Will be fabricating downpipe for 2L 16v turbo and wondering what diameter tubing to use, 2.25" or 2.5". Specs are:
Street driven, NOT race car, maybe occasional 1/4 mile at local track. 1984 Rabbit Gti, 2L 16v with 83mm pistons, 8.5:1 compression. T3 60 turbo with .63 A/R running 10-15 lbs boost, starion intercooler, running Holley Commander EFI with 50 lb injectors.
Downpipe will join to hollow cat, 2.25" TT cat back system with low restriction muffler.
I am assuming that I will get good boost around 3k rpm. Question is, what diameter pipe to get, 2.25" or 2.5". Don't know if 2.5" will even fit in Rabbit. Don't want to go overboard on downpipe because I want to keep decent exhaust flow velocity when off boost, but frankly don't know what size would be best. This is first turbo project so any input welcome. Idea is to get stainless mandrel bent U bends, flex pipe to fabricate downpipe.
Victor
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2.5 will fit. i have the ford t3 style exhuaust flange w/ interanl wastegate on my turbo. The exhaust dumps on the left side of the car (driver). it has 2 studs, and a "cup" that allows the downpipe to rock some. this eliminates the flex pipe that u would otherwise have to put in the downpipe. i took the stock ford downpipe (2.25) and used that for about 6 inches so i could angle the dowmpipe away from the linkage and have the stock mounting flange intact. Cut it off at around 6 inches and from there, it is 2.5 str8 back and over the axle beam. True, it aint pretty- but it is pretty cheap:) I had a universal aftermarket 2.5 cat ($50) in place, but took it out and str8 pipe since no emissions for a yr. Went the cheapest "legal" way i could go to pass visual inspection, so i used a cherry bomb muffler ($20). In pa, all u need is exhaust to exit rear of car, have a cat, and a muffler. The cherry bomb made my car quieter it sounds like. Don't sound like ass either if ur looking for something to please ur ears. Personally- i was looking to please my wallet which is why i used it. the 2.5 system was fab'd from mandrel bends from www.stahlheaders.com so 100 max for bends should get u done. If u got a welder, ur in "bidness". 170 bucks and ur time into a 2.5 turbo back exhaust that dont look pretty, but works!
sails
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The biggest pipe you can fit on the hotside outlet is always best. The turbine works on pressure differential so any back pressure at all is detrimental. 3"-4" would be good as far back as you can run it, but that probably won't fit under an A1.
> Don't want to go overboard on downpipe because I want
> to keep decent exhaust flow velocity when off boost
Are you thinking that the exhaust works the same on turbo motors as it does on NA motors? This is definitely not the case, as there is no extraction effect whatsoever post-turbo. You might get some pulse effects up to the hotside housing, if you have tuned length runners on the EM, but there is nothing you can do except get rid of the used up gasses after the turbine.
Just one rule to remember on turbo cars: BP is Bad.
Eric
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hey victor, i go to my boss' house all the time. do you want me to stop by sometime and show you my downpipe? we can laugh at my welds together (note to self: must get tank of argon). i ended up having jim re-weld my manifold and it is now very similar to yours so the downpipe should work too.
also, because of the angle the manifold puts the turbo at, i was unable to use the ford internal wastegate flange. so i dont think you would be able to use one either, but i have one if you want to try it. i ended up using one off a volvo, but a saab would work too.
answering your first question, i went with 2.5 from the turbo back. i have to weld on the shell from a cat still.
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Sure sounds great. I just moved to Silver Spring, just a couple miles north of where I used to live. I am going camping this weekend, but I'll hit you up next week. Would love to see your setup.
BTW, the wastegate I have is from a Saab 900.
Victor
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We sell a 3" and a 3.5" ($100) mandrel pipe kit that was used to build our downpipe and exhaust system with. We are using the IHI Rhb5 turbo from a Thunder chicken. We had to clearence the shift linkage to 1/2 the normal size to allow the 3" DP fitment. We used a flex section after we broke one ($275) manifold. use the 3" DP you will like it.
K
www.perfectchoicemotorsports.com
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