MECCANO Posted June 9, 2011 Share Posted June 9, 2011 Guys, I've got to cobble together and exhaust system soon, and am trying to establish the sizing of silencers. For ease of installation i'm thinking of using two silencers instead of one larger. So my question is: Do two 12"x6" free flowing silencers in series equal one longer 24" x 6" free flowing silencer? (Given they are both a 2.5" system) Or do the smaller silencers work less efficiently to the longer single? Thanks in advance Chris Quote Link to comment Share on other sites More sharing options...
Dunc Posted June 9, 2011 Share Posted June 9, 2011 If by free-flowing you mean a straight through silencer with minimal baffles, then two would be marginally more restrictive. It wouldn't be due to the silencers themselves, but to the restriction on the flow of gasses caused by the short length of pipe between them. If it's for a V8, I built a system several years ago that had only one silencer, from a Ford Cargo. That was quiet enough but let things breathe nicely and seemed to provide adequate back pressure. Best of luck, remember to joggle the joints so you don't leave a weld flange on the inside. Have fun. Quote Link to comment Share on other sites More sharing options...
MECCANO Posted June 9, 2011 Author Share Posted June 9, 2011 Cheers Dunc Yeah thats the type i mean Its actually for a 2.0l turbo 4 pot (Rover t16) Hopefully the turbo will be of some assitance to quieting it down as well. Chris Quote Link to comment Share on other sites More sharing options...
Dunc Posted June 9, 2011 Share Posted June 9, 2011 Same as the Tomcat motor? Not sure how much back pressure they need, but yes the turbo will hush it down loads. There was a Vizzard book on Turbos I read years back, that had a load on building exhausts in it. Quote Link to comment Share on other sites More sharing options...
MECCANO Posted June 9, 2011 Author Share Posted June 9, 2011 Same as the Tomcat motor? Not sure how much back pressure they need, but yes the turbo will hush it down loads. There was a Vizzard book on Turbos I read years back, that had a load on building exhausts in it. Indeed it is I beleive a small amount helps to save the bearings in the turbo. Cheers for the tip off, will go off and google. Quote Link to comment Share on other sites More sharing options...
nicks90 Posted June 10, 2011 Share Posted June 10, 2011 Indeed it is I beleive a small amount helps to save the bearings in the turbo. Cheers for the tip off, will go off and google. the bit about back pressure saving turbo bearings is a red herring i;m afraid. If your turbo is set up to produce 18psi, then you will have a pressure differential across the turbine of X psi on the exhaust side to produce 18 psi on the inlet side of the impellor. (reason i say X psi is because there are efficiency losses in a turbo, its never 100%). At maximum boost, you are still having to create the same pressure differential across the exhaust turbine to spin the intake impellor fast enough to create 18 psi in the inlet. So for every bit of back pressure your exhaust creates in the system, the pressure on the exhaust manifold side of the turbo has to increase by an identical amount to overcome it. Quote Link to comment Share on other sites More sharing options...
Dunc Posted June 10, 2011 Share Posted June 10, 2011 Not heard about the bearing thing, although it's possible that may be slight confusion between exhaust flow and dump-to-atmosphere valves. They supposedly have the added benefit of prolonging turbo life because of less see-saw effect on the bearings at high loadings; high boost gearchanges for example where the turbo can momentarily stall. Dump valves by virtue of removing boost pressure altogether to help assist with fast spooling will naturally affect that. From the racing cars I worked on, and I admit my knowledge of turbo exhausts is much less, the purpose of back pressure was to smooth out the exhaust gas pulses. If the pulses aren't in sync it's possible for the exhaust gasses to almost 'block' (for want of a better word) the exhaust momentarily, obviously having a detrimental effect on performance. Once you're used to listening for it, if you hold a screwdriver at the collector just past the manifold and then put your ear to it, you'll hear a whooshing noise with an exhaust that flows efficiently with smooth exhaust gas pulses. When those pulses aren't smoothed out you can hear a faint tinny ringing noise over the top of the whooshing sound. Not the most technical of descriptions I admit, but it's the best I can do! Just build it, then refine it. Loads of good books out there too. Powerpro book on building and one of Vizard's many great books Vizard book Quote Link to comment Share on other sites More sharing options...
MECCANO Posted June 10, 2011 Author Share Posted June 10, 2011 I think you guys have hit the nail on the head. I've crossed my paths with so called "dump valves, Blow off valves" etc. Its always nice to gain a bit of clarity Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.