Zmanco Posted May 14, 2009 Share Posted May 14, 2009 I need advice on my exhaust choices. Although I haven't found it yet, I'm planning on a T3/T04E-50 turbo with the stock turbo exhaust manifold. My question is whether to go with a 2.5" or 3" exhaust? Performance target: I'm aiming for 250-275 whp using a shaved P90 head (8.4:1 CR), unshrouded valves, with MSA stage I turbo cam. Drivability is key for me. I would like to have decent boost by 3k rpm, full boost by 3500 with power to 6500. 2.5" Pros: my existing 2.5" piping is in good condition. I plan to replace the NA muffler with a straight through magnaflow. I could go with the MSA 2.5" downpipe which would make getting the car to the muffler shop a lot easier. I would only have to pay to weld up a flange to connect to the existing pipe and change the muffler. 2.5" Cons: Won't breath as well as 3", might result in the turbo spooling up slower. 3" Pros: better top-end power, faster turbo spool 3" Cons: I'll need a full custom exhaust which is bound to be a lot more expensive than if I stay with 2.5", no easy way to get the car over to the muffler shop without causing noise problems in my neighborhood. So I'm looking for feedback if the benefits of a 3" system make it worth the cost and hassle. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 15, 2009 Share Posted May 15, 2009 So I'm looking for feedback if the benefits of a 3" system make it worth the cost and hassle. Its worth it. Cost and hassle are one time things. Driving around with your two and a half incher wishing you had a three incher will be with you the entire time you own the car. Quote Link to comment Share on other sites More sharing options...
softopz Posted May 15, 2009 Share Posted May 15, 2009 It will get you to 260 hp easier but you did mention you are looking for drivability. Not that 2.5 " wont. Hows this get rid of that NA muffler and go with a 3" magnaflow muffler. Just run a reducer then if that still doesnt cut it you can always change the rest.You also mentioned you wanted power pretty low so what if the turbo spools faster My setup with my l28et 2.5"downpipe ----> 3" ---> 20 " resonator no muffler yet, its not loud at all. You also have to consider turbos muffle it down, however if you do change the exhaust side of the turbo to a t4 than it will be much louder. Quote Link to comment Share on other sites More sharing options...
jc052685 Posted May 15, 2009 Share Posted May 15, 2009 Go 3" Quote Link to comment Share on other sites More sharing options...
Rustyfriend Posted May 15, 2009 Share Posted May 15, 2009 How bad is it to run a 2.5" downpipe to a 3" exhaust? Does it mess with the turbulence of exhaust flow or does it not really matter because turbos just want no pressure at all? I ask because I have an MSA 2.5" downpipe and I am in need of exhaust. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted May 15, 2009 Share Posted May 15, 2009 (edited) I ran a 2.5" mandrel bent downpipe to 3" mandrel bent exhaust, put down 232rwhp and 281ft-lbs with the stock turbo. There is little point in putting a 3" downpipe immediately after a 2-1/8" (or in the case of the T3/T4E-50, 2.5") diameter turbo outlet in my opinion, for packaging reasons I still plan on doing a 2.5" DP to 3" exhaust with nice transitions with my T3/T4E-50 as well. I do believe it's important to use 3" as much as you can, but ideally I'd use a 2.5" to 3" cone off the turbo, as long as I could fit. Edited May 15, 2009 by Drax240z Quote Link to comment Share on other sites More sharing options...
Zmanco Posted May 15, 2009 Author Share Posted May 15, 2009 I hadn't thought of using the MSA 2.5" downpipe and then going 3" the rest of the way. That solves my problem of getting the car from my garage to the shop. But that has me wondering if anyone sells a prebuilt 3" downpipe? I've seen a few people mention Vildini Motorsport in their signature, but wonder if they just do local work. Quote Link to comment Share on other sites More sharing options...
Rustyfriend Posted May 15, 2009 Share Posted May 15, 2009 Are you using the stock turbo? Based on what I have seen with fitment of the 2.5" downpipe from MSA, I wouldn't want to go much larger with a 3". It is tight enough trying to get nuts on with the smaller 2.5" pipe. Quote Link to comment Share on other sites More sharing options...
Pyro Posted May 15, 2009 Share Posted May 15, 2009 if your 2-1/2 pipe is in good shape then use it for now. Get the car running first and upgrade the exhaust later. I'm using 2-1/2 inch mandrel bent system and a dynomax turbo muffler with a msa turbo stage 1 cam, full boost by 3500 and power to 6500. t04b-h3 compressor with a T3 stage 3 turbine. makes around 275hp with 13 psi of boost (110 mph in the 1/4 mile). Quote Link to comment Share on other sites More sharing options...
cockerstar Posted May 16, 2009 Share Posted May 16, 2009 With a 3-inch system you're going to see gains like everyone has said, but it might be a good idea to clamp up the existing 2.5" system to get all of the kinks worked out of the system if you aren't made of money. Your only cost for the 2.5" system is the down-pipe, which will be the same with either application, and you can always move to 3" in a few weeks for approximately the same price. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted May 16, 2009 Author Share Posted May 16, 2009 Thanks for the idea Pyro and Cockerstar, I think going with the MSA down pipe and the rest of my existing exhaust to get the car up and running is a good idea. From there I can decide if I do a full 3" or just the back half when I change the muffler. Quote Link to comment Share on other sites More sharing options...
Zee77 Posted June 7, 2009 Share Posted June 7, 2009 Zmanco, you should check out this topic: http://www.zcar.com/forums/read/1/2057378 on zcar dot com by slownrusty. He is from down here in Colo Spgs though I am not sure if that is where the custom exhaust was manufactured. IHTH, and thanks for the info on the machinist for my flywheel! Kevin Quote Link to comment Share on other sites More sharing options...
Turbo7MN Posted June 7, 2009 Share Posted June 7, 2009 Can you really have to big of tubing after the turbo Best to do it right the first time and not have to go back and do it again. Quote Link to comment Share on other sites More sharing options...
Tony D Posted June 11, 2009 Share Posted June 11, 2009 Yes, the debate over the 3.5" got heated... I "cherry picked my facts", LOL Quote Link to comment Share on other sites More sharing options...
Hitman Z Posted June 11, 2009 Share Posted June 11, 2009 Go with the 3 inch. Quote Link to comment Share on other sites More sharing options...
slownrusty Posted June 11, 2009 Share Posted June 11, 2009 Go with the 3 inch. nah...3.5in! Quote Link to comment Share on other sites More sharing options...
johnc Posted June 11, 2009 Share Posted June 11, 2009 (edited) How about 5"? Here's a car I crewed on at the Rolex 24 way back when. You could not stand with your ankle next to the exhaust when the car fired up. It would actually light your pants leg on fire. Edited June 11, 2009 by johnc Quote Link to comment Share on other sites More sharing options...
Zmanco Posted July 29, 2009 Author Share Posted July 29, 2009 I was just reading the exhaust section in Maximum Boost and saw his curve on p133 that correlates exhaust pipe diameter to max hp. According to him, 2.5" is good to about 475 hp! That seems rather optimistic compared to the experience on this forum. Any ideas why he is so far off of what others here experience? Quote Link to comment Share on other sites More sharing options...
big-phil Posted July 29, 2009 Share Posted July 29, 2009 join the 4" club, I'm lonely:icon53: Quote Link to comment Share on other sites More sharing options...
Pyro Posted July 29, 2009 Share Posted July 29, 2009 maybe he is talking dual 2.5 inch on a V8. 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.