onephatz Posted November 27, 2003 Share Posted November 27, 2003 hey I've got a '75 with a '82 turbo motor sitting in it. the stock downpipe runs a little to close to the tension rod for me so I wanted to make a new dowepipe for it. question is how big can I go with a stock turbo? the pipe running out of the turbo itself looks rather small. I was going to use a piece of 3" mandrel bent pipe but, to me it looks like it might not fit there. Am I going to have to use a piece of 2.5" and info would be great. jesse Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 27, 2003 Share Posted November 27, 2003 2.5 is max for the T3 flange, but you can expand it to 3 inch after 6 inches or so from the flange and have a 3 inch DP. that's how mine is done. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 28, 2003 Share Posted November 28, 2003 Okay I see a lot of people recommending this... and I have one big question about the whole 3" exhaust thing. Isn't your exhaust only as big as it's diameter at it's smallest point? What I mean is like... okay if the whole xhaust is 3" mandrel, but you have one point in it that goes down to 2.5", wouldn't that mean the whole thing only functions as well as a 2.5"? Doesn't that render it useless to go any bigger in pipe from that initial opening from the turbo? I seem to remember learning this stuff in science class in school.... Quote Link to comment Share on other sites More sharing options...
onephatz Posted November 29, 2003 Author Share Posted November 29, 2003 *****Isn't your exhaust only as big as it's diameter at it's smallest point? I had this very same question when I posed it to a friend of mine who is a mechanical engineer. according to him, and the theory of fluid flow pressure is increased the longer the pipe that you have. so because the total length of pipe is going to be about the same, the only way to decrease the pressure is to increase the size of pipe. on a n/a car you smaller/larger pipe does matter, but because we are dealing with a turbo, it provides all the backpressure that the engine will need. after the turbo the quicker you can get your pipe big, the better. SO. 8' of 3" gives us X amount of back pressure and 1' of 2.5" gives us Y amount of back pressure, then you just add and bang, you have your total resistance. I really wish I could explain a little better, I suppose I will just have to wait for my fluid dynamics class. needless to say the way he explained it made more sense and bigger is better even if you have a few more restrictive areas. there really is no such thing as too big of an exhaust on a turbo car. jesse Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 29, 2003 Share Posted November 29, 2003 I was also told that the hotter air can travel better even in smaller diameter until it loses it's heat. Something to do with thermal dynamic. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 30, 2003 Share Posted November 30, 2003 onephatz - that was actually a pretty good explanation.. makes more sense now. I always thought a pipe system would be as restrictive as it's most restrictive point... i.e.: 8' of 3" and 1' of 2.5" would effectively make the whole exhaust act as 2.5". But it's easy to see how the TOTAL length and diameter of pipe, and different diameters, would all add up to effect the total pressure. LOL I make it sound even more confusing. In other words, I think I get it Quote Link to comment Share on other sites More sharing options...
BRAD D Posted November 30, 2003 Share Posted November 30, 2003 Use a 2.5" to 3" reducer (see photo) Quote Link to comment Share on other sites More sharing options...
onephatz Posted November 30, 2003 Author Share Posted November 30, 2003 *BRAD D* Is that all 2.5" piping. I have the stock down pipe off the car now and it only measured 2" going into the pipe (booooo). I bought some 3/8 steel to be cut into a new flange, is making a 2.5" opening goint to cause turbulance or should I go 2->2.5->3 for a smoother transition? jesse btw. that thing looks wicked. (me wants one Quote Link to comment Share on other sites More sharing options...
BRAD D Posted November 30, 2003 Share Posted November 30, 2003 That is all 3" but the little cone that is welded to the flange, it starts at 2.5" then goes to 3" 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.