Quote:
Originally Posted by Juiced46
This is very nice and I cant wait for this to come out because I will most likely be purchasing one. However IMO a 4" DP on this turbo may be to big. Bigger is not always better. Yes the object is to have less backpressure and get the exhaust out as fast as possible. A 3" pipe would be plenty sufficient for the stock turbo(even for an upgraded one) to do this. I have a feeling that the 4" DP will actually sacrifice spool time and not help it spool quicker.
For example. Im heavy into modding late model mustangs. Ive built a few single turbo 4.6s that make in excess of 800rwhp. The setup consists of usually a single 76mm or 78mm turbo and a 3" downpipe. When we switched to a 4" DP, it took the turbo about 300-500rpm longer to spool. We did pick up power, but spool time did sacrifice. Now doing this on a much smaller turbo, I dont know how it will react. I hope Im wrong, but its just something to think about or maybe even test if you have the time to do such a comparison.
Dave
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There's a simple explanation for your experience on turbo Fords.
76/78mm is right at 3". Putting on a 4" exhaust will add an expansion loss as the exhaust flow slows down as it transitions from 3" to 4". That loss is much bigger than the extra flow area of the 4" for spooling.
This downpipe looks like it will also expand a bit after the turbo flange. A 3" might be better for spool, but like you said, you picked up power on your Fords with the 4".
Now someone get this thing on a N55 and start tuning. I want to see how the turbo does at high RPM where Shiv was reporting difficulty holding boost (no more than 12-13 psig I think).
On my old STI a better DP was key to letting the turbo spool higher and produce higher boost at high rpm. I'm guessing the N55 will be the same...