The best turbo for a 998?
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Thanks Wil,
Wasnt expecting it all done for me.

A job worth doing is a job worth over doing

Wil, that looks spot on.

What we now need to do is to compare the turbine performance of each. Ulitamtely the back pressure created by the turbo has a far greater impact on performance than the compressor efficiency. To a some extent a poor compressor efficiency can e overcome by a good intercooler.

Compare the turbine performance for the GT1544:


With that for a GT1548:


Doing anything mathematically with these turbine curve is a long complex process, but I've been able to use this data in simulations and hence my opinions.

See how they peak at 6.4 and 7.9 lb/min. That is nearly 25% difference.

What that actually means is that the larger turbine will use more air and therefore less back pressue to drive the compressor. The power to drive the compressor is derived from a combination of flow and pressure. Say the compressor needs 30 units of energy. It can either get that from 10 flow units and 3 pressure units or 7.5 flow units and 4 pressure units. Efficiency also plays a role here but lets assume thet are the same.

Therefore, it can be roughly assumed that the GT1544 will generate 25% more back pressure than the GT1548. At 1.8 bara boost that would probably be around 1 barg extra back pressure.

How this impacts power/VE of the engine depends on many factors, but the difference is going to be far greater than the difference in compressor efficiency.

BTW, I'm 99% certain that the GT1548 turbine is identical to the R5 T2.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

How does opening the wastegate effect the back pressure?

I still like the 44 and we shal see how it works when I build it.

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The wastegate will dump the air that the turbine does not need.

The back pressure is largely determined by the size of the nozzle in the turbine housing.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I agree with all of that Paul, especially the fact that the 48 is the same as the T2.

I reckon to make a 100bhp 998 with supercharger like driveability but is all out of puff at 6k the 44 is the way to go.

To make a more conventional driving turbo engine that will make more like 120bhp at 7k I'd pick the 48.

Obviously, a hybrid of the two would be nice.

I wonder though if the turbines fitted to the 44s that are on diesels are the same spec as shown above?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Personally if I'm driving along at 3k and want some acceleration, I change down a gear, rather than wait for boost. Depends on personal preference.

Hybrid wise, the R5 T2 compressor is a 50 trim version of the Gt1548, so will have higher compressor efficiency at the flows considered.

Not sure about OEM GT1544s. If the flanges are as Garrett show, then my money would be on them being the same.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The problem comes when cornering speed for junctions, usually taken in 2nd gear, is below boost threshold. It's even worse when the junction you are turning into is then uphill.

In this situaltion, which is common for a daiy drive, having to change down is a PITA. And this is why a GT17 would be a dog. My IHI and the T2 are/were ok at the above in most cases, the 1544 would be very good.

Having said all that I have about the GT1544, I had one as an option and instead used the larger IHI.

Considereing availability, fitment, cost and target bhp, the 1544 is still a good choice in this instance. Garret list it as a 1.0l to 1.6l 100bhp to 150bhp.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

doesnt all the above depend on which turbine housing is fitted ? which a/r is used on the two turbine maps ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I think that we agreed a couple of years ago that the official Garrett data for the GT1544 is at best vague and at worst misleading.

The A/R of the turbines is shown on the maps. Supposedly 0.34 and 0.35 but vastly different

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Any ideas what sort of boost the standard actuator on a gt1544 would give me.

A job worth doing is a job worth over doing

Have a look at the pug gt15 from the 1.6 110hp model its a vnt as well abit bigger than the vaux ones but they are really smooth

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I gave a look at the vnt 15 turbo(gt1544v), it looks like the way to go alright, never heard of vnt untill you mentioned it but it looks like a good concept. according to the link below its also in the vw tdi engines.

http://www.ehow.com/list_7785525_garret-vn...ifications.html

Would this give as faster or simular spool up to a gt1544 and would it hold boost for longer. Ive also read that the actuator requires vacume pressure rather than boost. How would i get the vacume.

Anyone else running a vnt turbo.

i also came across this site, might be of use to someone. It gives the maps and specs of the gt series turbos (well some of them) and also the cars they can be got in.

http://turbochargerspecs.blogspot.com/2011...-hp-turbos.html

A job worth doing is a job worth over doing

I think these are the maps for it.
I plotted the points wil h gave for his 998 turbo on the map and they look good to me,
What do ye make of it, because to be honest i dont have a clue.

http://i1226.photobucket.com/albums/ee420/...Commpressor.jpg

http://i1226.photobucket.com/albums/ee420/.../gt1544vmap.jpg

Edited by jdisel on 8th Oct, 2011.

A job worth doing is a job worth over doing

did somone say VNT?

I've been dabling with the VNT's for a while now, there are a few quirks to them, they cam make boost from very low down, with a GT25 (which is big) ive seen boost at 2-2.5k,

som of them come with pressure actuators, and you can swap a normal actiuator onto them to use them on a petrol, they always seem to have a boost curve that rises with RPM, my current one on the std actuator climbs from about 5 psi at 2400 to 11 at 6000 in a fairly linear manner.

you can put an MBC inline to up the boost lower down, in which case you'l see the 5 psi at 2400 and max boost by about 3500 maybe less depending on engine load. trouble with the MBC is it makes it not very nice to drive, on the motorway at 50 if you give it 5% throttle to pass somthing it'll come on boost to over 10psi and take off, like wise if you come to an incline, keeping the throttle the same the incline will load the engine and you'll gain 10-15 mph, conversly on down hill you can find the boost drops and you slow down...

Really to make the most of the VNT you need to use some kind of closed loop boost controller to make it do what you want it to.

Thanks for all the replies but i have more questions.

How does engine load effect the boost when using a mbc.

How could i tell if the turbo was fitted with a pressure actuator and whats the difference to a normal actuator.

And is a vnt gt15 a better choice than the wasgate gt1544.

A job worth doing is a job worth over doing

The GT1544V still has that restrictive turbine.

If you are thinking of going VNT, then the Gt1749V would give you the low down response of the GT1544 and the unrestricted top end of the GT1752.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Is the GT1749V available in a "standard" layout, and if so, from what ???

The two I've just had apart (Mondeo TDCi) ar built into a custom exhaust manifold, ie, they don't have a conventional exhaust housing that bolts to a flange on an exhaust manifold, it's all one enourmous casting. From what I can see of pictures of other Ford and VW diesel applications, the same applies.

I too would like to know why they use a vacuum actuator in the diesel applications - I presume it's so the ECU can control the guide vanes rather than boost pressure alone, but that's just an assumption.

The other interesting point is that, as far as I can see, the 1752 (non-VNT) compressor wheel/housing is a straight swap.

Schrödinger's cat - so which one am I ???

Rod, A quick check of ebay reveals that VAG, BMW, Renault and even Honda have used the Gt1749V with a conventional turbine housing.

Joe, is the VNT control a bit too much for the MS3 to handle?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

i see what you mean paul. would the gt1749v have the same turbine map to the gt17,
Any ideas where i could find the maps for it, cant find them anywhere.

the only thing is all this seems to be getting very technical, would i be better off sticking with the gt1544 as this is my first turbo build. Might be a bit more straight forward than going with a vnt.

And out of curiousity joe, what would be the ideal setup for a vnt turbo in relation to when you get min and max boost and how does a closed loop boost controller do this.

Edited by jdisel on 9th Oct, 2011.

A job worth doing is a job worth over doing

Paul, I thnk the MS should handle it fine, either use a soenoid to bleed of to make the desired boost in closed loop, or as the output IS PWM you should be able to use it to control servo to move the vanes, in which case I suspect you can rig them up back to front so the vanes are open and the MS closes them to make boost, but thats somthing I need to try....


jd, ideally wou want to map the boost from an ECU, Ive been meaning to do this for ages but havent got round to it yet, essentially you have anm actuator set to the minimum boost you want to see, and the boost controller looks at this an bleeds off more and more signal air until it see's the boost that youve told it to look for.

theoretically you can do this with a simple MBC but in my experiance they go to a iger figure and then drop a bit of pressure through the rev range, when I had my MBC set for 20 it'd hot 20 at about 3k, and then drop to 15 at the red line, but as I said with the MBC you get the crap drivability.

Never really thought much about VNTs before. Need to walk before running sort of thing.

BUT what worries me is that without a wastegate, all engine exhaust flow has to pass though the turbine. Seeing as we usually only need a fraction of the gas to drive the turbine, is this not going to cause far higher back pressure than is healthy???

Apologies for thread jack.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I think the converse may be true,

size the turbine to be efficient at full chat, then bring it in earlier by speeding the gas up with the VNT ring,

That's right Joe, but where is the data that you need to correctly size the turbine?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Never realised the MS could give a PWM output,

would i be right in saying, that if you managed to get the MS to control a servo you could get whatever boost you want through out the rev range,

Found this link, shows how to wire up a boost solenoid to the MS with the addition of some electronic gizmos.

http://miataturbo.wikidot.com/ms-mods

Spoilt for choice i think.
But what worries me is not many people have used vnt turbos in their minis. Is wastegate just more straight forward and more reliable.

Edited by jdisel on 9th Oct, 2011.

A job worth doing is a job worth over doing

Alpa built a 998 using that VNT15, see here:

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=222687

After much messing around it got taken off, story here:

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=218764

It was swaped for a standard wastegated IHI RHF4

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=364031

Fastest 998 mini in the world? 13.05 1/4 mile 106mph