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One of the not pretty things we saw with the ISR manifold was that the ports were all sized a little differently and a little crooked, but at least the holes were bigger than the ports and gasket holes so there was no flow robbing overhang of the flange and thus no real serious performance issue.One thing that we noted was that there were bits of welding wire and stuff that looked like machine turnings stuck in the runners. This sort of stuff can damage your turbine if it breaks loose. We spent a few minutes with a die grinder knocking it out. Not a big deal but it’s wise to inspect the insides of your runners before installing.
The ISR manifold came with these composite gaskets which are probably okay but we changed them out for MLS stainless OEM Nissan gaskets. We will try the provided hardware as well but if it gets loose we will switch to to ARP studs or genuine Nissan Inconel studs, lock plates and nuts which we have found to be bullet proof.
For a Turbocharger we selected one of Turbonetics new TNX series turbochargers, the TNX 20/52. The 20/52 has the capability to flow up to 450 hp which is more than enough for our use. The 20/52 has a T25 size frame and footprint so it is a great bolt on replacement for the SR20DET.The 20/52 uses an efficient TO4B compressor housing with a 0.60 A/R and a 0.85 A/R exhaust housing with an internal wastegate. The CHRA or center section uses a low friction dual ball bearing floating cartridge. Ball bearings can reduce transient response time by as much as 20% over conventional sleeve bearings.
With a floating bearing cartridge, the rotating assembly has vibration damping due to its suspension on a thin layer of the lubricating and cooling oil trapped between it and the housing. Typically found only in OEM turbo designs, this helps control shaft motion caused by higher order harmonics that can be damaging.
The bearing cartridge uses twin ceramic bearings which are longer lasting and lower friction than the typical steel bearings with dual oil seals at each end of the shaft. The ball bearings use steel bearing separators so the center section can be run dry for racing use. Great if you are trying to simplify your underhood plumbing.
The 20/52 compressor housing has a radiused 3″ inlet. The compressor wheel has a 52mm inducer and a 67mm major diameter. The compressor wheel and housing are designed using plenty of CFD (Computational Fluid Dynamics) analysis to optimize the aerodynamics for best flow and efficiency.The CFD goes hand in hand with FEA (Finite Element Analysis) stress analysis which enables Turbonetics engineers to pare down the hub size and thin the blades as much as possible. This improves aero without sacrificing burst or fatigue strength. FEA thus works hand in hand with CFD to maximize flow, broaden the operating range and minimize rotating inertia. This means more power, less lag and better durability.
The hot side of the turbo uses an inconel turbine wheel that has a 54mm major diameter with a 43mm exducer. The exhaust housing we chose is a free flowing 0.85 A/R although a faster spooling but more restrictive 0.65 A/R housing is available.Like the compressor side of the turbo, the turbine and housing make extensive use of CFD and FEA analysis for performance optimization. What we really like is that you can easily see that the turbine housing and wastegate will flow so much better than the typical T25 based designs that are common with this size turbo.
The turbine discharge diffuses into a large chamber with a 3″ V-band exit. It has a straight free flowing exit with a diffusion ring right at the exit to prevent odd flow mixing from the wastegate discharge disrupting the flow. The wastegate flow is introduced at an angle so as to be less turbulent. We feel that the design of this area alone will account for a decent bit of power and less lag than common legacy T25 related designs.
The internal wastegate actuator has a heat shield to help prevent it from getting cooked. We have seen this a lot with internal wastgate turbo on competition cars that are low mounted where they get a lot of heat soak. It’s a nice touch to prevent actuator failure from happening.
