Greetings to all,

I am interested in learning more about turbo housings, differences, sizing, as well as understanding the difference between different turbines and compressor wheels.

This is my current knowledge, which may or may not be 100% correct, I'm happy to be corrected if my knowledge is in error.

16g, 18g, 20g, TD04, TDO5, TD06, are all different types of housings. (the first three are compressor housings and the last three are exhaust housings unless I have them back to front). I don't have any context as to how big or how small they are or how to identify one from another or what mass flow rating they are suited for. For the more technically minded, I'm not a fan of the peak power number; instead I'm more interested in the area under the curve for those to whom that makes sense.

The A/r ratio; which is dictated by the casting of the housing; will influence the spool characteristics as well as the power potential of the turbo.

How does the trim of the compressor and exhaust turbine wheels affect the behavior and the spool? As well as, to what extent does it affect the behavior and the spool?

Also, how does a VF48 compare to the TD06 etc?

For the record this is going to be fitted to an EJ25 on an STI.

 

you're right on the compressor wheels, but the TD0x is more than the exhaust housing. The CHRA (bearing housing in the middle) is also different between the different turbo series. For example, the td04 turbine shaft is smaller than the td05 / td06 turbine shaft, and the housing itself is much smaller. A td06-20g compressor wheel cover also will not fit directly onto a td05 series CHRA etc, so some care is needed if building a hybrid turbo from scratch.

The td04 further comes in a bunch of different exhaust wheel / housing configurations, all the way from the tiny td04, through td04L, td04H, and td04HL in increasing size (I might have the L vs H in the wrong order). The td04HL should support up to about 340 bhp, which is already into the TD05H territory that the classic STIs came with.

I used to run a td05H-20g hybrid turbo on a 2.0 WRX, and it had great peak power IMO (370hp on normal pump fuel), but it was quite laggy looking back at things. I then tried a td06-20g (i.e. the bigger series) - this was worse in terms of spool threshold (1 bar at about 3600RPM on a 2.1 (stroker) with WRX heads). Would have probably broken 400hp, but I also didn't like the lag of the thing. Personally I have now detuned massively, to a td04HL with a 15T wheel - I think this has put me in the high 200s, and once the engine is properly run in I will change it to a td04HL-19T, which should get about 330hp hopefully.

I think you need to decide what kind of power you want to achieve. With your EJ25 you will be getting better spool than me on my puny little 2.1, so you would probably have _great_ spool / lag from something like a td05-16g/18g billet. Having said that, people keep saying that things have moved on in terms of turbos. If you have lots of money to spend on a turbo, it might be worth looking at some garret based offerings (or indeed the IHI VFxx series), maybe, but personally I think that for the bang for the buck, the mitsubishi based turbos are hard to beat (i.e. the TD series).


In terms of what affects spool, it is basically:
- Larger exhaust wheel and exhaust housing size makes the turbo laggier, because of increased mass of wheel, but also because the flow goes across a larger area so is comparably slower to the same amount of exhaust across a smaller area), but has higher peak flow capacity. I.e. a larger exhaust wheel / housing combo will make more power than a smaller one, within reason.
- Larger compressor wheel usually makes the turbo laggier again, but will flow more air so will make more power.

You can't however compare sizes directly between manufacturers. For example, if you compare a Mitsubishi TD05 series turbo sizew-ise to something like a Holset HX-35 (off some diesel trucks), the Holset has ginormous wheels, and you'd think it would never spool up, but it will make full boost on a 2.0 WRX (probably before 4k RPM). I think this might be because the compressor wheel doesnt' have to spin as fast as on a td05, because it is so much larger and has so much more flow capacity.

When I've ran "weird" turbos on my cars, the ones that have been rubbish have been the ones where the exhaust housing has been too big for the compressor wheel, so it's probably best to play safe with well known combinations (or at least not stray massively from them). I saw a 16g wheel kit for a td04 based turbo, for example, which I think will be absolutely terrible (but I am willing to be proven wrong).

 

Henrik,

Engine is in the process of getting rebuilt. Going to be fitted with forged pistons and Manhley aftermarket rods. Whilst I am interested in upping the power from 260bhp/200kW ATW; which was achieved with a turbo back exhaust and retune; as I mentioned earlier, I'm more interested in area under the curve than peak power. Currently have what I believe is a TD06 18g Kinugawa turbo.

I am a bit old school in terms of wanting to understand what I'm choosing and why, not just XYZ turbo for ABC horsepower

 

hmm, the td06 turbine is pretty big IMO, especially for an 18g wheel, but then you're on a 2.5 so have more exhaust to spool the turbo with. It will work, but I think you'd get better response with a td05 turbine and the 18g wheel, for not a lot of sacrifice in terms of outright power.

Having said that, a td05-18g is a very common turbo - if it's one of them you have, then that would probably work really nicely on the ej25
I think an 18g will make up to about 370-380 flywheel hp (some make more), which should give about 285 awhp, with a 25% loss factor.

​​​​​​i think the td06 will make similar power, maybe a tad more, but sacrificing at least a couple of hundred RPMS of spool.

 

Hang on - I misread .. do you currently have the td06-18g already fitted, and it made 260whp?

if so, you could probably fit a 20g wheel and cover, and get maybe 15-20whp more with similar spool, or go down one size exhaust size to td05 and get similar power but better spool.

 

Currently it has a VF48 that has chosen to make itself unserviceable.

Have gotten my on the TD06 18g, though it hasn't yet been fitted.

Off memory , the car is only running 17psi. As I understand, after the turbo back exhaust and tune, the main limitation to boost was the hyperutectic pistons. Though while on track, I did wonder how close to the limits of efficiency the VF48 already was.

You can continue to push a turbo harder, the problem is as it pushes harder the efficiency drops and the outlet temperature goes through the roof.

So the aim of the upgrade is to try and maintain it at peak efficiency.

Oh and for the record the 260bhp was achieved with the VF48.

 

if your on a standard piston/head gasket EJ25 than i would probably leave the track work alone- these engines just cant take it- a vf48 is about as far as i would go -all of the tdo5/6 based housings are fairly laggy and 25 year old designs,,,,although the ej25 will spin them all 5-600 rpm sooner than any 2.0litre engine and make **** loads more torque