Hey guys looking for a bit of insight regarding turbine wheel sizes. I've never given this any thought at all but what are the pros/cons of say an s480 with a 102mm turbine wheel compared to the same turbo with a 96mm wheel with let's say a 1.15 housing?? More power less power?? Back pressure?? Faster/slower spool?? Or is it more of a snake oil until compressor wheel size comes up too?? Educate me guys I've never given it a second thought until recently that I've been hearing few guys talking about it. Thanks guys.

 

I'm no expert but in general a bigger turbine wheel should mean less back pressure. That could be good and mean more power on top. It could also mean your spool takes too long and car gets lazy. A lot of these drag race guys want the bigger turbo and just use a transbrake, high stall converter, nitrous and other tricks to get the turbo to spool earlier (or get to an rpm where the turbo is spooled, not really the same but same effect, hard launches and staying in boost). A guy who just uses a foot brake or manual shift or just wants a responsive street car has to be careful with turbo sizing. Its a good thing to check boost pressure vs backpressure... Typically street cars want 2:1 back pressure to boost pressure for good response without choking the turbo too much. If I were you I would find people with similar combos and see what turbo they use and how they like it, maube message them to see how spool is.

One more thing, for 1:1 backpressure to boost, using the best cam for an NA version of the engine will be best for power. Once you start getting into 2:1 you probably want less camshaft overlap. Maybe even a little negative overlap. I can't tell you the exact crossover points though. I can say Sloppy Stage 2 cam has 5 degrees overlap I believe and works fine with your typical 5.3/6.0 with 7875 turbo everybody has, its been done literally thousands of times. A turbo specific cam with slightly less overlap won't hurt though, might help depending on your combo. A cam with 30 degrees overlap will probably kinda suck to drive on and may hurt power.

I know I spoke in generalities but hope this helps!

PS: I'm a big fan of stock type long runner intake manifolds. In my humble opinion its not optimal for your typical 6000rpm street turbo to run a short runner manifold. Its going to hurt low end torque and cause it to spool later. Now if you are going over 7000rpm with a high stall converter then it makes more sense. I DO like aluminum intakes for durability reasons but a stock LS6 will take you really far.

PPS: that 6000rpm guy might find he likes something like the Truck Norris cam too. No cam is the best all around though, some are better than others but they are all a compromise.