Turbine housing size vs turbine wheel size

After doing some back to back turbine housing swaps, data logging spool up ect with a 200 rpm spool gain, I am now left wondering what effect could changing the exhaust wheel size have on spool up. Does the smaller wheel spool quicker due to its smaller rotating diameter and mass ( not talking about transient response here) or could a larger wheel in the same small housing actually out spool the smaller one due to a greater leverage angle due to its larger diameter. I have not measured exhaust manifold back pressure as yet but just trying to get the most out of the setup down low, without sacrificing top end.

I cant really find any real info anywhere on this kind of swap ...... If anyone has some real world experience .... fill me in !!

You will always reach a point to where you cannot improve the turbo anymore.

Changing the turbine wheel would increase the spool, but going larger or smaller will always result in less performance.

Smaller will only cause it to spool faster, making the turbo efficiency point lower in its top end (what will eventually happen is you will overspeed the compressor, and no more gains are seen)

Large will just cause more lag, and in fact same result if you just go bigger turbine housing, so a useless thing to do.

So to answer your question, doing stuff to turbine wheels or compressor wheels is something you leave to F1 teams or top engineering guru's, nobody else does it and with the tech and choice of turbo's these days, there no reason to.

It will just give you one step forward, and then two steps back...

Instead of looking at the turbo to increase performance, take a look at what your engine is, what modifications it has and what you can do to improve it. Too many people only consider turbo size and leave it at that. When really, you need to make your choice of turbo on the basis of your engine, your goals, and what you can do/ have done.

Think of your engine as the pump, if you can increase its performance and flow, it will increase the turbo's performance and efficiency.

the turbo will in return recirculate this and it will be a repeat of itself (how a turbo works blahblah)

There are many things you can change to improve the turbo's performance, even without having to change it.

Cylinder head mods make alot of difference, cams etc. Which manifold you are using, the wastegates and their size, your intercooler and piping size.

Once you have improved these as far as possible to increase flow and efficiency, you could also opt for a quick spool valve.

Hopefully this gives you a bit of an idea, im trying not to go to deep into this as we could write a book lol.

I saw a lot of people that are trying to prepare a low displacement engine with WIDE torque rack. Just beleive that`s impossible only changing dosen turbocharger versions. The small turbocharger gives you good low rpm torque and dead engine on high rpm, the medium one will not have enough exhaust gases in low rpm and in some cases will die far ahead of redline. The big one will completely kill the low and medium rpm torque, but give you top end torque burst. It`s everything about the low displacement engines until you can change the volumetric efficiency of the engine using VVT. After altering to VVT you will stop messing up with turbocharger selection. I`ll give an example.

I had a lot of 3Gen 3SGTEs 2.0 seen on dyno in diffirent configurations. Different cams (from stock to 272 duration), turbochargers (from stock and GTX2867 to GT3582) and so on. And there was no car that could shift torque rack earlier than 4000 RPM. Car owners showed dyno graphs to each other and were happy. After that I saw a EJ20 on the dyno fitted the same GTX2867 and it bursted 700 H*m of torque from 3300 RPM falling to 400 H*m on 7000 RPM. It has 500 H*m of difference with another 2.0 engine fitted the same turbocharger on 3300 RPM! What I`m talking about? Do not waste your money)