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yeah you don't see to many people running the wastegates right off the manifold outlet.. I was always under the assumption that exhaust gas will take the least resistance path and if I were to angle the wastegates nicely on the manifolds my idea would work....but that's why I'm here asking questions. think I'm just going to do what everyone else has done and maybe just run a single 60mm wastegate right before the turbo inlet, and use the tried and true 2.25" O.D. pipe, coated and wrapped of course. that way I can potentially upgrade later on and get her up to the 800whp range without having to redo the whole hotside.
are you in the PNW? there is a local mandrel bending place other than CRMB that sells stainless bends for very inexpensive.
I'm thinking about just getting 2 of these.
http://m.ebay.com/itm/2-25-2-1-4-OD-16-GAUGE-MANDREL-BENT-SWAN-CUT-MANDREL-BENDS-ALUMINIZED-/262659618395?hash=item3d27bbb65b%3Ag%3AHyYAAOSwZJBYBkpj&_trkparms=pageci%253A04d26974-b268-11e6-88ed-005056bb1834%257Cparentrq%253A974b66641580a5e0b6fdf8d0ffee9ecb%257Ciid%253A4
that ebay link up there is my source. he's in Clackamas and is about half the price of CRMB for 16ga stainless. I did my most of my up pipes with one "swan-cut"
This is a close friends garage project I help advise on, it hasn't been to a dyno but it does has several time slips that might give you an idea on performance.
The system is 16 gauge mild, 1-5/8" headers in to 2" crossover, 3" DP, 78/75 Turbonetics. L33, e-bay studs, LS9 gaskets, BTR spring package, cam spec'd for this combo and turbo.
This is in an 87 Short Bed GMC truck. he hasn't weighed the truck, but we know it's well north of 4000lbs. the system was built small to be an instant spool for a fun street toy with a goal of low 11's to high 10's. so far it's drastically exceeded expectations as it has been 9.71 @ 138 on a "test and tune prepped track with 20lbs of boost. the truck started with 78/68 Turbonetics, then the 78/75, so far it seems the turbo is still the exhaust choke point. i'd like to see him put a bigger turbine turbo on it and see what it does.
here's one of the early build pics, just a simple routed system.
So after more reading, I think I'm gonna go for it. however, I think I'm going to run a 44mm wastegate per bank coming right off the manifold outlet BEFORE the 2" crossover pipe, that way there will be no back pressure issues while still having the fastest spool possible running the small pipes. if that makes sense. sounds good anyway...
Smaller piping won't raise or lower the back pressure unless it is the choking point in the system. In your case the turbo will be, not the piping. Using larger or multiple gates won't effect back pressure... at all. It will take "X" amount of drive pressure to make "Y" lbs of boost on your specific setup, period. Adding 4 60mm gates won't change that, or lower back pressure.
Smaller piping adds speed/velocity to the exh. gas, which is what aids spool. Once your exhaust gas passes a certain speed the flow becomes turbulent and causes drag. If your exhaust ever goes sonic (around 1100 FPS) it runs into serious drag. You want to avoid that.
IMO, keep the rpm reasonable and you'd be fine with those goals on a 5.3. 2 38mm gates in plenty (assuming they are placed correctly), 44 is needless overkill.
Smaller piping won't raise or lower the back pressure unless it is the choking point in the system. In your case the turbo will be, not the piping. Using larger or multiple gates won't effect back pressure... at all. It will take "X" amount of drive pressure to make "Y" lbs of boost on your specific setup, period. Adding 4 60mm gates won't change that, or lower back pressure.
Smaller piping adds speed/velocity to the exh. gas, which is what aids spool. Once your exhaust gas passes a certain speed the flow becomes turbulent and causes drag. If your exhaust ever goes sonic (around 1100 FPS) it runs into serious drag. You want to avoid that.
IMO, keep the rpm reasonable and you'd be fine with those goals on a 5.3. 2 38mm gates in plenty (assuming they are placed correctly), 44 is needless overkill.
I was under the impression that if I had the wastegates mounted BEFORE the 1.78 I.D hot pipes/cross over pipes, was that IF I did have a restriction, then when the wastegates both opened it would relieve that 'over pressure' almost like a band aid for having slightly too small of pipes. So what your saying is that the wastegates won't relieve backpressure but will relieve drive pressure and that only the turbo can be the culprit of high backpressure from the turbine side limiting exhaust gas flow? if my 1.78 i.d pipes won't cause any serious turbulance/drag I may try to use them for the fastest spool possible on the 7875 I have, however being that I will be using a pro billet 3800 stall, th400, and a 3.73 gear with a rather large cam and stock heads, I will probably have absolutely no issues spooling up this turbo in a 3300lb car. so maybe just go with the 2.25 o.d pipes lol, this is my first ls turbo build so please go easy on me.
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