OM602 IP/turbo upgrade - PeachParts Mercedes-Benz Forum

Bimmer-Bob · #1 05-23-2017, 02:32 PM

***Cross-post from STD for more exposure***

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.

jake12tech · #2 05-23-2017, 02:40 PM

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.

Bimmer-Bob · #3 05-23-2017, 02:50 PM

Quote:

Originally Posted by jake12tech

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.

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.

jake12tech · #4 05-23-2017, 02:54 PM

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..

tomnik · #5 05-24-2017, 02:07 AM

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

Bimmer-Bob · #6 05-25-2017, 02:14 PM

Quote:

Originally Posted by jake12tech

If you put a bigger turbo, you mine as well customize the exhaust and make it a little bit bigger.

Quote:

Originally Posted by tomnik

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.

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...

tomnik · #7 05-25-2017, 03:45 PM

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

Bimmer-Bob · #8 08-27-2017, 01:17 PM

Quote:

Originally Posted by tomnik

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

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.

Phillytwotank · #9 05-25-2017, 04:08 PM

Quote:

Originally Posted by Bimmer-Bob

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.

Just curious as to the details of this.

awsrock · #10 08-29-2017, 12:17 AM

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.

Bimmer-Bob · #11 08-31-2017, 05:58 PM

Quote:

Originally Posted by awsrock

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.

Are you intercooling?

awsrock · #12 08-29-2017, 12:22 AM

As for headers, you can get some custom made but they are not cheap. I went from HX30 with stock manifold and exhaust to headers, BW s200 turbo and 3" exhaust and the top end came alive like crazy. I still think headers probably aren't needed for our power levels but the US 603 manifold was awful.

Bimmer-Bob · #13 08-31-2017, 06:02 PM

Quote:

Originally Posted by awsrock

As for headers, you can get some custom made but they are not cheap. I went from HX30 with stock manifold and exhaust to headers, BW s200 turbo and 3" exhaust and the top end came alive like crazy. I still think headers probably aren't needed for our power levels but the US 603 manifold was awful.

I just think the headers are good to do while the turbo is off anyway, and I'm just a fan in general. Plus it seems like a nice place to mount an EGT probe.

For the exhaust, I guess you went the custom route? How does that work, will any muffler shop just run pipes from the headers back? I would definitely add a muffler back in, and maybe a resonator. I don't want TOO much noise and definitely no drone.

awsrock · #14 09-01-2017, 07:31 AM

I do have an intercooler, it's 27x9x...3 I think. There lies the benefit of huge SDL bumpers! Anyway, I made my exhaust myself, it's a 3" with just a Thrush Hush muffler. It is surprisingly quiet, like not really any more loud than stock, at least from my driver's seat perspective. I may have some drone around 1700 but I am 98% sure it is because the downpipe vibrates on the body from time to time. Still need to fix that.

Bimmer-Bob · #15 09-01-2017, 11:24 AM

Quote:

Originally Posted by awsrock

I do have an intercooler, it's 27x9x...3 I think. There lies the benefit of huge SDL bumpers!

Did you do that mainly for more power, or did you think it was needed because of the bigger elements? I keep hearing conflicting opinions - generally, US folks seem to on the very conservative side of things, thinking you need a huge intercooler or you're gonna melt pistons, while the Euro guys (who do this a lot more) seem to take more of a "don't worry about it" approach. Of course, it's easy to be cavalier about a stranger's engine on the internet.

Ideally, I would like to intercool, but there's just such limited space on the W124 - I guess a could fit a tiny intercooler somewhere, but then is it even doing anything?

The bigger issue is actually my complete lack of welding and fabricating skills - so I have no ability to weld brackets or whatever to mount the thing or, more importantly, any way (that I know of) to run the intercooler pipes into the intake manifold.

I'm just kind of hoping the bump in fueling is modest enough (plus this whole shorter injection duration thing, with no late burn) that the IC won't be needed. I'm not looking for crazy power, just want the thing to run better - and Dieselmeken's pump actually worked out cheaper than a rebuilt stock unit. I mean, obviously I want some extra power, but I mean I'm not trying to break any records on STD. Leaving that to the Finns.

In any case, most of my driving is on twisty backroads. No real hills to speak of, rarely able to exceed 60mph. Interstate driving once in a blue moon (and I have other vehicles for that, too). So also hoping relatively light loads will keep EGTs down.