Increasing W123 300D top end power - Page 2 - PeachParts Mercedes-Benz Forum

R-3350 · #16 02-04-2018, 05:40 AM

under square bore stroke doesn't limit rpm/performance like you would think. the BMW S54 in the E46 M3 is an under square in-line 6 (86mm bore 89.6mm stroke) that revs to 8000 rpm. the real limiter is the structural limits of the rods and ring flutter. the 617 can handle up to 6000 rpm on stock parts. the longer stroke can help breathing in some cases. the S54 uses a larger rod stroke ratio to play with dwell at BDC and TDC to improve the VE (for certain rpm bands it is over 100%) in conjunction with a tuned length intake tract. something else to think about is the effect bigger elements have on diesels notable the shorter injection pulse width, higher peak pressures, and finer atomization. my fuel economy went up slightly at steady state cruise after i installed the 8mm M pump on my car. with that the new turbo and exhaust i have been clocking around 33-35MPG @70 on the highway averaged out over the past 7 tanks. before i swapped everything i got 28-31. also you don't always have to add more air or fuel to get more power dieselmeken has shown on the dyno that a N/A 617 can produce over 100HP with mild port work and larger fuel elements set to the stock fueling. and all this is not even getting into the effects cam timing and injection timing can have on your power. these engines were designed with emissions and smoothness of operation in mind not performance.

leathermang · #17 02-04-2018, 10:31 AM

Quote:

Originally Posted by R-3350

under square bore stroke doesn't limit rpm/performance like you would think. the BMW S54 in the E46 M3 is an under square in-line 6 (86mm bore 89.6mm stroke) that revs to 8000 rpm. the real limiter is the structural limits of the rods and ring flutter. the 617 can handle up to 6000 rpm on stock parts. the longer stroke can help breathing in some cases. the S54 uses a larger rod stroke ratio to play with dwell at BDC and TDC to improve the VE (for certain rpm bands it is over 100%) in conjunction with a tuned length intake tract. something else to think about is the effect bigger elements have on diesels notable the shorter injection pulse width, higher peak pressures, and finer atomization. my fuel economy went up slightly at steady state cruise after i installed the 8mm M pump on my car. with that the new turbo and exhaust i have been clocking around 33-35MPG @70 on the highway averaged out over the past 7 tanks. before i swapped everything i got 28-31. also you don't always have to add more air or fuel to get more power dieselmeken has shown on the dyno that a N/A 617 can produce over 100HP with mild port work and larger fuel elements set to the stock fueling. and all this is not even getting into the effects cam timing and injection timing can have on your power. these engines were designed with emissions and smoothness of operation in mind not performance.

I agree that ' structural limits of the rods...'' does come into play AND also that the ability of the engine to OIL those rod bearings.... also.. valve float.. which is related to the spring resonance and pressure available.. often modified by having two springs per valve in race engines... Also.. for mpg increases often one needs to make Gearing changes to take advantage of changes in the power curve... your statement ''' these engines were designed with emission ans smoothness of operation in mind'''' leaves out what most people most appreciate in these engines... they were also designed for LONGEVITY.......

R-3350 · #18 02-04-2018, 02:50 PM

oiling issues on the 617 are not really an issue. the rods and mains have a high priority feed off the primary duct and the combined with the massive oil pressure they run of 7 bar basically stops any issues so long as you keep oil in the engine. valve float is not a serious issue till quite high rpm with the light valve train of an OHC engine it also helps that the stock cam is tiny(.313 lift) limiting the lift rates to low values again allowing lighter springs. also while dual springs can help limit resonance valve float beehive springs do the same thing while being lighter and simpler. you don't always need to change gearing to gain fuel efficiency there is a lot to be said about aero work on these cars. the stock C/D is 0.43 which is similar to a 90's pickup truck. the W210 is down to 0.29 so you can see the improvements in just two generations. also running larger elements in you injection pump plus more modern turbos all help to improve the BSFC of the engine even if you don't make any more power it will still help. and finally as for longevity, these engines can reach quite a few miles with careful maintenance but most don't. i have had to swap 5 engines in the last year on customer cars due to poor maintenance and bad luck. people hear these are million mile engines and figure thats a clear pass to not do oil changes or any work on them. i suspect there are quite a few engines and cars out there that would last just as long if there was as large a DIY community as there is for W123's.

awsrock · #19 02-05-2018, 12:01 AM

The STD forum is useful but very 606 oriented, and most of the active 617 users from there are on your thread already 😏

BillGrissom · #20 02-05-2018, 11:02 AM

I doubt a turbo rebuild would help, since that is mainly to cure oil loss. If the compressor wheel spins easy and the shaft feels tight (no wobble), and you have no oil loss, the turbo would seem fine. How it performs is answered by plumbing in a boost gage. That takes 5 min for a temp setup. Not sure why anybody would even ask here about performance without having done that first.

The OM617 has intake and exhaust on the same side, which restricts air-flow, compared to a cross-flow design like the later M-B diesels. Still, it performs fairly well at high-rpm compared to most other vintage diesel engines.

Maxbumpo · #21 02-05-2018, 03:08 PM

Quote:

Originally Posted by NZScott

On top of that, the 617s have a really crappy VE at high RPM.

What is VE?

Maxbumpo · #22 02-05-2018, 03:13 PM

Check the stretch of the timing chain, fix as needed. Retarded timing of valves and injection pump will rob some power. Consider an offset key in the camshaft gear to advance the camshaft timing.

Once timing chain is correct, advance the injection pump timing one or two degrees.

Test your ALDA with pressure or vacuum to make sure it can hold pressure (preferable) or vacuum. Replace the o-rings inside if it can't, or get a new ALDA, or just remove it and risk melting your pistons (install an exhaust gas temperature gauge?).

Adjust the injection pump governor for higher RPM fuel cut-off, and increase the fueling a bit. Turn up the turbo boost a bit by adjusting the waste gate, go for 15 - 18 psi.

The only real expenses will be an EGT gauge and a boost gauge, and your time.

NZScott · #23 02-05-2018, 11:57 PM

Quote:

Originally Posted by Maxbumpo

What is VE?

Volumetric Efficiency. How well the gases get into and out of the cylinder. For an example, the two valve reverse flow head OM617A has less power (not torque) than the naturally aspirated four valve crossflow OM606.

leathermang · #24 02-06-2018, 11:07 AM

Quote:

Originally Posted by BillGrissom

......
The OM617 has intake and exhaust on the same side, which restricts air-flow, compared to a cross-flow design like the later M-B diesels. Still, it performs fairly well at high-rpm compared to most other vintage diesel engines.

When talking about a FORCED AIR engine...
And one which also has the advantage of a tiny area of UNSWEPT volume ( diesel compression ratio ) in the bore..
the disadvantages of the valves being on one side are greatly reduced...

Now, the old 1950's Offenhauser Engines.... and also GRAVELY two wheeled tractor engines took advantage of that flow through concept...

https://en.wikipedia.org/wiki/Offenhauser

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