Originally Posted by Boosted Performance

Although they are both 6266 turbos, they are drastically different when it comes to performance due to the turbine housing size.



The V-band turbine (.82 a/r) is significantly smaller in physical size, and flows a lot less than the T4 1.15 a/r. I would only ever suggest the (largest available) 1.32 a/r for built engines...why?:



When I performed flow tests on the BP 1.15 a/r turbine by measuring the EBP (exhaust back pressure...pressure in the exhaust before the turbine) I found that the 1.15 a/r turbine is optimal for up to 600whp (6-14 psi of boost on pump gas) on this engine. Pushing more than that is possible, but efficiency goes out the window. The VHR is extremely efficient, and moves a lot of air...so the larger turbine IMO is the only way to go.



Basically, you do not want the exhaust back pressure to exceed the manifold boost pressure by more than 2 fold. So, if you are at 12 psi of boost, the EBP should not exceed 24psi. The 1.15 a/r turbine was tested at around 18 psi of EBP when the manifold pressure was at around 11-12 psi.



What most people forget is that whatever comes out of the compressor side is sent to the combustion chamber, fuel is added, and the mixture is ignited. All this hot gas has only one way out, and that is through a turbine housing. If the turbine is small, the exhaust will not vacate the combustion chamber as efficiently, in tern not allowing fresh new air to enter. (Yes, some goes through the wastegate, but most has to go through the turbine).



This is why I am so excited about the all new PTE 6870 turbo. It has a larger compressor wheel, but more importantly a much larger turbine wheel (high flow capability). This turbo should be the number one choice for those that have their engines built, and really want to push things the extra mile.