quick garrett turbo question... opinions

Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
OK I really should be searching for this but I did give it a try and I'm in a bit of a hurry.

Choice of Garrett turbos for a 3b. T25 or T3? I thought I'd settled on T25 being optimum, but I see a lot of people are using T3's.

Shop is starting work today so please give me a quick opinion. Is it more along the lines of people use what's available, or is it more personal preference?

So far the engineer at my shop agreed about the T25, and he has a new one in stock.
 
Joined
Jun 10, 2007
Messages
5,503
Location
Kiwiland
Visit site
The T3 series is very old and isn't made by garrett anymore. Many other turbo makers make T3 based turbos and they come in a massive array of sizes.

The T25 series aren't currently in production either, but they are everywhere used in various conditions and directly interchange with some of the current Garrett GT series.

There are chinese copies of everything. If you're being sold a garrett, then make sure it is a garrett.

That turbo he's got appears to be a GT25 used on a 2.8 diesel chevy S10 sold in Brazil. It should work fine, but personally I'd be going smaller for more low end boost.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
yeah that's what his book said too, S10. And well they have "Garrett" deeply imprinted into the metal on the side, and no chinese lettering anywhere. They're a pretty solid outfit, I don't doubt the brand. I think it's most likely that being in South America they don't have the latest stock... especially on smaller size stuff since they mostly seem to do big rig stuff.
I don't think it's mapped to a 3b. Is that bad? I mean the stuff you guys pull out of junk yards isn't mapped to a 3b either right? One thing is though he had another T25 in his show cabinet but he said it was all wrong for my engine... it was a water cooled one.

As far as going smaller... is it a question of amount of boost power, or will it spool up later with the bigger one?
 
Joined
Jun 10, 2007
Messages
5,503
Location
Kiwiland
Visit site
As far as going smaller... is it a question of amount of boost power, or will it spool up later with the bigger one?

A smaller turbo will make boost at lower rpm and can also produce higher maximum boost. However with a 3B you won't be using the maximum boost your turbo can produce anway.
A bigger turbo will provide a little more power at high rpm for the same amount of boost.

The process of mapping a turbo is simply checking the engines airflow requirements are within the capabilities of the compressor and making sure the turbine is the right size to make boost when you want it.
Junkyard turbos can be a perfect match, even if the original manufacturer didn't design things that way.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
Rats. I thought I'd done enough research, but it looks like I really haven't. I think the guys were looking on my chassis for airflow requirements and such, but of course all that related to the 3FE. When I said T25 I guess they kinda shrugged and pulled one out of the back, thinking I meant GT25...

I've signed the work order and left Snowy with them, but I could probably still change turbo units at this point. They still have to put together the kit... (when I asked them about the exhaust manifold, they told me they would custom make one...!)


MERCEDES BENZ OM014A (IMPROVED) SPRINTER 310D VAN / VAN / PICK-UP A/R 0.35 GT25 704090-5001 DD704090-5001

So while we're on the topic... what does A/R stand for?
 
Last edited:
Joined
Jun 10, 2007
Messages
5,503
Location
Kiwiland
Visit site
So while we're on the topic... what does A/R stand for?

A/R describes the geometry of the scroll in the turbine/exhaust and compressor housings.
For a turbine, smaller A/R means it'll spin up faster. If this turbo does have a 0.35 A/R turbine housing then it probably is suitable for your engine.
Often you can get a range of turbine housings for each turbo with different A/R's to tune them for the engine.

For the compressor, don't worry about the A/R. You don't get any options on that side.


To confuse you further.
The old turbo model range had T25's and T28 which was bigger.
The T28 is the same family but has a slightly bigger core so exhaust housings aren't interchangable between the T25 and T28.
The old T25's had model numbers starting with a 4. My T25 is a "455767-0003"
The old T28's had model numbers starting with a 7.
Looks like that GT25 you've been shown is using the T28 size housing which is now used down to the GT20 size. I've got no idea on wheel size and trim though.
 
Last edited:
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
A/R describes the geometry of the scroll in the turbine/exhaust and compressor housings.
For a turbine, smaller A/R means it'll spin up faster. If this turbo does have a 0.35 A/R turbine housing then it's suitable for your engine.
Often you can get a range of turbine housings for each turbo with different A/R's to tune them for the engine.

So with this A/R this turbo should spin up sooner (I am assuming this means it will spin up at lower RPMs... am I wrong?) than say the GT2056 or the other two you mentioned before, but won't have as much boost at those lower RPM's?
 
Joined
Jun 10, 2007
Messages
5,503
Location
Kiwiland
Visit site
So with this A/R this turbo should spin up sooner (I am assuming this means it will spin up at lower RPMs... am I wrong?) than say the GT2056 or the other two you mentioned before, but won't have as much boost at those lower RPM's?

Changing exhaust A/R shifts the whole boost curve up and down. So smaller gives you more low end boost and boost at lower rpm.

I added some more to that post just above too. Finding more information on that OM014A engine that it's fitted to will help a lot.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
Changing exhaust A/R shifts the whole boost curve up and down. So smaller gives you more low end boost and boost at lower rpm.

So would you then take back what you said above, about going smaller for more low end boost? Because taking into account the new information that it has a .35 AR, that gives it a significantly smaller AR than previous models you've suggested...

If turbine AR shifts the boost curve, does that also affect the minimum RPM's to gain initial boost?

Also, what variable affects the curve width? (by that I mean RPM range at which you get boost).
My main concern with this turbo is altitude compensation... as a result I think what I want is one that will be operating during the maximum range of RPM's possible... I'll never be setting the wastegate high as the engine is 27 years old and has a long way to go...

On that note... with a larger or smaller turbo am I likely to notice different behaviours/handicaps as a result of low ambient pressure?

Sorry so much for my quick question. Thanks so much for all your help Dougal, this is really great.
 
Last edited:
Joined
Jun 10, 2007
Messages
5,503
Location
Kiwiland
Visit site
So would you then take back what you said above, about going smaller for more low end boost? Because taking into account the new information that it has a .35 AR, that gives it a significantly smaller AR than previous models you've suggested...

If turbine AR shifts the boost curve, does that also affect the minimum RPM's to gain initial boost?

The normal GT25 turbos have 0.64 A/R turbine. That was why I first said it was a little too big.
But with a 0.35 A/R turbine it is looking like a good match. To know for sure we'd need some more information on the engine that turbo is intended for.

It seems that your turbo shop will be familiar with that engine and have recommended that turbo to you because of that. In short, they know more than we do about this turbo.
But it is always good peace of mind to come to the same conclusion yourself.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
Now I'm really into the GT2056. I just did some more reading... looking at those graphs it looks like it would be the best in the size range for high altitude use... unless I'm totally off in left field. Crap, I hope they don't crank the price on me for that...
 

brownbear

Mod in Hibernation
Moderator
Joined
Sep 6, 2004
Messages
7,154
Location
North West Ontario
Visit site
The turbo if it is made for a 3 litre diesel should "work".

Anything about the right size will work. Mapped is something I would be having them do if I was buying new, junkyard is a toss up.

I bet you find it works great after they are done. Looking forward to pictures and such.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
Cheers mel, haven't had much chance to edit and upload pics lately, but updates on the way!
Went back to the shop first thing this morning. Turns out I was wrong about those numbers, and their attitude. The turbo has a turbine AR of .48, and the engineer spent a good deal of time this time with me explaining the inner workings of turbos, and showing me on various cutaways he had. He said he was particularly pleased with this turbo for this engine.
Before I left, he took me on a tour of their shop... they have a large repairs area where there were like 100 turbos being fixed. All very clean and tidy, with all the right gear. Then he gave me a small booklet (in english!) that explains more about turbos... history, workings, assembly, troubleshooting guide. Very cool. My confidence is restored in these guys... photos to come.
 
Joined
Jun 20, 2007
Messages
952
Location
Tahsis, BC
Visit site
Here's some photos of the shop, my turbo to-be, and one of their cutaway example turbos...
IMG_1061.JPG
IMG_1064.JPG
IMG_1066.JPG
 

Users who are viewing this thread

Top Bottom