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Down pipe size, fabricating my own...

Old 09-18-2018, 12:45 AM
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Default Down pipe size, fabricating my own...


I bought the el-cheapo Chinese casting everybody hates but is used with a fair amount of success by many. I have a Garrett GT2554R turbo and a 1.8 VVT engine. Now I am fabricating the down pipe and, well, there is very little room. Here's what I was hoping to do:

It's a 2" welding ell, but I think it comes way too close to the bulkhead, doesn't leave room for the heater lines, and I cannot fit the nuts (or at the moment the temporary bolts) in the flange. Now I have the data on the turbo, the exducer size is 42 mm. If I use a 1.5" weld ell, that is 43,2 mm inside diameter. And it clears everything very well. Would this be very restrictive? I read about 3" down pipes. I am not looking for a ton of power, 200 whp is the goal. Of course after making the turn out of the turbo I can go larger.

I found this pic (not mine) of two down pipes for this application, the one on the left doesn't seem very large, either, from what I can scale from the picture:


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Old 09-18-2018, 09:00 AM
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2.25" would work.
2.5" is recommended and most setups use this size.
3" is best but tough to fit.

make the bend downward sharper to clear the shelf.
heater lines can be moved out of the way. And you can cut off the lip of the shelf for some more clearence
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Old 09-18-2018, 10:12 AM
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Do 3 inch if you can. It has way more better.
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Old 09-18-2018, 12:06 PM
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make it 2.25" and step it out to 3" after the bend.
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Old 09-18-2018, 12:32 PM
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Keep in mind, a 2" schedule 40 carbon steel pipe is about the same ID (~2.067" vs ~2.125") as 2.25" exhaust tubing, but quite a bit bigger OD (2.38" vs. 2.25").
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Old 09-18-2018, 03:07 PM
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Why don't you all just to millimetres?

I am using thick wall piping and weld ells at the moment, I get the feeling shouldn't. Reading your answers and other topics, should I go to thin wall exhaust tubes? Those 2.5" tubes are actually 2.5", not a lot more. And it seems they are available in a shorter radius, and I can whack them into a prefered shape. Right?


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Old 09-18-2018, 10:06 PM
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Like schedule 10 thick? I do believe you would want something ~.060" wall on 2.5/3" Dia.
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Old 09-19-2018, 07:34 AM
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You could also use FM’s down pipe, it’ll work with that manifold
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Old 09-19-2018, 07:57 AM
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2" out of the turbine is fine, i have customers make 450+whp with 2" out of the turbine and 1.5" out of the wastegate flapper.

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Old 09-19-2018, 09:28 AM
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Originally Posted by curly View Post
You could also use FMís down pipe, itíll work with that manifold
im sure thats "out of budget"
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Old 09-19-2018, 09:54 AM
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You can buy pretty tight radius pre-bends in any diameter you like. I buy the 180s and cut the amount of bend out that i need. You can go past 90 to get it away from the shelf and water lines then come back below the shelf.

this is the tightest 2.5" bend that I could find on summit

and probably the tightest bend you'll find. 2" pipe

or just filter down and choose the tightest radius you can find in the bend and diameter you need.

45-180s are also super useful for downpipes
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Old 09-19-2018, 10:12 AM
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+1 for buying a 45-180
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Old 09-19-2018, 03:45 PM
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Originally Posted by borka View Post
im sure thats "out of budget"
Well, yes considering I need to add 120 buck shipping and 25% import tax and VAT. It'll be 500 bucks before I get my hands on it. And if I can make something myself for a tenth of that price, I think it is worth a shot. Besides that, I like fabricating myself.

Anyway, thanks for all the useful info and data. I have found some 1,5mm wall thickness piping (bends, Y-pipes, reducers from one size to the other, etc) which comes close to what you all recommend. I was just looking at the wrong piping, first, with weld ells and matching tube. All bigger than the name suggests and thick walled.

I'll go do some shopping, now, hope to get the stuff in the weekend.


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