.50 trim vs .55 trim Garret - OM603 - PeachParts Mercedes-Benz Forum

babymog · #1 10-14-2010, 03:42 PM

So I'm looking at the two turbos, don't see any difference, apparently the same housings (except for the ARV but lets ignore that for the moment).

My limited understanding about turbos is that the trim is the geometry of the compressor wheel, and a higher number will move/compress more air at a given RPM.

Is this correct or is my information flawed?

compu_85 · #2 10-14-2010, 05:24 PM

There must be some difference, I doubt the extra .5l of displacement would make the 350 spool up so much quicker then the 300.

-J

DeliveryValve · #3 10-14-2010, 11:31 PM

In a perfect world a T3 wastegate turbo with a 55 trim would flow more but have a longer spool up time then a 50 trim turbo which would flow less but have a faster spool time. So the larger trim would have more turbo lag but theoretically more top end power.

Other factors to consider with the trim is the A/R ratio. Theoretically a lower A/R ratio would have a faster spool time and a higher A/R ratio would flow more for more top end power.

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babymog · #4 10-15-2010, 09:23 AM

Thanks, that is part of my question, does this mean then a higher flow per amount of exhaust flow due to a higher compressor wheel pitch (presuming all else in the turbo is the same)?

If so, I can see a slower spool due to compressor wheel resistance, but the ability to move more air once spooled.

DeliveryValve · #5 10-15-2010, 10:01 AM

Yes that is correct. It will flow a higher amount of compressed air per exhaust flow in a perfect world but with less efficiency.

But again that is one piece of the puzzle. You can end up with a lower trim turbo and flow more with other factors considered, which gets more involved.

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babymog · #6 10-15-2010, 12:55 PM

Thanks. I'm just looking for moderatly more flow without the turbine spinning faster than its designed max., thinking the .55-trim is almost a direct replacement (from the 603.970) for my .50-trim on the .960. Also going to eliminate the AFM under the air filter, which means new plumbing, and allows me to hook to the shorter intake-side of the .970 turbo which doesn't have the ARV.

Having my local Bosch shop turn the pump up for 20% more flow, should be a decent match.

ConnClark · #7 10-15-2010, 05:46 PM

babymog here is my two bits.

back when I researched it I think I found out all the 40,45,50,55, and 60 trim T3 turbos use the same compressor blank. They are cut differently to fit the different trim sized compressor housings. Its hard to say how a going from a 50 trim compressor to a 55 trim compressor will work because there are no published maps for the 55 trim compressor. I suspect that the 55 trim compressor was kept secret because it was the sweet spot and they didn't want competitors to reverse engineer their compressor.

In general with all things kept the same, going from a smaller to a larger trim means you are going to have the capability to flow more air. It also has other implications. You have to spin the thing faster to make the same boost. The efficiency at lower boost levels drops. The surge line generally moves to the right as trim increases.

When I replaced my 45 trim turbo with a 50 trim one I scaled and overlaid the maps and was able to see I wasn't giving up much low end or low boost efficiency. What I gained was top end power. I could see that this might be justifiable because in 83 they increased the lift of the cam on the OM617 so it would breath better.

If you were to intercool your 3.0l OM603 I would say going to the 55 trim compressor is a good bet. I don't know if it is a win without doing that however.

Also the compressor wheel is the weak link not the turbine.

babymog · #8 10-16-2010, 01:15 PM

Thanks CC, I appreciate the insight.

The .55 trim was on the same HP rated engine as the .50, the .970 vs the .960/1. Differences between the engine were more torque at low RPM, and a lower RPM limit on the .970 w/ .55-trim turbo. Since the turbo doesn't know the engine RPM, only the exhaust flow and intake flow, it must have been put there either for better efficiency, lower emissions, or more low-end. Your comment indicates it was not for more low-end, which must have been accomplished by the longer stroke, so it therefore was either efficiency or emissions or both.

So my application looking for moderately more boost/power, is perhaps a stretch, but I'll give it a try, it's a bolt-on change when I swap heads anyway. Intercooler? Not yet, working on it though. I'll look at EGTs and see where to tune the wastegate rod, hoping I can safely get to 16psi or 17psi. That with 20% more fuel via the re-tuned 603.970 IP should give me a bit more power with minumal smoke increase, provided the EGTs are not a problem. At this point the aftercooler/intercooler is merely an obstruction to airflow, not adding power. If I get to the limit of my turbo's available boost or to un-safe EGTs, then I will be able to use the cooling of the aftercooler for a denser charge or to reduce EGTs, it's on the wish-list, but a difficult task for such a small increase in fuel and pressure at this point.

Thanks again for the info, and all input/comments are welcome / invited.

ConnClark · #9 10-18-2010, 03:11 PM

babymog,

Seriously consider intercooling and if you do pay close attention to the forward boost drop. An intercooler can provide power all by itself (no additional fuel) due to less heat loss to the cooling system. Whether it is just an obstruction for air depends on if the boost drop has more of an effect than the change in charge density on trapped air mass. An intercooler can also provide benefits by reducing the work required on the turbine section to provide the same trapped air mass.

See the attached picture to see what an intercooler can do by itself with no change in fueling.

Dieselkraut23 · #10 10-19-2010, 01:10 AM

I put a kkk turbo on my 617 from 603 coz i was told it had 5 more fins.......ive seen no difference at all.

I had stock T3 Garrett before.

babymog · #11 10-19-2010, 09:44 AM

Needs more fuel.

More air with no more fuel will yield no additional power, can actually (slightly) decrease power from the additional heat and exhaust restriction.

Conversely, more fuel with no additional air/boost will add power, just not as efficiently, and only to a point. It is the cheapest (and crappiest) way to add a little power, the reason you see so many pickup trucks blowing soot through oversized pipes.

Tractor-pull engines etc. on the other hand, overfuel to cool the cylinders much like a piston aircraft. A completely different level in power/tune however.

Renntag · #12 10-19-2010, 10:30 PM

Has anyone made a neat install of an Air to air intercooler on a W124 or W123?
I have considered a water/methanol injection system. My 6.5 Suburban uses water/meth and it works well.

chuni959 · #13 01-05-2020, 12:02 PM

Quote:

Originally Posted by babymog

So I'm looking at the two turbos, don't see any difference, apparently the same housings (except for the ARV but lets ignore that for the moment).

Sorry for the blast from the past but this is the closest thing to an answer I have been able to find to far. I am swapping a 3.0l 603.961 (from an 87 300SDL) into a 93 w140 300sd with a seized engine and turbo. Instead of throwing down on a new turbo or CHRA I want to swap the .50 trim turbo into the w140 manifold. I wasn't sure if it would bolt right up but according to babymog the housings are the same so it should drop right in, right? Do I have to worry about clocking or anything? I know the turbo is .50 vs .55 trim but that's just the impeller not the actual compressor inlet size right?

If this doesn't work it's going to be really hard to justify $600-$1200 on a new stock turbo, I would probably just go down the holset/superturbo rabbithole at that point.

tjts1 · #14 01-05-2020, 01:52 PM

Yes you'll have to reclock the 50 trim if you use the .970 exhaust manifold. Its really easy assuming the bolts are not seized. Do it on a bench. Both impeller and housing are different. The T3 is really easy to rebuild and this is the time to do it. At the very least clean out all the soot build up in the center housing.
https://imgur.com/a/JHTUtt9

Addressing some of the earlier posts from 2010, on my 3.0 with a .970 manifold the 55 trim spools up faster than my old 50 trim. I think that's mostly because of the .970 manifold. It's just a much more efficient design than the 3 piece nightmare that came stock on my 87.
https://imgur.com/a/QK9t7oA