Thumper Posted August 3, 2005 Share Posted August 3, 2005 Ok i'm getting ready to install my engine. I am going to fabricate a dp for it once its installed. I am running the stock t3 turbo on 74 260z with the n/a 5-spd tranny. I have a 3" mandrel bent exhaust with a 3" straight through muffler. I will have about 250-280hp. My next purchase, which will be around christmas, will be a new turbo so I will have to make a new dp when I up the power anyways. I just cut off the stock dp from the flange. I will be reusing the stock flange. As I see it I have three options. A. Run a 2.5" dp with two 45 degree angles B. Have one 45 degree angle as a 2.5" then b4 the next 45 increase it to 3" C. Run about 1" of 2.5" piping then increase it too 3" while making the first 45 degree angle I have both the 2.5" and 3" mandrel bent piping. I have also ported the exhaust manifold and turbo. The dp hole and flange has been enlarged by 1/16". So what do you guys think is the added complexity and difficutly factor going to be worth it to run the 3" system or should I just be happy with my 2.5"? Thanks Quote Link to comment Share on other sites More sharing options...
Guest 73Turbo240z Posted August 3, 2005 Share Posted August 3, 2005 dump to 3" as soon as you possibly can in the exhaust path and call it a day. which btw, i have some very sweet machined 2.5" to 3" rings that i was going to use back during the volvo's days still sitting around, it's a hell of alot easier than filling the difference w/ welding slag. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted August 3, 2005 Share Posted August 3, 2005 I'm using Scottie's 2-1/2" down pipe. I used a Flowmaster cone to move it out to 3", it is a gradual opening over 8" of pipe. No complaints, it seems a perfect match to the stock T3 turbine. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 3, 2005 Share Posted August 3, 2005 This obsession with 3" DPs on the stock turbo's 2"+ exhaust outlet just cracks me up. I am doing just fine with a 3" DP on a P-trim exhaust and 520rwhp and a 2.5" DP is not enough for a little hair dryer and less than half that power? Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 3, 2005 Author Share Posted August 3, 2005 and a 2.5" DP is not enough for a little hair dryer and less than half that power? I have been reading alot of old posts and came to the same conclusion. I think I will go ahead and run 2.5" intill I clear the tranny then run 3" the rest of the way. Thanks Quote Link to comment Share on other sites More sharing options...
EZ-E Posted August 3, 2005 Share Posted August 3, 2005 You cant put it any better then that, the outlet on the T3 is 2.25 inches I believe if I remember correctly, so what would the 3 straight off really help, I think I would go with the 2.5 dp and then go to 3 and leave it at that. Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted August 4, 2005 Share Posted August 4, 2005 edit Quote Link to comment Share on other sites More sharing options...
proxlamus© Posted August 4, 2005 Share Posted August 4, 2005 notice how this downpipe starts at 2.5" and expands very quickly? Buy a reducer cone.. and weld it to the flange Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 4, 2005 Author Share Posted August 4, 2005 I do like the reducer cone. But I do not like the 90 bend then the 90 then the 60 then two 30's. I would rather run a 2.5" with two 45's similar to the downpipe scottie made awhile back. Picture stolen from wigenout-s30 post:twak: So I think i'm going to try to squeeze the 2.5" pipe right next to the tranny like scottie did. And if I can run 3" yay but I won't lose any sleep if I don't. Quote Link to comment Share on other sites More sharing options...
Guest 73Turbo240z Posted August 4, 2005 Share Posted August 4, 2005 This obsession with 3" DPs on the stock turbo's 2"+ exhaust outlet just cracks me up. I am doing just fine with a 3" DP on a P-trim exhaust and 520rwhp and a 2.5" DP is not enough for a little hair dryer and less than half that power? unless your mod time line involves a larger turbo soon there after to where doing the R&D now will save you fab time then. then again, could be like me, and just have a slightly bigger than stock snail on there... with a 3" outlet already there. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 5, 2005 Share Posted August 5, 2005 Most of your gain is going to be in the 45 angle replacing the stock 90 degree angle. I had read the 2.5" with 45 degree bend will flow better than 3" with 90 degree bend. So the 2.5" 45 degree should make a huge difference and be more than enough, as already stated. Perhaps the effort of 3" may prove useful on a ZX were the 90 degree bend is still present in the downpipe, as it will flow less than the 2.5" in the Z. Quote Link to comment Share on other sites More sharing options...
HeatRaveR Posted August 5, 2005 Share Posted August 5, 2005 So just where would one be able to get one of those 2.5", 2x 45-degree bend, downpipes...? I saw a groupbuy thread but nothing seemed to have come of it. Quote Link to comment Share on other sites More sharing options...
Thumper Posted August 5, 2005 Author Share Posted August 5, 2005 A couple of people on this site have made downpipes in the past. But the amount of time and the profit margin was to slim to justify continuing. As of right now if you want a downpipe you are stuck with either doing it yourself or buying it from MSA.http://www.zcarparts.com/store/merchant.mvc?Screen=PROD&Product_Code=15-6037-8-9&Category_Code=PTC15 Since I'm a cheap bastard i'm doing it myself. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 5, 2005 Share Posted August 5, 2005 The hardest thing for having one made for you at a local shop or by yourself pertains to making the turbo flange from which the 2.5" pipe can be welded to. I got a very nice pre-made flange from GrayZee on this site (very well priced). You can PM him and see if he can get you one (he might even be able to get you a complete downpipe as well, cheaper than MSA, but I'm not sure, just check with him). It will make it a lot easier (and much cheaper) to go to a good local muffler shop with the flange at hand than to have them make one, if they even will. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 5, 2005 Share Posted August 5, 2005 It will make it a lot easier (and much cheaper) to go to a good local muffler shop with the flange at hand than to have them make one, if they even will. Assuming this shop does mandrel bending. Quote Link to comment Share on other sites More sharing options...
Afshin Posted August 5, 2005 Share Posted August 5, 2005 You can also have them weld 2 pre-purchased 45 degree mandrel bends (will need several other pieces to be sectioned/welded for the final product). That way a good shop without a mandrel bender (which is rare in many areas) can make one for you. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 5, 2005 Share Posted August 5, 2005 Good point! Another critical thing about making the DP that routes between the bellhousing and tranny tunnel is the angle of the pipe off the turbo flange. You only need to be off by a couple of degress at the turbo end to have clearance issues. If anyone plans to mass produce these, get the 1st one perfect then make an accurate jig, else you are asking for trouble. Quote Link to comment Share on other sites More sharing options...
jeffp Posted October 8, 2005 Share Posted October 8, 2005 >You cant put it any better then that, the outlet on the T3 is 2.25 inches I believe if I remember correctly, so what would the 3 straight off really help, I think I would go with the 2.5 dp and then go to 3 and leave it at that.< That statement is true, but not entirely true. I have run the stock exhaust turbine housing for two of my builds. The stock housing is in fact 2 1/4" however, the housing, and the waste gate flapper and outlet(the part the bolts to the housing) can and SHOULD be machined out to 2 1/2" and a stage 5 wheel run to get to the higher hp output levels. That is minimum! I have tested the system back pressure with the 2 1/2" turbine housing, and my downpipe that starts at 2 1/2" ID and transitions to a 3" ID in about a 1/2" flare. My testing of the system yielded me exceptional results. @ 25psi of boost, I was getting 25psi or 24psi of back pressure @ the turbo inlet, the system NEVER reached the cross over point and my test was made @ 7K rpm's. To my knowledge, no one has ever done that test of a system. I did not waste my time with a 2 1/2" system, I was interested in getting the best results the first time so that is what I did. Now I am running a GT35 Garret and the exhaust turbine housing is perfect! the wheel is 68mm and the housing transitions to 3" @ the outlet of the housing. I reconfigured the DP to fit a quick disconnect and now the sytem is 3" all the way through. It took about 3 years for Garret to catch up with what I was doing with their old turbo's and, I also have two housings a .63 A/R and the standard .82 A/R turbine housing. The .63 housing was not available at the time I bought the turbo, and when I found out about the production of the .63 housing I got it, for about another 450.00 the turbo got expensive, but I now have all the options I want and need to optimize the turbo, and my 3" system. The parts are out there, but you are not going to get it for the standard 700-800 dollars like many want. But, when you go from zero boost to full boost @ 3K rpms, in the blink of an eye, all the way to redline, it sure makes it worth the time and trouble. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted October 8, 2005 Share Posted October 8, 2005 No disputing the results of your testing Jeff. Now, all the Zers out there with the stock or hybrid turbos with hogged out housings running 25psi and approaching 7000RPMs, please raise your hand. When someone gets to that point then 2.5" DPs, J/Y or eBay "JDM" I/Cs , SVO injs, etc, go out the window. What I have been saying all along is that if someone is using the stock turbo or one with the stock T3 turbine side and looking to make up to the 300hp range, a 2.5" mandrel-bent DP with 45* bends serves the purpose well. I would say that probably applies to 90% or more of the turboZs here. Quote Link to comment Share on other sites More sharing options...
GrayZee Posted October 9, 2005 Share Posted October 9, 2005 I remember when I first got my 3" downpipe. At the time, word around here was.. "it couldn't be done" A friend of mine convinced me to at least try and build one. Hey, I wasn't gonna argue, he welded it up for me! Scottie is right about the room for error. Basically there isn't any. If you are just a hair out on the angle it will be touching the firewall. That's the biggest reason I never really made a huge effort to build them. I also think that the difference between the 2.5" to 3.0" pipe is likely minimal. However if I were to build another one, I would see no reason to go backwards and make a 2.5" downpipe. It does take more time and fitting but I still wouldn't go back. I think that if you have the means to put one together yourself then you should go 3.0" just for the hell of it. All you need is the flange, reducer cone, two 45 degree bends and some straight pipe. If anybody wants these peices I can get them for you guys no problem. In fact, it's only the connection between the top and the first bend that is so critical. I might even be able to get them pre-assembled with the exception of that one connection. Then you could take it to a muffler shop and have them put the rest together. Of course, for anybody who dosn't aready know, a 3" downpipe with two 45 degree bends will only fit on a Z (not a zx) and it MUST be a Nissan tranny and not a Borg Warner. Oh, and if anybody wants parts to build their own 2.5" downpipe, I can get that too. Quote Link to comment Share on other sites More sharing options...
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