Couple things:

Currently working on a '92 300D 2.5, with an OM602. Been looking at replacing DV seals and springs, and maybe the lift pump, but I figured I might as well price a replacement pump with upgraded nozzles for comparison - turns out it's not too much, but it of course leads to more questions.

I'm looking at upgrading my stock 5,5mm elements to 6,0mm. It's not a huge difference, only about 10%, but I'll be happy if it translates to a 10% performance increase. I'm basically looking for the reliability of a fresh pump and any upgrade will be a bonus. But will this work with a stock engine? I don't want to get into installing an intercooler, monitoring EGTs, or replacing the clutch or transmission.

My second question is about the turbo - should I upgrade, or do I have to? I'm looking at rebuilding my T25, and have the option of converting to T28 components. I don't really know what the difference is. I gather my max boost won't change, since I'll be converting to a pressure-activated wastegate, and anything over 15PSI or so will be wasted. But will it spool up faster or otherwise perform better than the T25 at equal boost pressures?

Thanks for any opinions/advice.

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It will be reliable if that's what you're asking too.

If you put a bigger turbo, you mine as well customize the exhaust and make it a little bit bigger. It will spool faster than a t25, they used those turbos on 300zxs I believe. They're good for 250-300hp.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Well, reliability is definitely a good thing - but will it be safe? I'm hoping that the increase is modest enough that I won't need an intercooler. I mean, it's not anything crazy like you see on STD (7,5mm+ elements w/ monster turbos).

Custom exhaust would be cool, but I don't know if I trust some random shop to just put bigger pipes on the thing. I mean, there is a point of diminishing returns with increasing exhaust outlet size, and my understanding is that you can actually lose power if you get too aggressive. I feel like if I had something custom-made it would just be trial and error trying to get it right, basically.

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nah you'll be ok, you're not gonna need that much air. it will be safe, you're not going to be putting a lot of stress on the bottom end if that's what you mean. the 5 cylinder is pretty tough. i think you could run 250hp before you'd have to worry about rods..

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Hi,

From my experience with 603a with 8.5 and 7.5 mm elements, stock engine, stock turbo and just custom 3" exhaust I don't see the need of an intercooler. EGT is lower compared to stock. What matters is the adjusted max quantity not mainly the element diameter. 75 ccm i.e. with 6mm is worse than with 7.5 mm in terms of EGT and mpg (injection duration).
Don't change to a bigger turbo unless you aim for >200 hp.
Go for 7.5 or 6.5mm element upgrade ip and you'll be happy without messing with intercooler and turbo change.
(6.5 mm we use for n/a engines)

Tom

Will a larger turbo need a larger-diameter exhaust to work properly? I can see going to a custom exhaust shop and having wider pipes fabricated from the headers back, but wouldn't the exhaust manifold itself still be a bottleneck? I'm not aware of any larger-diameter, mandrel-bent headers for these cars...

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Many people tend to go too big on turbos.
You are considering 6mm elements so no need for a bigger turbo unless you like to drive a dyno queen with huge lag if your ip can spool the turbo at all.
Start with the ip 6.5 or bigger and leave all the other things stock for the moment.
As written I ran the 8.5 mm ip quite a while to see what is going on with performance and EGT then 3" exhaust (header still stock) and still with the stock turbo.
Go step by step and start with bigger elements.

Tom

Just curious as to the details of this.

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Current fleet
2006 E320 CDI
1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

Decided to go with Dieselmeken pump with 7,5mm elements @ 90cc. You think EGTs won't be an issue, because of the increased injection duration? i.e., more fuel = more heat, but spread out over a longer time = less heat at any given moment?

Hopefully my transmission is up to it.

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Injection duration is decreased that's why EGT is lower.
90ccm is way too much.
A healthy tranny will handle it.

I was under the impression that 90 was quite low for these pumps - what would you recommend?

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It's not the question what the pump (elements) can deliver. It's more about how efficient you want it and what your setup can burn. I don't want black smoke so I'm in the 70s with my 603a. Ask Göran what he recommends.

He said 90 sounded good, but the pump has an external ALDA so I think I should be able to adjust the fueling easily, correct? i.e., turn it down so that it won't smoke?

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Follow his advice and report back the results.

I have 90cc from 6mm in my 603 and don't have any smoke at all besides the normal soot cleanout that occurs since I rarely floor it. It should be ok. I also have an almost too big turbo but that is another story, still no smoke on ALDA enrichment though.