for your input. If that is true then its a no brainer I will go 4 inch all the way. Quote Link to comment Share on other sites More sharing options...
mattdavies Posted May 19, 2013 Share Posted May 19, 2013 Some one uploaded a link for a company who dyno'd a car and change the exhaust a component at a time from the back to 4" and documented the power gains, with everything in 4" they made an extra 80bhp or something Quote Link to comment Share on other sites More sharing options...
Parry_10 Posted May 19, 2013 Author Share Posted May 19, 2013 Some one uploaded a link for a company who dyno'd a car and change the exhaust a component at a time from the back to 4" and documented the power gains, with everything in 4" they made an extra 80bhp or something Interesting was that a supra though? I was always going to go 4" catback its just the dp+mp I want to get a better understanding on really what the difference would be between 3" and 4" apart from 4" being louder and sitting closer to the ground. I was under the impression a 3" dp+mp are not a restriction upto around 700hp. But if what Johnny has said is correct that if I went 4" dp+mp I could make the same power at a lower boost setting then its a no brainer. Quote Link to comment Share on other sites More sharing options...
Paul Whiffin Posted May 19, 2013 Share Posted May 19, 2013 Interesting was that a supra though? I was always going to go 4" catback its just the dp+mp I want to get a better understanding on really what the difference would be between 3" and 4" apart from 4" being louder and sitting closer to the ground. I was under the impression a 3" dp+mp are not a restriction upto around 700hp. But if what Johnny has said is correct that if I went 4" dp+mp I could make the same power at a lower boost setting then its a no brainer. If I were aiming for 700bhp, personally I would stick to 3" all the way through, we regularly build 700+bhp cars with this setup no problem. Anything above around 750bhp you should be going up to 3.5", anything above around 900 then go 4". Quote Link to comment Share on other sites More sharing options...
dandan Posted May 20, 2013 Share Posted May 20, 2013 (edited) From memory I think my switchable exhaust system which can be either... 1) 3" with two straight through silencers 2) 4" with one straight through silencer and dumping out short, near the diff ...gained me about 30lb-40lbft and 30-40hp running in 4" mode. This is at the 590-620hp level with a T67 at 1.7bar with a 4" DP and MP. The gains may well be more if you go all the way back to the turbo at 3". IMHO 3" vs. 4" would depend on what power you are aiming for, whether you can get it all to the ground under 120mph (very important) and what you can tolerate noise wise. Edited May 20, 2013 by dandan (see edit history) Quote Link to comment Share on other sites More sharing options...
Dan_Turism0 Posted May 20, 2013 Share Posted May 20, 2013 Some one uploaded a link for a company who dyno'd a car and change the exhaust a component at a time from the back to 4" and documented the power gains, with everything in 4" they made an extra 80bhp or something think this is the thread you are on about - http://www.modified.com/tech/modp-1102-exhaust-test-tech/ Quote Link to comment Share on other sites More sharing options...
Parry_10 Posted May 20, 2013 Author Share Posted May 20, 2013 Cheers for the help everyone. Some good info in this thread which will probably help someone else out in the future like myself. I already have a 4 inch back box and metre long pipe so I'm going to go full 4 inch I think as I'm not bothered about the noise I can always fit one of them exhaust valves that jamie has in his gtr exhaust if needs be. Quote Link to comment Share on other sites More sharing options...
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