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Old 04-08-2019, 04:42 PM   #1
89_740Turbo
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Default What mandrel bends are required to fabricate a 740 downpipe

What piping do I need to make my own downpipe? I figured a two 45° bends and a straight pipe? I dont want to over buy pipes and waste anything.
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Old 04-08-2019, 07:06 PM   #2
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On summit they sell 90 degree bends that have a lot of excess straight. You'll really want to put a flex joint somewhere in line because the engine moves so much, you"ll end up breaking something and it'll cause less vibrations down the line. Do yourself a favor and use a v-band right after the downpipe too.
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Old 04-08-2019, 07:16 PM   #3
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A v band is nice. I use the lap joint clamps down by the cat and under the car. Last time I made a down pipe I bought one 180 degree U bend and used that for both bends. Two O2 sensor bungs in the vertical down section facing to the front. A trans bracket and the suggested flex pipe are good, too.

For the connection to the turbo I had Summit exhaust and performance shop in Pemberton make me up a short stub pipe with the flare on the end to meet up to the turbo. For the flange I had some cut but you can probably buy some at ATP turbo or use an old one.
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Old 04-08-2019, 07:18 PM   #4
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Also one three foot piece of 3" tubing.
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Old 04-08-2019, 08:59 PM   #5
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Here's what I did, basically what people above said, but with pics No V band though, and the bottom flange is for a 3" cat. Also, this is a 2 piece unit that I used a SS band clamp on rather than welding.





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Old 04-08-2019, 09:03 PM   #6
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two 90's and a 22 to do it properly, otherwise you could make it with two 45's but a flex pipe helps.
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Old 01-13-2020, 10:36 PM   #7
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Quote:
Originally Posted by 2turbotoys View Post
Here's what I did, basically what people above said, but with pics No V band though, and the bottom flange is for a 3" cat. Also, this is a 2 piece unit that I used a SS band clamp on rather than welding.





How's that blow off valve working for you. Heard they are annoying. Aftermarket ones of course
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Old 01-13-2020, 10:57 PM   #8
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That is an external Wastegate, the Blow off valve goes on the intake side (typically replaces the stock CBV)
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Old 01-15-2020, 05:39 PM   #9
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Originally Posted by thelostartof View Post
That is an external Wastegate, the Blow off valve goes on the intake side (typically replaces the stock CBV)
Is there any benefit to replacing the stock CBV to a BOV other than the swish sound lol
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Old 01-15-2020, 07:44 PM   #10
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Quote:
Originally Posted by 89_740Turbo View Post
Is there any benefit to replacing the stock CBV to a BOV other than the swish sound lol
Just the opposite most of the time, just slap a mitsu. 15g on and make you life easier.
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