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Originally Posted by SSE 4 2SS
Sell the headers and like the others have said, you can use shorties or the stock manifolds... The shorties will flow better than stock manifolds....
Until you get into high boost levels (greater than 12 lbs) the stock manifolds are fine...
Headers are designed to scavenge exhaust by one pulse creating a vacumn to help pull the next pulse etc...
Turbo "manifolds" are just a device to get the exhaust to the turbos... The shorty "headers" will work better than stock manifolds, but like before, until you exceed 12 or so lbs of boost, stock manifolds are fine...
I was creating too much back pressure with the stock manifolds but I'm running as much as 24 lbs of boost to this point, soon to be around 30 lbs of boost... We have custom turbo "manifolds" made for the car...
Anything that will flow more air will allow for more power, and the stock manifolds do neck down quite a bit inside...
One pic is my original exhaust manifold, and the other is my new custom Turbo manifolds...
As you can see on the original manifold, there was a ton of backpressure and lots of associated heat... It was costing me power... at 18 lbs of boost, so we built the custom manifolds... We now have substantially less back pressure, and lots more available boost... We are tuned for 24 lbs with the right fuel in the tank but are going to 30 lbs before long...
One more thing to consider, is that if you are going to use Shorties, make sure they are substantial enough to support the turbos... With all the associated heat and weight of the turbos, you dont want them sagging and creating other problems...
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Given the turbocharger itself is the ultimate restriction in the system. When you changed the manifolds, and were able to make use of more boost, was that the only change made at that time ?
Ive just adapted some truck manifolds for my car, and decided to retain a single 2" ID Sch10 pipe to the turbo.
But even the BW with the 68mm turbine and 0.88 open scroll, where it necks down is surprisingly a lot smaller than the 2" ID tube I used to reach the turbo itself.
I know headers are more efficient in terms of power, and flow. But when you see how small the scroll is inside, it does make you wonder.
Also, how much backpressure vs boost were you seeing with the stock manifolds vs the tubular with the same turbos etc ?